Patent Application
20230110324
This description relates to optical devices. More specifically, this disclosure relates to design, development, manufacturing and operation of light-emitting diodes (LEDs), such as micro-LEDs.
Light-emitting diodes (LEDs) are used in a number of applications, such as in various consumer electronic devices. For instance LEDs are widely used in display devices, such as, for example, in smartphones, computers, televisions, etc. As resolution of such displays increase (e.g., number of display pixels per inch), LEDs used to implement a display have been reduced in size to achieve such increases in display resolution. However, achieving desired performance (e.g., efficiency, brightness, etc.) as dimensions of LEDs decrease has become a challenge. One approach that has been implemented is to increase a number of light emitting layers, or regions, i.e., stacked quantum wells (QWs), of such LEDs. However, such approaches are limited in their benefit, as only a portion (e.g., one or two) of the QWs of a stack may emit light (e.g., light that can be perceived by a viewer).
In one general aspect, the techniques described herein relate to a method for electrical operation of a micro-LED. The method includes driving the micro-LED with an electrical power via at a p-type contact disposed on at least one of: a horizontal face of the micro-LED; or a non-horizontal face of the micro-LED, where the p-type contact contacts a p-type layer. The method further includes injecting, by driving the micro-LED with the electrical power, holes from the p-type contact into the p-type layer, and laterally injecting, along the non-horizontal face of the micro-LED, the holes from the p-type layer to a plurality of quantum wells (QWs). The plurality of QWs have respective horizontal regions arranged along a horizontal direction of the micro-LED, the holes being laterally injected to the plurality of QWs via the p-type semiconductor layer.
Implementations can include one or more of the following features in various combinations. In some aspects, the micro-LED can have a lateral dimension along the horizontal direction between 0.5 micrometers (μm) and 5 μm. The injected holes can diffuse laterally in the plurality of QWs over a distance greater than 0.5 μm.
In some aspects, the non-horizontal face can be arranged along a semi-polar plane of the micro-LED.
In some aspects, at least one QW of the plurality of QWs can have a recombination lifetime greater than 5 nanoseconds (ns) corresponding with the driving of the micro-LED with the electrical power.
In some aspects, driving the micro-LED with the electrical power can include driving the micro-LED with a current density between 1 amp/centimeter-squared (A/cm2) and 100 A/cm2.
In another general aspect, the techniques described herein relate to a micro-LED that includes a semiconductor mesa having a lateral dimension less than Sum along a horizontal direction of the micro-LED. The micro-LED also includes a contact formed on at least one of: a horizontal face of the semiconductor mesa, or a non-horizontal face of the semiconductor mesa. The semiconductor mesa includes a plurality of quantum wells (QWs), and a p-type semiconductor layer formed between the contact and the plurality of QWs. The contact, the p-type semiconductor layer and the plurality of QWs are configured such that, when the micro-LED is driven at an effective current density less than 50 A/cm2, holes are injected from the contact to p-type layer; and laterally injected from the p-type layer to the plurality of QWs, where the injected holes diffuse laterally in the plurality of QWs over a distance greater than 1 micrometer (μm).
Implementations can include one or more of the following features in various combinations. In some aspects, the non-horizontal face can be a slanted sidewall of the semiconductor mesa. The slanted sidewall can be arranged at an angle between 10 degrees and 80 degrees with respect to a line along the horizontal direction.
In some aspects, the non-horizontal face can be arranged along a semi-polar plane of the semiconductor mesa.
In some aspects, the plurality of QWs can include at least three QWs. Respective percentages of the injected holes that are diffused in the at least three QWs are less than 50 percent and greater than 25 percent.
In another general aspect, the techniques described herein relate to a micro-LED mesa including a semiconductor mesa having a lateral dimension along a horizontal direction of the micro-LED mesa of less than or equal to 5 micrometers (μm). The semiconductor mesa includes at least one slanted sidewall, a planar top surface, and a multiple quantum well (MQW) portion having a planar region arranged along the planar top surface and a slanted region arranged along the at least one slanted sidewall. First p-type material is disposed on the planar region of the MQW portion, and second p-type material is disposed on the slanted region of the MQW portion. A p-type contact is disposed on the second p-type material.
Implementations can include one or more of the following features in various combinations. In some aspects, the micro-LED mesa can further include an insulating layer disposed on at least a portion of the first p-type material, and a reflective layer disposed on the insulating layer.
In some aspects, during electrical operation of the micro-LED mesa, hole injection can occur at a first carrier density through the first p-type material, and hole injection can occur at a second carrier density through the second p-type material. The second carrier density can be negligible relative to the first carrier density.
In some aspects, quantum wells (QWs) of the MQW portion have respective diffusion coefficients of greater than or equal to 1 centimeter-squared per second (cm2/s) at a current density of less than 20 amps per centimeter-squared (A/cm2).
In some aspects, in response to injection of holes from the p-type contact, light can be emitted from the MQW portion at a lateral distance along the horizontal direction of greater than or equal to 1 micrometer (μm) from the p-type contact.
In some aspects, the micro-LED mesa can include a plurality of GaN-based materials.
In some aspects, the planar top surface can be arranged along a c-plane of at least one of the plurality of GaN based materials, and the at least one slanted sidewall can be arranged along a semi-polar plane of at least one of the plurality of GaN based materials.
In another general aspect, the techniques described herein relate to a micro-LED mesa include a semiconductor mesa having a horizontal top surface arranged along a horizontal direction of the micro-LED mesa, at least three non-vertical sidewalls, and a plurality of epitaxial layers. The plurality of epitaxial layers include a first portion arranged along the horizontal direction. The first portion of the plurality of epitaxial layers define a first plurality of quantum wells (QWs) of a first thickness and a first bandgap. The plurality of epitaxial layers also include a second portion arranged along the at least three non-vertical sidewalls. The second portion of the plurality of epitaxial layers define a second plurality of QWs of a second thickness and a second bandgap. The micro-LED further includes an electrical contact disposed on at least one non-vertical sidewall of the at least three non-vertical sidewalls.
Implementations can include one or more of the following features in various combinations. In some aspects, the micro-LED mesa can be configured such that holes, injected during electrical operation of the micro-LED mesa, travel from the electrical contact to the second plurality of QWs and, then to the first plurality of QWs.
In some aspects, the micro-LED mesa can be configured such that, during electrical operation of the micro-LED mesa, light is emitted from at least two QWs of the first plurality of QWs.
In some aspects, the first portion of the plurality of epitaxial layers can be included in a central portion of the micro-LED mesa. The central portion of the micro-LED mesa can have a lateral width along the horizontal direction of greater than or equal to 500 nanometers (nm).
In some aspects, the micro-LED mesa can have a width of less than or equal to 20 micrometers (μm), and a height of greater than or equal to 100 nanometers (nm). The height can be less than or equal to 10 μm.
In some aspects, the second portion of the plurality of epitaxial layers can be located in a perimeter portion of the micro-LED mesa.
In some aspects, the horizontal direction can be arranged along a c-plane of a crystalline structure of the micro-LED mesa. The at least three non-vertical sidewalls can be arranged along respective semipolar planes of the crystalline structure.
In some aspects, the at least three non-vertical sidewalls can have respective angles from a vertical direction of the micro-LED mesa that are between 10 degrees and 80 degrees.
In some aspects, the first plurality of QWs and the second plurality of QWs can be connected in a one-to-one relationship.
In some aspects, the second bandgap can be greater than the first bandgap.
In some aspects, the second thickness can be less than the first thickness.
In some aspects, the electrical contact can be a first electrical contact. The micro-LED mesa can include a second electrical contact disposed on the horizontal top surface.
In another general aspect, the techniques described herein relate to a method for electrical operation of a micro-LED mesa. The micro-LED mesa includes at least one non-vertical sidewall including a p-type material with a first bandgap and a first thickness. The micro-LED mesa also includes an epitaxial layer with a second bandgap and a second thickness. The p-type material is disposed on the epitaxial layer. The micro-LED mesa further includes a plurality of quantum wells (QWs) with a planar orientation along a horizontal direction of the micro-LED mesa, a third bandgap, and a third thickness. The epitaxial layer is disposed between the p-type material and the plurality of QWs. The micro-LED mesa also includes an electrical contact disposed on the p-type material. The first bandgap is greater than the second bandgap, the second bandgap is greater than the third bandgap, and the second thickness is less than the third thickness. The method includes injecting a plurality of holes from the electrical contact to the p-type material, injecting the plurality of holes from the p-type material to the epitaxial layer, and injecting the plurality of holes from the epitaxial layer to at least two QWs of the plurality of QWs.
Implementations can include one or more of the following features in various combinations. In some aspects, the p-type material can include p-type gallium nitride (GaN).
In some aspects, the epitaxial layer can be a non-planar and non-vertical QW arranged along a semi-polar plane of the micro-LED mesa. The epitaxial layer can include at least 1 percent indium. The plurality of QWs with the planar orientation can include at least 15 percent indium.
In some aspects, injecting the plurality of the holes into the plurality of QWs can include injecting no more than 30 percent of the plurality of holes into a single QW of the plurality of QWs.
In some aspects, the injected plurality of holes diffuse laterally along the horizontal direction in the plurality of QWs for a distance of greater than or equal to 500 nanometers (nm).
In some aspects, injecting the plurality of holes from the p-type material to the epitaxial layer can include injecting the plurality of holes through an electron blocking layer (EBL).
In the drawings, which are not necessarily drawn to scale, like reference symbols may indicate like and/or similar components (elements, structures, etc.) in different views. The drawings illustrate generally, by way of example, but not by way of limitation, various implementations discussed in the present disclosure. Reference symbols shown in one drawing may not be repeated for the same, and/or similar elements in the same view, or in related views. Reference symbols that are repeated in multiple drawings may not be specifically discussed with respect to each of those drawings, but are provided for context between related views. Also, not all like elements in the drawings are specifically referenced with a reference symbol when multiple instances of an element are illustrated in a given view.
Conventional light-emitting diodes (LEDs), such as LEDs used in display devices, operate via vertical electrical carrier injection. That is, injected electrical carriers, particularly holes, travel in a direction that is parallel to a growth direction for epitaxial layers included in the LEDs, e.g., to reach light emitting regions, such as quantum wells (QWs). Improving the performance of LEDs that operate with vertical carrier injection can be challenging.
The present disclosure relates to optoelectronic devices, which are referred to herein as micro-LEDs (or LEDs), in which electrical carrier injection occurs, at least in part, in a lateral direction, or a horizontal direction, e.g., in a direction that is perpendicular to an epitaxial layer growth direction. While the disclosed embodiments are generally described with respect to small devices, e.g., with lateral dimensions on the order of 10 micrometers (μm), or less, in some implementations, the approaches described herein can be used to implement larger devices, e.g., LEDs with lateral dimensions of 100 μm or more, 500 μm or more, or 1 millimeter (mm) or more. As used in the present disclosure, the terms horizontal, lateral and vertical are referenced relative to corresponding structure of the example LEDs (e.g., micro-LEDs) described herein. That is, horizontal and/or lateral refer to a direction that is perpendicular to a growth direction of epitaxial layers used to implement an LED, while vertical refers to a direction that is parallel to, or in a same direction as, the epitaxial growth direction. Also in the present disclosure, the terms LED and micro-LED (μLED) may be used interchangeably. Further, LEDs and micro-LEDs may also be referred to as devices, optical devices, etc. The terms carrier and electrical carrier can be used interchangeably, and can refer to holes and/or electrons.
In some implementations, such as the example devices described herein, lateral carrier injection can improve the performance of such micro-LEDs as compared to prior approaches, as it can allow for light emission from more QWs than prior device implementations, can improve light emission distribution, etc. In the example implementations, such lateral carrier injection can occur in doped layers (e.g., doped semiconductor layers), in light-emitting layers (e.g., QWs), or in a combination thereof. For instance, the present disclosure is directed to LEDs in which lateral carrier diffusion occurs in an active, or QW region, and/or to LEDs in which lateral carrier diffusion occurs in doped layers (e.g., n-type semiconductor layers and/or p-type semiconductor layers).
In some examples, such as the examples of
For instance, in some implementations, electrical carriers are laterally injected into a plurality of QWs of a QW stack from a non-vertical contact, e.g., a contact and/or p-type region included in, or disposed on a slanted (non-vertical and non-horizontal sidewall). Using the approaches described herein, an associated LED can be configured such that the injected carriers diffuse laterally in the QWs for a desired distance (e.g., diffusion length), e.g., 0.5 micrometers (μm) or more before recombining and emitting light.
In the example implementations described herein, performance improvements are achieved, at least in part, based on the determination that carrier diffusion lengths in a QW, instead of being a constant value, depend both on the epitaxial configuration (e.g. composition, thickness and micro-structure of a QW) and on carrier density in the QW during electrical operation of an associated LED. For instance, diffusion length in a QW can be expressed by Equation 1 as follows:
L=sqrt(D*tau(n)) (1),
where D is a diffusion coefficient, and tau(n) is a recombination lifetime (or carrier lifetime), which is a function of a carrier density n and, accordingly, depends on an injected current density J. Therefore, a desired value for a diffusion length L can be achieved by jointly configuring (adjusting, altering, modifying, etc.) the diffusion coefficient D and the current density n for a given LED to predetermined values. This approach can be applied for both holes and electrons, and the diffusion coefficient D can be an ambipolar diffusion coefficient.
In some implementations, an ambipolar diffusion coefficient D (e.g., for a QW of an LED), which can be an average of a hole diffusion coefficient Dh and an electron diffusion coefficient De, can be increased using a number of approaches. For instance, an increased value of D can be achieved by implementing a QW active region with sharp interfaces, e.g., with a transition region of less than 0.5 nanometers (nm), less than 0.3 nm, or less than 0.1 nm between the QW and associated barrier materials. Increased values of D can also be achieved by reducing atomic disorder in a QW, e.g., by producing InGaN QWs using growth conditions that reduce atomic disorder to be less that of a random alloy distribution. Using such approaches, diffusion coefficients D of at least 6 centimeters-squared per second (cm2/s), at least 8 cm2/s, or at least 10 cm2/s can be achieved.
The carrier lifetime, e.g., in a QW, is governed by several factors. In one model, a carrier recombination rate R(n) is given by Equation 2 as follows:
R(n)=An+Bn2+Cn3 (2),
where with A is a Shockley-Read-Hall (SRH) coefficient, B is a radiative coefficient, C is an Auger coefficient, and n the carrier density, as previously discussed. The differential lifetime is then given by Equation 3 as follows:
1/tau=A+2Bn+3Cn2. (3)
Based on this model, a number of approaches, or techniques can be used to achieve a desired carry lifetime (tau) and a corresponding desired diffusion length L. For instance, an LED may be driven at a specific current density J to affect carrier lifetime and carrier diffusion length. In some implementations, a current density J used to drive (electrically operate an LED) can be less than 1 A/cm2, less than 2 A/cm2, less than 3 A/cm2, less than 5 A/cm2, less than 10 A/cm2, less than 20 A/cm2, less than 30 A/cm2, less than 50 A/cm2, or less than 100 A/cm2. In some implementations, a current density J can be selected to achieve a carrier density n in a corresponding QW that is less than 1E17/cm3, less than 2E17/cm3, less than 3E17/cm3, less than 5E17/cm3, less than 1E18/cm3, less than 2E18/cm3, less than 3E18/cm3, less than 5E18/cm3, or less than 1E19/cm3.
In some implementations, QWs of an LED can be configured (produced) to have a desired (e.g., increased) SRH lifetime, such as by implementing epitaxial layer growth process that reduce the SRH coefficient A. For instance, such reductions in the SRH coefficient A for a given QW can be achieved by reducing a defect density in the QW. For example, in gallium nitride (GaN) based LEDs, a defect density of the associated QWs can be reduced through the use of underlayers containing indium gallium nitride (InGaN), and/or by increasing a thickness of the QWs, such that an overlap in electron and hole wavefunctions decreases. In some examples, a density of SRH-causing defects of less than 1E17/cm3, less than 1E16/cm3, less than 1E15/cm3, or less than 1E14/cm3 can be achieved. In some examples, a QW of an LED can have a thickness of at least 2.5 nm, at least 3 nm, at least 3.5 nm, or at least 4 nm, which can be implemented in combination with an In percentage composition in the QW of at least 20%, at least 25%, at least 30%, or at least 35%. In such implementations, a corresponding SRH lifetime t_SRH of at least 10 nanoseconds (ns), at least 20 ns, at least 50 ns, at least 100 ns, at least 200 ns, at least 500 ns, at least 1000 ns, at least 2000 ns, at least 5000 ns, or at least 10000 ns can be achieved. For clarity, t_SRH and the SRH coefficient A are related by Equation 4 as follows:
t_SRH=1/A (4).
In some implementations, QWs of an LED can be configured (produced) to have a desired (e.g., reduced) radiative coefficient B and/or a desired (e.g., reduced) Auger coefficient C, such as in the model described above. For instance, in some implementations, the B and C coefficients can be reduced by increasing QW thickness, such that electron-hole overlap decreases, and/or by adding barriers of appropriate composition, e.g. aluminum gallium nitride (AlGaN) barriers, in order to increase a polarization field in the QW. In some implementations, B can be less than 1E-10 cm3/s, less than 1E-11 cm3/s, less than 1E-12 cm3/s, less than 1E-13 cm3/s, or less than 1E-14 cm3/s). In some implementations, C can be less than 1E-30 cm6/s, less than 1E-31 cm6/s, less than 1E-32 cm6/s, less than 1E-33 cm6/s, or less than 1E-34 cm6/s).
It is noted that the current density n is a volume, three-dimensional (n3D) carrier density. Surface current density is a per area, two-dimensional (n2D) current density. Surface current density and volume carrier density are related by Equation 5 as follows:
n2D=n3D/t (5),
where t is a thickness of the active QW layer. In some example implementations, t may be 2 nm, 3 nm, or 4 nm, and t may be a nominal (effective) value rather than an exact (physical) value.
It is noted that for the example micro-LEDs (LEDs) described herein, definitions of current density may be ambiguous, dependent on the area, or the portion of an LED being considered or evaluated. Accordingly, for purposes of clarity, current density can be referred to herein as effective current density, where effective current density is defined as current (e.g., total current) divided by a corresponding area of a planar portion an LED's active (QW) region, where that area can be similar to an area of an upper surface of a mesa used to implement a corresponding micro-LED.
In some implementation, a diffusion coefficient for holes in an active region (in QWs) of an LED can be at least 2 cm2/s, e.g., with the LED being operated at an effective current density J of less than 50 A/cm2, resulting in a recombination lifetime of more than 30 ns. In this example, the corresponding hole diffusion length would, therefore, be at least 2.5 μm. In one example implementation, the LED is a micro-LED (μLED) with a mesa having a lateral (horizontal) dimension of less than 5 um, and contacts (e.g., p-type contacts) formed on (disposed on) the sidewalls of the mesa. In this example, lateral diffusion over the diffusion length of 2.5 μm can lead to a substantial hole population even near the center of the mesa of the μLED device (e.g., a μLED mesa).
In each of
After forming the growth template 115, the uLED mesa 105 can be selectively grown in the opening using epitaxial regrowth process operations, where the composition of the epitaxial layers is modified during growth of the uLED mesa 105 to produce different portions (layers) of the uLED mesa 105. For instance, an n-type region 120 can be formed, followed by an active region 130 (which can also be referred to as a multiple QW region, or MQW region), and then a p-type layer 125 can be formed. As shown in
The active region 130 of the uLED mesa 105 includes a QW 130a, a QW 130b, and QW 130c and a QW 130d. While the uLED 100 is shown as including four QWs, in other implementations, a different number of QWs can be included, such as three, five, seven, ten, and so forth. In this example, the QWs 130a-130d and the p-type layer 125 are grown both along an upper portion 105a of the uLED mesa 105 and along the slanted sidewalls 105b of the uLED mesa 105. The QWs 130a-130d can be considered as portions, such as a planar portion arranged the horizontal direction, and slanted portions arranged along non-horizontal and non-vertical planes. As shown in
In the uLED 100, an electrical contact 135, such as a p-type contact can be formed on (disposed on) the p-type layer 125. In example implementations, the electrical contact 135 can be formed using a metal layer, such as silver, platinum, titanium, nickel, and/or tungsten, as some examples. Upon electrical operation of the uLED 100, as illustrated by the arrows 140 in
In some examples, the QWs 130a-130d of the active region 130 (the MQW region) can be undoped (e.g., undoped GaN), n-doped (e.g., n-doped GaN), or lightly p-doped (p-doped GaN) as compared to a doping concentration of the p-type layer 125. A region of the uLED mesa 105 where lateral injection of holes occurs may correspond with a lateral p-n junction of the uLED mesa 105, and the slanted portions of the QWs 130a-130b may be positioned in a depletion region of that lateral p-n junction.
In the example of
Accordingly, the slanted sidewalls 405b, in this example, include either lateral p-n junctions, or lateral p-i-n junctions that inject carriers (e.g., holes) received from a contact 435 into the QWs of the MQW region 430. For instance, a p-type layer 425 and an n-type region 420 can define the lateral p-n or p-i-n junctions, where the dashed in
The p-type layer 425, in the uLED mesa 405, is also present along a top surface of the uLED mesa 405, and can form a planar p-n junction or planar p-i-n junction along a top facet of the uLED mesa 405. In example implementations, carriers injected (e.g., laterally injected) from the p-type layer 425 into the QWs of the MQW region 430 can then diffuse laterally over a corresponding diffusion length L in the QWs of the MQW region 430, such as shown by the arrows 440 in
In this example, a contact 735 (p-type contact) is disposed on the horizontal facet of the uLED mesa 705. An insulating material 745 (a transparent insulating material) is disposed on slanted sidewalls 705b of the uLED mesa 705, and mirrors 750 are disposed on the insulating material 745. Accordingly, in this example, as is shown by the arrows 740 in
MQW region 730 in the slanted region 732. Accordingly, lateral injection from p-material to the QWs may occur from a peripheral portion of the mesa and/or from an inner portion of the mesa.
In this example, similar to the uLED 700, a contact 835 (p-type contact) is disposed on the horizontal facet of the uLED mesa 805. An insulating material 845 (a transparent insulating material) is disposed on slanted sidewalls 805b of the uLED mesa 805, and mirrors 850 are disposed on the insulating material 845. Accordingly, in this example, as is shown by the arrows 840 in
In example implementations, the growth interface 910 can be a surface of the n-doped buffer 912. The n-doped buffer 912 is formed on a substrate 950. The substrate 950 can include, as some examples, sapphire, silicon, silicon carbide (SiC), bulk GaN, or bulk aluminum nitride (AlN), e.g., for III-nitride LEDs. The n-doped buffer 912 can be an n-doped semiconductor material, such as n-type GaN. In some implementations, an electrical connection (e.g., contact) to the n-type region 920 can be made in other ways than as shown in
In some implementations, after forming the uLED 900, the substrate 950 may be removed using one or more process operations, such as grinding, etching, and/or lift-off operations. The n-doped buffer 912, or a portion thereof, may also be removed or thinned. In some cases, the contact 935 can be reflective, and the uLED 900 can emit light towards (from) the n-type region 920 (e.g., either through a transparent substrate, or after substrate removal). For instance, the uLED 900 can be implemented in a flip-chip device.
As shown by the arrows 940 in
As shown by the arrows 942 in
In some implementations, the region surrounding the MQW region 930 (e.g., the n-type region 920 in
As illustrated by the example implementations of
For instance in some implementations, a contact can be formed on (disposed on) at least a portion of a slanted sidewall, and holes can be injected from the sidewall contact to sidewall p-type GaN, without hole injection occurring on the top facet of the μLED. The holes can then be laterally injected into the QWs. In other implementations, a contact can be formed on (disposed on) at least a portion of a top, or horizontal facet of a μLED, and holes can be injected from the contact to top p-type GaN, conducted from the top p-type GaN to sidewall p-type GaN, and then injected from the sidewall p-type GaN laterally into the QWs (e.g., either slanted portions of QWs, or QWs of a planar MQW). Other example implementations can have variations in contact geometry. For instance, a lateral contact can be disposed (formed) only on a portion of the lateral, slanted sidewall, while other portions of the lateral, slanted sidewall can be covered by an insulating layer to electrical contact prevent contact.
Also, for purposes of illustration, the epitaxial layer stack 1000 is shown in a vertically stacked arrangement. In some implementations, such as the examples of
As shown in
In the example of
As further shown in
As described herein, and as noted above, in some implementations the MQW region 1030 and/or the p-type region 1025 can also be extended into slanted portions (e.g., slanted sidewalls) of a corresponding μLED. In some implementations, layers of the MQW region 1030 and p-type region 1025 may have different thicknesses and/or composition in the slanted portions, e.g., as compared to a planar portion of a corresponding μLED.
For each QW configuration modeled, a corresponding electron wavefunction (e.g., electron wavefunction 1220) and hole wavefunction (e.g., wavefunction 1240) are computed by solving Schrodinger's equation. A corresponding oscillator strength O (e.g., equal to the squared overlap integral between the electron and hole wavefunctions) is then computed. Respective recombination coefficients are then computed, e.g., based on an empirical relationship between O and corresponding recombination coefficients (e.g., such as the coefficients discussed above) are determined, e.g., as B=O*B0, A=O{circumflex over ( )}0.8*A0, C=O{circumflex over ( )}1.2*C0, where A0, B0, and C0 are bulk-like coefficients (without quantum confinement effects) for the SRH, radiative and Auger rates. Respective carrier lifetime can then be given by 1/tau=A+2Bn+3Cn2, and the diffusion length L can be given by L=sqrt(D*tau), with D=2 cm2/s, which can be a nominal diffusion coefficient value for InGaN QWs. While operation of physical devices can depart from this model, the model provides guidance on the relationship between QW configuration (e.g., thickness and/or In percent composition) and diffusion length.
In a general aspect, epitaxial layers of a μLED in an active region can be configured, e.g., including QW layers' and barrier layers' composition, thickness, doping, level of disorder, such that an electrostatic structure and density of states in the active region can be achieved, which results in a desired carrier lifetime and desired diffusion length at a desired (e.g., predetermined) operating current density for the μLED. In some implementations, a desired wavelength of emitted light, a desired IQE, and other performance properties of QWs of a μLED can be achieved. That is, in some implementation, an epitaxial structure of a μLED active region can be produced to achieve a desired wavelength for emitted light, a desired diffusion length for carriers injected into QWs of an active region of the μLED, and a desired IQE, at an operating current density J. In some implementations, a diffusion length of at least 1 um, at least 2 um, or at least 3 um can be achieved, and a corresponding IQE of at least 20%, at least 30%, or at least 40%, at an operating current density J of 1 A/cm2, 5 A/cm2, 10 A/cm2, 50 A/cm2, or 100 A/cm2, can be achieved.
As discussed above, using the approaches described herein, LEDs (μLEDs) can be produced and operated with improved performance as compared to prior LED implementations. For instance, example μLED implementations described herein can operate with improved carry distribution and, as result, improved light output and distribution.
Such carrier density distributions can, in turn, result in improved distribution of light output across an associated μLED or LED, e.g., from the QW 1530 and other QWs included in a corresponding μLED device. For instance,
As can be seen in
In μLEDs implemented and operated using the approaches and techniques described here, lateral injection can allow for increasing N, which shifts the corresponding relative wavelength curves to higher current densities. As shown by the curve 1720 (N=3) and the curve 1730 (N=10), assuming approximately equal carrier injection in all injected QWs, the respective relative wavelengths are approximately 97% (for N=3) and above 97.5% (for N=10).
In some implementations, a μLED can have a number N of QWs (e.g., N is at least 3, at least 4, at least 5, at least 6, at least 7, at least 8, at least 9, or at least 10) that are substantially injected during electrical operation at a current density J, e.g., with J being at least 1 A/cm2, at least 5 A/cm2, at least 10 A/cm2, or at least 20 A/cm2. In some implementations, a μLED may have a peak wavelength of emitted light of at least 430 nm, at least 440 nm, at least 450 nm, at least 510 nm, at least 520 nm, at least 530 nm, at least 540 nm, at least 600 nm, at least 610 nm, or at least 620 nm when operated at a given current density J. That is, a μLED may have a peak wavelength of emitted light in a range of 430-480 nm, or 510-550 nm, of 600-650 nm. In some implementations, a μLED may have an operating IQE above 20%, above or 30%, above 40%, above 50%, or above 60%. In some implementations, a μLED may have an operating EQE above 5%, above 10%, above 15%, above 20%, above 25%, above 30%, above 35%, above 40%). In some implementations, a μLED may have an operating WPE above 5%, above 10%, above 15%, above 20%, above 25%, above 30%, above 35%, or above 40%.
In some implementations, a μLED may have a low-current centroid wavelength lambda0 (e.g., defined by a plateau of the wavelength at low current density) and an operating centroid wavelength lambda at a higher current density J, with the relative wavelength lambda/lambda0 being greater than 0.9, greater than 0.92, greater than 0.94, greater than 0.96, or greater than 0.98. In some implementations, a μLED can have a wavelength shift (lambda0-lambda) that is less than 50 nm, less than 30 nm, less than 20 nm, less than 15 nm, less than 10 nm, or less than 5 nm. In such implementations, lambda0 may be at least 450 nm, at least 470 nm, at least 490 nm, at least 550 nm, at least 570 nm, at least 620 nm, at least 630 nm, at least 640 nm, at least 650 nm, or at least 660 nm.
In some implementations, a μLED can have a reduced efficiency droop, or IQE droop, as compared to prior LED implementations. Such a reduction in IQE (efficiency) droop can be achieved as a result lateral injection approximately equally spreading injected carriers over a desired number of QWs. IQE droop can be defined as a relative value (a percentage), e.g., as an IQE at a given current density J divided by a peak IQE for a given μLED. In some implementations, a μLED can have an IQE droop that is greater than 50%, greater than 60%, greater than 70%, greater than 80%, or greater than 90%. In some implementations, a μLED can have an EQE droop that is greater than 50%, greater than 60%, greater than 70%, greater than 80%, or greater than 90%. In some implementations, a μLED can have a WPE droop that is greater than 50%, greater than 60%, greater than 70%, greater than 80%, or greater than 90%.
In addition to, or in place of the operations of process flows described above, other processing operations can be used. For instance, a μLED mesa may be defined by etching (e.g. dry etch, wet etch), then regrown to form a MQW and/or a slanted region, and regrown (e.g., further regrown) to form a p-doped region. In some implementations, process operations of one method implementation can be performed in another method implementation, e.g. to produces μLEDs with different configurations, such as the example μLEDs described herein.
For instance, in some implementations, a μLED can be produced with QWs that are conformal with a μLED mesa, and have slanted portions present at slanted sidewalls of the μLED mesa. In some implementations, the QWs along the sidewalls can be thinner than QWs along a planar region of the corresponding μLED. In some implementations, the QWs along the sidewalls do not emit a substantial fraction of the light emitted by the μLED, and most (or all) of the light is emitted from the planar portion QWs.
In some implementations, a μLED can have a mesa that includes gallium and nitrogen, e.g. GaN and/or a III-nitride compound. Such compounds may include Ga, In, Al, N and/or other elements. In some implementations, a mesa of a μLED can have a planar top surface corresponding to a c-plane (or a c-plane with a small offcut, e.g., less than 5 degrees) of a crystalline structure of the mesa.
In some implementations, a mesa of a μLED can have slanted sidewalls. The slanted sidewalls can be along a semi-polar direction, corresponding with a respective crystalline structure of the mesa. The mesa can have a hexagonal or circular base shape, such as shown respectively, in
In some implementations, a μLED, or μLED mesa can a lateral dimension LD (e.g., along a horizontal direction, as defined herein) and a diffusion length L across a corresponding QW that is at least LD/5, at least LD/2, or at least LD. In some implementations, this relationship may hold true for the diffusion length for holes, if holes are injected laterally, and it may also hold true for the diffusion lengths of both electrons and holes, if both are injected laterally. In some implementations, having a lateral dimension commensurate with the diffusion length can facilitate substantially uniform lateral carrier injection across a plurality of QWs. In some implementations, a LED (e.g., a μLED μLED mesa) can have a lateral dimension LD that is less than Sum, and the LED can be configured to inject holes into the QWs, where the QWS have a lateral diffusion length L of at least 1 um.
In some implementations, a μLED can include a lateral injection region (e.g., from one or more p-layers into QWs), and the QWs can extend for a distance LQW away from the lateral injection region. In such examples, the epitaxial structure of the μLED can be produced and electrically operated, using the approaches described herein, to achieve a lateral diffusion length L (for electrons and/or holes) that is at least LQW/5, at least LQW/2, at least LQW or at least 2*LQW.
In some implementations, improving performance of a LED (e.g., a uLED), such as the examples described herein can include one or more of the following. A desired target for a performance metric can be selected (e.g. IQE, EQE, WPE, wavelength at an operating current density, etc.), where the selected performance metric is not achieved in an LED where less than 3 quantum wells are substantially injected with carriers. A desired number N of quantum wells for lateral injection can be selected, where N is greater than or equal to 3. A series of LEDs (e.g., different wafers) with at least N quantum wells, and with varying structures (e.g. epitaxial stack, device architecture, contact configuration, and so forth) can be produced, with uniform injection into the N quantum wells increasing over the series. A series of LEDs (e.g., different wafers) with at least N quantum wells, and with varying structures (e.g. epitaxial stack, device architecture, contact configuration) can be produced, with the selected performance metric increasing over the series (e.g. the IQE/EQE/WPE increasing, or the wavelength getting closer to a desired value). As a result of one or more of the foregoing, an LED with substantial lateral injection into the N quantum wells, that achieves the desired performance metric can be obtained.
For instance, in an example implementation, an EQE of at least 10% at a current density of 10 A/cm2 can be selected as a desired performance metric. A series of μLED structures with 10 QWs can be grown, where the epitaxial layers are varied across the series (including compositions, thicknesses, and/or doping levels of some epitaxial layers). This can facilitate an increased number of injected quantum wells across the series, and, in turn, lead to obtaining an LED with an increase of EQE to a value above 10%.
In some implementations, a μLED or μLED mesa can have one or more of the following features:
1) A lateral dimension that less than 10 μm, less than 8μm, less than 6 μm, less than 4 μm, less than 3 μm, less than 2 μm, or less than 1.5 μm.
2) A MQW active region, where:
a) QWs of the MQW provide lateral carrier transport.
b) The QWs have a diffusion coefficient of at least 1 cm2/s.
c) The diffusion coefficient is for electrons, for holes, or is an ambipolar diffusion coefficient.
d) The QWs have a diffusion length of at least 0.5 μm, at least 1 μm, at least 2 μm, at least 3 μm, at least 4 μm, at least 6 μm, at least 8 μm, or at least 10 μm for a predetermined operating current (current density).
e) Carrier density in each QW has a lateral uniformity greater than 50%.
f) There are at least 2 QWs, at least 3 QWs, at least 4 QWs, or at least 5 QWs.
3) The LED has an IQE of at least 5%, at least 10%, at least 15%, at least 20%, at least 30%, or at least 50%.
a) The IQE is a peak IQE.
b) The IQE is determined at an operating current density of 10 A/cm2.
4) The LED has an EQE of at least 2%, at least 4%, at least 6%, at least 8%, at least 10%, at least 15%, or at least 20%.
a) The EQE is a peak IQE.
b) The EQE is determined at an operating current density of 10 A/cm2.
5) The LED has an emission wavelength for emitted light of at least 600 nm, at least 550 nm, at least 520 nm, or at least 430 nm.
6) The current density of operation is in a range 1-100 A/cm2, 1-50 A/cm2, 1-20 A/cm2, 0.1-50 A/cm2, 0.1-20 A/cm2, or 0.1-10 A/cm2.
7) Lateral injection facilitates a reduction in efficiency droop.
a) A relative IQE at an operating current density of 10 A/cm2 (relative to a peak IQE) is at least 30%, at least 50%, or at least 70%.
b) The peak IQE is at least 30%, at least 40%, at least 50%, at least 60%, or at least 70%.
8) Lateral injection facilitates injection in multiple QWs, with some QWs on an n-side receiving a substantial hole injection.
9) Less than 50% of injected holes are injected into a top two QWs (e.g., QWs on a p-side).
10) Less than 50% of the light is emitted by a top two QWs.
11) Less than 50% of the holes are confined in the top QW (e.g., a first QW adjacent to the p-side).
12) Less than 50% of emitted light is emitted by the top QW.
13) Diffusion length of holes in the QWs is larger than a lateral dimension of the μLED.
14) Diffusion length of holes in the QWs is larger than a lateral dimension of the LED times a factor of 0.25, times a factor of 0.5, times a factor of 1, times a factor of 2, or times a factor of 5.
15) At least 30%, at least 50%, or at least 70% of holes are injected through interfaces other than horizontal interfaces (e.g., other than an interface arranged along a c-plane).
a) The other interfaces are arranged along semipolar planes.
16) A contact is formed on a non-horizontal surface.
a) The contact is a p-type contact.
b) At least one of the other surfaces is a slanted sidewall.
c) At least one of the other surfaces corresponds to a semipolar pane of a wurtzite crystal structure.
d) The horizontal surface is arranged along (corresponds with) a c-plane of a wurtzite crystal structure.
e) The contact is ohmic.
17) A contact is formed on a horizontal surface.
18) No p-contact is formed on a horizontal surface.
19) The uLED includes a micro-mesa.
a) The micro-mesa has non-vertical sidewalls.
b) The micro-mesa has a c-plane horizontal surface.
c) The micro-mesa has semipolar sidewalls.
20) There is a first p-GaN layer formed on a top (horizontal) surface and a second p-GaN layer formed laterally (e.g. on mesa sidewalls, on non-vertical sidewalls).
a) The first and second p-GaN layers have different doping concentrations.
b) A doping concentration of the first p-GaN layer is less than a doping concentration of the second p-GaN layer.
21) There is a first EBL formed on a top surface and a second EBL formed laterally.
a) The first EBL and the second EBLs have different characteristics (e.g., different compositions, and/or thicknesses).
b) The first EBL and the second EBLs include AlGaN.
22) A first resistance for holes injected from a top surface is different from a second resistance for holes injected laterally.
a) The first resistance is higher than the second resistance.
b) The first and second resistances are contact resistances.
c) The first and second resistances are spreading resistances.
d) The first and second resistances are total resistances.
23) A metallic contact is formed on at least one of a non-vertical sidewalls, or on a horizontal surface.
a) The metallic contact has a reflectivity of at least 80%, at least 90%, or at least 95%.
b) The reflectivity is at normal (orthogonal) incidence, at a peak wavelength of light emission of the μLED.
In some implementations, a μLED can have a geometry as follows:
1) The uLED has a mesa shape, with a horizontal top surface and at least three non-vertical sidewalls.
2) A first portion of the uLED has first epitaxial layers oriented along a horizontal direction, where the first epitaxial layers include a first plurality of quantum wells with a first thickness and a first bandgap.
3) A second portion of the μLED has second epitaxial layers oriented along the non-vertical sidewalls, where the second epitaxial layers include a second plurality of quantum wells with a second thickness and a second bandgap.
4) Contacts are formed on at least one of the horizontal top surface, or on the non-vertical sidewalls.
5) One or more of the following aspects can be present:
a) The first portion of the LED is located near the center of the mesa.
b) The first portion of the LED has a lateral width of at least 500 nm, at least 1 μm, or at least 2 μm.
c) The mesa has a width of less than 20 μm, less than 10 μm, less than 5 μm, or less than 2 μm.
d) The mesa has a height of at least 100 nm, at least 200 nm, at least 500 nm, at least 1 μm, or at least 2 μm.
e) The mesa has a height of less than 10 μm, less than 5 μm, less than 2 μm, or less than 1 μm.
f) The second portion of the μLED is located near the sidewalls of the mesa.
g) The horizontal direction is along a c-plane and the non-vertical sidewalls are along semipolar planes.
h) The non-vertical sidewalls have an angle from the vertical direction that is at least 10 degrees, or at least 20 degrees.
i) The non-vertical sidewalls have an angle from the vertical direction that is less than 80 degrees, or at least 70 degrees.
j) QWs of the first plurality of QWs, and QWs of the second plurality of QWs are respectively connected to each other in a one-to-one relationship.
k) The second bandgap is greater than the first bandgap.
l) The second thickness is less than the first thickness
m) Contacts are formed on the horizontal top surface.
In some implementations, possible electrical contacts include metallic contacts, such as contacts including silver, aluminum, gold, titanium, nickel, platinum, and/or tungsten, as well multi-layer contacts and alloys. In some implementations, transparent metal contacts can be used, such as indium tin oxide, zinc oxide, and/or indium zinc oxide, as well as stacks of transparent metal contact materials.
In some implementations, a μLED can be configured and operated to increase lateral injection as compared to vertical injection. Such approaches may be desirable because vertical injection can lead to carriers spreading to fewer QWs, whereas lateral injection can lead to more QWs being injected for a same total current. Accordingly, in some implementation, a resistance for lateral injection can be lower than a resistance for vertical injection, which can be facilitated by configuration of the respective contact resistances (or even the Schottky barrier heights), by the use of spreading resistances (e.g., achieved through doping and thickness control), and/or by other approaches. In some implementations, an operating current density can be selected (e.g. 10 A/cm2, or at least 10 A/cm2), and a corresponding LED can be configured (produced) to provide current spreading at the selected current density.
In some examples, a plurality of LED mesas can be connected and operated electrically, to provide a light source for a display, and/or to provide a light source for illumination.
In some implementations, producing a μLED can include:
1) Selecting a minimum number of QWs that is higher than one.
2) Selecting an operating current density.
3) Preparing a series of μLEDs with non-vertical sidewalls and corresponding sidewall contacts.
4) Over the series, configuring the epitaxial layers and the sidewall contacts to facilitate lateral injection of carriers and increase IQE at the selected current density.
5) Obtaining a uLED with an IQE may that is at least 10%, at least 20%, at least 30%, at least 40%, or at least 50%.
In some implementations, a method for improving performance of a μLED can include the following:
1) Preparing a series of LEDs having increasing uniformity of carrier injection, where each LED of the series has an IQE, at a predetermined current density, of at least 20%.
2) Determining respective increases in IQEs, at the predetermined current density, between at least two LEDs of the series, where increases in IQE are facilitated by increases in lateral injection.
3) Preparing at least an additional LED of the series by improving lateral injection relative to a previously obtained highest lateral injection.
4) Repeating steps 2 and 3 until an increase in IQE of at least 5% between two LEDs of said series is obtained.
In some implementation of the method, the predetermined current density can be at least 10 A/cm2, at least 2 A/cm2, at least 5 A/cm2, at least 20 A/cm2, or at least 50 A/cm2.
In some implementations, an active region of a μLED can have QWs separated by barrier layers, and the barrier layers can have a concentration of In (percent composition) of at least 1%, at least 2%, at least 3%, or at least 5%. For instance, the barrier layers can be InGaN layers with an In percent composition of at least 1%, up to 5%. Such approaches can facilitate injection across the barrier layers, and allow for lowering a corresponding μLED's operating voltage. In some implementations, the foregoing example In percent compositions can be for barrier layers in a slanted region of a μLED (e.g., along a semipolar plane), or in a lateral region of a uLED (e.g., a region that is located laterally with respect to a planar region).
In some implementations, uLEDs of different colors (e.g. red, green, and/or blue) can be formed on a same wafer. Combinations of electrical contact schemes can be used. In some implementations, μLEDS of each color can have lateral contacts (and/or lateral carrier injection) and, as a result, can benefit from lateral carrier injection and diffusion. In some implementation, μLEDs of a subset of colors can have lateral contacts (and/or lateral carrier injection). For instance, red LEDs, for which performance may, relative to blue and green LEDs, suffer the most from efficiency droop and/or uneven carrier injection, can achieve more benefit from having lateral contacts and/or lateral carrier injection.
In some implementations, lateral carrier transport in a uLED can occur as a result of following series of events:
1) Holes are injected from a contact layer to a p-material having a slanted orientation, the p-material having a first bandgap and a first thickness.
2) The holes are then injected from the p-material to an intermediate layer having the slanted orientation, a second bandgap, and a second thickness.
3) The holes are injected from the intermediate layer to a plurality of QWs with a planar orientation, a third bandgap and a third thickness.
In some implementation, facilitation of lateral carrier transport in accordance with the foregoing series of event can be achieved where one or more of the following aspects of μLED are present:
1) The uLED has a perimeter that is bound by slanted orientations.
2) The uLED has a perimeter that is bound by p-material.
a) The p-material is located laterally respective to a MQW.
3) The uLED is a mesa with slanted sidewalls along the slanted orientations.
4) The uLED is a mesa with p-material sidewalls.
5) The uLED has one or several inner lateral injection regions, located away from the perimeter, with p-material.
a) The inner lateral regions extend vertically in an MQW region and provide lateral injection in the MQW region.
6) The p-material is p-GaN.
7) The second bandgap is less than the first bandgap, and greater than the third bandgap.
8) The intermediate layer include at least 1% In, at least 2% In, at least 3% In, at least 5% In, or at least 10% In.
9) The QWs include at least 15% In, at least 20% In, at least 30% In, at least 40% In, or at least 50% In.
10) The intermediate layer is a slanted QW.
11) The second thickness is less than the third thickness.
12) The slanted orientation is along a semipolar plane.
13) No more than 30%, no more than 50%, or no more than 70% of the holes are injected into a single QW of the plurality of QWs.
14) The holes diffuse laterally for at least 500 nm, at least 1 um, or at least 2 um in the planar (horizontal) direction in the QWs.
15) The holes are further injected through other layers, such as non-planar EBL layers (e.g. slanted EBL layers, vertical EBL layers), as they are injected from the p-material to the intermediate layer.
While the foregoing discussion is generally directed to uLEDs, in some implementations, the approaches described herein can be used to implement and operate other optoelectronic devices, such as large-scale LEDs (e.g., with lateral dimensions of 100 um or more, 500 um or more, 1 mm or more). In the case of a large LED, a plurality of lateral injection regions may be formed across the LED to promote lateral hole injection. For instance, a plurality of p-doped injection regions, similar to those of
In the foregoing discussion regarding vertical carrier transport, and as used herein, slanted refers to an orientation which is neither along a horizontal, nor along a vertical direction (e.g., such as described with respect to the example μLED implantation of
In some example, a LED (e.g., a μLED) can operate with lateral carrier diffusion (lateral carrier transport) occurring in one or more doped semiconductor layers, which may not be active, light-emitting layers. For instance, in some implementations, a μLED can include one or more tunnel junctions (TJs), where a TJ includes an n-doped layer, a p-doped layer, and can include one or more junction layers between the n-doped and the p-doped layer. A TJ can operate such that electrons in an n-doped layer (on a first side of the TJ) tunnel through the TJ and become holes in a p-doped layer (on a second, opposite side of the TJ). In such implementations, a corresponding LED can be configured such that lateral carrier diffusion (e.g., for electrons) occurs in n-doped layers, which can lead to better current spreading than if only p-layers were used for current spreading.
In this example, the contact 2235b only contacts (is only disposed on) a portion of n-doped layer 2220b. As shown in
The LED 2300 differs from the LED 2200 in that a QW active region 2330b is disposed on the 2320b, a p-doped layer 2325b is disposed on the QW active region 2330b. A contact 2335c is made to the p-doped layer 2325b, which can uniformly inject holes into the p-doped layer 2325b. By applying an appropriate voltage between the contact 2335c and the 2335b, the QW active region 2330b can be controlled to emit light. For instance, electrons spread laterally in the n-doped layer 2320b, which facilitating uniform electron injection into the QW active region 2330b (or into the TJ 2360 when operating the QW active region 2330a).
In some implementations, a LED can have more than two QW active regions. In such implementation, TJs can be formed between each of the QW active regions (e.g., an LED with three QW active regions can include two TJs). For instance, in some implementations, a diode can have a blue QW active region, a green QW active region, and a red QW active region. By driving appropriate voltages across QW regions, uniform current injection and light emission can be obtained, where the TJs facilitate lateral current spreading and conversion of electrons to holes.
As an example,
As shown in
Referring to
Referring to
In some implementations, lateral conduction through n-type layers and lateral injection through quantum wells can be combined in an LED. For instance, an LED may have a tunnel junction whose n-layers facilitate lateral spreading of holes outside the QW, and a lateral injection region for injection in the QWs.
It will be understood, for purposes of this disclosure, that when an element, such as a layer, a region, or a substrate, is referred to as being on, disposed on, disposed in, connected to, electrically connected to, coupled to, or electrically coupled to another element, it may be directly on, connected or coupled to the other element, or one or more intervening elements may be present. In contrast, when an element is referred to as being directly on, directly disposed on, directly disposed in, directly connected to or directly coupled to another element or layer, there are no intervening elements or layers present. Although the terms directly on, direct in, directly connected to, or directly coupled to may not be used throughout the detailed description, elements that are shown as being directly on, directly connected or directly coupled can be referred to as such. The claims of the application may be amended to recite exemplary relationships described in the specification or shown in the figures.
As used in this specification, a singular form may, unless definitely indicating a particular case in terms of the context, include a plural form. Spatially relative terms (e.g., over, above, upper, under, beneath, below, lower, and so forth) are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. In some implementations, the relative terms above and below can, respectively, include vertically above and vertically below. In some implementations, the term adjacent can include laterally adjacent to, vertically adjacent to, or horizontally adjacent to.
Some implementations may be implemented using various semiconductor processing and/or packaging techniques. Some implementations may be implemented using various types of semiconductor processing techniques, such as epitaxial growth processes, associated with semiconductor substrates and materials including, but not limited to, for example, silicon (Si), gallium arsenide (GaAs), gallium nitride (GaN), silicon carbide (SiC), and/or so forth.
While certain features of various example implementations have been illustrated as described herein, many modifications, substitutions, changes and equivalents will now occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the scope of the implementations. It should be understood that they have been presented by way of example only, not limitation, and various changes in form and details may be made. Any portion of the apparatus and/or methods described herein may be combined in any combination, except mutually exclusive combinations. The implementations described herein can include various combinations and/or sub-combinations of the functions, components and/or features of the different implementations described.
This application claims the priority benefit of U.S. Provisional Application No. 63/254,840, entitled “SMALL DEVICES WITH LATERAL CURRENT INJECTION”, filed Oct. 12, 2021, and of U.S. Provisional Application No. 63/347,066, entitled “SMALL DEVICES WITH LATERAL CURRENT INJECTION”, filed May 31, 2022, both of which are hereby incorporated by reference in their entireties.
| Number | Date | Country | |
|---|---|---|---|
| 63254840 | Oct 2021 | US | |
| 63347066 | May 2022 | US |
