Group III-V compound and Group III-VI compound semiconductors have particularly wide band gaps and are capable of emitting green or blue light. Recently, semiconductor devices, such as photo-electric conversion devices using III-V or II-VI group compound semiconductor crystals as base materials have been developed to improve efficiency and life time of the semiconductor devices.
However, one drawback to Group III-V compound and Group II-VI compound semiconductors are their poor optical gain characteristics.
In one embodiment, a semiconductor device includes an active layer and one or more barrier layers disposed on either one side or both sides of the active layer. The active layer may be composed of a first compound semiconductor material, and the one or more barrier layers may be composed of a second compound semiconductor material. In some embodiments, the composition of the one or more barrier layers may be adjusted to increase an optical dipole matrix element.
The foregoing summary is illustrative only and is not intended to be in any way limiting. In addition to the illustrative aspects, embodiments, and features described above, further aspects, embodiments, and features will become apparent by reference to the drawings and the following detailed description.
a) and 1(b) are schematic diagrams of an illustrative embodiment of a semiconductor device.
a) and 2(b) are schematic diagrams showing band gaps of the semiconductor device of
a)-12(e) are schematic diagrams illustrating an illustrative embodiment of a method for fabricating a semiconductor device.
In one embodiment, a semiconductor device includes an active layer composed of a first compound semiconductor, and one or more barrier layers disposed on either one side or both sides of the active layer and composed of a second compound semiconductor material. The composition of the barrier layer can be adjusted to increase an optical dipole matrix element of the active layer.
The optical dipole matrix element can be increased by making the sum of an internal polarization field of the active layer and an internal polarization field of the one or more barrier layers zero. The composition of the active layer can be controlled in accordance with the composition of the one or more barrier layers. A band gap of the first compound semiconductor material is smaller than that of the second compound semiconductor material.
The second compound semiconductor material can include a ternary or a quaternary compound semiconductor material. The first and second compound semiconductor materials can each include a III-V group compound semiconductor material or a II-VI group compound semiconductor material. The first compound semiconductor material can include, for example, GaN, InGaN, AlN, AlP, AlAs, GaP, GaAs, InN, InP, InAs, AlGaN, AlGaP, AlGaAs, InGaN, InGaP, InGaAs, InAlN, InAlP, InAlAs, AlGaInN, AlGaInP, AlGaInAs, ZnO, ZnS, CdO, CdS, CdZnS, CdZnO, MgZnO, MgZnS, CdMgZnO, or CdMgZnS. The second compound semiconductor material can include, for example, AlGaInN, InGaN, AlGaN, AlGaP, AlGaAs, InGaN, InGaP, InGaAs, InAlN, InAlP, InAlAs, AlGaInP, AlGaInAs, CdZnS, CdZnO, MgZnO, MgZnS, CdMgZnO, or CdMgZnS.
In one embodiment, the first compound semiconductor material can be composed of InxGa1−xN (0≦x≦1), and the second compound semiconductor material can be composed of AlGa1−yInyN (0≦y≦1). The variable x can be in the range of about 0 and 0.30 and the variable y can be in the range of about 0.01 and 0.30. The relation between x and y may be linear.
In another embodiment, the first compound semiconductor material can be composed of CdxZn1−xO (0≦x≦1), and the second compound semiconductor material can be composed of MgyZn1−yO (0≦y≦1). The variable x can be in the range of about 0 and 0.20 and the variable y can be in the range of about 0.01 and 0.80. The relation between x and y may be logarithmic.
The thickness of the active layer may be in the range of about 0.1 nm and 300 nm. The thickness of the one or more barrier layers may each be in the range of about 0.1 nm and 500 nm.
In another embodiment, a method for fabricating a semiconductor device is provided. An active layer composed of a first compound semiconductor material can be formed on a substrate. One or more barrier layers can be formed on either one side or both sides of the active layer. The barrier layer can be composed of a second compound semiconductor material. The composition of the barrier layer can be adjusted to increase an optical dipole matrix element of the active layer. The first compound semiconductor material can include a III-V group compound semiconductor material or a II-VI group compound semiconductor material. The second compound semiconductor material can include a quaternary group compound semiconductor material or a ternary group compound semiconductor material. The active layer or the one or more barrier layers can be formed by, for example, radio-frequency (RF) magnetron sputtering, pulsed laser deposition, metal organic chemical vapor deposition (MOCVD), molecular beam epitaxy or radio-frequency plasma-excited molecular beam epitaxy. The composition of the one or more barrier layers can be adjusted by controlling the amount of precursor gases or by controlling a processing temperature or processing time.
In the following detailed description, reference is made to the accompanying drawings, which form a part hereof In the drawings, similar symbols typically identify similar components, unless context dictates otherwise. The illustrative embodiments described in the detailed description, drawings, and claims are not meant to be limiting. Other embodiments may be utilized, and other changes may be made, without departing from the spirit or scope of the subject matter presented herein. It will be readily understood that the aspects of the present disclosure, as generally described herein, and illustrated in the Figures, can be arranged, substituted, combined, separated, and designed in a wide variety of different configurations, all of which are explicitly contemplated herein.
With reference to
As depicted in
In some embodiments, active layer 120 may be composed of a III-V group compound semiconductor material or a II-VI group compound semiconductor material. III-V group semiconductor materials include, without limitation, GaN, InGaN, AlN, AlP, AlAs, GaP, GaAs, InN, InP, InAs, AlGaN, AlGaP, AlGaAs, InGaN, InGaP, InGaAs, InAlN, InAlP, InAlAs, AlGaInN, AlGaInP or AlGaInAs. II-VI group semiconductor materials include, without limitation, ZnO, ZnS, CdO, CdS, CdZnO, CdZnS, MgZnO, MgZnS, CdMgZnO, or CdMgZnS. Active layer 120 can have a thickness of about 0.1 nm to 300 nm, or about 1 nm to 50 nm.
Upper and lower barrier layers 110 and 130 may be composed of a III-V group compound semiconductor material or a II-VI group compound semiconductor material. In some embodiments, upper and lower barrier layers 110 and 130 may also be composed of a ternary compound semiconductor material or a quaternary compound semiconductor material. Examples of ternary or quaternary III-V group compound semiconductor materials include, without limitation, AlGaInN, InGaN, AlGaN, AlGaP, AlGaAs, InGaN, InGaP, InGaAs, InAlN, InAlP, InAlAs, AlGaInP or AlGaInAs. Examples of ternary or quaternary II-VI group compound semiconductor materials include, without limitation, CdZnS, MgZnS, CdZnO, MgZnO, CdMgZnO, or CdMgZnS. Upper and lower barrier layers 110 and 130 may each have a thickness of about 0.1 nm to 500 nm, or about 1 nm to 100 nm.
A quantum efficiency is a quantity defined as the percentage of photons that produces an electron-hole pair, and can be measured by, for example, an optical gain of a semiconductor device. An optical gain g(ω) can be calculated by using a non-Markovian model with many-body effects due to interband transitions. The “many-body effects” refer to a band gap renormalization and an enhancement of optical gain due to attractive electron-hole interaction (Coulomb or excitonic enhancement). Optical gain g(ω) is given by Equation (1) as below. For theory on the optical gain, see Doyeol Ahn, “Theory of Non-Markovian Gain in Strained-Layer Quantum-Well Lasers with Many-Body Effects”, IEEE Journal of Quantum Electronics, Vol. 34, No. 2, pp. 344-352 (1998), and Ahn et al., “Many-Body Optical Gain and Intraband Relaxation Time of Wurtzite InGaN/GaN Quantum-Well Lasers and Comparison with Experiment”, Appl. Phys. Lett. Vol. 87, p. 044103 (2005), which are incorporated by reference herein in their entireties.
where ω is an angular frequency of photon in active layer 120; μ is a vacuum permeability; nr is a refractive index of active layer 120; c is the speed of light in free space; V is the volume of active layer 120; ƒc and ƒhσ are the Fermi functions for conduction band and valence band of Hσ, respectively; Mlmη σ({right arrow over (k)}∥) is the dipole matrix element between the conduction band with a spin state η and the valence band of the 3×3 block Hamiltonian Hσ; {circumflex over (ε)} is the unit vector in the direction of the photon polarization; and Clmησ({right arrow over (k)}∥) is a renormalized lineshape function.
As shown in Equation (1) above, optical gain g(ω) increases in accordance with the increase of an optical dipole matrix element Mlmη σ({right arrow over (k)}∥) for example, the increase of an optical dipole matrix element Mlmη σ({right arrow over (k)}∥) in quantum well 240. The optical dipole matrix element Mlmη σ({right arrow over (k)}∥) increases as the electron-hole separation becomes narrower. Further, the electron-hole separation becomes narrower as an internal polarization field decreases. Accordingly, the optical dipole matrix element Mlmη σ({right arrow over (k)}∥) is largely enhanced due to the disappearance of the internal polarization field. For additional detail on the relationship between the optical dipole matrix element and the internal polarization filed, see Ahn et al., “Optical Gain in InGaN/InGaAlN Quantum Well Structures with Zero Internal Field”, Appl. Phys. Lett. Vol. 92, p. 171115 (2008), which is incorporated by reference herein in its entirety.
An internal polarization field in quantum well 240 arises from a spontaneous polarization PSP and a piezoelectric polarization PPZ. Piezoelectric polarization PPZ refers to a polarization that arises from the electric potential generated in response to applied mechanical stress, such as a strain of a layer. Spontaneous polarization PSP refers to a polarization that arises in ferroelectrics without external electric field. Although piezoelectric polarization PPZ can be reduced by reduction of the strain, spontaneous polarization PSP remains in quantum well 240. For additional detail on spontaneous and piezoelectric polarizations and the internal polarization field, see Ahn et al., “Spontaneous and piezoelectric polarization effects in wurtzite ZnO/MgZnO quantum well lasers”, Appl. Phys. Lett. Vol. 87, p. 253509(2005), which is incorporated herein by reference in its entirety.
Thus, the increasing of optical gain g(ω) is achieved by the reduction of a total internal polarization field including the spontaneous and piezoelectric polarizations. The total internal polarization field Fzw in quantum well 240 can be determined from the difference between the sum of spontaneous polarization PSP and piezoelectric polarization PPZ in quantum well 240 and the sum of spontaneous polarization PSP and piezoelectric polarization PPZ in upper and lower barrier layers 110 and 130, as represented by Equation (2) below.
F
Z
W=[(PSPb+PPZb)−(PSPw+PPZw)]/(εw+εb Lw/Lb) Equation (2)
where P is the polarization, the superscript w and b denote quantum well 240 and upper and lower barrier layers 110 and 130 respectively, L is the thickness of a layer, and ε is the static dielectric constant.
In one embodiment, total internal polarization field Fzw can have a value of zero by making sum (PSPb+PPZb) of the spontaneous and piezoelectric polarizations at upper and lower barrier layers 110 and 130 and the sum (PSPw+PPZw) of the spontaneous and piezoelectric polarizations at quantum well 240 the same. For example, this can be achieved by controlling the mole fractions of the compound in upper and lower barrier layers 110 and 130, with respect to active layer 120.
With reference to
As depicted in
AlGaInN barrier layer 310 may have a thickness of several nanometers to several hundreds nanometers (nm). For example, AlGaInN barrier layer 310 may have a thickness of about 0.1 nm to 500 nm, or about 1 nm and to 100 nm. In other embodiments, a III-V group compound semiconductor material having a band gap greater than a band gap of a III-V group compound semiconductor material of the active layer can be selected for the barrier layer.
InGaN active layer 320 has a smaller band gap than the band gap of AlGaInN barrier layer 310, thus forming a quantum well in InGaN active layer 320. For example, the band gap of InGaN active layer 320 is in the range of about 0.7 eV and 3.4 eV, and the band gap of AlGaInN barrier layer 310 is in the range of about 0.7 eV and 6.3 eV. The difference between the band gaps of InGaN active layer 320 and AlGaInN barrier layer 310 can be controlled by adjusting the composition of InGaN active layer 320, the composition of AlGaInN barrier layer 310, or the compositions of both InGaN active layer 320 and AlGaInN barrier layer 310. In some embodiments, aluminum (Al) composition of AlGaInN barrier layer 310 can be controlled so that AlGaInN barrier layer 310 has a larger band gap than that of InGaN active layer 320. For example, the composition of AlGaInN barrier layer 310 can be controlled to achieve a mole fraction of Al composition of the range of about 0.05 to about 0.3, assuming that the total mole value of III group semiconductor materials, that is, Al, In, and Ga is one.
As illustrated with respect to Equation (2) above, the internal polarization field in the quantum well can be reduced by controlling the mole fractions of the compositions of InGaN active layer 320 and AlGaInN barrier layer 310, which will now be described in detail.
The graph shown in
As depicted in
The In composition of active layer 320 and barrier layer 310 can be controlled. The graph shown in
As shown in the graph of
Accordingly, by using the linear line of the zero internal polarization field as shown in
In some embodiments, the relationship between III-V group compound semiconductor materials of an active layer and a barrier layer can show a non-linear relationship, such as logarithmic or exponential relationship in accordance with the type of the III-V group compound semiconductor materials of the active layer and the barrier layer and the variety of compositions of the III-V group compound semiconductor materials.
In some embodiments, the mole fractions of In compositions of InGaN active layer 320 and AlGaInN barrier layer 310 can be selected based on the amount of the compressive strain in a layer. Since the higher In composition (e.g., about 0.3 or more) of InGaN active layer 320 results in a larger compressive strain, and the growth of the strained layers is limited to a critical thickness, the lower In composition (e.g., about 0.01 to 0.30) of AlGaInN barrier layer 310 can be selected.
As described above, optical dipole matrix element Mlmησ({right arrow over (k)}∥) in the quantum well increases as the internal polarization field decreases. Accordingly, by reducing the internal polarization field, the optical dipole matrix element can be increased and, thus, optical gain g(ω) can be enhanced. The change of the optical dipole matrix for different compositions of the barrier layer is illustrated in
The graph shown in
The graph shown in
In another embodiment, a semiconductor device may have a II-VI group compound semiconductor material. Such a II-VI group compound semiconductor device will be described with reference to
As depicted in
Upper and lower MgZnO barrier layers 810 and 830 each may have a thickness of several nanometers to several hundreds nanometers. For example, upper and lower MgZnO barrier layers 810 and 830 can each have a thickness of about 0.1 nm to 500 nm, or about 1 nm and to 100 nm. The II-VI group compound semiconductor material of the upper and lower barrier layers (e.g., MgZnO barrier layers 810 and 830) have wider band gaps than that of the II-VI group compound semiconductor material of the active layer (e.g., CdZnO active layer 820), thus forming a quantum well in the active layer (e.g., CdZnO active layer 820). In other embodiments, a II-VI group compound semiconductor material having a wider band gap than that of a II-VI group semiconductor material of the active layer can be selected for the upper and lower barrier layers.
CdZnO active layer 820 has a band gap of about 2.2 eV to 3.35 eV, and upper and lower MgZnO barrier layers 810 and 830 each have a band gap of about 3.35 eV to 5.3 eV. The band gaps of MgZnO compound semiconductor material and CdZnO compound semiconductor material can vary depending on the compositions of Mg, Zn or Cd. Thus, due to the differences between the band gaps of CdZnO active layer 820 and MgZnO barrier layers 810 and 830, a quantum well is formed in CdZnO active layer 820. As illustrated with respect to Equation (2) above, the internal polarization field in the quantum well can be reduced by controlling the mole fractions of the compositions of CdZnO active layer 820 and upper and lower MgZnO barrier layers 810 and 830.
With reference to the graph shown in
As an example, when Cd composition of CdxZn1−xO active layer 820 and Mg composition of upper and lower MgyZn1−yO barrier layers 810 and 830 are approximately zero and 0.1, respectively (that is, semiconductor device 800 has the active/barrier layers of ZnO/Mg0.1Zn0.9O), the internal polarization field becomes approximately zero. As another example, the internal field becomes approximately zero when the variables x and y are approximately 0.05 and 0.37, 0.1 and 0.5, 0.15 and 0.6, and 0.2 and 0.7, respectively. In the case where the variables x and y are 0.2 and 0.7, respectively, semiconductor device 800 has the active/barrier layers of Cd0.2Zn0.8O/Mg0.7Zn0.3O. When Cd composition (x) of CdxZn1−xO active layer 820 is in the range of about zero (0) and 0.2, Mg composition (y) of upper and lower MgyZn1−yO barrier layers 810 and 830 can be in the range of about 0.01 and 0.8.
The relationship between Mg and Cd compositions is illustrated in graph (a) of
Graph (b) in
Graph (a) in
Graph (b) in
With reference to
As depicted in
A lower barrier layer 1230 can be optionally formed over buffer layer 1220, as depicted in
As depicted in
As depicted in
In some embodiments, lower barrier layer 1230 or upper barrier layer 1250 can be selectively formed on active layer 1230. For example, semiconductor device 1200 can have lower barrier layer 1230 disposed on a bottom surface of active layer 1230, upper barrier layer 1250 disposed on a top surface of active layer 1230, or both lower and upper barrier layers 1230 and 1250 disposed on the bottom and top surfaces, respectively, of active layer 1230.
As depicted in
A semiconductor device (e.g., semiconductor device 1200) fabricated according to the illustrated method can reduce internal polarization field in a quantum well by forming one or more barrier layers (e.g., upper barrier layer 1250 and lower barrier layer 1230) of a III-V group or a II-VI group compound material on an active layer (e.g., active layer 1240) of a III-V group or a II-VI group compound material. Further, the semiconductor device can reduce the internal polarization field in the quantum well by controlling the mole fractions of a II-VI group compound material or a III-V group compound material in the active layer (e.g., active layer 1240) or the one or more barrier layers (e.g., upper barrier layer 1250 and lower barrier layer 1230). Through the reduction of the internal polarization field in the quantum well, the optical dipole matrix of the active layer (e.g., active layer 1240) is enlarged and the optical gain of the semiconductor device (e.g., semiconductor device 1200) enhanced.
In some embodiments, a photo-electric conversion device, an optoelectronic device, a quantized electronic device, a short wavelength emitter, a photo detector, a laser, a high electron mobility transistor, or a light emitting device in which the semiconductor device (e.g. semiconductor devices 100, 300, 800, and 1200) described above is installed can be provided.
One skilled in the art will appreciate that, for this and other processes and methods disclosed herein, the functions performed in the processes and methods may be implemented in differing order. Furthermore, the outlined steps and operations are only provided as examples, and some of the steps and operations may be optional, combined into fewer steps and operations, or expanded into additional steps and operations without detracting from the essence of the disclosed embodiments.
The present disclosure is not to be limited in terms of the particular embodiments described in this application, which are intended as illustrations of various aspects. Many modifications and variations can be made without departing from its spirit and scope, as will be apparent to those skilled in the art. Functionally equivalent methods and apparatuses within the scope of the disclosure, in addition to those enumerated herein, will be apparent to those skilled in the art from the foregoing descriptions. Such modifications and variations are intended to fall within the scope of the appended claims. The present disclosure is to be limited only by the terms of the appended claims, along with the full scope of equivalents to which such claims are entitled. It is to be understood that this disclosure is not limited to particular methods, reagents, compounds compositions or biological systems, which can, of course, vary. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only, and is not intended to be limiting.
With respect to the use of substantially any plural and/or singular terms herein, those having skill in the art can translate from the plural to the singular and/or from the singular to the plural as is appropriate to the context and/or application. The various singular/plural permutations may be expressly set forth herein for sake of clarity.
It will be understood by those within the art that, in general, terms used herein, and especially in the appended claims (e.g., bodies of the appended claims) are generally intended as “open” terms (e.g., the term “including” should be interpreted as “including but not limited to,” the term “having” should be interpreted as “having at least,” the term “includes” should be interpreted as “includes but is not limited to,” etc.). It will be further understood by those within the art that if a specific number of an introduced claim recitation is intended, such an intent will be explicitly recited in the claim, and in the absence of such recitation no such intent is present. For example, as an aid to understanding, the following appended claims may contain usage of the introductory phrases “at least one” and “one or more” to introduce claim recitations. However, the use of such phrases should not be construed to imply that the introduction of a claim recitation by the indefinite articles “a” or “an” limits any particular claim containing such introduced claim recitation to embodiments containing only one such recitation, even when the same claim includes the introductory phrases “one or more” or “at least one” and indefinite articles such as “a” or “an” (e.g., “a” and/or “an” should be interpreted to mean “at least one” or “one or more”); the same holds true for the use of definite articles used to introduce claim recitations. In addition, even if a specific number of an introduced claim recitation is explicitly recited, those skilled in the art will recognize that such recitation should be interpreted to mean at least the recited number (e.g., the bare recitation of “two recitations,” without other modifiers, means at least two recitations, or two or more recitations). Furthermore, in those instances where a convention analogous to “at least one of A, B, and C, etc.” is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., “a system having at least one of A, B, and C” would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, etc.). In those instances where a convention analogous to “at least one of A, B, or C, etc.” is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., “a system having at least one of A, B, or C” would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, etc.). It will be further understood by those within the art that virtually any disjunctive word and/or phrase presenting two or more alternative terms, whether in the description, claims, or drawings, should be understood to contemplate the possibilities of including one of the terms, either of the terms, or both terms. For example, the phrase “A or B” will be understood to include the possibilities of “A” or “B” or “A and B.”
In addition, where features or aspects of the disclosure are described in terms of Markush groups, those skilled in the art will recognize that the disclosure is also thereby described in terms of any individual member or subgroup of members of the Markush group.
As will be understood by one skilled in the art, for any and all purposes, such as in terms of providing a written description, all ranges disclosed herein also encompass any and all possible subranges and combinations of subranges thereof. Any listed range can be easily recognized as sufficiently describing and enabling the same range being broken down into at least equal halves, thirds, quarters, fifths, tenths, etc. As a non-limiting example, each range discussed herein can be readily broken down into a lower third, middle third and upper third, etc. As will also be understood by one skilled in the art all language such as “up to,” “at least,” and the like include the number recited and refer to ranges which can be subsequently broken down into subranges as discussed above. Finally, as will be understood by one skilled in the art, a range includes each individual member. Thus, for example, a group having 1-3 cells refers to groups having 1, 2, or 3 cells. Similarly, a group having 1-5 cells refers to groups having 1, 2, 3, 4, or 5 cells, and so forth.
From the foregoing, it will be appreciated that various embodiments of the present disclosure have been described herein for purposes of illustration, and that various modifications may be made without departing from the scope and spirit of the present disclosure. Accordingly, the various embodiments disclosed herein are not intended to be limiting, with the true scope and spirit being indicated by the following claims.