PATENT DOCUMENT

Publication Number: US-10825952-B2
Application Number: US-201816477205-A
Country: US
Kind Code: B2

Title: Combining light-emitting elements of differing divergence on the same substrate

Abstract:
An optoelectronic device includes a semiconductor substrate and a monolithic array of light-emitting elements formed on the substrate. The light-emitting elements include a first plurality of first emitters, configured to emit respective first beams of light with a first angular divergence, at respective first positions in the array, and a second plurality of second emitters, configured to emit respective second beams of light with a second angular divergence that is at least 50% greater than the first angular divergence, at respective second positions in the array.

Claims:
The invention claimed is: 
     
       1. An optoelectronic device, comprising:
 a semiconductor substrate; and 
 a monolithic array of light-emitting elements formed on the substrate comprising epitaxial structures of multiple epitaxial layers, the light-emitting elements comprising:
 a first plurality of first emitters, configured to emit respective first beams of light with a first angular divergence, at respective first positions in the array, wherein the first emitters comprise vertical-cavity surface-emitting lasers (VCSELs); and 
 a second plurality of second emitters, in which one or more of the epitaxial layers have been modified, relative to the first emitters, so that the second emitters emit respective second beams of light with a second angular divergence that is at least 50% greater than the first angular divergence, at respective second positions in the array, wherein the second emitters comprise incoherent light-emitting elements. 
 
 
     
     
       2. The optoelectronic device according to  claim 1 , wherein the incoherent light-emitting elements comprise resonant-cavity light-emitting diodes (RCLEDs). 
     
     
       3. The optoelectronic device according to  claim 2 , wherein the VCSELs comprise first upper multilayer Bragg reflectors comprising a first number of mirror layers, and the RCLEDs comprise second upper multilayer Bragg reflectors comprising a second number of mirror layers, which is smaller than the first number. 
     
     
       4. The optoelectronic device according to  claim 1 , wherein the second positions are interspersed with the first positions in the array. 
     
     
       5. The optoelectronic device according to  claim 1 , wherein the first positions form an uncorrelated pattern. 
     
     
       6. The optoelectronic device according to  claim 1 , wherein the first emitters and the second emitters are coupled to be driven separately so that the device emits either or both of the first beams from the first emitters and the second beams from the second emitters. 
     
     
       7. The optoelectronic device according to  claim 6 , wherein the first beams emitted by the first emitters form a pattern of spots on a region in space, while the second beams cast flood illumination on the region. 
     
     
       8. An optoelectronic device, comprising:
 a semiconductor substrate; and 
 a monolithic array of light-emitting elements formed on the substrate comprising epitaxial structures of multiple epitaxial layers, the light-emitting elements comprising:
 a first plurality of first emitters, configured to emit respective first beams of light with a first angular divergence, at respective first positions in the array; and 
 a second plurality of second emitters, in which one or more of the epitaxial layers have been modified, relative to the first emitters, so that the second emitters emit respective second beams of light with a second angular divergence that is at least 50% greater than the first angular divergence, at respective second positions in the array, 
 
 wherein the monolithic array comprises an arrangement of mutually adjacent unit cells, wherein each unit cell comprises a set of radiators capable of functioning as VCSELs, and wherein in at least some of the unit cells at least one of the radiators is converted to an incoherent light-emitting element by modification of the one or more of the epitaxial layers. 
 
     
     
       9. The optoelectronic device according to  claim 8 , wherein the first emitters comprise first VCSELs, and the second emitters comprise second VCSELs. 
     
     
       10. The optoelectronic device according to  claim 9 , wherein the first VCSELs have first optical apertures, and the second VCSELs have second optical apertures, which are smaller than the first optical apertures. 
     
     
       11. The optoelectronic device according to  claim 10 , wherein the first VCSELs comprise first mesas having a first width, and the second VCSELs comprise second mesas having a second width, which is smaller than the first width. 
     
     
       12. The optoelectronic device according to  claim 8 , wherein the positions of the radiators in at least some of the unit cells are shifted as compared to the positions in the adjacent unit cells. 
     
     
       13. The optoelectronic device according to  claim 8 , wherein the second positions are interspersed with the first positions in the array. 
     
     
       14. The optoelectronic device according to  claim 8 , wherein the first positions form an uncorrelated pattern. 
     
     
       15. The optoelectronic device according to  claim 8 , wherein the first emitters and the second emitters are coupled to be driven separately so that the device emits either or both of the first beams from the first emitters and the second beams from the second emitters. 
     
     
       16. A method for producing an optoelectronic device, the method comprising:
 providing a semiconductor substrate; and 
 forming a monolithic array of light-emitting elements on the substrate, comprising:
 forming a first plurality of first emitters, configured to emit respective first beams of light with a first angular divergence, at respective first positions in the array; and 
 forming a second plurality of second emitters, configured to emit respective second beams of light with a second angular divergence that is at least 50% greater than the first angular divergence, at respective second positions in the array, 
 
 wherein forming the monolithic array of light-emitting elements comprises defining in the monolithic array mutually adjacent unit cells, and forming in each unit cell a set of radiators capable of functioning as vertical-cavity surface-emitting lasers (VCSELs), wherein each of the first emitters comprises a respective one of the VCSELs, and forming the second plurality of the second emitters comprises converting in at least some of the unit cells at least one of the radiators to serve as one of the second emitters. 
 
     
     
       17. The method according to  claim 16 , wherein the VCSELs comprise Bragg reflectors comprising multiple layers, and wherein converting the at least one of the radiators comprises etching away at least some of the layers so as to convert the at least one of the radiators to a resonant-cavity light-emitting diode (RCLED). 
     
     
       18. The method according to  claim 16 , wherein the first and second emitters respectively comprise first and second VCSELs, wherein the first VCSELs have first optical apertures, and wherein converting the at least one of the radiators comprises etching the VCSELs so as to form second optical apertures, smaller than the first optical apertures, in the second VCSELs. 
     
     
       19. The method according to  claim 16 , wherein the second positions are interspersed with the first positions in the array. 
     
     
       20. An optoelectronic device, comprising:
 a semiconductor substrate; and 
 a monolithic array of light-emitting elements formed on the substrate, the light-emitting elements comprising:
 a first plurality of first emitters, configured to emit respective first beams of light with a first angular divergence to form a pattern of structured radiation on a region in space, at respective first positions in the array, wherein the first emitters comprise vertical-cavity surface-emitting lasers (VCSELs); and 
 a second plurality of second emitters, configured to emit respective second beams of light with a second angular divergence that is greater than the first angular divergence to cast flood illumination on the region, at respective second positions in the array, wherein the second emitters comprise incoherent light-emitting elements.

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to optoelectronic devices, and particularly to devices capable of emitting both patterned and flood illumination. 
     BACKGROUND 
     Various methods are known in the art for generating light sources based on arrays of multiple light-emitting elements of optical radiation on a monolithic semiconductor substrate. Some light sources comprising arrays of multiple light-emitting elements are based on monolithic arrays of vertical-cavity semiconductor lasers (VCSELs). 
     SUMMARY 
     Embodiments of the present invention that are described hereinbelow provide improved sources of illumination. 
     There is therefore provided, in accordance with an embodiment of the invention, an optoelectronic device, including a semiconductor substrate and a monolithic array of light-emitting elements formed on the substrate. The light-emitting elements include a first plurality of first emitters, configured to emit respective first beams of light with a first angular divergence, at respective first positions in the array, and a second plurality of second emitters, configured to emit respective second beams of light with a second angular divergence that is at least 50% greater than the first angular divergence, at respective second positions in the array. 
     In the disclosed embodiments, the first emitters include vertical-cavity surface-emitting lasers (VCSELs). In some embodiments, the second emitters include incoherent light-emitting elements, for example resonant-cavity light-emitting diodes (RCLEDs). In a disclosed embodiment, the VCSELs include first upper multilayer Bragg reflectors including a first number of mirror layers, and the RCLEDs include second upper multilayer Bragg reflectors including a second number of mirror layers, which is smaller than the first number. 
     Alternatively, the first emitters include first VCSELs, and the second emitters include second VCSELs. Typically, the first VCSELs have first optical apertures, and the second VCSELs have second optical apertures, which are smaller than the first optical apertures. In a disclosed embodiment, the first VCSELs include first mesas having a first width, and the second VCSELs include second mesas having a second width, which is smaller than the first width. 
     In some embodiments, the monolithic array includes an arrangement of mutually adjacent unit cells, wherein each unit cell includes a set of radiators capable of functioning as VCSELs, and wherein in at least some of the unit cells at least one of the radiators is converted to an incoherent light-emitting element. In a disclosed embodiment, the positions of the radiators in at least some of the unit cells are shifted as compared to the positions in the adjacent unit cells. 
     In the disclosed embodiments, the second positions are interspersed with the first positions in the array. Additionally or alternatively, the first positions form an uncorrelated pattern. 
     In some embodiments, the first emitters and the second emitters are coupled to be driven separately so that the device emits either or both of the first beams from the first emitters and the second beams from the second emitters. In one embodiment, the first beams emitted by the first emitters form a pattern of spots on a region in space, while the second beams cast flood illumination on the region. 
     There is also provided, in accordance with an embodiment of the invention, a method for producing an optoelectronic device. The method includes providing a semiconductor substrate and forming a monolithic array of light-emitting elements on the substrate. Forming the monolithic array includes forming a first plurality of first emitters, configured to emit respective first beams of light with a first angular divergence, at respective first positions in the array, and forming a second plurality of second emitters, configured to emit respective second beams of light with a second angular divergence that is at least 50% greater than the first angular divergence, at respective second positions in the array. 
     In the disclosed embodiments, forming the monolithic array of light-emitting elements includes defining in the monolithic array mutually adjacent unit cells and forming in each unit cell a set of radiators capable of functioning as vertical-cavity surface-emitting lasers (VCSELs), wherein each of the first emitters includes a respective one of the VCSELs, and forming the second plurality of the second emitters includes converting in at least some of the unit cells at least one of the radiators to serve as one of the second emitters. 
     In some embodiments, the VCSELs include Bragg reflectors including multiple layers, and converting the at least one of the radiators includes etching away at least some of the layers so as to convert the at least one of the radiators to a resonant-cavity light-emitting diode (RCLED). 
     Alternatively or additionally, converting the at least one of the radiators includes placing a diffractive optical element over the at least one of the radiators. 
     In another embodiment, the first and second emitters respectively include first and second VCSELs, wherein the first VCSELs have first optical apertures, and converting the at least one of the radiators includes etching the VCSELS so as to form in the second optical apertures, smaller than the first optical apertures, in the second VCSELs. 
     There is additionally provided, in accordance with an embodiment of the invention, an optoelectronic device, including a semiconductor substrate and a monolithic array of light-emitting elements formed on the substrate. The light-emitting elements include a first plurality of first emitters, configured to emit respective first beams of light with a first angular divergence to form a pattern of structured radiation on a region in space, at respective first positions in the array, and a second plurality of second emitters, configured to emit respective second beams of light with a second angular divergence that is greater than the first angular divergence to cast flood illumination on the region, at respective second positions in the array. 
     The present invention will be more fully understood from the following detailed description of the embodiments thereof, taken together with the drawings in which: 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic top view of an optoelectronic device, in accordance with an embodiment of the invention; 
         FIG. 2  is a schematic illustration of a design of an example unit cell, in accordance with an embodiment of the invention; 
         FIGS. 3A-B  are partial cross-sections of an optoelectronic device, respectively illustrating patterned and flood radiation emitted by the device, in accordance with an embodiment of the invention; 
         FIGS. 4A-B  are schematic sectional illustrations and flowcharts of two alternative techniques for fabricating an optoelectronic device, in accordance with embodiments of the invention; and 
         FIG. 5  is a flowchart with schematic sectional illustrations of another technique for fabricating an optoelectronic device, in accordance with an alternative embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     Arrays of VCSELs on a monolithic substrate may be used as sources for structured illumination. There arises in some applications a need to alternate between structured illumination and flood illumination. Adding a separate source of flood illumination to the source of structured illumination can increase the complexity, component count, and size of the illumination source, and increases the fabrication costs of the source. 
     Embodiments of the present invention address the drawbacks of a separate source of flood illumination by forming light-emitting elements different angular divergences in a single monolithic array. Specifically, in the embodiments that are described below, emitters of wider angular divergence are formed in available locations of an array of VCSELs while utilizing the same epitaxial structures that are fabricated for the array of VCSELs. Alternatively, the principles of the present invention may be applied in forming arrays of other sorts of light-emitting elements with varying divergences. 
     The elements of wider angular divergence may comprise incoherent light-emitting elements, or they may simply comprise VCELs of different dimensions, which give rise to more divergent beams. In either case, the wider-divergence light-emitting elements typically have an angular divergence that is at least 50% greater than that of the (narrow-divergence) VCSELs. In some embodiments, the elements of wider angular divergence provide flood illumination when powered, whereas powering the VCSELs (of narrower divergence) provides structured illumination. 
       FIG. 1  shows a schematic top view of an optoelectronic device  10 , in accordance with an embodiment of the invention. Optoelectronic device  10  comprises a semiconductor substrate in the form of a semiconductor die  20  comprising the light-emitting elements formed in unit cells  101 , which in turn are arranged into an array  100 . In the pictured embodiment, the light-emitting elements are formed in hexagonal unit cells  101 , and array  100  forms a hexagonal lattice. Each unit cell  101  comprises VCSELs and incoherent light-emitting elements in varying numbers and locations, which will be further detailed in  FIG. 2 . A specific unit cell  101   a  is shown in an enlarged form next to semiconductor die  20 . Specific unit cell  101   a  comprises four VCSELs  102  and one incoherent light-emitting element  104 . By the term “incoherent” we refer here to light-emitting elements that are not coherent (as opposing to lasers that are coherent), regardless of the underlying structure. 
     In an alternative embodiment, shown in  FIG. 5 , incoherent light-emitting elements  104  are replaced by VCSELs of wider divergence than VCSELs  102 . With the exception of the differences in the fabrication process of these wider-divergence VCSELs, which are explained in detail hereinbelow, the principles of the embodiments shown in  FIGS. 1, 2 and 3A /B and the uses of incoherent light-emitting elements  104  in these embodiments may similarly be applied, mutatis mutandis, using such wider-divergence VCSELs. 
     Although the embodiment illustrated in  FIG. 1  comprises hexagonal unit cells  101  in corresponding array  100 , other embodiments of the present invention may use alternative unit cells (for example a square or an oblique parallelogram), and their corresponding arrays as are known from the theory of lattices. 
     VCSELs  102  and incoherent light-emitting elements  104  are formed on the semiconductor substrate by the same sort of photolithographic fabrication methods as are used to fabricate VCSEL arrays that are known in the art, with the addition of fabrication steps for differentiating between VCSELs  102  and incoherent light-emitting elements  104 . These fabrication steps will be described below with reference to  FIGS. 4A-B . The photolithographic fabrication methods comprise forming VCSELs  102  and incoherent light-emitting elements  104  with suitable thin film layer structures and forming conductors providing electric power and ground connections as well as signal connections between contact pads  106  and VCSELs  102  and between contact pads  108  and incoherent light-emitting elements  104 , respectively. 
     The power and ground connections and associated controls can be implemented using an integrated backplane. For example, the emitters can be integrated with control circuits in a single chip, which is formed by bonding together a III-V semiconductor substrate, such as a GaAs wafer, on which the emitters (VCSELs and wide-divergence elements) are fabricated, with a silicon substrate on which control circuits for the emitters are fabricated, using a CMOS process, for instance. 
       FIG. 2  is a schematic illustration of a design of specific unit cell  101   a , in accordance with an embodiment of the invention. The basis for the design is a full unit cell  109  comprising seven VCSELs  102  in seven locations  110   a - g , arranged in a hexagonal lattice within the full unit cell. The conversion of the design of full unit cell  109  to specific unit cell  101   a  comprises two parts:
         1. VCSELs  102  in locations  110   b  and  110   c  are disabled by not providing conductors between these locations and contact pads  106 . This generates inactive locations  103 .   2. VCSEL  102  in location  110   g  is converted to incoherent light-emitting element  104  by removing some of the mirror layers at that location (which can be done according to one or more process steps, such as those described in reference to a reflector etch step  128  in  FIG. 4A  and a wet etch step  136  in  FIG. 4B ) and by connecting incoherent light-emitting element  104  to contact pads  108 .       

     Specific unit cell  101   a  now comprises, as a result of the conversion from full cell  109 , functioning VCSELs  102  in four locations:  110   a ,  110   d ,  110   e , and  110   f , as well as incoherent light-emitting element  104  in location  110   g . Other unit cells  101  are similarly modified to have functioning VCSELs  102 , but with the VCSELs in different locations, as well as possibly with a different number of functioning VCSELs, than in specific unit cell  101   a.    
     It should be appreciated that the number and locations of VCSELs  102  and incoherent light-emitting elements  104  within the array (and any individual unit cells) may follow any desired pattern. In some instances, some or all unit cells may have VCSELs  102  and incoherent light-emitting elements  104  in the same locations. In other instances, the selection of which VCSELs  102  to remove and which to leave functioning in each unit cell  101  is performed in such a way that the resulting pattern of VCSELs on optoelectronic device  10  is uncorrelated. By “uncorrelated” we mean that, across optoelectronic device  10 , the auto-correlation of the positions of VCSELs  102  as a function of transverse shift is insignificant for any shift larger than the size of a VCSEL. Random, pseudo-random, and quasi-periodic patterns are examples of such uncorrelated patterns. This kind of uncorrelated pattern of coherent light-emitting elements is useful for applications where illuminating a region in space with an uncorrelated distribution of light spots is desired, for example 3D mapping. Alternatively, depending on application requirements, any other suitable pattern of VCSELs, not necessarily uncorrelated, may be created using the principles described herein. 
     Culling VCSELs  102  for generating a pattern of coherent light-emitting elements, as described herein, can provide on each unit cell  101  at least one location for converting an unused VCSEL  102  into an incoherent light-emitting element  104 , while at the same time benefiting from epitaxial layers and structures already fabricated for VCSELs  102 . Alternatively, incoherent light-emitting elements may be formed only in some, but not all, of the unit cells in a monolithic array. Similarly, the number of incoherent light-emitting elements in a unit cell may vary between unit cells  101 . As an example, some unit cells  101  may have a single incoherent light-emitting element  104  while other unit cells  101  may have two or more incoherent light-emitting elements. 
     In the pictured embodiment, unit cells  101  are designed in such a manner that VCSELs  102  and incoherent light-emitting elements  104  are typically (although not necessarily) interspersed, by which we mean that at least two of the nearest neighbors of each incoherent light-emitting element are VCSELs. Alternatively, the principles described herein may be applied in forming other arrangements of VCSELs and incoherent light-emitting elements. 
     In an alternative embodiment VCSELs  102  in full unit cell  109  are shifted slightly from their positions in the hexagonal lattice (much less than the separation between neighboring VCSELs  102 ), with the shifts varying between unit cells. These varying shifts further contribute to the generation of an uncorrelated pattern of VCSELs  102 . 
     In some embodiments incoherent light-emitting elements  104  comprise resonant-cavity light-emitting diodes (RCLEDs). RCLEDs are advantageous in that, as compared to light-emitting diodes (LEDs), they exhibit a higher electrical-to-optical conversion efficiency, a smaller angle of divergence (but larger than that of VCSELs), and a narrower emission spectrum. In alternative embodiments certain VCSELs can be overlaid with a local DOE (diffractive optical element) to increase the beam divergence, so that these particular VCSELs serve as the incoherent light-emitting elements and thus create the desired flood illumination. In still other embodiments, other sorts of incoherent light-emitting elements may be formed together with the VCSELs in the array. 
       FIGS. 3-4  are schematic illustrations of embodiments of the present invention, wherein incoherent light-emitting elements  104  comprise RCLEDs. 
       FIGS. 3A-B  are schematic sectional illustrations of optoelectronic device  10 , respectively illustrating patterned and flood radiation patterns emitted by the device, in accordance with an embodiment of the invention. Schematic sectional illustrations  111  and  112  illustrate the same section of optoelectronic device  10 , but with different light-emitting elements powered. For the sake of clarity, VCSELs  102  and RCLEDs  105  are shown as if they were all in the plane of  FIGS. 3A-B . 
     In  FIG. 3A  all VCSELs  102  are powered (but none of RCLEDs  105 ), and they emit narrow cones of light  114 . A typical half-angle of the beam divergence of VCSELs  102  ranges from 10° to 15°; this kind of illumination is useful, inter alia, for structured illumination used in 3D mapping. A projection lens (not shown in the figures) may be used to collimate the beams so as to form a corresponding pattern of spots on a region in space. 
     In  FIG. 3B  all RCLEDs  105  are powered (but none of VCSELs  102 ), and they emit broad cones of light  116 . The angular beam divergence of RCLEDs  105  may be tuned by selecting the number of mirror layers retained in an upper multilayer Bragg-reflector  122  in reflector etch step  128  in  FIG. 4A  and in wet etch step  136  in  FIG. 4B . RCLEDs  105  (or alternatively, the wide-divergence VCSELs that are shown in  FIG. 5 ) typically have an angular divergence that is at least 50% greater than that of VCSELs  102 , and may be 100% greater, i.e., twice the angular divergence. For example, the half-angle of the beam divergence of RCLEDs  105  can range from 20° to 40°, in order to provide uniform flood illumination. This flood illumination can be cast on the same region in space as the pattern of spots formed by the VCSELs. 
     Although  FIGS. 3A-B  illustrate VCSELs  102  and RCLEDs  105  powered separately, other embodiments of the present invention provide both separate and simultaneous powering of the VCSELs and RCLEDs, thus having optoelectronic device  10  emitting either or both of coherent structured illumination and incoherent flood illumination. 
       FIGS. 4A-B  are schematic sectional illustrations and flowcharts of two alternative techniques for fabricating optoelectronic device  10 , in accordance with embodiments of the invention. Each figure shows the fabrication of one VCSEL  102  and one neighboring RCLED  105 . The left side of each figure presents sectional illustrations of the semiconductor stack during various steps of the fabrication, whereas the right side shows a flowchart of the fabrication steps. These illustrations show only those fabrication steps in which VCSELs  102  and RCLEDs  105  are differentiated from each other. Intermediate fabrication steps that are known to those skilled in the art of semiconductor fabrication, for example photoresist patterning, are omitted for the sake of simplicity. 
     The fabrication steps illustrated in  FIG. 4A  start at a starting step  120  with a VCSEL epitaxy stack, wherein upper multilayer Bragg-reflector  122 , a lower multilayer Bragg-reflector  123 , and a quantum well layer  124  have been fabricated using a standard epitaxial process. In a mesa etch step  126 , VCSELs  102  and RCLEDs  105  are etched apart and defined in a single RIE (reactive-ion etching) step. In reflector etch step  128 , a number of top reflector layers are etched away from upper multilayer Bragg-reflector  122  at the position of RCLED  105 , leaving only 5-10 layers out of the original stack of 20-25 layers, for example. The number of layers etched is determined by the timing of the etch. This step reduces the reflectance of upper multilayer Bragg-reflector  122  sufficiently in order to convert a lasing VCSEL to a non-lasing RCLED, as indicated in the context of  FIG. 2 . As described above in reference to  FIG. 3B , the number of remaining layers in upper multilayer Bragg-reflector  122  may also be used for tuning the angular divergence of RCLEDs  105 . In a selective oxidation step  129 , both VCSELs  102  and RCLEDs  105  are selectively oxidized in their lateral dimensions in locations  130  for achieving lateral optical and electrical confinement. Other fabrication options, for example ion-implantation or a combination of oxidation and ion-implantation, may be used for achieving lateral confinement. 
     The fabrication steps illustrated in  FIG. 4B  start at a starting step  134  with a VCSEL epitaxy stack, wherein upper multilayer Bragg-reflector  122 , lower multilayer Bragg-reflector  123 , and quantum well layer  124  have been fabricated using a standard epitaxial process. In addition, an InGaP (indium-gallium-phosphide) etch stop layer  132  has been added in the epitaxial process to the upper multilayer Bragg-reflector  122  in a selected position within the multilayer. In wet etch step  136 , an isotropic wet etch, selective to InGaP etch stop layer  132 , is performed. In wet etch step  136  a number of top reflector layers are etched away from upper multilayer Bragg-reflector  122  at the position of RCLED  105 , similarly to reflector etch step  128  of  FIG. 4A , with the etch terminating at etch stop layer  132 . In a mesa etch step  138 , a RIE is performed down to the bottom of lower multilayer Bragg-reflector  123  in order to define VCSELs  102  and RCLEDs  105 . Similarly to selective oxidation step  129  of  FIG. 4A , in a selective oxidation step  140  both VCSELs  102  and RCLEDs  105  are selectively oxidized in their lateral dimensions in locations  142  for achieving lateral optical and electrical confinement. As in  FIG. 4A , other fabrication options, for example ion-implantation or a combination of oxidation and ion-implantation, may be used for achieving lateral confinement. 
     After each of the fabrication steps of  FIGS. 4A-B , the production of optoelectronic device  10  continues using standard semiconductor fabrication steps which are known to those skilled in the art of semiconductor fabrication. Thus, device  10  can be formed with only minor modifications to standard processes that are known in the art for designing and fabricating VCSEL arrays. 
       FIG. 5  is a flowchart together with schematic sectional illustrations of another technique for fabricating optoelectronic device  10 , in accordance with an alternative embodiment of the invention. In this case, as noted earlier, RCLEDs  105  are replaced by high-divergence VCSELs  158 , which are fabricated alongside low-divergence VCSELs  156  (which are similar or identical to VCSELs  102  as described above). Low-divergence VCSELs  156  can be used to provide structured radiation, and high-divergence VCSELs  158  provide flood radiation, as explained above with reference to  FIG. 3 . 
     As in  FIGS. 4A /B, the left side of  FIG. 5  presents sectional illustrations of the semiconductor stack during successive steps of the fabrication, whereas the right side is a flowchart of the fabrication steps. These illustrations show only those fabrication steps in which VCSELs  156  and  158  are differentiated from one another other. Intermediate fabrication steps that are known to those skilled in the art of semiconductor fabrication, for example photoresist patterning, are omitted for the sake of simplicity. 
     The fabrication steps illustrated in  FIG. 5  start with an epitaxial deposition step  150  to form a VCSEL epitaxy stack, including upper multilayer Bragg-reflector  122 , lower multilayer Bragg-reflector  123 , and quantum well layer  124  are fabricated using a standard epitaxial process. In a mesa etch step  152 , VCSELs  156  and  158  are etched apart and defined, for example using RIE. The mesas of VCSELs  156  are etched to a substantially greater width than those of VCSELs  158 , typically by appropriate definition of the mesa widths in the etch mask that is used at step  152 . (The width is measured in a direction parallel to the substrate, meaning the horizontal direction in  FIG. 5 .) For instance, the mesas of VCSELs  156  may be etched to a width of 12 μm, while those of VCSELs  158  are etched to 11 μm or less. 
     In a selective oxidation step  154 , both VCSELs  156  and  158  are selectively oxidized in their lateral dimensions in locations  160 , for example using a wet oxidation process, in order to achieve lateral optical and electrical confinement. This selective oxidation leaves optical apertures  162  and  164  at the centers of the mesas. The oxidation process is applied to the mesas of both VCSELs  156  and  158  for the same length of time, with the result that apertures  164  of high-divergence VCSELs  158  are substantially smaller than apertures  162  of low-divergence VCSELs  156 . Smaller apertures  164  give rise to wider beams from VCSELs  158 , relative to the narrower beams emitted through apertures  162 . The different widths of the VCSEL mesas can be chosen to yield the desired aperture sizes at step  154 . Alternatively, other fabrication options, for example ion-implantation or a combination of oxidation and ion-implantation, may be used for achieving the desired aperture differences. 
     It will be appreciated that the embodiments described above are cited by way of example, and that the present invention is not limited to what has been particularly shown and described hereinabove. Rather, the scope of the present invention includes both combinations and subcombinations of the various features described hereinabove, as well as variations and modifications thereof which would occur to persons skilled in the art upon reading the foregoing description and which are not disclosed in the prior art.

Metadata:
Filing Date: 20180111
Publication Date: 20201103
Grant Date: 20201103
Priority Date: 20170116
Inventors: LAFLAQUIERE, ARNAUD
DRADER, MARC
Assignee: APPLE INC
CPC Classifications: [{"code": "H10H20/034", "inventive": false, "first": false, "tree": "[]"}, {"code": "H10H29/142", "inventive": true, "first": false, "tree": "[]"}, {"code": "H10H20/862", "inventive": true, "first": false, "tree": "[]"}, {"code": "H10H20/01", "inventive": true, "first": false, "tree": "[]"}, {"code": "H10H20/813", "inventive": true, "first": true, "tree": "[]"}, {"code": "H10H29/142", "inventive": false, "first": false, "tree": "[]"}, {"code": "H10H20/042", "inventive": false, "first": false, "tree": "[]"}, {"code": "H10H20/034", "inventive": false, "first": false, "tree": "[]"}, {"code": "H10H20/862", "inventive": true, "first": false, "tree": "[]"}, {"code": "H10H20/813", "inventive": true, "first": false, "tree": "[]"}, {"code": "H10H20/01", "inventive": true, "first": false, "tree": "[]"}, {"code": "H10H29/142", "inventive": true, "first": false, "tree": "[]"}, {"code": "H10H20/042", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01S5/423", "inventive": true, "first": true, "tree": "[]"}, {"code": "H01S5/18361", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01S5/18344", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01S5/18311", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01S5/026", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01S5/423", "inventive": true, "first": true, "tree": "[]"}, {"code": "H01L27/156", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01L2933/0025", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L33/465", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01L33/08", "inventive": true, "first": true, "tree": "[]"}, {"code": "H01L33/005", "inventive": true, "first": false, "tree": "[]"}]
Family ID: 61157295