Patent Application
20240030686
A light-emitting semiconductor chip and a method for manufacturing a light-emitting semiconductor chip are specified.
Laser light sources are often used in optical devices such as projectors, so-called VR and/or AR glasses (VR: “virtual reality”; AR: “augmented reality”, etc.). However, due to the physical nature of coherent laser radiation, certain image artifacts such as interference and/or light granulation known as speckles or the like may occur, which are undesirable in many applications. In order to improve the image quality in this respect, it can be helpful to work with multiple-emitter devices, which, in the optimum case, have emission wavelengths that are shifted relative to one another. Particularly advantageous here can be devices with 2, 3, 4 or more emitters whose emission wavelengths are shifted relative to one another in a defined manner.
Changes in wavelength can be achieved by varying the laser geometry such as ridge width, resonator length and/or mirroring. However, these wavelength changes are usually accompanied by a change in laser parameters such as threshold, slope and operation current, which is undesirable since all emitters on a chip should have comparable laser parameters. Multiple-epitaxy can also be used to produce emitters with different wavelengths. However, this requires a high technical effort and is expensive. The epitaxy can also be influenced by strain-changing structures on the wafer in such a way that locally different wavelengths are formed. However, these structures require additional space on the chip, which is expensive, and can have undesirable side effects on laser parameters such as the far-field width.
The approaches chosen so far, for example a variation of the optical waveguide geometry parameters and/or the mirroring, are thus technically very difficult to implement in some cases and inevitably lead to a variation of the operating parameters with the emission wavelength, whereas a retention of comparable operating parameters would be desirable.
Embodiments provide a light-emitting semiconductor chip. Further embodiments provide a method for manufacturing a light-emitting semiconductor chip.
According to at least one embodiment, a light-emitting semiconductor chip comprises a semiconductor body having at least one emitter unit. Preferably, the light-emitting semiconductor chip comprises a plurality of emitter units, for example greater than or equal to 2 or greater than or equal to 3 or greater than or equal to 4 emitter units. Particularly preferably, the emitter units may be of the same or at least similar design, unless otherwise described. Particularly preferably, the plurality of emitter units is monolithically formed in the semiconductor body. In a method for manufacturing the light-emitting semiconductor chip, the semiconductor body is grown, for example on a substrate, the semiconductor body comprising the one or the plurality of emitter units. Unless otherwise specified, the features described below apply equally to a light-emitting semiconductor chip having one emitter unit and also to a light-emitting semiconductor chip having a plurality of emitter units. Furthermore, the following description applies equally to the light-emitting semiconductor chip as well as to the method for manufacturing the light-emitting semiconductor chip.
Each of the at least one emitter unit has an active region that is configured and intended to generate light during operation. Light may refer here and hereinafter in particular to electromagnetic radiation having one or more spectral components in an infrared to ultraviolet wavelength range. Accordingly, the terms light, radiation and electromagnetic radiation may be used interchangeably. The light generated in the active region may be specified by a characteristic wavelength. In this context, the characteristic wavelength may denote the wavelength of the spectrum of the generated light with the highest intensity. Alternatively, the characteristic wavelength may denote the average wavelength of the spectral range in which the generated light lies. Furthermore, the characteristic wavelength can also denote the average wavelength of the spectrum of the generated light weighted over the individual spectral intensities.
Furthermore, the active region of each of the at least one emitter unit is arranged in a resonator. The resonator is configured in particular to amplify the light generated in the active region. For example, the resonator can define a radiation emission direction along which light is emitted by an emitter unit during operation.
The semiconductor body can be manufactured as a semiconductor layer sequence based on different semiconductor material systems depending on the wavelength. For long-wave, infrared to red radiation, for example, a semiconductor layer sequence based on InxGayAl1-x-yAs, for red to yellow radiation, for example, a semiconductor layer sequence based on InxGayAl1-x-yP and for short-wave visible, i.e. in particular in the range from green to blue light, and/or for UV radiation for example a semiconductor layer sequence based on InxGayAl1-x-yN is suitable, wherein in each case 0≤x≤1 and 0≤y≤1 applies.
In particular, the semiconductor body can have or be a semiconductor layer sequence, especially preferably an epitaxially grown semiconductor layer sequence. In particular, the semiconductor body may be deposited on a substrate. For this purpose, the semiconductor layer sequence can be grown on a growth substrate by means of an epitaxy process, for example metal-organic vapor phase epitaxy (MOVPE) or molecular beam epitaxy (MBE), and provided with electrical contacts. By separating the growth substrate with the grown semiconductor layer sequence, a plurality of light-emitting semiconductor chips can be produced. Further, the semiconductor body can be transferred to a carrier substrate before singulation, and the growth substrate can be thinned or completely removed. The substrate may comprise a semiconductor material, such as a compound semiconductor material system mentioned above. In particular, the substrate may comprise or be made of sapphire, GaAs, GaP, GaN, InP, SiC, Si, and/or Ge.
The semiconductor body and in particular the at least one emitter unit can have as active region, for example, a conventional pn junction, a double heterostructure, a single quantum well structure (SQW structure) or a multiple quantum well structure (MQW structure). Furthermore, cascades of type-II transitions (ICL: “interband cascade laser”) or transitions only in the conduction band (QCL: “quantum cascade laser”) are also possible, for example. In addition to the active region, the semiconductor body can comprise further functional layers and functional regions, such as p- or n-doped charge carrier transport layers, i.e. electron or hole transport layers, undoped or p- or n-doped confinement, cladding or waveguide layers, barrier layers, planarization layers, buffer layers, protective layers and/or electrical contact points such as electrode layers, as well as combinations thereof. Furthermore, additional layers, such as buffer layers, barrier layers and/or protective layers can also be arranged perpendicular to the growth direction of the semiconductor body, for example around the semiconductor body, i.e. for example on the side surfaces of the semiconductor body.
For example, the active region of each of the emitter units may be formed as a laser medium in which, in operation, a population inversion is generated in conjunction with a suitable resonator. Due to the population inversion, the light in the active region is generated by stimulated emission resulting in the generation of laser light. Due to the generation of light by stimulated emission, the laser light usually has a very high coherence length, a very narrow emission spectrum, and/or a high degree of polarization, unlike light generated by spontaneous emission. The laser light generated in the active region forms one or more standing waves within the respective resonator corresponding to a respective length of the resonator. For this purpose, the length of the respective resonator can generally be an integer multiple of half the wavelength of the light generated in the active region during operation.
According to a further embodiment, the resonator of each of the emitter units has an outcoupling side and a rear side. In particular, the outcoupling side and the rear side may be formed by opposing side surfaces of the semiconductor body. Via the outcoupling side, an emitter unit can emit light during operation. For this purpose, the outcoupling side can be non-reflective or preferably partially reflective. The rear side can be embodied in such a way that no light or at least less light is emitted than via the outcoupling side. Thus, for example, the rear side can be fully mirrored or also partially mirrored. Furthermore, it is also possible for the rear side to be non-reflective.
“Anti-reflective” can mean here and hereinafter that there is as little reflection as possible, which may correspond to a reflection coefficient of less than or equal to 5% or of less than or equal to 2% or preferably of less than or equal to 1%. “Fully mirrored” can mean here and hereinafter that there is as little transmission as possible, which may correspond to a reflection coefficient of greater than or equal to 95% or of greater than or equal to 98% or preferably of greater than or equal to 99%. “Partially mirrored” can mean here and hereinafter that there is a reflection coefficient that is between the aforementioned values for anti-reflective and fully mirrored. Terms such as “non-reflective”, “partially reflective”, “fully reflective”, “reflective”, etc., refer beforehand and hereinafter, unless otherwise specified, to the light generated in the active region of the emitter units.
According to a further embodiment, the emission directions of the emitter units point in the same direction. The emitter units of the light-emitting semiconductor chip thus emit light in the same direction during operation. Furthermore, the emitter units can be formed next to each other in the semiconductor body, particularly preferably perpendicular to the radiation emission direction, so that the outcoupling side and the rear side of the emitter units can preferably be formed by the same side surfaces of the semiconductor body in each case.
According to a further embodiment, each emitter unit has the active region fully penetrated by at least one recess in the semiconductor body. This can mean that each emitter unit has at least one recess that completely penetrates the active region. In other words, the active region of each emitter unit is interrupted by a recess. The at least one recess is formed, for example, as a gap or slit and particularly preferably has a main extension direction that is non-parallel and preferably perpendicular to the radiation emission direction.
According to a further embodiment, each of the emitter units has a recess that is separate from the recesses of the other emitter units. In other words, the semiconductor body has separate recesses, with the active region of each emitter unit penetrated by a dedicated recess. Alternatively, the semiconductor body may have a recess extending through the active regions of two or more, and preferably all, of the emitter units. In the latter case, all active regions of the light-emitting semiconductor chip can thus be penetrated by a single recess.
The embodiments and features described below for the at least one recess refer both to the case where each of the emitter units has a respective recess dedicated to it and to the case where a common recess extends through the active regions of more than one emitter unit. Thus, the at least one recess referred to in the following may refer to a respective recess dedicated to each emitter unit or to a common recess.
According to a further embodiment, for each emitter unit the at least one recess has a first side surface and a second side surface opposite the first side surface. The first and second side surfaces are arranged in particular one after the other along the radiation emission direction and are thus those side surfaces of the at least one recess by which the at least one recess is bounded along the radiation emission direction. For example, the recess has a rectangular base surface. For example, the first side surface and the second side surface run parallel to the main extension direction. Furthermore, the recess may have, for example, a wedge-shaped and/or an at least partially rounded base surface. For this purpose, at least one side surface can run at least partially obliquely to the main extension direction and/or can run at least partially curved.
For each emitter unit, the at least one recess in the region of the active region has a recess width that is measured along the radiation emission direction. In particular, the recess width can thus be measured in a direction that is perpendicular or substantially perpendicular to the main extension direction of the recess. In the case of a recess having a non-rectangular base surface, the recess width may preferably be an average width averaged over the region in which light is generated in the respective emitter unit during operation. Preferably, for each emitter unit, the recess width is greater than or equal to 100 nm or greater than or equal to 300 nm or greater than or equal to 500 nm and less than or equal to 20 μm or less than or equal to 10 μm or less than or equal to 5 μm.
According to a further embodiment, the recess widths of the emitter units are at least partially different. In other words, at least one first emitter unit has a first recess width and at least one second emitter unit has a second recess width, wherein the first and second recess widths are different. In the case of more than two emitter units, the respective recess widths are preferably in pairs different and thus are all different. Furthermore, it is also possible that, for example, groups of two, three or more emitter units, for example pairs or triples of emitter units, have the same recess width, but the recess widths differ from group to group. The groups can have the same or different numbers of emitter units. Thus, for example, it may also be possible for the plurality of emitter units to have a group of multiple emitter units each having the same recess width, while the remaining emitter units of the plurality of emitter units have recess widths that differ from each other. By having a plurality of emitter units in a group, the respective emission spectrum can be amplified in the overall spectrum, for example, which can improve color reproduction. In the case of separately formed recesses for the emitter units, each of the recesses can particularly preferably be formed with a recess width that differs from the recess widths of the other emitter units. In the case of a recess extending through the active regions of several or preferably all emitter units, the recess width of the at least one recess may increase continuously or stepwise from emitter unit to emitter unit.
The recess widths of the emitter units may differ by an amount that is greater than or equal to 1 nm or greater than or equal to 2 nm or greater than or equal to 5 nm or greater than or equal to 10 nm. Further, the recess widths of the emitter units may differ an amount that is less than or equal to 2 μm or less than or equal to 1 μm or less than or equal to 500 nm or less than or equal to 200 nm or less than or equal to 100 nm or less than or equal to 90 nm or less than or equal to 75 nm or less than or equal to 60 nm or less than or equal to 50 nm. Further, the recess widths of the emitter units may differ by an amount that is greater than or equal to 1% or greater than or equal to 2% or greater than or equal to 5% or greater than or equal to 10% and less than or equal to 25% or less than or equal to 20% or greater than or equal to 15% or less than or equal to 10% of the characteristic wavelength of the light generated in the emitter units in operation.
According to a further embodiment, the light-emitting semiconductor chip comprises at least three emitter units, wherein the recess widths of the emitter units differ equidistantly from each other. In other words, the light-emitting semiconductor chip may have a first emitter unit with a first recess width, a second emitter unit with a second recess width, and a third emitter unit with a third recess width. The difference between the first and second recess widths is equal to the difference between the second recess width and the third recess width in the case of an equidistant difference. In the case of a fourth emitter unit having a fourth recess width, the difference between the third and fourth recess widths is equal to the two aforementioned differences. If more than four emitter units are present, the foregoing preferably applies analogously.
In the light-emitting semiconductor chip described here, at least one recess, for example in the form of a slit, is made for each emitter unit. The at least one recess can be defined, for example, by a photo technique and produced by plasma etching and/or wet chemical etching. In particular, all recesses of the semiconductor body can be fabricated together in the same process steps. Due to the at least one recess in the active region of each emitter unit, a wavelength-dependent reflectivity can be achieved, wherein the reflection spectrum is influenced by the recess width, i.e. the slit width.
In a light-emitting semiconductor chip with multiple emitter units, typically all emitter units would have the same wavelength with respect to the light generated in each case, with the same operating parameters. However, if they are to have emission wavelengths that differ from each other by a certain amount, this can be achieved by varying the recess width from emitter unit to emitter unit as described previously. For example, the recess width can increase from a first emitter unit to a last emitter unit. This shifts the reflection maximum so that the different emitter units are forced to different wavelengths. The operating parameters, i.e. in the case of a laser light source the laser parameters such as threshold, slope and voltage, essentially do not change as a result. For all of the following embodiments, the spectral adaptation of the emitter units by changing the recess width is technically easy to realize, but the operating parameters are at least essentially not affected.
For each emitter unit, the at least one recess may preferably be provided and arranged to electrically and/or optically isolate different segments of the emitter units of the semiconductor body from each other. The segments of the emitter units may have the same or different functionalities.
According to a further embodiment, for each emitter unit, the at least one recess has at least one coating that specifies a reflectivity of the recess for the light generated in the active region. In other words, a desired reflectivity of the at least one recess for the light generated in the active region of the respective emitter unit can be set by means of the coating, which can be formed, for example, in the form of one or more layers on at least one or more side surfaces of the at least one recess and/or as a filling. Alternatively, the at least one recess for one or more or all emitter units can also be free of a coating. The reflectivity of the recess can be adjusted for each emitter unit in particular such that the at least one recess is non-reflective, partially reflective or fully reflective as described above. Particularly preferably, the emitter units have the same coating. Particularly preferably, in the case of a coating in the at least one recess, the reflectivity of the at least one recess with the coating is less than or equal to 99.9% and greater than or equal to 80%.
According to a further embodiment, for each emitter unit, the first side surface has a first coating that specifies a reflectivity for the light generated in the active region. Alternatively or additionally, the second side surface has a second coating that specifies a reflectivity for the light generated in the active region. Particularly preferably, the emitter units have an identical coating, i.e. an identical first coating and/or an identical second coating.
According to a further embodiment, the first coating and the second coating are the same. Alternatively, the first and second coatings can also be formed differently from one another.
All features and embodiments described in connection with the first coating can also be embodied in the second coating and vice versa. In particular, the features and embodiments described above and below for the coating can be the same for all emitter units, so that the emitter units preferably differ only in the recess width.
As mentioned before, the first coating and/or the second coating advantageously set the reflectivity for the light of the active region of each of the emitter units to a predetermined value. For example, the first coating provides a different reflectivity for the light generated in the active region than the second coating. For example, the first coating has a low reflectivity while the second coating has a high reflectivity. Likewise, it is possible that the first coating is highly reflective while the second coating is low reflective. Thus, an electrical and/or optical isolation of different segments of the emitter units of the semiconductor body from each other can be achieved.
The term “highly reflective” means in particular that an element so designated reflects at least 20% or at least 40% or at least 50% or at least 80% of the light generated in the active region. The term “low reflective” means in particular that an element so designated reflects at most 20% or at most 5% or at most 2% and at least 0.1% or at least 1% of the light generated in the active region.
According to a further embodiment, the first coating is formed as a first layer sequence with a plurality of individual layers. For example, the individual layers are formed from two different materials and are arranged alternately. More than two different materials may also be used for the individual layers. Alternatively or additionally, the second coating may be formed as a second layer sequence having a plurality of individual layers. For example, the individual layers may have a thickness of λ/2 or λ/4 or multiples thereof, referring to the light generated in the active region, wherein λ can denote the characteristic wavelength of the light generated in the active region.
Preferably, the first coating and/or the second coating has a dielectric material or is formed from a dielectric material. For example, the individual layers have a dielectric material or are formed from a dielectric material. Suitable dielectric materials are, for example, compounds from the group of oxides or nitrides or oxynitrides of Al, Ce, Ga, Hf, In, Mg, Nb, Rh, Sb, Si, Sn, Ta, Ti, Zn, Zr.
For example, the first layer sequence and the second layer sequence are formed from individual layers of the same materials and with the same sequence, wherein a thickness of the first layer sequence in the region of the first side surface and a thickness of the second layer sequence in the region of the second side surface are formed identically or, particularly preferably, differently from one another.
According to a further embodiment, the thickness of the first coating in the region of the first side surface to a thickness of the second coating in the region of the second side surface has a ratio between 1:1 and 1:20 inclusive, preferably between 1:1 and 1:10 inclusive, more preferably between 1:1.5 and 1:4.5 inclusive.
According to a further embodiment, the thickness of the second coating in the region of the second side surface to a thickness of the first coating in the region of the first side surface has a ratio between 1:1 and 1:20 inclusive, preferably between 1:1 and 1:10 inclusive, particularly preferably between 1:1.5 and 1:4.5 inclusive.
According to a further embodiment, the second layer sequence is identical to the first layer sequence except for an additional symmetry-breaking layer. The symmetry-breaking layer can be a single layer or a layer sequence. Alternatively, it is also possible that the first layer sequence is formed identically to the second layer sequence except for an additional symmetry-breaking layer. In particular, a different formation of the first layer sequence and the second layer sequence, for example by including a symmetry-breaking layer and in particular a symmetry-breaking layer sequence in one of the two layer sequences, leads to different optical properties of the first coating and the second coating.
For example, the first coating and the second coating, for each emitter unit, completely fill the at least one recess. Further, it is also possible that between the first coating and the second coating, a region of the recess remains free of the first coating and the second coating. The region of the recess that remains free of the first coating and the second coating may be filled with a further material, which may also be referred to as a filling, and which is preferably formed with or from a dielectric such as silicon dioxide, titanium dioxide, silicon nitride. Thus, loss of light due to large refractive index differences between the semiconductor material and the dielectric can at least be reduced in the light coupling between the regions separated by the at least one recess.
According to a further embodiment, the light-emitting semiconductor chip comprises a semiconductor body having a plurality of emitter units each formed with a first segment and a second segment, the first segment being electrically and/or optically isolated from the second segment by the at least one recess. In particular, the emitter units may be formed identically with respect to the segments.
The first segment and the second segment have different functionalities, for example. Furthermore, it is also possible that several segments of an emitter unit have the same functionality. The first segment and the second segment are particularly preferably arranged along the radiation emission direction of the respective emitter unit. For example, a first contact point is applied to the first segment and a second contact point is applied to the second segment. The two contact points are set up to contact the two segments electrically independently of one another.
Each of the emitter units can also have more than two segments. In the following, only one emitter unit with two segments will be discussed in detail for the sake of simplicity. All embodiments and features disclosed in connection with the first and the second segment can also be embodied for further segments and in particular for all emitter units. Depending on the functionality of the segments, at least one recess can be arranged in the region of the rear side and/or at least one recess can be arranged in the region of the outcoupling side in each emitter unit.
According to a further embodiment, the first segment comprises the light generating part and the second segment comprises a modulation element embodied to modulate an intensity of the light generated in the active region. For example, light is generated in the first segment, preferably laser light, which enters the modulation element through the at least one recess. The modulation element can be made from transmissive to absorbent of the light via the second contact point by a variation in the current, in particular by an electrical control including reverse voltage and forward current. If the modulation element is embodied to be absorbent for the light from the light-generating part, the modulation element is embodied as an absorber element.
According to a further embodiment, the first segment and the second segment are electrically separated from each other and the second segment comprises an electrical switching element embodied to turn the emitter unit on and off.
According to a further embodiment, at least one or more or all of the emitter units comprise a segment having one or more of the following: photodiode, passive waveguide, active waveguide, beam splitter, beam combiner, lens, wavelength selective element, phase shift elements, frequency doubler, taper, amplifier, converter, transistor.
As an alternative to being embodied as a laser light source, the emitter units can also be embodied, for example, as a super luminescent diode, in which amplification of the light generated in the active region takes place within a resonator, but full laser operation is not achieved.
According to a further embodiment, for example, a semiconductor body is provided by growth comprising an active layer having a plurality of active regions embodied and intended to generate light in operation and arranged in a resonator. Each of the active regions is associated with an emitter unit, such that the semiconductor body comprises a plurality of monolithically integrated emitter units, each having an active region.
Furthermore, in each of the emitter units, at least one recess is created in the semiconductor body, wherein, for each of the emitter units, the at least one recess completely penetrates the respective active region. For each of the emitter units, the at least one recess has a first side surface and a second side surface, the first side surface being disposed opposite the second side surface. For example, for each emitter unit, the at least one recess is produced by etching. As described above, for each of the emitter units, the at least one recess has a recess width along the radiation emission direction, which may particularly preferably correspond to a distance between the first and second side surfaces along the radiation emission direction. The emitter units are manufactured such that the recess widths differ. Particularly preferably, this can be produced in a common process step both in the case where each emitter unit has a recess assigned specifically to it and in the case where a recess extends through the active regions of several emitter units.
According to a further embodiment, a coating is applied for each emitter unit, particularly preferably in a common process step, such as a first coating on the first side surface and/or a second coating on the second side surface.
For example, it may also be the case that, for each emitter unit, the second side surface of the at least one recess is provided with a protective layer. In a next step, the first side surface of the at least one recess can be provided with the first coating for each emitter unit and the protective layer can be removed again so that the semiconductor body is freely accessible in the region of the second side surface in each case. For example, a photoresist layer can be used as the protective layer.
For example, the first coating and/or the second coating can be deposited by means of evaporation, sputtering, atomic layer deposition (“ALD”) or chemical vapor deposition (“CVD”).
During evaporation and sputtering, the surface to be coated is provided in a volume. In the volume, at least one starting material in the gas phase is furthermore provided. The starting material condenses directly on the surface, forming a coating on the surface. In vapor deposition, the starting material is vaporized by applying temperature, while in sputtering, the starting material is vaporized by ion bombardment. Vapor deposition and sputtering are generally directional deposition processes in which more material is deposited along one preferred direction than along the other directions.
In the CVD process, the surface to be coated is also provided in a volume. Furthermore, at least one starting material is provided in the volume, from which a solid coating is deposited by a chemical reaction on the surface to be coated. Generally, at least a second starting material is provided in the volume, with which the first starting material chemically reacts to form the solid coating on the surface. Thus, the CVD process is characterized by at least one chemical reaction at the surface to be coated to form the CVD coating. More than two starting materials can also be used in the chemical vapor deposition process.
Atomic layer deposition refers to a process in which the first gaseous starting material is added to the volume in which the surface to be coated is provided, so that the first gaseous starting material adsorbs on the surface. After a preferably complete or nearly complete coverage of the surface with the first starting material, the part of the first starting material that is still present in gaseous form or not adsorbed on the surface is generally removed from the volume again and the second starting material is supplied. The second starting material is intended to react chemically with the first starting compound adsorbed on the surface to form a solid coating.
The CVD process and the ALD process are usually non-directional or also so-called isotropic deposition processes, in which the material is deposited uniformly along all directions.
Furthermore, it may be that the first coating is provided with a further protective layer at least in the region of the first side surface. This step usually takes place after the first coating has been applied to the first side surface. The second side surface particularly preferably remains free of the protective layer.
Furthermore, the second side surface can be provided with the second coating and the further protective layer can be removed again so that the first coating is freely accessible in the area of the first side surface. This is preferably done after the second coating has been applied. With the aid of the two protective layers, it is advantageous to be able to produce two coatings which are different from one another.
As described above, the first coating and the second coating may be applied to the first side surface and the second side surface in sequential steps in time.
According to a further embodiment, the first coating and the second coating are applied simultaneously to the first side surface and the second side surface. In this embodiment of the process, the first coating is preferably formed as a first layer sequence of a plurality of individual layers and the second coating is formed as a second layer sequence of a plurality of second individual layers. Particularly preferably, in this embodiment of the process, the first layer sequence and the second layer sequence have individual layers of the same materials and the same sequence. Particularly preferably, however, the first layer sequence and the second layer sequence differ in their thicknesses. Preferably, a thickness of the first layer sequence in the region of the first side surface to a thickness of the second layer sequence in the region of the second side surface has a ratio between 1:1 inclusive and 1:20 inclusive, preferably between 1:1 inclusive and 1:10 inclusive, particularly preferably between 1:1.5 inclusive and 1:4.5 inclusive.
To produce such coatings, preferably a deposition process is used in which a preferred direction for depositing the first coating and the second coating includes a predetermined angle with a main extension plane of the semiconductor body. Preferably, the angle is not equal to 90°. In this way, a first coating and a second coating can be obtained whose thicknesses, on the first side surface and the second side surface, are different from one another but have the same materials and sequences of individual layers. In other words, a directional deposition process, such as thermal evaporation or sputtering, is particularly preferred here.
According to a further embodiment, prior to applying the first coating and the second coating, a shading element is applied to a region of a major surface of the semiconductor body that is directly adjacent to the first side surface of the at least one recess for each emitter unit, such that the thickness of the first coating in the region of the first side surface is different from the thickness of the second coating in the region of the second side surface. Thus, even with the aid of a shading element, a first coating and a second coating can be applied simultaneously to the side surfaces, which have different thicknesses at least in the region of the first side surface and the second side surface.
According to a further embodiment, the first coating is formed as a first layer sequence with a plurality of individual layers. According to a further embodiment of the method, the second coating is formed as a second layer sequence with a plurality of individual layers.
The at least one recess can be arranged, for each emitter unit, in the region of the rear side or in the region of the outcoupling side. In the region of the rear side can mean in particular that the at least one recess is arranged, along the radiation emission direction, closer to the rear side than to the outcoupling side. In the region of the outcoupling side can mean in particular that the at least one recess is arranged, along the radiation emission direction, closer to the outcoupling side than to the rear side.
In a preferred embodiment, the at least one recess in each emitter unit is preferably formed in the region of the rear side of the resonator so that the rear side reflectivity can be modulated. By means of a purposeful coating, which can advantageously already be applied in the wafer composite, the appropriate reflectivity and modulation is generated depending on the recess width. Due to the fact that the at least one recess is formed in the rear side region, the light coupled out on the outcoupling side does not have to propagate through the at least one recess, resulting in a better beam quality.
Alternatively or additionally, at least one recess can also be formed in the area of the outcoupling side for each emitter unit, wherein a dependence on the recess width also results. This can be particularly advantageous for multi-sectional devices, while the design on the rear side is also possible for “simple” laser resonators.
Furthermore, it is also possible to form at least one recess in the region of the rear side and at least one recess in the region of the outcoupling side for each emitter unit in order to enhance the modulation effect or to achieve even narrower reflection maxima. Since the maxima of the reflection spectrum have a certain spectral width, a significantly narrower wavelength window in which the emitter units must emit can be achieved by two spectra slightly shifted against each other in the region of the rear side and in the region of the outcoupling side. Advantageously, the operation does not depend on the absolute recess width in the emitter units, but only on the relative recess width differences between the emitter units, since the modulation repeats periodically with the recess width. As a result, production fluctuations in the recess width are not critical and this solution is technically very easy to implement.
In the light-emitting semiconductor chip described herein, it may thus be possible to achieve a variation of the wavelength across the individual emitter units of a light-emitting semiconductor chip with a defined shift, which leaves the operating parameters approximately the same. Furthermore, such a solution may be applicable to special devices such as multi-segment lasers, since the formation of multiple segments may extend the functionality of the emitter units with respect to optimal usability in optical devices. For example, a light-emitting semiconductor chip with emitter units can each be formed with an amplifier section and a modulator section in order to be able to continuously control the light output even for low output powers, which can be very advantageous for high contrast imaging.
The light-emitting semiconductor chip described herein may be used in any of the following applications, for example: augmented reality, virtual reality, pico-projection, LIDAR (“light detection and ranging”), message transmission.
With the light-emitting semiconductor chip described here, it is possible in particular to realize different wavelengths with adjacent emitter units in a simple manner, which would otherwise be difficult to achieve. The simplicity of the process allows low-cost production. Due to the different wavelengths, a significantly improved image quality can be achieved, for example in AR/VR applications. The described process is insensitive to process variations, so high and stable manufacturing yields may be achievable. In-situ control is not necessary due to the stability against process fluctuations, which can save costs.
Further advantages, advantageous embodiments and further developments are revealed by the embodiments described below in connection with the figures.
In the embodiments and figures, identical, similar or identically acting elements are provided in each case with the same reference numerals. The elements illustrated and their size ratios to one another should not be regarded as being to scale, but rather individual elements, such as for example layers, components, devices and regions, may have been made exaggeratedly large to illustrate them better and/or to aid comprehension.
In connection with
The light-emitting semiconductor chip 100, which is embodied in particular as a multi-emitter laser light source, has a semiconductor body 1 which has a plurality of emitter units 101. Purely by way of example, four emitter units 101 are indicated in
The semiconductor body 1 is deposited as a semiconductor layer sequence on a substrate 3. For example, the semiconductor body 1 may be grown on the substrate 3 as described in the general part and may have a material described in the general part. The semiconductor layer sequence and in particular the active region 2, which may have for example one or as indicated in the figures several layers, may be formed as described in the general part. For the sake of clarity, no further individual layers of the semiconductor body 1 are indicated in the figures apart from the active region 2.
The active region 2 of each of the at least one emitter unit 10 is arranged in a resonator. In particular, the resonator is configured to amplify the light generated in the active region 2. For example, the resonator as well as an exemplary ridge waveguide structure 24, which may also be referred to as a ridge, may define the radiation emission direction 99 along which light is emitted by an emitter unit 101 during operation. In the illustrated embodiment, the resonator is bounded by a first layer 21 on a rear side and a second layer 23 on an outcoupling side 22, the rear surface 20 and the outcoupling side 22 being side surfaces of the semiconductor body 1. For example, the first layer 21 may be a layer or sequence of layers that partially or fully mirrors the rear side 20, while the second layer 23 may be a layer or sequence of layers that form(s) a partial mirroring on the outcoupling side 22.
A recess 4 is created in the semiconductor body 1 for each emitter unit 101, which completely penetrates the respective active region 2. In the embodiment shown, each emitter unit 101 has a dedicated recess 4 that is separate from the recesses 4 of the respective other emitter units 101. The recesses 4 may penetrate the semiconductor body 1 completely or, as indicated in the figures, partially. In particular, the recesses 4 may extend into a semiconductor layer of the semiconductor body 1 below the active region 2, for example, into a waveguide layer, a cladding layer or a buffer layer.
The recesses 4 each have a first side surface 6 and a second side surface 7 opposite the first side surface 6, and a bottom surface 11. The recesses 4 are created, for example, by etching such as plasma etching and/or wet chemical etching in a common-mask based and photo-based process. For this purpose, one or more etch stop layers may be present in the semiconductor body 1 to stop an etching process of the recesses 4 and thus define the bottom surface 11. Thus, a depth of the recesses 4 can be defined. The cross-sectional view of one of the recesses 4 with vertical side walls 6, 7 indicated in a partial view of a sectional view through the light-emitting semiconductor chip 101 in
The active region 2 of each emitter unit 101 is thus disconnected by a recess 4. The respective recess 4 is formed, for example, as a gap or slit and particularly preferably has a main extension direction, which is non-parallel and preferably perpendicular to the radiation emission direction 99, as indicated in a three-dimensional section in
For each emitter unit 101, the respective recess 4 in the region of the active region 2 has a recess width A, which is measured along the radiation emission direction 99. In particular, the recess width A can thus be measured in a direction that is perpendicular or substantially perpendicular to the main extension direction of the recess 4. Preferably, for each emitter unit 101, the recess width A is greater than or equal to 100 nm or greater than or equal to 300 nm or greater than or equal to 500 nm and less than or equal to 20 μm or less than or equal to 10 μm or less than or equal to 5 μm.
As indicated in
The recess widths A of at least two or more or all of the emitter units 101 may each differ in pairs by an amount that is greater than or equal to 1 nm or greater than or equal to 2 nm or greater than or equal to 5 nm or greater than or equal to 10 nm and that is less than or equal to 2 μm or less than or equal to 1 μm or less than or equal to 500 nm or less than or equal to 200 nm or less than or equal to 100 nm or less than or equal to 90 nm or less than or equal to 75 nm or less than or equal to 60 nm or less than or equal to 50 nm. Further, the recess widths A of the emitter units 101 may differ by an amount that is greater than or equal to 1% or greater than or equal to 2% or greater than or equal to 5% or greater than or equal to 10% and less than or equal to 25% or less than or equal to 20% or greater than or equal to 15% or less than or equal to 10% of the characteristic wavelength of the light generated in the emitter units 101 during operation.
In a particularly preferred embodiment, the recess widths A of the emitter units 101 are equidistantly different from each other. In the embodiment shown, this means that the difference between the recess widths of the two uppermost emitter units 101 shown in
By means of the respective recess 4 in the active region 2 of each emitter unit 101, a wavelength-dependent reflectivity can be achieved, wherein the reflection spectrum is influenced by the respective recess width A. By varying the recess widths A, the emitter units can thereby emit emission spectra E1, E2, E3 and E4 with different emission wavelengths, as exemplified in
For application in other wavelength ranges, for example shorter wavelengths or in the infrared spectral range, such as for infrared imaging, gas sensing or other applications where shifted emission wavelengths in a multi-emitter chip are relevant, typically the relevant wavelength spacing and the total wavelength width to be covered scales with the wavelength itself.
For the present embodiment and for all the following embodiments, the spectral adaptation of the emitter units by changing the slit width is technically easy to realize and it substantially does not affect the operating parameters.
For each emitter unit 101, the respective recess 4 is preferably provided and arranged to electrically and/or optically isolate different segments 25, 26 of the emitter units 101 of the semiconductor body 1 from each other. The segments 25, 26 of the emitter units 101 may have the same or different functionalities. In
The position of the recess 4 of each of the emitter units 101 may be located at any point along the overall resonator length, but preferably in the region and in particular close to the rear side 20, as is the case in the present embodiment, or in the region and in particular close to the outcoupling side 22, as is described further below.
By separating the cavities of the emitter units 101 into two segments or, in the case of forming multiple recesses 4 per emitter unit 101 as shown further below, into more than two segments, the segments can be formed for adjusting different properties of the light-emitting semiconductor chip 100. For example, a segment that is not electrically contacted and thus passive may be formed as a passive mode filter or for spectral broadening, for example in a super luminescent diode. An electrically separately contacted and thus active segment may be formed as a modulator or dimmer or with another functionality as described in the general part.
As can be seen in
Preferably, the first coating 10 and/or the second coating 13 has a dielectric material or is formed from a dielectric material. For example, the individual layers 12 have a dielectric material or are formed from a dielectric material. Suitable dielectric materials include, for example, compounds from the group of oxides or nitrides or oxynitrides of Al, Ce, Ga, Hf, In, Mg, Nb, Rh, Sb, Si, Sn, Ta, Ti, Zn, Zr. The thicknesses of the single layers 12 can be chosen, for example, to have a thickness of λ/2 or λ/4 or multiples thereof, wherein λ denotes the characteristic wavelength of the light generated in the active region 2.
For example, for each emitter unit the first coating 10 and the second coating 13 completely fill the respective recess 4. Furthermore, it is also possible that between the first coating 10 and the second coating 13 a region of the recess 4 remains free of the first coating 10 and the second coating 13, as indicated in
In the embodiments of
The rear side preferably has a coating with the first layer described above, which has a very low reflectivity, for example, so that back reflections into the resonator can be avoided. The coated recesses 4 themselves can thus serve as a highly reflective facet. As a result of the fact that the second segments 26 to the left of the recesses 4 are not electrically contacted and are thus passive, these are, so to speak, only an “appendage” and no longer have any influence on the reflectivity as a result of the anti-reflection coating described. Alternatively, it may also be possible to use the first layer on the rear side as a rear mirror with at least partial reflectivity.
When the recess 4 is filled with pairs of layers with individual layers 12 formed at least approximately as λ/4 layers, highly reflective mirrors with strong modulation can be produced.
The materials given in Table 1 and in the other tables are to be understood purely as examples to explain the underlying principles. Alternatively or additionally, other of the materials mentioned can also be used. In particular, the compositions of the materials may also deviate from a stoichiometric composition. The order of the materials from top to bottom given in Table 1 and the following tables corresponds to an order along the radiation emission direction from the first side surface to the second side surface of the recess, the side surfaces being formed by the semiconductor body, which is therefore also given at the beginning and at the end in the tables.
By changing the width of the recess, the width x of the filling given in the table changes while the coating remains the same, thus shifting the modulations. In
As can be easily seen in
Different reflectivities, modulation depths and periodicities can be adjusted by suitable coatings.
Compared to the previous embodiments, the second coating 13 on the second side surface 7 is half as thick as the first coating 10 on the first side surface 6. For this purpose, for example, the first coating 10 and the second coating 13 can be deposited separately from each other and thus one after the other. Suitable process steps as described in the general part can be used for this purpose. Furthermore, the first coating 10 and the second coating 13 can also be deposited simultaneously. For this purpose, for example, a deposition method is used which has a preferred direction 16 having an angle α with a main extension plane 17 of the semiconductor body 1. Thus, a simultaneous deposition of the first coating 10 and the second coating 13 takes place, the second coating 13 having a different thickness at least on the second side surface 7 than the first coating 10 on the first side surface 6. This is achieved by a self-shading of the recess 4 during the deposition due to the preferred direction 16. For example, sputtering or vapor deposition are suitable directional deposition processes. The thickness ratio between the first and second coatings 10, 13 on the side surfaces 6, 7 can be adjusted by a suitable selection of the angle α.
The first and second coatings 10, 13 produced in this way each have a layer sequence of individual layers 12 of the same material and the same sequence. The first coating 10 and the second coating 13 differ only in their thickness on the first side surface 6 and the second side surface 7 of the recess 4. The remaining gap is filled with a filling 15 as in the embodiment of
The recesses 4 are unfilled as shown or can alternatively be filled, for example, with a material having a certain refractive index. The second layer 23 on the outcoupling side 22 is formed by a coating with very low reflectivity, which avoids back reflections into the semiconductor body 1.
In the embodiment shown here, the second segments 26 are not electrically contacted at the outcoupling side 22 and are thus embodied as passive segments. Alternatively, however, as shown in
The second segments 26 do not affect the reflectivity at the outcoupling side 22 due to the non-reflective second layer 23, but rather the reflectivity is defined by the recesses 4. By effectively “relocating” the position of the outcoupling reflectivity from the facet of the semiconductor body 1 at the outcoupling side 22 of the light-emitting semiconductor chip 100 into the recesses 4, it can be advantageously achieved that the second segments 26 can be used with additional properties. For example, these can be used, possibly in combination with changes to the ridge waveguide geometry in the second segments 26, as a mode filter or for spectral broadening or as a modulator, etc.
In the simplest case, the modulation can be realized via an unfilled or a material-filled recess 4 in the active regions 2 of the emitter units 101. This allows, for example, reflectivities of less than about 50% in the AlInGaN material system with air-filled recesses 4, as shown in
As can be seen in
As can be seen in
The modulation spacing, i.e. the distance between reflection maxima, can be set, for example, via the refractive index of the filling. The higher the refractive index n of the filling, the smaller the modulation spacing, since this is proportional to λ2/(2×n×B), where B indicates the width of the filling.
From the dependency λ2/(2×n×B) of the modulation distance it can also be seen that with increasing width of the filling the distance of the reflection maxima becomes smaller. The position of the maxima repeats proportionally to λ/(2×n), and the shift of the maxima with the width B of the filling is proportional to λ/B. Thus, the larger the width of the filling and, consequently, the recess width with a fixed first and second coating, the smaller the shift of the maxima with change of the gap width.
Table 6 shows the structure of the coating reproduced in Table 3. Compared to Table 3, the width B of the filling is given variably.
The features and embodiments described above for the recesses and the coating of the recesses are to be understood as purely exemplary. In particular, depending on the wavelength spectrum and technical requirements of the light-emitting semiconductor chip, materials, layer thicknesses, layer combinations, fillings, recess widths and recess positions can be specifically adapted.
In connection with the following figures, further embodiments for the construction of the light-emitting semiconductor chip and in particular of the emitter units are shown, which represent modifications of the embodiments described above.
By combining multiple recesses 4 per emitter unit 101 such as the one shown in
The embodiment for the light-emitting semiconductor chip 100 shown in
In the embodiments of the light-emitting semiconductor chip 100 shown in
In the embodiments described above, each emitter unit 101 of the light-emitting semiconductor chip 100 has at least one dedicated recess 4, each of which is separate from all other recesses 4 in the semiconductor body 1. Alternatively, there may be at least one recess 4 in the semiconductor body 1 that extends through the active regions of a plurality, and preferably all, of the emitter units 101, as shown in
As shown in the previous embodiments, the ridge waveguide structures 24 may be designed, for example, as strips of constant width interrupted by the at least one recess 4. To achieve a better facet quality, the ridge waveguide structures 24 may also have a thickening 24′ in the region of the at least one recess 4 in the form of a widening along the main extension direction of the at least one recess 4, as indicated in
To reduce coupling losses, the at least one recess 4, as indicated in
The features and embodiments described in connection with the figures can be combined with each other according to further embodiments, even if not all combinations are explicitly described. Furthermore, the embodiments described in connection with the figures may alternatively or additionally have further features according to the description in the general part.
The invention is not limited by the description based on the embodiments to these embodiments. Rather, the invention includes each new feature and each combination of features, which includes in particular each combination of features in the patent claims, even if this feature or this combination itself is not explicitly explained in the patent claims or embodiments.
| Number | Date | Country | Kind |
|---|---|---|---|
| 102020133177.0 | Dec 2020 | DE | national |
This patent application is a national phase filing under section 371 of PCT/EP2021/084996, filed Dec. 9, 2021, which claims the priority of German patent application 102020133177.0, filed Dec. 11, 2020, each of which is incorporated herein by reference in its entirety.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2021/084996 | 12/9/2021 | WO |
