Patent Publication Number: US-2022224077-A1

Title: Horizontal Cavity Surface-Emitting Laser (HCSEL) Monolithically Integrated with a Photodetector

Description:
FIELD 
     The described embodiments relate generally to lasers and photodetectors. More particularly, the described embodiments relate to HCSELs, and to HCSELs or edge-emitting lasers (EELs) monolithically integrated with photodiodes. 
     BACKGROUND 
     There are two common types of semiconductor lasers, horizontal cavity edge-emitting lasers (EELs) and vertical-cavity surface-emitting lasers (VCSELs). 
     An EEL has its laser resonant cavity in plane with the epitaxial layers of the EEL so that light resonates horizontally and outputs horizontally (i.e., from an edge of the device). The length of the horizontal laser resonant cavity can be designed quite flexibly without restrictions. Generally, a longer cavity is needed for higher output power. Therefore, EELs with longer laser resonant cavities are suitable for applications requiring a high-power, spatially coherent light source. One such application example is a mid- to long-range, frequency- or phase-modulated light detection and ranging (LIDAR) system. 
     A disadvantage of EELs is that they cannot be tested at the epi/wafer level prior to die singulation, or without forming a non-trivial in-wafer test structure. Moreover, when mounting an EEL chip onto a circuit board, the horizontal light emission direction is not universally preferred and sometimes requires the use of an external 90° light-folding mirror to bend the laser&#39;s output beam to a vertical direction. The external 90° light-folding mirror may be used, for example, when fitting an EEL into a flat aspect-ratio device such as a hand-held device (e.g., a smart phone or a tablet computer) and requiring the laser beam to leave the device perpendicularly to one of the device&#39;s major surfaces (e.g., perpendicularly to the device&#39;s display). 
     VCSELs, on the other hand, have a light emission direction perpendicular to a chip surface, making them suitable for certain applications. The surface emission property also makes high-throughput wafer-level laser characterization (test) possible. However, since the light resonant direction of a VCSEL is perpendicular to the epitaxial layers of the VCSEL, the length of a VCSEL&#39;s laser resonant cavity is usually limited to the feasible epitaxial layer thickness and growth time, device heat dissipation, and operating voltage considerations. As a consequence, a single VCSEL has limited output power. VCSEL arrays can be used to boost the total output power, but the individual VCSELs of the array do not lase coherently. As a result, the array&#39;s aggregate light may have a higher power, but does not offer spatial coherence. VCSEL arrays are therefore more suitable for, e.g., near- to mid-range, intensity-modulated applications such as time-of-flight LIDAR systems. 
     As opposed to EELs, VCSELs can be tested at epi/wafer level at significantly higher throughput and lower cost. 
     SUMMARY 
     A hybrid type of device referred to as horizontal cavity surface-emitting laser (HCSEL) may combine the advantages of an EEL and a VCSEL, offering spatially coherence, fixed beam polarization, and high brightness/output power while still preserving the vertical emission property. One of the challenges to creating a HCSEL is the formation of a turning mirror inside the device—i.e., the formation of a mirror that reflects light propagating within a horizontal portion of the device&#39;s laser resonant cavity into a (typically smaller) vertical portion of the device&#39;s laser resonant cavity, and vice versa. Techniques for forming such a turning mirror are therefore described herein. 
     A HCSEL also preserves another EEL property, which is the provision of two emission ports (or two output facets). The HCSEL&#39;s “front side” output is the HCSEL&#39;s main power output and provides a vertical output beam. The HCSEL&#39;s “back side” output is typically fainter and provides a horizontal output beam. As described herein, a photodetector (e.g., a photodiode) can be monolithically integrated with the HCSEL using the same set of epitaxial layers, or by growing a separate set of epitaxial layers on the same substrate, and can be used as a laser power monitor. Described herein are new ways to coupling the HCSEL&#39;s back side output into the photodetector. 
     Similar to a VCSEL, a HCSEL can be readily tested at the epi/wafer level. The integration of a photodetector (PD) into a HCSEL enables compact and high fidelity laser power monitoring, for functionality and applications including laser safety, close loop power control, self-mixing interferometry (SMI), and so on. 
     In a system requiring a high-power output and a spatially coherent surface emission, a HCSEL monolithically integrated with a PD can reduce the component/assembly costs and module complexity, enhance assembly tolerances, improve module functionality, and/or improve laser performance and reliability. 
     Embodiments of the systems, devices, methods, and apparatus described in the present disclosure are directed to such integrated HCSELs and PDs. Some of the described embodiments and techniques also relate to EEL and PD integration, or to the formation of HCSELs regardless of whether they are integrated with a PD. 
     In a first aspect, the present disclosure describes an optoelectronic device. The optoelectronic device may include an off-cut III-V semiconductor substrate, a set of epitaxial layers formed on the off-cut III-V semiconductor substrate, and a HCSEL having a laser resonant cavity formed in the set of epitaxial layers. 
     In another aspect, the present disclosure describes another optoelectronic device. The optoelectronic device may include a semiconductor substrate; a laser, epitaxially grown on the semiconductor substrate and having a laser resonant cavity; a semiconductor device, epitaxially grown on the semiconductor substrate and separated from the laser by a single trench having a first vertical wall abutting the laser and a second vertical wall abutting the semiconductor device; and at least one coating on at least one of the first vertical wall or the second vertical wall. The laser resonant cavity of the laser may have a horizontal portion parallel to the semiconductor substrate, and each of the first vertical wall and the second vertical wall may be oriented perpendicular to the semiconductor substrate. 
     In still another aspect of the disclosure, the present disclosure describes an electronic device. The electronic device may include a housing; a cover mounted to the housing; a display positioned under the cover and viewable through the cover; and a HCSEL configured to emit short-wave infrared (SWIR) radiation through the display (i.e., the display&#39;s active area) and the cover. 
     In addition to the exemplary aspects and embodiments described above, further aspects and embodiments will become apparent by reference to the drawings and by study of the following description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The disclosure will be readily understood by the following detailed description in conjunction with the accompanying drawings, wherein like reference numerals designate like structural elements, and in which: 
         FIG. 1  shows an example of an optoelectronic device; 
         FIG. 2  shows another example of an optoelectronic device; 
         FIG. 3  shows an example of an optoelectronic device including a laser and another semiconductor device (e.g., a photodetector); 
         FIG. 4  shows a variation of the optoelectronic device described with reference to  FIG. 3 , in which the DBR is replaced with a single trench separating the laser and the photodetector; 
         FIGS. 5 and 6  show example embodiments of coatings that may be applied to a first vertical wall and/or a second vertical wall of a trench formed between a laser and a photodetector 
         FIGS. 7A-7E  illustrate one way to make the optoelectronic device described with reference to  FIG. 4 ; 
         FIG. 8  illustrates another way to make the optoelectronic device described with reference to  FIG. 4 ; 
         FIG. 9  shows another optoelectronic device that may be made using the process steps described with reference to  FIG. 7A-7E or 8 ; 
         FIGS. 10A and 10B  show a first example of a device that may include a particulate matter sensor; 
         FIGS. 11A and 11B  show a second example of a device that may include a particulate matter sensor; 
         FIG. 12  shows an example electrical block diagram of an electronic device. 
     
    
    
     The use of cross-hatching or shading in the accompanying figures is generally provided to clarify the boundaries between adjacent elements and also to facilitate legibility of the figures. Accordingly, neither the presence nor the absence of cross-hatching or shading conveys or indicates any preference or requirement for particular materials, material properties, element proportions, element dimensions, commonalities of similarly illustrated elements, or any other characteristic, attribute, or property for any element illustrated in the accompanying figures. 
     Additionally, it should be understood that the proportions and dimensions (either relative or absolute) of the various features and elements (and collections and groupings thereof) and the boundaries, separations, and positional relationships presented therebetween, are provided in the accompanying figures merely to facilitate an understanding of the various embodiments described herein and, accordingly, may not necessarily be presented or illustrated to scale, and are not intended to indicate any preference or requirement for an illustrated embodiment to the exclusion of embodiments described with reference thereto. 
     DETAILED DESCRIPTION 
     Reference will now be made in detail to representative embodiments illustrated in the accompanying drawings. It should be understood that the following description is not intended to limit the embodiments to one preferred embodiment. To the contrary, it is intended to cover alternatives, modifications, and equivalents as can be included within the spirit and scope of the described embodiments as defined by the appended claims. 
     The following description relates to HCSELs and PDs, including the formation of HCSEL turning mirrors, the integration of HCSEls with PDs, and the integration of EELs with PDs. The optoelectronic devices described herein may provide high coherence, high brightness, out-of-plane coupling, with high-throughput epi/wafer level testing. The optoelectronic devices may also be produced in a simplified way, at low cost, and with high reliability. 
     To create a Fabry-Perot (FP) type HCSEL having an output facet in plane with the device&#39;s epitaxial stack, a 90° turning mirror needs to be formed such that it intersects the horizontal portion of the device&#39;s laser resonant cavity. Total internal reflection (TIR) at the turning mirror&#39;s surface may then be used to bend light traveling along the horizontal portion of the laser resonant cavity by 45°. Depending on the orientation of the turning mirror, light may be bent away from or toward the HCSEL&#39;s substrate. When the turning mirror has a re-entrant, dovetail-like 45° angle, light may be bent away from a HCSEL&#39;s substrate. When the turning mirror has a wedge-like, sloped 45° angle, light may be bent toward a HCSEL&#39;s substrate. Typically, the turning mirror is formed by a dry etch process. However, techniques for engineering a HCSEL&#39;s substrate and epitaxial layers such that the turning mirror may be formed by a wet etch process are described herein. 
     Also described herein are ways to integrate a PD with a HCSEL or an EEL such that improved power monitoring may be achieved and/or interference with power monitoring may be reduced. 
     These and other aspects are described with reference to  FIGS. 1-12 . However, those skilled in the art will readily appreciate that the detailed description given herein with respect to these figures is for explanatory purposes only and should not be construed as limiting. 
     Directional terminology, such as “top”, “bottom”, “upper”, “lower”, “front”, “back”, “over”, “under”, “beneath”, “left”, “right”, etc. may be used with reference to the orientation of some of the components in some of the figures described below. Because components in various embodiments can be positioned in a number of different orientations, directional terminology is used for purposes of illustration only and is in no way limiting. The directional terminology is intended to be construed broadly, and therefore should not be interpreted to preclude components being oriented in different ways. The use of alternative terminology, such as “or”, is intended to indicate different combinations of the alternative elements. For example, A or B is intended to include, A, or B, or A and B. 
       FIG. 1  shows an example of an optoelectronic device. By way of example, the optoelectronic device is a HCSEL  100  (a type of laser), but other optoelectronic devices may be formed using some of the construction principles described herein. 
     The HCSEL  100  may include a semiconductor substrate  102 . A set of epitaxial layers  104  may be formed (i.e., epitaxially grown) on the semiconductor substrate  102 . A laser resonant cavity  106  may be formed in the set of epitaxial layers  104 . The laser resonant cavity  106  may include a horizontal portion  106 - 1  and a vertical portion  106 - 2 . Together, the horizontal and vertical portions  106 - 1 ,  106 - 2  form an L-shaped laser resonant cavity  106 . First and second electrodes  108 ,  110  may be formed on different sides of the laser resonant cavity  106 . For example, a first electrode  108  may be formed on a surface of the semiconductor substrate  102  opposite a surface of the semiconductor substrate  102  on which the set of epitaxial layers  104  is formed, and a second electrode  110  may be formed on the set of epitaxial layers  104  such that the semiconductor substrate  102  and set of epitaxial layers  104  are positioned substantially between the first and second electrodes  108 ,  110 . 
     As used herein, “horizontal” structures extend parallel to a semiconductor substrate, and light that propagates in a horizontal direction (or from an “edge”) propagates parallel to a semiconductor substrate. “Vertical” structures extend perpendicular to a semiconductor substrate, and light that propagates in a vertical direction (or from a “surface”) propagates perpendicular to a semiconductor substrate. “Surfaces” of structures generally extend parallel to a semiconductor substrate. “Edges” of structures generally extend perpendicular or non-perpendicularly to (but not parallel to) a semiconductor substrate. 
     A first reflective structure  112  may be oriented perpendicular to the semiconductor substrate  102  and bound a first end of the horizontal portion  106 - 1  of the laser resonant cavity  106 . A second reflective structure  114  may be oriented parallel to the semiconductor substrate  102  and bound a first end of the vertical portion  106 - 2  of the laser resonant cavity  106 . In some cases, the first reflective structure  112  and the second reflective structure  114  may be partially transmissive and partially reflective. A third reflective structure  116  may be oriented at a non-perpendicular angle with respect to an upper surface of the semiconductor substrate  102  (or with respect to the horizontal portion  106 - 1  of the laser resonant cavity  106 ) and may define a transition between the horizontal portion  106 - 1  of the laser resonant cavity  106  and the vertical portion  106 - 2  of the laser resonant cavity  106 . The non-perpendicular angle at which the third reflective structure  116  is oriented with respect to the upper surface of the semiconductor substrate  102  (or with respect to the horizontal portion  106 - 1  of the laser resonant cavity  106 ) may in some cases by a 45° angle+/−5°. 
     Each of the first, second, and third reflective structures  112 ,  114 ,  116  may include one or more coatings applied to a surface or edge of the set of epitaxial layers  104 . In some cases, the same one or more coatings may be applied to (i.e., deposited on) the set of epitaxial layers to form each of the reflective structures  112 ,  114 ,  116 . Each coating may be, for example, a dielectric coating, a metallic coating, a semiconductor coating, or a 2D or 3D photonic coating. In some embodiments, one or more of the reflective structures  112 ,  114 ,  116  may also or alternatively include an attached component. In some embodiments, one or more of the reflective structures  112 ,  114 ,  116  may be formed by means of a treatment (e.g., a polishing, roughening, etching, and or other treatment). In some embodiments, one or both of the reflective structures  112 ,  114  may be formed by a material-to-air (or material-to-other gas) interface. 
     To achieve the non-perpendicular angle of the third reflective structure  116 , one or more epitaxial layers in the set of epitaxial layers  104  may wet-etched or otherwise processed. The surface  118  may itself be reflective to light that propagates in a horizontal direction or a vertical direction within the laser resonant cavity  106 , and the surface  118  may be (or be part of) the reflective structure  116  (e.g., total internal reflection may occur at the angled boundary between the set of epitaxial layers  204  (n≥2.3) and air (n=1; or other overfill with n≤1.6). In some embodiments, coatings applied to the surface  118 , treatments of the surface  118 , or components attached to the surface  118  may provide the reflective structure  116  and/or cooperate with the surface  118  to provide the reflective structure  116 . 
     Depending on the materials used to form the semiconductor substrate  102  and set of epitaxial layers  104 , it can be difficult to remove portions of one or more of the epitaxial layers at an angle of 45°+/−5° to form the surface  118 . To better enable the one or more epitaxial layers to be removed at a somewhat uniform (e.g., planar) non-perpendicular angle, at 45°+/−5°, the semiconductor substrate  102  may be selected as an off-cut III-V semiconductor substrate (with n≥2.3). In addition, and in some cases, the set of epitaxial layers  104  may also be off-cut. For example, a set of indium gallium arsenide (InGaAs) or indium gallium arsenide phosphide (InGaAsP) epitaxial layers  104  may have an off-cut of 9.7°+/−5° from a (100) surface of an indium phosphide (InP) semiconductor substrate  102  (i.e., the non-off-cut (111) etch stop planes may be originally angled at 54.7°). A set of epitaxial layers  104  formed in this manner, on an off-cut III-V semiconductor substrate, may be partially removed at an angle of 45°+/−5°, with a surface roughness less than 100 nanometers (nm) (and preferably less than 70 nm, or even less than 50 nm). 
     In operation, the first and second electrodes  108 ,  110  may be used to apply a voltage or current to the laser resonant cavity  106 . Applying a voltage establishes an electrical field between the first and second electrodes  108 ,  110 , which results in carrier population inversion across the bandgap of the laser gain medium and stimulates coherent photon generation. As the light moves horizontally, it reflects off of the first reflective structure  112  toward the third reflective structure  116 , or off the third reflective structure  116  toward the second reflective structure  114 . Light that reflects off of the third reflective structure  116  toward the second reflective structure  114  may be reflected back toward the third reflective structure  116 , and from the third reflective structure  116  toward the first reflective structure  112 . A certain portion of the light reflected from the third reflective structure  116  toward the second reflective structure  114  (e.g., 50% or less) may pass through the second reflective structure  114  (e.g., through an aperture in the second reflective structure  114 ) and be emitted as an optical output of the HCSEL  100 . A portion of the emitted light may also be scattered and/or back-reflected and received back into the HCSEL  100  through the second reflective structure  114 , and may mix (i.e., self-mix) with the light generated as a result of lasing. Characteristics of the self-mixing can be detected by sensing changes in an electrical signal (e.g., a voltage or current) at the first or second electrode  108 ,  110 , and can be used to determine properties of an object or particle off which light emitted by the HCSEL  100  reflects external to the HCSEL  100 . Such properties may include the position, speed, texture, and so on of the object or particle. Additionally or alternatively to detecting the self-mixing by monitoring an electrical signal produced at the first or second electrode  108 ,  110 , a relatively small portion of the light reflected from the third reflective structure  116  toward the first reflective structure  112  may be allowed to pass through the first reflective structure  112  and be sensed by a photodetector adjacent the first reflective structure  112 . In this manner, an electrical signal generated by the photodetector may be used to determine characteristics of the self-mixing that occurs within the laser resonant cavity  106 , as well as properties of an object or particle external to the HCSEL  100 . Such a photodetector is not shown in  FIG. 1  but is shown in each of  FIGS. 3-9 . 
       FIG. 2  shows another example of an optoelectronic device. By way of example, the optoelectronic device is a HCSEL  200 . However, in contrast to the HCSEL described with reference to  FIG. 1 , which emits light away from the HCSEL&#39;s semiconductor substrate (i.e., the HCSEL makes a primary light emission away from the HCSEL&#39;s semiconductor substrate), the HCSEL  200  emits light toward and through the HCSEL&#39;s semiconductor substrate  202  (i.e., the HCSEL  200  makes a primary light emission through the semiconductor substrate  202 ). 
     Similarly to the HCSEL described with reference to  FIG. 1 , the HCSEL  200  may include a semiconductor substrate  202 ; a set of epitaxial layers  204  formed on the semiconductor substrate  202 ; a laser resonant cavity  206  formed in the set of epitaxial layers  204 ; first and second electrodes  208 ,  210 ; and first, second, and third reflective structures  212 ,  214 ,  216 . However, in contrast to the HCSEL described with reference to  FIG. 1 , the HCSEL  200  has a third reflective structure  216  that reflects light received from the horizontal portion  206 - 1  of the laser resonant cavity  206  into the vertical portion  206 - 2  of the laser resonant cavity  206 , and particularly through the second reflective structure  214 , due to a less than 100% reflectivity of the second reflective structure  214 , and through the semiconductor substrate  202 . Of note, the second reflective structure  214  may be buried in the set of epitaxial layers  204 . 
     To achieve the non-perpendicular angle of the third reflective structure  216 , one or more epitaxial layers in the set of epitaxial layers  204  may be etched at an angle (e.g., dry etched or wet etched). The surface  218  may itself be reflective to light that propagates in a horizontal direction or a vertical direction within the laser resonant cavity  206  (e.g., total internal reflection may occur at the angled boundary between the set of epitaxial layers  204  (n≥2.3) and air (n=1), and the surface  218  may be (or be part of) the reflective structure  216 . In some embodiments, coatings (e.g., dielectric, metallic, semiconductor, and/or 2D/3D photonic coatings) applied to the surface  218 , treatments of the surface  218 , or components attached to the surface  218  may provide the reflective structure  216  and/or cooperate with the surface  218  to provide the reflective structure  216 . 
     As discussed with reference to  FIG. 1 , depending on the materials used to form the semiconductor substrate  202  and set of epitaxial layers  204 , it can be difficult to remove portions of one or more of the epitaxial layers at an angle of 45°+/−5° to form the surface  218 . To better enable the one or more epitaxial layers to be removed at a somewhat uniform (e.g., planar) non-perpendicular angle, at 45°+/−5°, the semiconductor substrate  202  may be selected as an off-cut III-V semiconductor substrate (with n≥2.3). In addition, and in some cases, the set of epitaxial layers  204  may also be off-cut. For example, a set of InGaAs or InGaAsP epitaxial layers  204  may have an off-cut of 9.7°+/−5° from a (100) surface of an InP semiconductor substrate  202  (i.e., the non-off-cut (111) etch stop planes may be originally angled at 54.7°). A set of epitaxial layers  204  formed in this manner, on an off-cut III-V semiconductor substrate, may be partially removed at an angle of 45°+/−5°, with a surface roughness less than 100 nanometers (nm) (and preferably less than 70 nm, or even less than 50 nm). 
       FIG. 3  shows an example of an optoelectronic device  300  including a laser  302  and another semiconductor device (e.g., a photodetector  304 ), monolithically integrated on a semiconductor substrate  308 . At least a portion of the laser&#39;s laser resonant cavity  306  may extend in a horizontal direction. In some embodiments, the laser  302  may be a HCSEL, such as the HCSEL described with reference to  FIG. 1 or 2  or any other HCSEL described herein. In other embodiments, the laser  302  may be an EEL. 
     The laser  302  and the photodetector  304  may share a semiconductor substrate  308  and set of epitaxial layers  310 , with the set of epitaxial layers  310  being formed (e.g., epitaxially grown) on the semiconductor substrate  308 . In some cases, the photodetector  304  may share a first electrode  312  with the laser  302  and have a dedicated second electrode  314 . The first electrode  312  may be formed on a surface of the semiconductor substrate  308  opposite a surface of the semiconductor substrate  308  on which the set of epitaxial layers  310  is formed, and the second electrode  314  may be formed on the set of epitaxial layers  310  such that the semiconductor substrate  308  and set of epitaxial layers  310  are positioned substantially between the first and second electrodes  312 ,  314 . In alternate embodiments, the laser  302  and the photodetector  304  may be formed in different sets of epitaxial layers (e.g., adjacent epitaxial stacks formed on the semiconductor substrate). 
     A set of vertical trenches defining a distributed Bragg reflector (DBR)  316  may be formed (e.g., etched) between the laser  302  and photodetector  304 . The DBR  316  may form, for example, the first reflective structure described with reference to  FIG. 1 or 2 . The horizontal portion of the laser resonant cavity  306  may abut the DBR  316 . 
     A portion of the light that reflects within the laser resonant cavity  306  may pass through the DBR  316  and be sensed by the photodetector  304 . 
       FIG. 4  shows a variation of the optoelectronic device  300  in which the DBR  316  is replaced with a single trench  402  separating the laser  302  and the photodetector  304 . In some cases, the trench  402  may be etched (e.g., dry-etched). In the optoelectronic device  400 , the single trench  402  has a first vertical wall  406  abutting the laser  302  and a second vertical wall  404  abutting the photodetector  304 . At least one coating  408  (e.g., at least one dielectric, metallic, semiconductor, and/or 2D/3D photonic coating) may be applied to the first vertical wall  406  and/or the second vertical wall  404 . The at least one coating  408 , sometimes in combination with an optional gap  410 , may function as a DBR and/or the first reflective structure described with reference to  FIG. 1 or 2 . 
     The trench  402 , in combination with the coating(s)  408 , may be easier to form than the multiple, finer width trenches described with reference to  FIG. 3 . Furthermore, the single trench  402  and coating(s)  408  may maximize power coupling. In addition to, or as an alternative to, the trench  402  and coating(s)  408 , it is possible to form electrically-isolated vertical barriers via an ion implantation process, though the resulting refractive index change and optical path loss may be less controlled compared to a trench  402  with coating(s)  408 . 
       FIGS. 5 and 6  show example embodiments of coatings (e.g., dielectric, metallic, semiconductor, and/or 2D/3D photonic coatings) that may be applied to a first vertical wall and/or a second vertical wall of a trench formed between a laser and a photodetector.  FIG. 5  shows a cross-section of symmetrically applied coatings taken from the view of cut-line V-V in  FIG. 4 .  FIG. 6  shows an alternative cross-section of asymmetrically applied coatings. 
     As shown in  FIG. 5 , a trench  500  separates a laser  502  and a photodetector  504 . The trench  500  has a first vertical wall  506  abutting the laser  502  and a second vertical wall  508  abutting the photodetector  504 . At least one coating may be symmetrically applied to the first vertical wall  506  and the second vertical wall  508 . 
     By way of example, the coatings shown in  FIG. 5  include first, second, and third coatings  510 ,  512 ,  514 . Each of the coatings  510 ,  512 ,  514  may include aluminum oxide (Al 2 O 3 ). Each of the first, second, and third coatings  510 ,  512 ,  514  may symmetrically coat both the first vertical wall  506  and the second vertical wall  508 . One or more of the first, second, and third coatings  510 ,  512 ,  514  may also coat the bottom (or floor) of the trench  500 , and in some cases may overlap the top surfaces of the set of epitaxial layers forming the laser  502  and/or the photodetector  504 . 
     The second coating  512  may be separated from the first coating  510  by a first layer of amorphous silicon (a-Si)  516 , and the third coating  514  may be separated from the second coating  512  by a second layer of amorphous silicon  518 . The first and second coatings  510 ,  512 , in combination with the adjacent layers  516 ,  518 , may define first low-high-index quarter-wavelength DBR pairs abutting the first vertical wall  506 , and second low-high-index quarter-wavelength DBR pairs abutting the second vertical wall  508 . The third coating  514  may define a half-wavelength low-index layer (or a coating having a thickness that is an integer multiple of a half-wavelength layer). In some cases, additional coatings may be deposited within the trench to define additional DBR pairs (e.g., 1, 2, 3, . . . DBR pairs) between each vertical wall  506 ,  508  of the trench  500  and the half-wavelength low-index layer defined by the third coating  514 . 
     The above-mentioned quarter-wavelength or half-wavelength layers (or coatings) can each have their thicknesses increased independently by a positive-integer multiple of the half-wavelengths. (e.g., a ¼ wavelength layer can be replaced with a ¼+x/2 wavelength layer, where x is any positive integer. Also, or alternatively, the last ½ wavelength layer can be replaced with a y/2 wavelength layer, where y is any positive integer. The above mentioned air gap or fill material, or the lowest refractive-index-section between the laser  502  and photodetector  504 , in the middle of the entire reflective structure, may have a thickness of ¼+z/2 wavelength, where z is any positive integer. Of note, all of the above-mentioned coating thicknesses in wavelengths are defined as the wavelength inside that particular material, and not a free-space wavelength. 
     The third coating  514  may in some cases bound an air gap  520  disposed within the trench  500 . In other cases, the third coating  514  may bound a fill material (e.g., silicon dioxide) disposed within the trench  500 . The trench  500  may also include a combination of air and a fill material, or different combinations of fill materials. The coating(s)  510 ,  512 ,  514 ,  516 , and  518  applied to the first and second vertical walls  506 ,  508  of the trench  500 , in combination with the air gap  520  or a fill material, may form a dielectric-air-dielectric or dielectric-fill-dielectric HR mirror. The air gap  520  or fill material thickness can be ¼+m/2 wavelengths, where m is any positive integer. 
     In some embodiments, the air gap  520  or fill material may be absent. In such embodiments, the last layer (e.g., coating  514  in  FIG. 5 ) on the first vertical wall  506  and the last layer (e.g., coating  514  in  FIG. 5 ) on the second vertical wall  508  may coalesce. In such embodiments, the thickness of the coating  514 , for example, may be changed to ⅛+k/2 wavelengths, where k is any positive integer. 
     The thicknesses of the alternating low-reflective-index Al 2 O 3  coatings and high-reflective-index amorphous Si (a-Si) layers may be carefully designed to make the reflection from every interface in phase, such that a constructive interference can be built to achieve a high reflectivity (e.g., &gt;97%) with a minimum number of layers. Due to the standing wave nature of the reflections, all of the layer thicknesses, including the air gap or fill thickness, can be constructed as shown in  FIG. 5 , plus any multiple positive integer of λ/2, while still resulting in the same high reflectivity in a plane-wave calculation. For a practical-case calculation and design involving diffraction, which can happen in this coupling due to the lack of wave guiding structures, each layer thickness may be kept as thin as possible to minimize diffraction loss. 
     In alternative embodiments, different numbers of one or more coatings may be applied to the vertical walls and/or floor of the trench. One or more planarization and/or passivation materials may also be deposited on the vertical walls and/or floor of the trench  500 . 
     As shown in  FIG. 6 , a trench  600  separates a laser  602  and a photodetector  604 . The trench  600  has a first vertical wall  606  abutting the laser  602  and a second vertical wall  608  abutting the photodetector  604 . At least one coating (e.g., at least one dielectric, metallic, semiconductor, and/or 2D/3D photonic coating) may be applied to the first vertical wall  606 . 
     By way of example, the coatings shown in  FIG. 6  include first, second, and third coatings  610 ,  612 ,  614 . Each of the coatings  610 ,  612 ,  614  may include aluminum oxide. Each of the first, second, and third coatings  610 ,  612 ,  614  may coat the first vertical wall  606  or the second vertical wall  608 . By way of example, the first, second, and third coatings  610 ,  612 ,  614  are only applied to the first vertical wall  606 . In other embodiments, the first, second, and third coatings  610 ,  612 ,  614  may alternatively be applied only to the second vertical wall  608 . In other asymmetric applications, one or more of the coatings may be applied to the first vertical wall  606 , and one or more other coatings may be applied to the second vertical wall  608 ; or, one or more coatings may be applied only to the first vertical wall  606  or the second vertical wall  608 , and one or more other coatings may be applied to both the first vertical wall  606  and the second vertical wall  608 . One or more of the first, second, and third coatings  610 ,  612 ,  614  may also coat the bottom (or floor) of the trench  600 , and in some cases may overlap the top surfaces of the set of epitaxial layers forming the laser  602  and/or the photodetector  604 . 
     The second coating  612  may be separated from the first coating  610  by a first layer of amorphous silicon  616 , and the third coating  614  may be separated from the second coating  612  by a second layer of amorphous silicon  618 . The first coating  610 , in combination with the adjacent layer  616 , may define a first quarter-wavelength DBR. The second coating  612 , in combination with the adjacent layer  618 , may define a second quarter-wavelength DBR. The third coating  614  may define a half-wavelength DBR. 
     The third coating  614  may in some cases bound an air gap  620  disposed within the trench  600 . In other cases, the third coating  614  may bound a fill material (e.g., silicon dioxide) disposed within the trench  600 . The trench  600  may also include a combination of air and a fill material, or different combinations of fill materials. 
     In alternative embodiments, different numbers of one or more coatings may be applied to one or both of the vertical walls and/or floor of the trench. 
       FIGS. 7A-7E  illustrate one way to make the optoelectronic device described with reference to  FIG. 4 . As shown in  FIG. 7A , a set of epitaxial layers  702  may be grown on a semiconductor substrate  700 . The semiconductor substrate  700  (e.g., an InP substrate) may in some cases be an off-cut III-V semiconductor substrate. In addition, and in some cases, the set of epitaxial layers  702  may also be off-cut. For example, a set of InGaAs or InGaAsP epitaxial layers  702  may have an off-cut of 9.7°+/−5° from a (100) surface of an InP semiconductor substrate  700 . A laser resonant cavity  704  (e.g., a quantum well or multiple quantum well (MQW) structure) may be formed within the set of epitaxial layers  702 . Pads  706 ,  708  (e.g., pads including layers of titanium (Ti) and platinum (Pt)) may be deposited on the set of epitaxial layers  702  for the purpose of later depositing separate electrodes used to operate a laser  710  and a photodetector  712 . The pads  706 ,  708  may be protected by a layer of silicon dioxide (SiO 2 )  714  deposited on the set of epitaxial layers  702  and over the pads  706 ,  708 . 
     As shown in  FIG. 7B , a trench  716  may be formed in the structure of  FIG. 7A , to divide the set of epitaxial layers  702  into a laser portion and a photodetector portion. In some cases, the trench  716  may be etched (e.g., dry-etched). Alternatively, the set of epitaxial layers  702  may be removed in the location of the photodetector portion, and a new set of epitaxial layers may be grown for the photodetector portion and separated from the laser portion by a trench  716 . A number of reflective coatings  718  (e.g., dielectric, metallic, semiconductor, and/or 2D/3D photonic coatings) may then be applied to the upper and vertical surfaces of the laser  710 , photodetector  712 , and trench  716  (as well as to the floor of the trench  716 ). 
     In  FIG. 7C , the coatings  718  and silicon dioxide layer  714  may be etched (e.g., dry etched) to expose a surface  720  of the set of epitaxial layers  702 , and the surface  720  may be wet-etched to form a surface  722  having a non-perpendicular angle (e.g., an angle of 45°+/−5°) with respect to the semiconductor substrate  700 . The surface  722 , in some cases in combination with coatings applied thereto, may function as a turning mirror. 
     In  FIG. 7D , additional coatings  724  may be applied to the upper and vertical surfaces of the laser  710 , photodetector  712 , and trench  716 . In some cases, the coating(s)  718 , or the combination of coatings  718  and  724 , may be highly reflective to minimize optical loss (HR; e.g., the coating(s)  718  may have a reflectivity of approximately 85% or higher). The coating(s)  724  may be lowly reflective (LR; e.g., the coating(s)  724  may have a reflectivity of approximately 60% or less). The coating(s)  718  and/or  724  applied to the vertical surfaces of the trench  716 , in combination with an air gap or fill within the trench  716 , may form a dielectric-air-dielectric HR mirror. 
     As shown in  FIG. 7E , the coatings  718 ,  724  may be etched (e.g., dry etched) to expose the pads  706 ,  708 , and conductive material may be deposited into and over the etched holes to form the upper electrodes  726 ,  728  (e.g., p-electrodes or p-pads) of the laser  710  and the photodetector  712  respectively. Conductive material may also be deposited on the bottom surface of the semiconductor substrate  700  to form a lower shared electrode  730  (e.g., an n-electrode or n-pad) of the laser  710  and photodetector  712 . The electrodes  726  and  730  may be used to forward-bias the laser (a p-n diode) and inject current into the laser. When MQWs or other structures formed by the set of epitaxial layers  702  are electrically pumped, the laser may “lase” and emit a beam of light. The electrodes  728  and  730  may be used to reverse-bias the photodetector (another p-n diode), and may initiate the quantum-confined Stark effect (QCSE), which causes the MQWs or other structures formed by the set of epitaxial layers  702  to absorb light generated by the laser that passes through the coatings  718 ,  724  and air gap (or fill) and reaches the photodetector. For improved absorption of laser light by the photodetector, a more absorptive material may be regrown on the semiconductor substrate  700  to form the photodetector. In this case, the set of epitaxial layers  702  may be etched away in the photodetector region, and followed by a selective-area growth (SAG) to selectively grow a narrower bandgap material in the photodetector region. Since this regrown material is already absorptive (i.e., able to absorb and convert light into carriers) without the need of other effects such as the previously mentioned QCSE, the photodetector bias voltage can be extremely small (or in some cases the photodetector may not be biased). The regrown photodetector absorption layer can also be grown thick enough to match the diffracted laser beam spot size coming from the laser. For example, the photodetector absorption layer may be regrown with the same thickness as the entire set of optical confinement layers in the laser (i.e., the total thickness of the laser&#39;s MQWs plus any undoped/lightly p/n-doped spacers), or the photodetector absorption layer may be regrown thicker than the entire set of optical confinement layers in the laser. Here, “light doping” is defined as &lt;5×10 17 /cm 3 . This may increase the in-coming light coupling into the photodetector and increase the photodetector&#39;s light-capturing efficiency. A re-grown photodetector approach may also allow the use of a much shorter photodetector for a given responsivity design target, hence more HCSEL-PD optoelectronic devices (dies) can be yielded on a wafer. 
     In  FIGS. 7A-7E , the coatings  718 ,  724  are deposited before the conductive material of the upper electrodes  726 ,  728  is deposited. Alternatively, and as shown in  FIG. 8 , the silicon dioxide layer  714  may be etched after the process steps shown in  FIG. 7A  or after the trench  716  is formed in  FIG. 7B , and the conductive material of the upper electrodes  726 ,  728  may be deposited before any of the coatings  718 ,  724  are applied. 
       FIG. 9  shows another optoelectronic device  900  that may be made using the process steps described with reference to  FIG. 7A-7E or 8 . The optoelectronic device  900  differs from the optoelectronic devices described with reference to  FIGS. 7A-7E and 8  in that the surface  902  defining the turning mirror is etched such that the turning mirror directs light through the device&#39;s semiconductor substrate  700 . Also, a DBR layer  904  may be formed at the bottom of the set of epitaxial layers  702  to act as an LR mirror. As bent light travels downwards (vertically), there is no wave guiding the light, hence, the light starts to diffract and may diverge (i.e., form a wider beam) as it travels. Therefore, a DBR layer  904  very close to the laser&#39;s active layer (e.g., MQW layer, or laser resonant cavity) may be used to reflect light back to the horizontal portion of the laser resonant cavity  704 . The DBR layer  904  structure and location inside the set of epitaxial layers  702  may be optimized to create the shortest possible vertical round-trip distance within the laser resonant cavity, to avoid undue expansion of the width of the light that is coupled back into the horizontal portion of the laser resonant cavity  704 . Matching the reflected light spot size and the horizontal waveguide mode as closely matched as possible helps to minimize mode coupling loss. 
     In some embodiments, the above-mentioned HCSELs and optoelectronic devices can be made into distributed feedback (DFB) type devices using gratings inside the laser resonant cavities, to provide reflection feedback instead of relying on the coatings that form reflective structures (e.g., HR and LR mirrors) at the two ends of a laser resonant cavity. In these cases, there may not be an HR or LR mirror, but an anti-reflective (AR) coating may be needed on the surface of the semiconductor substrate or set of epitaxial layers where the primary emission occurs, to minimize reflection. For a bottom-emission (through-substrate emission) HCSEL, the DBR inside the epi stack can be eliminated, because an LR mirror is not needed. 
       FIGS. 10A and 10B  show a first example of a device  1000  that may include a HCSEL or optoelectronic device (e.g., a laser in combination with a photodetector) configured as described herein. The device&#39;s dimensions and form factor, including the ratio of the length of its long sides to the length of its short sides, suggest that the device  1000  is a mobile phone (e.g., a smartphone). However, the device&#39;s dimensions and form factor are arbitrarily chosen, and the device  1000  could alternatively be any portable electronic device including, for example a mobile phone, tablet computer, portable computer, portable music player, health monitor device, portable terminal, vehicle navigation system, robot navigation system, wearable device (e.g., a head-mounted display (HMD), glasses, watch, earphone or earbud, and so on), or other portable or mobile device. The device  1000  could also be a device that is semi-permanently located (or installed) at a single location.  FIG. 10A  shows a front isometric view of the device  1000 , and  FIG. 10B  shows a rear isometric view of the device  1000 . The device  1000  may include a housing  1002  that at least partially surrounds a display  1004 . The housing  1002  may include or support a front cover  1006  or a rear cover  1008 . The front cover  1006  may be positioned over the display  1004 , and may provide a window through which the display  1004  may be viewed. In some embodiments, the display  1004  may be attached to (or abut) the housing  1002  and/or the front cover  1006 . In alternative embodiments of the device  1000 , the display  1004  may not be included and/or the housing  1002  may have an alternative configuration. 
     The display  1004  may include one or more light-emitting elements and may be configured, for example, as a light-emitting diode (LED) display, an organic LED (OLED), a liquid crystal display (LCD), an electroluminescent (EL) display, or other type of display. In some embodiments, the display  1004  may include, or be associated with, one or more touch and/or force sensors that are configured to detect a touch and/or a force applied to a surface of the front cover  1006 . 
     The various components of the housing  1002  may be formed from the same or different materials. For example, the sidewall  1018  may be formed using one or more metals (e.g., stainless steel), polymers (e.g., plastics), ceramics, or composites (e.g., carbon fiber). In some cases, the sidewall  1018  may be a multi-segment sidewall including a set of antennas. The antennas may form structural components of the sidewall  1018 . The antennas may be structurally coupled (to one another or to other components) and electrically isolated (from each other or from other components) by one or more non-conductive segments of the sidewall  1018 . The front cover  1006  may be formed, for example, using one or more of glass, a crystal (e.g., sapphire), or a transparent polymer (e.g., plastic) that enables a user to view the display  1004  through the front cover  1006 . In some cases, a portion of the front cover  1006  (e.g., a perimeter portion of the front cover  1006 ) may be coated with an opaque ink to obscure components included within the housing  1002 . The rear cover  1008  may be formed using the same material(s) that are used to form the sidewall  1018  or the front cover  1006 . In some cases, the rear cover  1008  may be part of a monolithic element that also forms the sidewall  1018  (or in cases where the sidewall  1018  is a multi-segment sidewall, those portions of the sidewall  1018  that are non-conductive). In still other embodiments, all of the exterior components of the housing  1002  may be formed from a transparent material, and components within the device  1000  may or may not be obscured by an opaque ink or opaque structure within the housing  1002 . 
     The front cover  1006  may be mounted to the sidewall  1018  to cover an opening defined by the sidewall  1018  (i.e., an opening into an interior volume in which various electronic components of the device  1000 , including the display  1004 , may be positioned). The front cover  1006  may be mounted to the sidewall  1018  using fasteners, adhesives, seals, gaskets, or other components. 
     A display stack or device stack (hereafter referred to as a “stack”) including the display  1004  may be attached (or abutted) to an interior surface of the front cover  1006  and extend into the interior volume of the device  1000 . In some cases, the stack may include a touch sensor (e.g., a grid of capacitive, resistive, strain-based, ultrasonic, or other type of touch sensing elements), or other layers of optical, mechanical, electrical, or other types of components. In some cases, the touch sensor (or part of a touch sensor system) may be configured to detect a touch applied to an outer surface of the front cover  1006  (e.g., to a display surface of the device  1000 ). 
     In some cases, a force sensor (or part of a force sensor system) may be positioned within the interior volume below and/or to the side of the display  1004  (and in some cases within the device stack). The force sensor (or force sensor system) may be triggered in response to the touch sensor detecting one or more touches on the front cover  1006  (or a location or locations of one or more touches on the front cover  1006 ), and may determine an amount of force associated with each touch, or an amount of force associated with the collection of touches as a whole. Alternatively, the force sensor (or force sensor system) may trigger operation of the touch sensor (or touch sensory system in response to detecting a force on the front cover  1006 . In some cases, the force sensor (or force sensor system) may be used to determine the locations of touches on the front cover  1006 , and may thereby function as a touch sensor (or touch sensor system). 
     As shown primarily in  FIG. 10A , the device  1000  may include various other components. For example, the front of the device  1000  may include one or more front-facing cameras  1010 , speakers  1012 , microphones, or other components  1014  (e.g., audio, imaging, and/or sensing components) that are configured to transmit or receive signals to/from the device  1000 . In some cases, a front-facing camera  1010 , alone or in combination with other sensors, may be configured to operate as a bio-authentication or facial recognition sensor. The device  1000  may also include various input and/or output devices  1016 , which may be accessible from the front surface (or display surface) of the device  1000 . In some cases, the front-facing camera  1010 , I/O devices  1016 , and/or other sensors of the device  1000  may be integrated with a display stack of the display  1004  and moved under the display  1004 . 
     In some cases, one or more of the camera  1010 , components  1014 , and/or I/O devices  1016  may include one or an array of HCSELs or optoelectronic devices configured as described herein. The HCSELs of the optoelectronic devices may have laser resonant cavities that extend largely parallel to the output surface of the display  1004 , but emit light through or adjacent the display  1004 . Alternatively, a HCSEL of an optoelectronic device may have a laser resonant cavity that extends largely parallel to a button surface or housing surface, but emit light perpendicularly through the button or housing surface. Such HCSELs or other optoelectronic devices may be used for visible or invisible (e.g., infrared) illumination of a person (e.g., a face) or an object; as the transmitter portion of a proximity sensor; for sensing purposes (e.g., as self-mixing interference (SMI) sensors, line scanners, dot scanners, and so on); for measurement purposes (e.g., for time-of-flight measurements); as spatially or temporally shaped/modulated light sources for range finding, depth imaging, optical touch sensing, fingerprint sensing, or bio-authentication; and so on. In some cases, the HCSELs may emit infrared light (e.g., SWIR electromagnetic radiation) through the front cover  1006  or rear cover  1008 . 
     The device  1000  may also include buttons or other input devices positioned along the sidewall  1018  and/or on a rear surface of the device  1000 . For example, a volume button or multipurpose button  1020  may be positioned along the sidewall  1018 , and in some cases may extend through an aperture in the sidewall  1018 . The sidewall  1018  may include one or more ports  1022  that allow air, but not liquids, to flow into and out of the device  1000 . In some embodiments, one or more sensors may be positioned in or near the port(s)  1022 . For example, an ambient pressure sensor, ambient temperature sensor, internal/external differential pressure sensor, gas sensor, particulate matter sensor, or air quality sensor may be positioned in or near a port  1022 . 
     In some embodiments, the rear surface of the device  1000  may include a rear-facing camera  1024  or other optical sensor (see  FIG. 10B ). A flash or light source  1026  may also be positioned along the rear of the device  1000  (e.g., near the rear-facing camera). In some cases, the rear surface of the device  1000  may include multiple rear-facing cameras. In some cases, the camera  1024 , light source  1026 , and/or other optical sensors may include one or an array of HCSELs or optoelectronic devices configured as described herein. 
     The camera(s), microphone(s), pressure sensor(s), temperature sensor(s), biometric sensor(s), button(s), proximity sensor(s), touch sensor(s), force sensor(s), particulate matter or air quality sensor(s), and so on of the device  1900  may form parts of various sensor systems. 
       FIGS. 11A and 11B  show a second example of a device  1100  that may include a HCSEL or optoelectronic device (e.g., a laser in combination with a photodetector) configured as described herein. The device&#39;s dimensions and form factor, and inclusion of a band  1104 , suggest that the device  1100  is an electronic watch. However, the device  1100  could alternatively be any wearable electronic device.  FIG. 11A  shows a front isometric view of the device  1100 , and  FIG. 11B  shows a rear isometric view of the device  1100 . The device  1100  may include a body  1102  (e.g., a watch body) and a band  1104 . The watch body  1102  may include an input or selection device, such as a crown  1114  or a button  1116 . The band  1104  may be used to attach the body  1102  to a body part (e.g., an arm, wrist, leg, ankle, or waist) of a user. The body  1102  may include a housing  1106  that at least partially surrounds a display  1108 . The housing  1106  may include or support a front cover  1110  ( FIG. 11A ) or a rear cover  1112  ( FIG. 11B ). The front cover  1110  may be positioned over the display  1108 , and may provide a window through which the display  1108  may be viewed. In some embodiments, the display  1108  may be attached to (or abut) the housing  1106  and/or the front cover  1110 . In alternative embodiments of the device  1100 , the display  1108  may not be included and/or the housing  1106  may have an alternative configuration. 
     The housing  1106  may in some cases be similar to the housing described with reference to  FIGS. 10A and 10B , and the display  1108  may in some cases be similar to the display described with reference to  FIGS. 10A-10B . 
     The device  1100  may include various sensor systems, and in some embodiments may include some or all of the sensor systems included in the device described with reference to  FIGS. 10A-10B . In some embodiments, the device  1100  may have a port  1118  (or set of ports) on a side of the housing  1106  (or elsewhere), and an ambient pressure sensor, ambient temperature sensor, internal/external differential pressure sensor, gas sensor, particulate matter sensor, or air quality sensor may be positioned in or near the port(s)  1118 . 
     In some cases, the rear surface (or skin-facing surface) of the device  1100  may include a flat or raised area  1120  that includes one or more skin-facing sensors. For example, the area  1120  may include a heart-rate monitor, a respiration-rate monitor, or a blood pressure monitor. The area  1120  may also include an off-wrist detector or other sensor. 
     In some cases, one or more cameras, sensors, light sources, or I/O devices  1122  of the device  1100  (or in its band  1104  or band attachment mechanism) may include one or an array of HCSELs or optoelectronic devices configured as described herein. The HCSELs of the optoelectronic devices may have laser resonant cavities that extend largely parallel to the front cover  1110  (or output surface of the display  1108 ), the rear cover  1112 , a surface of the crown  1114 , or a surface of the button  1116 , so that the HSCELs emit light through the display  1108 , rear cover  1112 , crown  1114 , or button  1116 . Such HCSELs or other optoelectronic devices may be used for visible or invisible (e.g., infrared) illumination of a person (e.g., a face) or an object; for sensing purposes (e.g., as self-mixing interference (SMI) sensors, line scanners, dot scanners, and so on); for measurement purposes (e.g., for time-of-flight measurements); and so on. In some cases, the HCSELs may emit infrared light (e.g., SWIR electromagnetic radiation) through the front cover  1110 , rear cover  1112 , crown  1114 , or button  1116 . 
       FIG. 12  shows a sample electrical block diagram of an electronic device  1200 , which electronic device may in some cases take the form of the device described with reference to  FIGS. 10A-10B  or  FIGS. 11A-11B  and/or include the HCSEL or optoelectronic device described with reference to any of  FIGS. 1-9 . The electronic device  1200  may include a display  1202  (e.g., a light-emitting display), a processor  1204 , a power source  1206 , a memory  1208  or storage device, a sensor system  1210 , or an input/output (I/O) mechanism  1212  (e.g., an input/output device, input/output port, or haptic input/output interface). The processor  1204  may control some or all of the operations of the electronic device  1200 . The processor  1204  may communicate, either directly or indirectly, with some or all of the other components of the electronic device  1200 . For example, a system bus or other communication mechanism  1214  can provide communication between the display  1202 , the processor  1204 , the power source  1206 , the memory  1208 , the sensor system  1210 , and the I/O mechanism  1212 . 
     The processor  1204  may be implemented as any electronic device capable of processing, receiving, or transmitting data or instructions, whether such data or instructions is in the form of software or firmware or otherwise encoded. For example, the processor  1204  may include a microprocessor, a central processing unit (CPU), an application-specific integrated circuit (ASIC), a digital signal processor (DSP), a controller, or a combination of such devices. As described herein, the term “processor” is meant to encompass a single processor or processing unit, multiple processors, multiple processing units, or other suitably configured computing element or elements. 
     It should be noted that the components of the electronic device  1200  can be controlled by multiple processors. For example, select components of the electronic device  1200  (e.g., the sensor system  1210 ) may be controlled by a first processor and other components of the electronic device  1200  (e.g., the display  1202 ) may be controlled by a second processor, where the first and second processors may or may not be in communication with each other. 
     The power source  1206  can be implemented with any device capable of providing energy to the electronic device  1200 . For example, the power source  1206  may include one or more batteries or rechargeable batteries. Additionally or alternatively, the power source  1206  may include a power connector or power cord that connects the electronic device  1200  to another power source, such as a wall outlet. 
     The memory  1208  may store electronic data that can be used by the electronic device  1200 . For example, the memory  1208  may store electrical data or content such as, for example, audio and video files, documents and applications, device settings and user preferences, timing signals, control signals, and data structures or databases. The memory  1208  may include any type of memory. By way of example only, the memory  1208  may include random access memory, read-only memory, Flash memory, removable memory, other types of storage elements, or combinations of such memory types. 
     The electronic device  1200  may also include one or more sensor systems  1210  positioned almost anywhere on the electronic device  1200 . In some cases, sensor systems  1210  may be positioned as described with reference to  FIGS. 10A-10B  or  FIGS. 11A-11B . The sensor system(s)  1210  may be configured to sense one or more type of parameters, such as but not limited to, light; touch; force; heat; movement; relative motion; biometric data (e.g., biological parameters) of a user; particulate matter concentration, air quality; proximity; position; connectedness; and so on. By way of example, the sensor system(s)  1210  may include a heat sensor, a position sensor, a light or optical sensor, an accelerometer, a pressure transducer, a gyroscope, a magnetometer, a health monitoring sensor, a particulate matter sensor, an air quality sensor, and so on. Additionally, the one or more sensor systems  1210  may utilize any suitable sensing technology, including, but not limited to, magnetic, capacitive, ultrasonic, resistive, optical, acoustic, piezoelectric, or thermal technologies. 
     The I/O mechanism  1212  may transmit or receive data from a user or another electronic device. The I/O mechanism  1212  may include the display  1202 , a touch sensing input surface, a crown, one or more buttons (e.g., a graphical user interface “home” button), one or more cameras (including an under-display camera), one or more microphones or speakers, one or more ports such as a microphone port, and/or a keyboard. Additionally or alternatively, the I/O mechanism  1212  may transmit electronic signals via a communications interface, such as a wireless, wired, and/or optical communications interface. Examples of wireless and wired communications interfaces include, but are not limited to, cellular and Wi-Fi communications interfaces. 
     The foregoing description, for purposes of explanation, uses specific nomenclature to provide a thorough understanding of the described embodiments. However, it will be apparent to one skilled in the art, after reading this description, that the specific details are not required in order to practice the described embodiments. Thus, the foregoing descriptions of the specific embodiments described herein are presented for purposes of illustration and description. They are not targeted to be exhaustive or to limit the embodiments to the precise forms disclosed. It will be apparent to one of ordinary skill in the art, after reading this description, that many modifications and variations are possible in view of the above teachings. 
     As described above, one aspect of the present technology may be the gathering and use of data available from various sources, including biometric data (e.g., face or fingerprint data). The present disclosure contemplates that, in some instances, this gathered data may include personal information data that uniquely identifies or can be used to identify, locate, or contact a specific person. Such personal information data can include, for example, biometric data (e.g., fingerprint data) and data linked thereto (e.g., demographic data, location-based data, telephone numbers, email addresses, home addresses, data or records relating to a user&#39;s health or level of fitness (e.g., vital signs measurements, medication information, exercise information), date of birth, or any other identifying or personal information). 
     The present disclosure recognizes that the use of such personal information data, in the present technology, can be used to the benefit of users. For example, the personal information data can be used to authenticate a user to access their device, or gather performance metrics for the user&#39;s interaction with an augmented or virtual world. Further, other uses for personal information data that benefit the user are also contemplated by the present disclosure. For instance, health and fitness data may be used to provide insights into a user&#39;s general wellness, or may be used as positive feedback to individuals using technology to pursue wellness goals. 
     The present disclosure contemplates that the entities responsible for the collection, analysis, disclosure, transfer, storage, or other use of such personal information data will comply with well-established privacy policies and/or privacy practices. In particular, such entities should implement and consistently use privacy policies and practices that are generally recognized as meeting or exceeding industry or governmental requirements for maintaining personal information data private and secure. Such policies should be easily accessible by users, and should be updated as the collection and/or use of data changes. Personal information from users should be collected for legitimate and reasonable uses of the entity and not shared or sold outside of those legitimate uses. Further, such collection/sharing should occur after receiving the informed consent of the users. Additionally, such entities should consider taking any needed steps for safeguarding and securing access to such personal information data and ensuring that others with access to the personal information data adhere to their privacy policies and procedures. Further, such entities can subject themselves to evaluation by third parties to certify their adherence to widely accepted privacy policies and practices. In addition, policies and practices should be adapted for the particular types of personal information data being collected and/or accessed and adapted to applicable laws and standards, including jurisdiction-specific considerations. For instance, in the US, collection of or access to certain health data may be governed by federal and/or state laws, such as the Health Insurance Portability and Accountability Act (HIPAA); whereas health data in other countries may be subject to other regulations and policies and should be handled accordingly. Hence different privacy practices should be maintained for different personal data types in each country. 
     Despite the foregoing, the present disclosure also contemplates embodiments in which users selectively block the use of, or access to, personal information data. That is, the present disclosure contemplates that hardware and/or software elements can be provided to prevent or block access to such personal information data. For example, in the case of advertisement delivery services, the present technology can be configured to allow users to select to “opt in” or “opt out” of participation in the collection of personal information data during registration for services or anytime thereafter. In another example, users can select not to provide data to targeted content delivery services. In yet another example, users can select to limit the length of time data is maintained or entirely prohibit the development of a baseline profile for the user. In addition to providing “opt in” and “opt out” options, the present disclosure contemplates providing notifications relating to the access or use of personal information. For instance, a user may be notified upon downloading an app that their personal information data will be accessed and then reminded again just before personal information data is accessed by the app. 
     Moreover, it is the intent of the present disclosure that personal information data should be managed and handled in a way to minimize risks of unintentional or unauthorized access or use. Risk can be minimized by limiting the collection of data and deleting data once it is no longer needed. In addition, and when applicable, including in certain health related applications, data de-identification can be used to protect a user&#39;s privacy. De-identification may be facilitated, when appropriate, by removing specific identifiers (e.g., date of birth, etc.), controlling the amount or specificity of data stored (e.g., collecting location data at a city level rather than at an address level), controlling how data is stored (e.g., aggregating data across users), and/or other methods. 
     Therefore, although the present disclosure broadly covers use of personal information data to implement one or more various disclosed embodiments, the present disclosure also contemplates that the various embodiments can also be implemented without the need for accessing such personal information data. That is, the various embodiments of the present technology are not rendered inoperable due to the lack of all or a portion of such personal information data. For example, content can be selected and delivered to users by inferring preferences based on non-personal information data or a bare minimum amount of personal information, such as the content being requested by the device associated with a user, other non-personal information available to the content delivery services, or publicly available information.