Self-mixing interferometry devices for sensing applications

Abstract

Disclosed herein is a self-mixing interferometry (SMI) sensor, such as may include a vertical cavity surface emitting laser (VCSEL) diode and a resonant cavity photodetector (RCPD). The structure of the VCSEL diode and the RCPD is disclosed. In some embodiments, the VCSEL diode and the RCPD are laterally adjacent and formed by a set of common semiconductor layers epitaxially formed on a common substrate. In some embodiments, a first VCSEL diode and a second VCSEL diode are laterally adjacent and formed by a set of common semiconductor layers epitaxially formed on a common substrate, and the RCPD is formed on the second VCSEL diode. In some embodiments, the VCSEL diode may include two quantum well layers with a tunnel junction layer therebetween. In some embodiments, the RCPD may be vertically integrated with the VCSEL diode.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This Patent Cooperation Treaty patent application claims priority to U.S. Non-Provisional Patent Application No. 16 / 913,645, filed on June 26, 2020, entitled “Self-Mixing Interference Device for Sensing Applications,” and U.S. Provisional Patent Application No. 62 / 869,442, filed on July 1, 2019, entitled “Self-Mixing Interference Device for Sensing Applications,” the contents of which are incorporated herein by reference in their entirety. Technical Field

[0003] The present disclosure as a whole relates to the structure and configuration of vertical cavity surface emitting laser (VCSEL) diodes and associated photodetectors (PDs), such as resonant cavity photodetectors (RCPDs). The VCSEL diodes and associated PDs may be part of a sensor or detector that measures or determines the displacement, distance, motion, rate, or velocity of a surface or object. Such detectors or sensors may be involved in determining force or touch input on an electronic device.

[0004] The VCSEL diode and / or its associated RCPD can utilize self-mixing interference caused by reflection or backscattering of laser light emitted by the VCSEL diode. Through self-mixing interference, the received reflection causes the emitted laser light to change or alter in the VCSEL diode from the state of the laser light emitted without the received reflection. The change in the emitted laser light can be related to the distance or motion of an object or target, such as an input surface of an electronic device. Background Art

[0005] Electronic devices are very common in today's society. Exemplary electronic devices include mobile phones, tablet computers, personal digital assistants, etc. Some of these electronic devices include one or more input elements or surfaces, such as buttons or touch screens, through which a user can apply touch or pressure to input commands or data. The touch or pressure can be detected by a component of the electronic device for detecting displacement or movement of the input element or surface.

[0006] Such detection means may utilize a light source in which a beam of light, such as laser light, is emitted toward an input surface. Detection of displacement or movement of the input surface may be inferred from reflection or backscatter of the emitted laser light from the input surface.

[0007] A particular class of such detection components may include VCSEL diodes. A VCSEL diode may undergo self-mixing interference, in which reflections of its emitted laser light are received back into its laser cavity and transform a property (such as wavelength) of the emitted laser light to a state different from that in the absence of the received reflection (i.e., free emission). In the case where the received reflection is from an input surface, the transformation of the property may be associated with a displacement or motion of the input surface. Summary of the invention

[0008] This summary is provided to introduce a series of concepts in a simplified form, which are further described in the detailed description below. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter.

[0009] A self-mixing interferometry sensor is disclosed herein. The self-mixing interferometry sensor may include a vertical cavity surface emitting laser (VCSEL) diode and a resonant cavity photodetector (RCPD). The VCSEL diode and RCPD may be formed from a set of common semiconductor layers.

[0010] In a first embodiment, a self-mixing interferometry sensor may include a VCSEL diode and a RCPD laterally adjacent to the VCSEL diode. The VCSEL and the RCPD may include a set of common semiconductor layers formed on a common substrate including an active region layer. The VCSEL diode and the RCPD may be at least partially separated by a trench passing through the set of common semiconductor layers, the trench extending through the active region layer. The VCSEL diode may include an additional semiconductor layer stacked with the set of common semiconductor layers.

[0011] The VCSEL diode is configured to emit laser light under forward bias and undergo self-mixing interference caused by a first reflection or backscattering of the emitted laser light from an object, which changes the characteristics of the emitted laser light. The RCPD may be configured to be reverse biased during the emission of laser light by the VCSEL diode and receive a second reflection or backscattering of the emitted laser light from an object, and the RCPD may generate a measurable parameter related to the changed characteristics of the emitted laser light.

[0012] In another embodiment, the additional semiconductor layer can be formed on the set of common semiconductor layers and can include an etch stop layer adjacent to the set of common semiconductor layers, which can be indium gallium phosphide. A bias power supply electrical contact can be connected to the layer of the additional semiconductor layer farthest from the set of common semiconductor layers. In various embodiments, the VCSEL diode can be configured to have an intrinsic wavelength of 940 nanometers (nm), 850 nm, 1060 nm, or another intrinsic wavelength.

[0013] In another embodiment, the self-mixing interferometry sensor may include a first VCSEL diode and a second VCSEL diode, the second VCSEL diode being laterally adjacent to the first VCSEL diode. The first VCSEL diode and the second VCSEL diode include a set of common semiconductor layers formed on a common substrate, the common substrate including an active region layer. The self-mixing interferometry sensor may also include an RCPD positioned vertically adjacent to the second VCSEL diode on a side of the second VCSEL diode opposite to the common substrate. The first VCSEL diode and the second VCSEL diode are at least partially separated by a trench passing through the set of common semiconductor layers.

[0014] The first VCSEL diode may be configured to emit laser light while forward biased and experience self-mixing interference caused by receiving a first reflection or backscattering from an object, which changes the characteristics of the emitted laser light. The RCPD and the second VCSEL diode may be configured to be reverse biased during the emission of laser light by the first VCSEL diode. The RCPD may be configured to receive a second reflection or backscattering of the emitted laser light from an object, and the changed characteristics of the emitted laser light may be detectable using the measured parameters of the RCPD.

[0015] In some embodiments, the RCPD may include a tunnel junction layer comprising a first semiconductor material, which may be indium gallium arsenide different from the second semiconductor material in the active region layer. An etch stop layer may be present between the RCPD and the second VCSEL diode, which may be indium gallium phosphide. In one example, the VCSEL diode may be configured to emit laser light having an intrinsic wavelength of 940 nanometers, but in other embodiments, the VCSEL may have an intrinsic wavelength of 850 nm, 1060 nm, or another intrinsic wavelength.

[0016] The active region layer may include a first active region layer, a second active region layer, and a tunnel junction layer between the first active region layer and the second active region layer.

[0017] In another embodiment, a self-mixing interferometry sensor may include a VCSEL diode and an RCPD vertically adjacent to the VCSEL diode. The RCPD may include a first group of semiconductor layers formed on a substrate, and the VCSEL diode may include a second group of semiconductor layers formed on the first group of semiconductor layers opposite to the substrate. The VCSEL diode may be configured to emit laser light when forward biased, and self-mixing interference occurs when receiving a reflection or backscattering of the emitted laser light from an object, and the self-mixing interference changes the characteristics of the emitted laser light. The RCPD may be configured to be reverse biased during the emission of the laser light by the VCSEL diode, and detect changes in the characteristics of the emitted laser light. An etching stop layer may be present between the first group of semiconductor layers and the second group of semiconductor layers, and the etching stop layer may be indium gallium phosphide. The VCSEL diode may be configured to emit a laser light having an intrinsic wavelength of 940nm, 850nm, 1060nm, or another intrinsic wavelength. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The present disclosure will be more easily understood through the following detailed description in conjunction with the accompanying drawings, in which like reference numerals represent like structural elements.

[0019] Figure 1A A first configuration for sensing an object using a vertical cavity surface emitting laser (VCSEL) diode is shown according to one embodiment.

[0020] Figure 1B A second configuration for sensing an object using a VCSEL diode and an associated photodetector (PD) is shown according to one embodiment.

[0021] Figure 1C A third configuration is shown for sensing an object using a VCSEL diode and a vertically integrated PD according to one embodiment.

[0022] Figure 2A Exemplary components of a laser diode according to one embodiment are shown.

[0023] Figure 2B Self-mixing interference within a laser is shown according to one embodiment.

[0024] Figure 2C is a graph of power variation of laser light from a laser diode undergoing self-mixing interference versus feedback cavity length according to one embodiment.

[0025] Figure 3A The structure of a VCSEL diode according to one embodiment is shown.

[0026] Figure 3BThe structure of another VCSEL diode according to one embodiment is shown.

[0027] Figure 4 Shown is a configuration of components of a self-mixing interferometry (SMI) sensor according to one embodiment.

[0028] Figure 5A Another configuration of components of an SMI sensor according to one embodiment is shown.

[0029] Figure 5B A configuration of components of a resonant cavity photodetector according to one embodiment is shown.

[0030] Fig. 6A Another configuration of components of an SMI sensor according to one embodiment is shown.

[0031] Figure 6B An energy band diagram of two active region layers and a tunnel junction within a VCSEL diode is shown according to one embodiment.

[0032] Figure 6C An equivalent circuit for two active region layers and a tunnel junction within a VCSEL diode is shown according to one embodiment.

[0033] Fig. 7A A fabrication and epitaxial growth process for a self-mixing interferometry sensor is shown according to one embodiment.

[0034] Figure 7B A method for Fig. 7A Flip chip and substrate removal processes for self-hybrid interferometry sensors.

[0035] Figure 8 The configuration of components of a self-mixing interferometry sensor according to one embodiment is shown.

[0036] Fig. 9 The configuration of components of a self-mixing interferometry sensor according to one embodiment is shown.

[0037] Fig.10 A quantum well configuration of an active region layer according to one embodiment is shown.

[0038] The use of cross-hatching or shading in the drawings is generally provided to clarify boundaries between adjacent elements and also to facilitate legibility of the drawings. Thus, the presence or absence of cross-hatching or shading does not express or indicate any preference or requirement for particular materials, material properties, element proportions, element sizes, commonality of similar illustrated elements, or any other characteristic, property, or attribute of any element shown in the drawings.

[0039] Furthermore, it should be understood that the proportions and sizes (relative or absolute) of the various features and elements (and collections and groupings thereof) and the boundaries, spacings, and positional relationships presented therebetween are provided in the accompanying drawings solely to facilitate understanding of the various embodiments described herein, and therefore may not necessarily be presented or illustrated to scale and are not intended to indicate any preference or requirement for the embodiments illustrated to exclude the embodiments described in conjunction therewith. DETAILED DESCRIPTION

[0040] Reference will now be made specifically to the representative embodiments shown in the accompanying drawings. It should be understood that the following description is not intended to limit the embodiments to a preferred embodiment. On the contrary, it is intended to cover alternatives, modifications and equivalent forms that may be included in the spirit and scope of the embodiments defined by the appended claims.

[0041] Embodiments described herein relate to self-mixing interferometry sensors (such as can be used for touch or input sensors) and structures thereof. Such self-mixing interferometry sensors can use vertical cavity surface emitting laser (VCSEL) diodes and associated resonant cavity photodetectors (RCPDs). Electronic devices can use such self-mixing interferometry sensors in the process of detecting displacement, distance, motion, rate or speed of an input surface such as a touch screen. Hereinafter, for convenience, all such possible measured parameters will be referred to simply as "displacement or motion".

[0042] Such self-mixing interferometry sensors detect displacement or motion by applying a forward bias to cause one or more VCSEL diodes to emit laser light toward an input surface or object (hereinafter simply "object"). Reflections of the emitted laser light from the input surface or object may be received back into the laser cavity of the VCSEL diode. This may cause self-mixing interference, in which the wavelength of the emitted laser light shifts to a new, altered value. This shift in wavelength may be correlated to the displacement or motion of the object.

[0043] Other reflections of the emitted laser light can be detected simultaneously by the RCPD, the structure of which can include a pn diode junction. Under reverse voltage bias, no significant current flows through the pn junction of the RCPD. However, the received reflection of the emitted laser light can induce a photocurrent on the pn junction. The intensity of the photocurrent or another related interference characteristic can be related to the wavelength of the received reflection, which in turn can be related to the converted wavelength of the emitted laser light. A processing circuit (e.g., a processor or other circuit) included in the self-mixing interferometric measurement sensor can then be able to infer the distance or motion value of the object.

[0044] The various embodiments described below describe the structure or configuration of one or more VCSEL diodes and RCPDs as components of such self-mixing interferometry sensors. The VCSEL diodes and RCPDs may be formed by a set of common semiconductor layers, which are formed epitaxially from a common substrate and then electrically separated by etching grooves. In addition to or in place of epitaxial growth, alternative methods for forming the set of common semiconductor layers may also be used. For ease of explanation, the deposition or growth of the set of common semiconductor layers is described as epitaxial formation below, but those skilled in the art will recognize that alternative methods are within the scope of the present disclosure. The RCPD is then laterally adjacent to the VCSEL diode. In some embodiments, the self-mixing interferometry sensor may include two VCSEL diodes, both of which are formed by a set of common semiconductor layers, wherein the first VCSEL diode is operable to emit laser light, and the second VCSEL diode is reverse biased and has a vertically adjacent RCPD at the top to receive reflections of the emitted laser light. In this configuration, additional embodiments may include a tunnel junction within the first VCSEL diode.

[0045] Additional and / or alternative embodiments may utilize another configuration in which a VCSEL diode is epitaxially formed on an RCPD. Some of the laser light from the VCSEL diode is also emitted into the RCPD, and direct measurements are made of one or more interference characteristics of either the VCSEL diode or the RCPD.

[0046] The following reference Figures 1A to 10 These and other embodiments are described. However, those skilled in the art will readily appreciate that the detailed description given herein with respect to these drawings is for illustrative purposes only and should not be construed as limiting.

[0047] Figures 1A to 1C Exemplary configurations are shown in which VCSEL diodes can be used within self-mixing interferometry sensors to detect displacement or motion of an object, such as may be caused by a touch or force input from a user. The three configurations illustrate ways in which self-mixing interference may be induced in a VCSEL diode, and ways in which such self-mixing interference may be monitored.

[0048] Figure 1A 1 shows a configuration 100 of a self-mixing interferometry sensor using a VCSEL diode 102, wherein the VCSEL diode 102 is configured to emit a laser 106, which may be directed toward an object 110. The VCSEL diode 102 may emit the laser 106 under a forward voltage bias (or simply "forward bias") of its diode structure. During such a forward bias, the bias current I 偏置104 flows through the VCSEL diode 102. The charge carriers passing through the pn junction of the VCSEL diode 102 may cause laser emission from the VCSEL diode 102.

[0049] There may be reflections 112 of the emitted laser light 106, which may travel in multiple directions from the object 110. Some of the reflections 112 may be received back into the laser cavity of the VCSEL diode 102, causing the VCSEL diode to undergo self-mixing interference and change the characteristics of the emitted laser light 106 or the electrical characteristics of the VCSEL diode 102 itself. For example, the voltage monitor 108 may detect a change in the junction voltage of the VCSEL diode 102 that is related to the distance or motion of the object 110.

[0050] Figure 1B An input or object detection sensor configuration 120 is shown using a VCSEL diode 122. Under a forward voltage bias, the VCSEL diode 122 emits laser light 106 through an intervening glass layer 128 toward an object 110. The glass layer 128 may cause some reflection 107 of the emitted laser light 106. The forward voltage bias causes a bias current I 偏置 124 flows through the VCSEL diode 122. There may be reflections 112 of the emitted laser light 106 from the object or target, some of which may be received back into the laser cavity of the VCSEL diode 122, causing the VCSEL diode to experience self-mixing interference and changing the characteristics of the emitted laser light 106. Reflections 107 from the glass layer 128 may also affect how the VCSEL diode 122 experiences self-mixing interference. However, if the object is at least a certain minimum distance from the glass layer 128, spectral analysis of the electrical signal associated with the self-mixing interference may allow separation of a first effect in the electrical signal caused by the self-mixing interference caused by the reflections 107 from the glass layer 128 and a second effect caused by the self-mixing interference caused by the reflections 112 from the object. In some embodiments, a spacing of at least 100 μm between the object and the glass layer 128 is sufficient.

[0051] Configuration 120 may include a photodetector (PD) 126 operable to receive some of the reflections 112 from object 110. Changes in the emitted laser light 106 may in turn change an electrical characteristic of PD 126 that may be detectable. For example, a bias current I of PD 126 may be PD The change in can be detected by the current monitor 130.

[0052] Figure 1CA configuration 140 of a self-mixing interferometry sensor using a VCSEL diode 142 is shown. Under a forward voltage bias, the VCSEL diode 142 can emit laser light 106 toward an object 110. The forward voltage bias causes a bias current I 偏置 144 flows through the VCSEL diode 142 .

[0053] Some of the reflections 112 of the emitted laser light 106 may be received within the VCSEL diode 142, causing the VCSEL diode to experience self-mixing interference and change the characteristics of the emitted laser light 106. The VCSEL diode 142 may include an integrated PD 146. The PD 146 may detect operational changes in the VCSEL diode 142 due to the self-mixing interference. For example, the VCSEL diode 142 may also emit some laser light downward into the PD 146. Any changes in the emitted laser light 106 due to the self-mixing interference may also occur in the downwardly emitted laser light and cause operational changes in the PD 146. For example, the bias current I of the PD 146 may be set to 0. PD It can be detected by the current monitor 132 .

[0054] FIG. 2A to FIG. 2C The characteristics of the self-mixing interference of the emitted laser light in the laser diode are shown. These descriptions are intended only to describe certain aspects of the self-mixing interference required for understanding the disclosed embodiments. Other aspects of the self-mixing interference will be apparent to those skilled in the art.

[0055] Figure 2A An exemplary configuration of a laser diode 200 that can be used as part of a self-mixing interferometry sensor is shown, such as any of the VCSEL diodes 102, 122, and 142 described above. In any type of laser, an input energy source causes a gain material within a cavity to emit light. Mirrors 202 and 204 at opposite ends of the cavity feed light back into the gain material to cause amplification of the light and cause the light to become coherent and (mostly) have a single wavelength. A hole in one of the mirrors allows the laser light to be transmitted (e.g., toward an object or input surface).

[0056] In laser diode 200, there are two mirrors: 202 and 204 on opposite ends of the cavity. Laser light occurs within cavity 206. In the case of a VCSEL diode, the two mirrors 202 and 204 can be implemented as distributed Bragg reflectors, which are alternating high and low refractive index layers. Cavity 206 contains a gain material, which can include multiple doped layers of III-V semiconductors. Specific details of semiconductor materials will be presented below for various embodiments. The emitted laser light 210 can be emitted through the topmost layer or surface of laser diode 200. In some VCSEL diodes, coherent light can also be emitted through the bottom layer.

[0057] Figure 2B A functional diagram of self-mixing interference (or also called "optical feedback") within a laser is shown. Figure 2B , cavity 206 is shown reoriented so that emitted laser light 210 is emitted to the right from cavity 206. Cavity 206 has a fixed length that is determined at the time of manufacture. Emitted laser light 210 travels away from cavity 206 until it contacts an input surface or another object (such as the one described above with respect to Figures 1A to 1C The distance gap from the emission point through the reflector 204 of the emitted laser 210 to the target 216 is called the feedback cavity 208. Since the target 216 can move relative to the laser diode 200, the length L of the feedback cavity 208 is variable.

[0058] The emitted laser light 210 is reflected by the target 216 back into the cavity 206. The reflected light 212 enters the cavity 206 to coherently interact with the initially emitted laser light 210. This results in a new state shown with newly emitted laser light 214. The newly emitted light 214 in this new state may have different characteristics (e.g., wavelength or power) than the emitted laser light 210 would have in the absence of reflection and self-mixing interference.

[0059] Figure 2C 2 is a graph 220 showing the power of the newly emitted laser light 214 as a function of the length L of the feedback cavity 208 (i.e., the distance from the emission point through the reflector 204 of the emitted laser light 210 to the target 216). The graph shows a primarily sinusoidal variation with a period λ / 2. Theoretical considerations suggest that the variation is given by a proportional relationship: ΔP∝cos(4πL / λ). This relationship generally holds in the absence of strong specular reflections. For such strong specular reflections, the cosine becomes distorted, i.e., higher order harmonics are present in the relationship. However, the peak-to-peak spacing remains at λ / 2. For an initially stationary target 216, this relationship can be used to determine that a deflection has occurred. In combination with other techniques, such as counting the number of cycles completed, the extent of the deflection can also be determined.

[0060] While graph 220 shows the power of newly emitted laser light 214 as a function of length L of feedback cavity 208, similar results and / or graphs may apply to other interferometric properties of VCSEL diodes or other types of laser diodes measured by a self-mixing interferometry sensor. Measurement of one or more such interferometric parameters by a self-mixing interferometry sensor may be used to infer displacement or motion of target 216 from laser diode 200.

[0061] Now it will be relative to FIG. 3A to FIG. 3B More details of the structure of the VCSEL diode are presented.

[0062] FIG. 3A to FIG. 3B Two exemplary configurations of the structure and operation of a VCSEL diode are shown. The embodiments described below may utilize these structures or variations thereof. Those skilled in the art will recognize that other configurations and variations are within the scope of the present disclosure.

[0063] Figure 3A A first configuration 300 of a VCSEL diode 302 is shown in forward bias and emitting laser light 306a toward an object 110. In forward bias, a bias current 304 (I 偏置 ) flows into the VCSEL diode 302 , with some or all of the current returning to the ground plane or contact 312 .

[0064] As previously described, some reflections 112 of the emitted laser light 306a may be received back into the VCSEL diode 302 to cause self-mixing interference. Some of the reflections 112 may also become reflected light 314a toward a photodetector (not shown), as described above with respect to Figure 1B described.

[0065] The VCSEL diode 302 may include an emission side (or "top side") distributed Bragg reflector 303a that serves as a first (or "emission side") reflector for the laser structure. The emission side distributed Bragg reflector 303a may include a set of pairs of alternating materials having different refractive indices. Each such alternating material pair will be referred to herein as a Bragg pair. One or more of the materials in the emission side distributed Bragg reflector 303a is doped to p-type and thus forms part of the anode segment of a pn diode junction. Exemplary material pairs that can be used to form the emission side distributed Bragg reflector 303a are aluminum gallium arsenide (AlGaAs) and gallium arsenide (GaAs).

[0066] The VCSEL diode 302 may include a base-side distributed Bragg reflector 303b that serves as a second (or "base-side") reflector for the laser. The base-side distributed Bragg reflector 303b may also include a set of Bragg pairs of alternating materials having different refractive indices. One or more of the materials in the base-side distributed Bragg reflector 303b are doped to n-type and thus form part of the anode segment of a pn diode structure. An exemplary material pair that can be used to form the base-side distributed Bragg reflector 303b is aluminum arsenide and GaAs.

[0067] The VCSEL diode 302 may include an active region layer 318 that functions in part as a laser cavity. In a laser diode such as the VCSEL diode 302, the active region layer may include one or more quantum wells. The active region layer 318 of the VCSEL diode 302 may be adjacent to an oxide layer 316 having a hole through which the emitted laser light 306a exits.

[0068] The VCSEL diode 302 may be formed by epitaxial growth of layers for each of the emitter-side distributed Bragg reflector 303a and the base-side distributed Bragg reflector 303b, the active region layer 318, and the oxide layer 316, and possibly other layers. These various layers may be formed by epitaxial growth on the substrate layer 308, followed by formation of the ground layer or contact 312. The power contacts 305a, 305b may be formed on the outermost (i.e., emitter-side) layers of the VCSEL diode 302. Although in Figure 3A Although shown as separated in FIG. 1 , the power contacts 305 a , 305 b may be connected, such as to form, for example, a ring or horseshoe connection on the top side of the VCSEL diode 302 .

[0069] The VCSEL diode 302 may alternatively be formed by epitaxial growth from a substrate, first with the layers for the emission-side distributed Bragg reflector 303a. The substrate may then be separated from the substrate, such as by etching or dicing, and a flip-chip process used to attach the VCSEL diode 302 to another substrate or circuit, so that the emission-side distributed Bragg reflector 303a is configured to emit laser light 306a.

[0070] Figure 3B A second configuration 320 of a VCSEL diode 322 is shown in forward bias and emitting laser light 306b toward an object 110. Some reflections 112 of the emitted laser light 306b may be received back into the VCSEL diode 322 to cause self-mixing interference. Some other of the reflections 112 may also become reflected light 314b directed in a direction toward a photodetector (not shown), as described above with respect to FIG. Figure 1B described.

[0071] Configuration 320 of VCSEL diode 322 has many of the same features as configuration 300 of VCSEL diode 302, such as having multiple semiconductor layers extending from substrate layer 308 to which ground layer or contact 312 is attached. Also as described with respect to VCSEL diode 302 are power contacts 305a, 305b, which may be formed on the outermost (i.e., emitting side) layers of VCSEL diode 322, and which may be as described with respect to configuration 300. VCSEL diode 322 may also include active region layer 318 and oxide layer 316, both of which may be as described with respect to configuration 300. VCSEL diode 322 may include base distributed Bragg reflector 323b, which may be as described above with respect to base side distributed Bragg reflector 303b.

[0072] The VCSEL diode 322 may include an emission side (or "top side") distributed Bragg reflector 323a that is different from the Bragg reflector of the VCSEL diode 302. The emission side distributed Bragg reflector 323a may include a layer that serves as an etch stop layer during fabrication. Those skilled in the art will recognize that a variety of materials may be used as an etch stop layer. One such material is indium gallium phosphide (InGaP), which may have an InGaP layer. x Ga 1-x P (for 0≤x≤1). Due to the significant difference in etching rate between the etch stop layer and the GaAs / AlGaAs layer, the etch stop layer allows wet chemical etching to stop at the etch stop layer. After stopping at the etch stop layer, different chemical solutions can be used to remove only the etch stop layer without significantly etching the underlying GaAs or AlGaAs layer. By using this method, the etch stop layer can be inserted into any position in the epitaxial layer stack as an etch stop layer, so that etching can be stopped at the layer below the etch stop layer and the intracavity contact placed on the layer. Those skilled in the art will know that such an etch stop layer can be InGaP or another material, as long as the etching rate of the material under certain chemical solutions is significantly different from that of the layer to be blocked (such as GaAs and / or AlGaAs layers).

[0073] In some embodiments, VCSEL diodes 302 and 322 can be configured to emit respective laser light 306a and 306b having an intrinsic wavelength of approximately 940 nanometers (nm), the intrinsic wavelength being the wavelength of the respective emitted laser light 306a, 306b when there is no change due to self-mixing interference caused by reflection of the respective emitted laser light 306a, 306b. In other embodiments, the intrinsic wavelength can be 850nm, 1060nm, or another intrinsic wavelength. Hereinafter, for ease of illustration only, embodiments of VCSELs having an intrinsic wavelength of 940nm will be discussed. Those skilled in the art will recognize that these embodiments can be implemented with VCSELs having another intrinsic wavelength. Due to the intentional application of I with respect to a constant (DC) value, the VCSEL diodes 302 and 322 can be configured to emit respective laser light 306a and 306b having an intrinsic wavelength of approximately 940 nanometers (nm). 偏置 The intrinsic wavelength can vary within a range of about 940 nm. For example, in some embodiments, triangular or sinusoidal modulation can be applied to I 偏置 Such bias may be applied by a self-mixing interferometry sensor as part of determining the displacement or motion of object 110. As an example, I 偏置 The amplitude of such modulation can be about 1 mA and induces a self-mixing interference shift of wavelength from the natural wavelength of 940 nm by about 0.5 nm. In other embodiments, VCSEL diodes 302 and 322 can be configured to emit respective lasers 306a and 306b of different natural wavelengths and use different modulation amplitudes to produce different self-mixing interference wavelength shifts from the natural wavelength.

[0074] The specific configurations 300 and 320 are exemplary; those skilled in the art will recognize variations of the configuration within the scope of the present disclosure.The structure of VCSEL diodes 302 and 322, and variations thereof, may be part of a self-mixing interferometry sensor as will now be described.

[0075] Figure 4 An embodiment of at least a portion of a configuration 400 of a self-mixing interferometry sensor is shown. The self-mixing interferometry sensor may include at least two components: a VCSEL 402, which is operable to emit laser light 306b toward an object 110 when forward biased, and a resonant cavity photodetector (RCPD) 406, which is operable to detect reflected light 314b from all reflections 112 of the emitted laser light 306b. Some of the reflections 112 of the emitted laser light 306b may be received back into the VCSEL 402 and cause self-mixing interference that changes, for example, the wavelength of the emitted laser light 306b.

[0076] exist Figure 4 In the embodiment shown, the VCSEL diode 402 has Figure 3BHowever, VCSEL diode 402 may have another configuration, such as Figure 3A Configuration of the VCSEL diode 302. Figure 4 In a specific embodiment, the VCSEL diode 402 may include a base-side distributed Bragg reflector 403 b , an emission-side distributed Bragg reflector 403 a including an etch stop layer 424 (which may be InGaP), an active region layer 418 , and an oxide layer 416 .

[0077] Figure 4 The illustrated embodiment may include a RCPD 406 positioned laterally adjacent to a VCSEL diode 402. Both the VCSEL diode 402 and the RCPD 406 are positioned on a common substrate 408. The common substrate 408 may include a ground contact or layer 412. More details regarding the structure and fabrication of the VCSEL diode 402 and the RCPD 406 will be presented below.

[0078] exist Figure 4 In the embodiment of the present invention, RCPD 406 has a structure similar to Figure 3A The structure of the VCSEL diode 302 is shown in FIG. 4. Specifically, the RCPD 406 may include an n-type doped base side distributed Bragg reflector 407b. The active region layer 418 and the oxide layer 416 extend into the RCPD 406, as further described below. The RCPD 406 may also include a p-type doped top side distributed Bragg reflector 407a, so that the RCPD 406 forms a pn junction. Figure 4 In an embodiment of the present invention, the emission side distributed Bragg reflector 407 a has fewer layers than the emission side distributed Bragg reflector 403 a of the VCSEL diode 402 .

[0079] Each of the VCSEL diode 402 and the laterally adjacent RCPD 406 has a corresponding power contact. For the VCSEL diode 402, it is assumed that the power contacts 405a and 405b are electrically connected and attached to the topmost (farthest from the common substrate 408) of the semiconductor layer forming the VCSEL diode 402. The forward bias voltage +V applied to the power contact 405b is 偏置 Can cause current I 偏置 The current flows through the pn diode junction formed by the p-type emitter side distributed Bragg reflector 403a and the n-type base side distributed Bragg reflector 403b and is collected at the ground contact or layer 412. For the RCPD, it is assumed that the power contacts 417a and 417b are electrically connected and attached to the topmost semiconductor layer forming the RCPD 406.

[0080] RCPD 406 can be reverse biased during at least a portion of the time that VCSEL diode 402 is forward biased. This reverse bias can be caused by a negative voltage applied at power contact 417b (eg, −V PD 414a). When reverse biased, RCPD 406 can operate as a photodetector. When operating in this manner, reflected light 314b can be projected onto the topmost layer of RCPD 406, some of which becomes secondary reflection 414b, while the rest becomes absorbed light 414a. Under the applied reverse bias, no significant current flows through the pn junction of RCPD 406. However, absorbed light 414a can cause charge carriers to cross the junction and generate a photocurrent I PD The variation of the emitted laser light 306b from the VCSEL diode 402 may generate a photocurrent I PD The self-mixing interferometry sensor can then use those detectable changes to infer the displacement or motion of object 110.

[0081] Both the VCSEL diode 402 and the RCPD 406 may be formed from a set of common semiconductor layers that are epitaxially formed on a common substrate 408. That is, the various semiconductor layers for the base-side distributed Bragg reflectors 403 b and 407 b, the active region layer 418, the oxide layer 416, and the layers for the emission-side distributed Bragg reflectors 403 a and 407 a may be sequentially applied to a common substrate 408, which may be a semiconductor material or another type of substrate, such as sapphire, glass, or another material.

[0082] After all semiconductor layers are epitaxially formed, the individual layers at various locations may be removed, such as by etching or another process. Hereinafter, etching will refer to any known method of removing material from a semiconductor during fabrication. Figure 4 In some embodiments, trench 410 is etched through the semiconductor layer, including through the active region layer 418. In some embodiments, trench 410 may extend through common substrate 408, but this is not required. Trench 410 may provide electrical separation between VCSEL diode 402 and RCPD 406, thereby allowing alternating biasing of each.

[0083] exist Figure 4In an embodiment of the present invention, some of the semiconductor layers used for the emission-side distributed Bragg reflector 403a (e.g., the etch stop layer 424 and the layers above it) are also initially epitaxially formed at the location of the RCPD 406, but are subsequently removed by etching. The first purpose for removing those semiconductor layers is to provide higher absorption of the reflected light 314b. The second purpose is to allow a wider acceptance angle for the reflected light 314b: the absorbed light 414a can enter the RCPD 406 at a larger angle to the normal and still enter the active region layer. Other advantages are also possible.

[0084] Those skilled in the art will recognize that Figure 4 The VCSEL diode 402 and associated RCPD 406 shown, as well as the various VCSEL diodes and RCPDs shown in each of the embodiments disclosed herein, can be part of an array of such elements used within a self-mixing interferometry sensor. The epitaxial formation of the set of common semiconductor layers can allow such arrays to be formed more efficiently.

[0085] In some embodiments, during the formation of a specific layer in the set of common semiconductor layers, techniques such as masking and doping can be used to change the doping or chemical composition of a particular layer. For example, during the epitaxial formation of active region layer 418, its doping type or chemical composition can be changed at the location of RCPD 406. This can allow for improved detection of absorbed light 414a.

[0086] FIG. 5A to FIG. 5B 5 shows certain details of the configuration of a self-mixing interferometry sensor 500. The self-mixing interferometry sensor may include a first VCSEL diode 502 formed on a common substrate 508, a second VCSEL diode 522 of similar structure that is laterally adjacent, and a resonant cavity photodetector (RCPD) 532 that is vertically adjacent to the second VCSEL diode 522. A ground contact or ground plane 512 may be attached to a side of the common substrate 508 opposite the first VCSEL diode 502.

[0087] The structure of the first VCSEL diode 502 may be similar to Figure 3A The VCSEL diode 302. Figure 5AIn an embodiment of the present invention, the first VCSEL diode 502 may include a base-side distributed Bragg reflector 503b, which may be as previously described. The first VCSEL diode 502 may include an active region layer 518 and an oxide layer 516 thereover (i.e., on the side of the active region layer 518 opposite the common substrate 508). The first VCSEL diode 502 may include an emission-side distributed Bragg reflector 503a, which may be as previously described. Connectable power contacts 505a and 505b are attached to the emission side of the first VCSEL diode 502. As previously described, the emission-side distributed Bragg reflector 503a may have a p-type doping and the base-side distributed Bragg reflector 503b may have an n-type doping to form a diode pn junction structure.

[0088] A forward voltage bias (shown as +V 偏置 ). When the first VCSEL diode 502 is forward biased, the bias current I 偏置 will flow through the pn junction and be received at the ground contact or layer 512. During an applied forward bias, the first VCSEL diode may emit laser light 306a, such as toward an object (not shown), such as the object 110 described previously.

[0089] The structure of the second VCSEL diode 522 can be similar to the first VCSEL diode 502, such as by being formed from a set of common semiconductor layers, as described below. FIG. 5A to FIG. 5B In an embodiment of the present invention, the second VCSEL diode 522 may include a base-side distributed Bragg reflector 523b, a separate extension of the active region layer 518, a separate extension of the oxide layer 516, and an emission-side distributed Bragg reflector 523a. Connectable power contacts 535a and 535b are connected to semiconductor layers parallel to the topmost (emitting-side) semiconductor layer of the first VCSEL diode 502.

[0090] The self-mixing interferometry sensor 500 may include an RCPD 532 formed on an emission-side distributed Bragg reflector 503a of a second VCSEL diode 522. An etch stop layer 533, which may be InGaP, may be located between the RCPD 532 and the second VCSEL diode 522. During at least a portion of the time when the first VCSEL diode 502 is forward biased to emit laser light 306a, the second VCSEL diode 522 may be reverse biased by applying a negative voltage at the power contacts 535a, 535b. This may reduce the photodetector current I PD 536's undesired contribution, as will now be referred to Figure 5B Explanatory.

[0091] Figure 5B 532 is shown in more detail. The structure of RCPD 532 can be similar to a VCSEL diode. Figure 5B In an embodiment, the RCPD 532 may include a base-side distributed Bragg reflector 534b, a photodetector active region layer 538, and an emission-side distributed Bragg reflector 534a. The base-side distributed Bragg reflector 534b may have p-type doping and the emission-side distributed Bragg reflector 534a may have n-type doping to form a diode pn junction.

[0092] RCPD 532 has power contacts 537a and 537b on the topmost layer of its transmit-side distributed Bragg reflector 534a. Power contacts 537a and 537b may be connected, such as by being part of the same power contact, as previously described.

[0093] During the time when the first VCSEL diode 502 is forward biased to emit the laser 306a, the second VCSEL diode 522 can be powered by a negative voltage -V applied to the power contacts 535a and 535b. PD Reverse bias. RCPD 532 can also be reverse biased by setting power contacts 537a and 537b to ground (0V). When reflected light 314a is projected onto RCPD 532, some of the reflected light may be absorbed and cause the photodetector current I PD The photodetector current I PD These changes in can be related to changes in reflected light 314a caused by self-mixing interference occurring in first VCSEL diode 502. Processing circuitry (not shown) can measure photodetector current I PD These changes in , and infer the displacement or motion of the object causing the reflected light 314a, as previously described.

[0094] In various embodiments, the number of Bragg pairs in the emission-side distributed Bragg reflector 534a is less than the number of Bragg pairs in the base-side distributed Bragg reflector 523b. This can provide the RCPD 532 with an increased acceptance angle for the reflected light 314a. This can result in an improved signal-to-noise ratio, such as in I PD In one embodiment, 4 Bragg pairs are used for the transmit-side distributed Bragg reflector 534a, and 11 Bragg pairs are used for the base-side distributed Bragg reflector 534b.

[0095] Various advantages are attributed to the configuration of the self-mixing interferometry sensor 500. Under reverse bias, the RCPD 532 and the second VCSEL diode 522 can be formed to act as a selective wavelength filter for the wavelength of the emitted laser light 306a. Another advantage is that the photodetector active region layer 538 can be InGaAs or can include InGaAs. InGaAs has a lattice structure that is incompatible with the lattice structure of AlGaAs, which can be a material used as part of a distributed Bragg reflector adjacent to the photodetector active region layer 538. Because the InGaAs in the photodetector active region layer 538 has a more limited thickness than the various semiconductor layers in the first VCSEL diode 502 and the second VCSEL diode 522, there is less mechanical stress. In yet another advantage, the photodetector active region layer 538 can be formed with a doping or chemical composition that is different from the doping or chemical composition of the active region layer 518.

[0096] The configuration of the self-mixing interferometry sensor 500 can be as described above for Figure 4 532. The first VCSEL diode 502 and the second VCSEL diode 522 can both be formed from a set of common semiconductor layers that are epitaxially formed on a common substrate 508. Additional semiconductor layers for the RCPD 532 can then be epitaxially formed on those layers. Etching can then be used to form trenches 510 and remove the additional semiconductor layers added for the RCPD 532 from above the location of the first VCSEL diode 502, from above the location of the power contacts 535a and 535b, and possibly from other desired locations.

[0097] FIG. 6A to FIG. 6C Shows FIG. 5A to FIG. 5B A variation of the embodiment shown. FIG. 6A to FIG. 6C The described embodiments can provide a strong feedback signal, such as through the I PD The signal-to-noise ratio is measured in FIG. 6A to FIG. 6C The described embodiments involve reducing the internal reflectivity of an emission-side distributed Bragg reflector used as a reflector for a laser. Reducing the internal reflectivity allows for stronger reflections from objects, such as by increasing the amount of laser light emitted, and thus allows for stronger reflections to be absorbed by the associated RCPD. However, the reduced internal reflectivity may be detrimental to the VCSEL diode reaching the threshold for lasing. FIG. 6A to FIG. 6C The described embodiments allow the reflectivity of the emission side distributed Bragg reflector to be reduced by reducing the threshold for lasing. This is achieved by including a tunnel junction in one or more active region layers. These considerations will now be described in detail.

[0098] Fig. 6AA configuration of a self-mixing interferometry sensor 600 is shown, which is similar to the configuration described for the self-mixing interferometry sensor 500. The self-mixing interferometry sensor 600 may include a first VCSEL diode 602 and a second VCSEL diode 622 laterally adjacent to the first VCSEL diode 602, both formed from a set of common semiconductor layers on a common substrate 608. A ground layer or contact 612 is formed on a side of the common substrate 608 opposite the first VCSEL diode 602. The self-mixing interferometry sensor 600 may also include a resonant cavity photodetector (RCPD) 632 vertically adjacent to a side of the second VCSEL diode 622 opposite the common substrate.

[0099] The first VCSEL diode 602 may include an emission side distributed Bragg reflector 603a and a base side distributed Bragg reflector 603b. The first VCSEL diode 602 may include connectable power contacts 605a and 605b that may be adjacent to the topmost of the set of common semiconductor layers or on the topmost layer of the emission side distributed Bragg reflector 603a.

[0100] The first VCSEL diode 602 may include both a first active region layer 618a and a second active region layer 618b positioned between an emission side distributed Bragg reflector 603a and a base side distributed Bragg reflector 603b, wherein the first active region layer 618a is adjacent to the emission side distributed Bragg reflector 603a. The first VCSEL diode 602 may include an oxide layer 616 positioned between the first active region layer 618a and the emission side distributed Bragg reflector 603a. The first VCSEL diode 602 may include an n-doped first tunnel junction layer 624a and a p-doped second tunnel junction layer 624b. The first tunnel junction layer 624a and the second tunnel junction layer 624b are positioned between the first active region layer 618a and the second active region layer 618b. More details of the structure and operation of the tunnel junction layers 624a, 624b will be referred to below. FIG. 6B to FIG. 6C Shown.

[0101] The second VCSEL diode 622 may include an emission-side distributed Bragg reflector 623a and a base-side distributed Bragg reflector 623b. The second VCSEL diode 622 may include connectable power contacts 635a and 635b adjacent to the topmost of the set of common semiconductor layers.

[0102] The self-mixing interferometry sensor 600 may also include an RCPD 632 formed of an additional semiconductor layer adjacent to and extending vertically from the emission-side distributed Bragg reflector 623a of the second VCSEL diode 622. The RCPD 632 may include an etch stop layer 633, which may be InGaP, adjacent to the topmost semiconductor layer of the emission-side distributed Bragg reflector 623a. The RCPD 632 may include an active region layer 638. The RCPD 632 may include connectable power contacts 637a and 637b positioned on the topmost of the additional semiconductor layer.

[0103] The self-mixing interferometry sensor 600 can be biased by applying a forward voltage +V to the power contacts 605a, 605b. 偏置 The RCPD 632 and the second VCSEL diode 622 are reverse biased at least a portion of the time when the first VCSEL diode 602 emits the laser light 306a. The reverse bias may be applied as a negative voltage -V applied to the power contacts 635a, 635b. PD The reflected light 314b may enter the RCPD 632 and cause the photodetector current I PD As previously described, this photocurrent may then become an input to a processor or processing circuit which may infer the value of the new wavelength and / or the distance or motion of the reflecting object.

[0104] The self-mixing interferometry sensor 600 can be formed as previously described. A set of common semiconductor layers for the first VCSEL diode 602 and the second VCSEL diode 622 are epitaxially formed on a common substrate 608. Additional semiconductor layers for the RCPD 632 can then be epitaxially formed on the set of common semiconductor layers. Etching can then remove any additional semiconductor layers formed above the location of the first VCSEL diode 602. Etching can also remove a portion of the set of common semiconductor layers to form a trench 610. The trench 610 can extend through the first active region layer 618a and the second active region layer 618b.

[0105] Figure 6B The energy band diagram 640 of the first VCSEL active region 618a and the second VCSEL active region 618b and the two tunnel junction layers 624a and 624b in the first VCSEL diode 602 is shown. The energy band diagram 640 shows the energy bands denoted as Ec The conduction band and is represented by E v The first tunnel junction layer 624a adjacent to the first active region layer 618a may be highly doped (eg, a doping level greater than 1×10 19 cm -3 ) n-type semiconductor, such as the highly doped n-type (n++) GaAs shown. The second tunnel junction layer 624b adjacent to the second active region layer 618b can be a highly doped p-type semiconductor, such as the highly doped p-type (p++) GaAs shown. In other embodiments, the tunnel junction layer can use semiconductor materials other than GaAs. A non-limiting group of such semiconductor materials includes Al x Ga 1-x As(0≤x≤1), InP, In x Ga 1-x As(0≤x≤1), In 1-x-y Al x Ga y As(0≤x≤1,0≤y≤1) and In x Ga 1-x As y P 1-y (0≤x≤1, 0≤y≤1).

[0106] The first active region layer 618a may include at least three segments: a top segment of p-type doped aluminum gallium arsenide (AlGaAs) 642a adjacent to the emission-side distributed Bragg reflector 603a, a bottom segment of n-type doped aluminum gallium arsenide (AlGaAs) 642b adjacent to the first tunnel junction layer 624a, and a center segment of intrinsic InGaAs and AlGaAs 642c forming alternating pairs of quantum wells.

[0107] The second active region layer 618b may include at least three segments: a top segment of p-type doped AlGaAs 644a adjacent to the second tunnel junction layer 624b, a bottom segment of n-type doped aluminum gallium arsenide (AlGaAs) 644b adjacent to the base-side distributed Bragg reflector 603b, and a center segment of intrinsic InGaAs and AlGaAs 644c forming alternating pairs of quantum wells.

[0108] Figure 6CA circuit model 650 indicating the functions of the various layers of the first VCSEL diode 602 is shown, which is shown horizontally for ease of illustration. The first tunnel junction layer 624a and the second tunnel junction layer 624b are used together as a resistor to separate the first active area layer 618a and the second active area layer 618b. The first active area layer 618a and the second active area layer 618b are each modeled as a diode. As in the embodiment of Figure 5, a single active area layer itself may not be sufficient to provide sufficient gain to generate laser light when the reflectivity of the emission side reflector (such as the emission side distributed Bragg reflector 603a) is reduced to generate more emitted laser light. The resistance provided by the first tunnel junction layer 624a and the second tunnel junction layer 624b allows the first active area layer 618a and the second active area layer 618b to provide an increased total gain, which is sufficient to generate laser light even if the reflectivity of the emission side reflector is reduced.

[0109] For example, in a single conventional VCSEL diode with a single active region layer, the bottom reflector may require R B >99.99% reflectivity, and the top reflector may require R T >99.3% reflectivity. FIG. 6A to FIG. 6C In some embodiments of the present invention, the top reflectivity provided by the emission-side distributed Bragg reflector 603a can be reduced to just meet R T >98.5%. In some embodiments, the reduction in reflectivity of the emission-side distributed Bragg reflector 603a can be achieved by having fewer Bragg pairs.

[0110] In the circuit model 650, the power contact 605a acts as an anode, where a positive bias voltage is provided, and the ground plane or contact 612 acts as a cathode. FIG. 6A to FIG. 6C In an embodiment of the self-mixing interferometry sensor 600, the forward bias voltage may need to be higher than the forward bias voltage in an embodiment in which only one active region layer is present to produce lasing because a diode voltage drop needs to be provided for both the first active region layer 618a and the second active region layer 618b. In the circuit model 650, the transmitting side distributed Bragg reflector 603a and the base side distributed Bragg reflector 603b each act as a resistor.

[0111] Figure 4 , FIG. 5A to FIG. 5B and FIG. 6A to FIG. 6C An embodiment of a self-mixing interferometry sensor in has laterally adjacent RCPDs designed to receive reflections of emitted laser light that are different from the reflections that produce self-mixing interference in the laser VCSEL diode. Figure 8 and Fig. 9Additional and / or alternative embodiments of the described self-mixing interferometry sensor utilize an RCPD vertically adjacent to a laser VCSEL diode.

[0112] Fig. 7A and Figure 7B The manufacturing and epitaxial growth process of the self-mixing interferometry sensor 700 as shown and described herein is shown. As part of the epitaxial growth of the self-mixing interferometry sensor 700, a first etch stop layer 706 (e.g., an InGaP etch stop layer) can be epitaxially formed on the substrate 701. The semiconductor layers for the VCSEL diode 702 can be epitaxially formed on the first etch stop layer 706.

[0113] A second etch stop layer 704 (eg, an InGaP etch stop layer) may be epitaxially grown on a top portion of the semiconductor layer constituting the VCSEL diode 702. The second etch stop layer may separate the semiconductor layer for the VCSEL diode 702 from the semiconductor layer for the RCPD 722. Fig. 7A As shown, RCPD 722 may be epitaxially formed from second etch stop layer 704. Substrate layer 708 may be formed on or otherwise disposed over the semiconductor layer for RCPD 722.

[0114] The VCSEL diode 702 may include an emission-side distributed Bragg reflector 703a adjacent to a first etch stop layer 706, an oxide layer 716 (eg, a high-aluminum Al x Ga 1-x As layer, where X is approximately equal to 0.98), an active region layer 718, and a base-side distributed Bragg reflector 703b adjacent to the second etch stop layer 704. In some embodiments, the active region layer 718 can be a plurality of forward-biased quantum wells (e.g., forward-biased quantum wells configured to generate light). In some embodiments, the number of quantum wells comprising the active region layer 718 can be less than six and / or can have a quantum well thickness of less than 10 nm. The base-side distributed Bragg reflector 703b and the emission-side distributed Bragg reflector 703a can function as previously described.

[0115] RCPD 722 may include an emission side distributed Bragg reflector 723a, an active region layer 724, and a base side distributed Bragg reflector 723b. The emission side distributed Bragg reflector 723a and the base side distributed Bragg reflector 723b may function as described above. The active region layer 724 may be a photon absorption layer (e.g., an InGaAs photon absorption layer). In some embodiments, the active region layer 724 has a thickness between 15nm and 60nm. In some embodiments, the active region layer 724 may be formed by a quantum well. The substrate layer 708 may be grown and / or positioned above the RCPD 722 (e.g., adjacent to the base side distributed Bragg reflector 723b).

[0116] Figure 7B The self-mixing interferometry sensor 700 is shown after the flip chip process has occurred. Figure 7B In the embodiment, the substrate 701 and the first etch stop layer 706 may have been removed during the removal process. The substrate layer 708 may be positioned adjacent to the ground contact layer 712. Figure 7B As shown, the self-mixing interferometry sensor 700 can be turned upside down (e.g., in a flip chip process) so that, for example, the VCSEL diode 702 is positioned above the RCPD 722. After the flip chip process, the self-mixing interferometry sensor 700 can undergo a further substrate removal process and can be transformed into the following relative Figure 8 A self-mixing interferometry sensor 800 is shown and described.

[0117] Figure 8 A configuration of a self-mixing interferometry sensor 800 is shown, which may include a VCSEL diode 802 vertically adjacent to a RCPD 822. The self-mixing interferometry sensor 800 may be configured as described above with respect to Fig. 7A and Figure 7B 822 can be fabricated and epitaxially grown using the processes described herein, or can be epitaxially grown upward from substrate layer 808 as described herein. Semiconductor layers for RCPD 822 can be epitaxially formed on substrate 808. Ground contact layer 812 can be formed in or on the substrate, such as on a side of substrate 808 opposite to RCPD 822.

[0118] The etch stop layer 804, which may be InGaP, may separate the semiconductor layers for the RCPD 822 from the additional layers forming the VCSEL diode 802. The VCSEL diode 802 may include a base side distributed Bragg reflector 803b, an active region layer 818, an oxide layer 816, and an emission side distributed Bragg reflector 803a adjacent to the etch stop layer 804. The base side distributed Bragg reflector 803b and the emission side distributed Bragg reflector 803a function as previously described. Connectable power contacts 805a and 805b are attached to the topmost layer of the VCSEL diode 802.

[0119] The RCPD 822 itself can be constructed with an active region layer 824 positioned between the emission side distributed Bragg reflector 823a and the base side distributed Bragg reflector 823b. The base side distributed Bragg reflector 823b and the emission side distributed Bragg reflector 823a function as previously described. The semiconductor layer for the RCPD 822 can extend laterally beyond the semiconductor layer forming the VCSEL diode 802. Such a configuration can be formed by initially epitaxially forming all the layers included in the self-mixing interferometry sensor and then etching a portion of the layer of the VCSEL diode 802. The power contact 825 is attached to the topmost layer of the RCPD at a position where the RCPD extends laterally beyond the VCSEL diode 802.

[0120] In operation, the forward voltage is biased to +V 偏置 is applied to the power contacts 805a and 805b, which causes a bias current I 偏置 822 flows into the VCSEL diode 802 and causes the emission of the laser 306a, as previously described. During at least a portion of the time when the VCSEL diode 802 is emitting laser light, the RCPD 822 may provide a negative voltage -V at the power contact 825. PD and is reverse biased, causing the photodetector current I PD In addition to the emitted laser light 306a, some of the laser light generated in the active region layer 818 may be directed downward and absorbed or received in the reverse biased RCPD 822.

[0121] If some of the emitted laser light 306a is reflected from an object (not shown) and received in the VCSEL diode 802, self-mixing interference may occur, which causes a change in the wavelength of the emitted laser light 306a. Some of such changed laser light may then be received in the RCPD 822, thereby causing a change in the photodetector current I PD Or produce a measurable change in another electrical property or interference property of RCPD 822. This measurable change can be used to infer the distance or movement of the reflecting object.

[0122] Fig. 9 900. The self-mixing interferometry sensor may include a VCSEL diode 902 and a laterally adjacent RCPD 932. The RCPD 932 is formed as part of a set of common semiconductor layers epitaxially formed on a substrate 908. The VCSEL diode 902 is formed vertically above the set of common semiconductor layers. A trench 910 may be etched at least partially through the set of common semiconductor layers to provide electrical separation between the VCSEL diode 902 and the RCPD 932.

[0123] Starting from the group of common semiconductor layers, the VCSEL diode 902 may include, in sequence: an etching stop layer 904, a semiconductor layer forming a base-side distributed Bragg reflector 903b, an active region layer 918, an oxide layer 916, and a semiconductor layer forming an emission-side distributed Bragg reflector 903a. Figure 8 802 of the VCSEL diode. Contacting the topmost layer of the VCSEL diode 902 are connectable power contacts 905a and 905b.

[0124] Starting from substrate 908, RCPD 932 may include, in order: a semiconductor layer forming a base-side distributed Bragg reflector 933b, an active region layer 934, and a semiconductor layer forming an emission-side distributed Bragg reflector 933a. The layers for these three structures have corresponding lateral extensions separated by trench 910 and below VCSEL diode 902: layer 923b, layer 924, and layer 923a. These layers may be constructed as RCPD 922 as previously described. In addition, the RCPD 922 may also be used to detect self-mixing interference in laser light emitted by forward-biased VCSEL diode 802, such as for Figure 8 There is an etch stop layer 904 between the layer 923a of the base side distributed Bragg reflector 903b and the semiconductor layer, which may be InGaP. Contacting the topmost layer of the RCPD 932 are connectable power contacts 925a and 925b.

[0125] The self-mixing interferometry sensor 900 can operate similarly to the previous embodiments. 偏置 is applied to the power contacts 905a and 905b, which causes a bias current I 偏置Flows into VCSEL diode 902 and causes emission of laser light 306a, as previously described. If some of the emitted laser light 306a is reflected from an object (not shown) and received in VCSEL diode 902, self-mixing interference may occur, causing a change in the wavelength of the emitted laser light 306a.

[0126] During at least a portion of the time when VCSEL diode 902 is lasing, RCPD 932 may provide a negative voltage, −V pd The other reflections in the altered laser light can then be received in the RCPD 932, thereby causing the photodetector current I PD Or produce a measurable change in another electrical property or interferometric property of RCPD 922. This measurable change can be used to infer the distance or motion of the reflecting object.

[0127] Fig.10 1 shows a quantum well configuration of an active region layer 1000 of a self-mixing interferometry sensor. The active region layer 1000 may include quantum wells 1002a to 1002c and may be defined by a first barrier 1004 and a second barrier 1006. In some embodiments, the active region layer 1000 may correspond to the active region layer 718 of the VCSEL diode 702, as described above with respect to Fig. 7A and Figure 7B In such embodiments, the active region layer 1000 can be configured to emit light (e.g., photons), and the quantum wells 1002a-1002c can be forward biased quantum wells. In alternative or additional embodiments, the active region layer 1000 can correspond to the active region layer 724 of the RCPD 722, as described above with respect to Fig. 7A and Figure 7B In such embodiments, the active region layer 1000 may be configured to absorb light (e.g., photons), and the quantum wells 1002a to 1002c may be reverse biased. Under reverse bias, a quantum confined Stark effect (QCSE) may make the quantum wells 1002a to 1002c photon absorptive, and the absorbed light may be converted into a photocurrent signal.

[0128] In some embodiments, three quantum wells 1002a-1002c may be positioned in the active region layer 1000. In some embodiments, there may be up to six quantum wells in the active region layer 1000. In other embodiments, there may be six or more quantum wells in the active region layer 1000. In some embodiments, the thickness of each quantum well 1002a-1002c may be less than 10 nm. In some embodiments, the thickness of each quantum well 1002a-1002c may be equal to or greater than 10 nm. The quantum wells 1002a-1002c may be at least 10 nm in thickness relative to the active region layer 1000. Fig. 7A and Figure 7B The epitaxial growth process shown and described may be formed during the epitaxial growth process or may be formed relative to Figure 8 The reverse epitaxial growth process is described.

[0129] Other examples and specific implementations are within the scope and essence of the present disclosure and the appended claims. For example, features that implement functions may also be physically located at various locations, including being distributed so that functional parts are implemented at different physical locations. In addition, as used herein, including in the claims, the "or" used in a series of items prefixed with "at least one" indicates a disjunctive list, so that, for example, "at least one of A, B, or C" refers to A or B or C, or AB or AC or BC, or ABC (i.e., A and B and C). In addition, the term "exemplary" does not mean that the example is preferred or better than other examples.

[0130] For the purpose of illustration, the foregoing description uses specific naming to provide a thorough understanding of the embodiments. However, it will be apparent to those skilled in the art that the embodiments can be practiced without specific details. Therefore, for the purpose of illustration and description, the foregoing description of the specific embodiments described herein is presented. These descriptions are not intended to be exhaustive or to limit the embodiments to the disclosed precise forms. It will be apparent to those of ordinary skill in the art that many modifications and variations are feasible in accordance with the above teachings.

Claims

1. A self-mixing interferometry (SMI) sensor, the SMI sensor comprising: Vertical Cavity Surface Emitting Laser VCSEL diode; as well as a resonant cavity photodetector, RCPD, the RCPD being vertically adjacent to the VCSEL diode, wherein: The RCPD includes a first set of semiconductor layers formed on a substrate; The first set of semiconductor layers includes a first active region layer positioned between a first emitter-side distributed Bragg reflector and a first base-side distributed Bragg reflector; The VCSEL diode includes a second set of semiconductor layers formed on the first set of semiconductor layers; and The second set of semiconductor layers includes a second active region layer positioned between a second emitter-side distributed Bragg reflector and a second base-side distributed Bragg reflector, wherein The VCSEL diode is configured to emit laser light under forward bias and to undergo self-mixing interference caused by first reflection or backscattering of the emitted laser light from an object, the self-mixing interference changing a characteristic of the emitted laser light; The RCPD is configured to be reverse biased during emission of the laser light by the VCSEL diode and receive a second reflection or backscattering of the emitted laser light from the object; and The RCPD produces a measurable parameter related to the altered property of the emitted laser light.

2. The SMI sensor according to claim 1, wherein: An etch stop layer is positioned between the RCPD and the VCSEL diode; and A forward bias supply electrical contact is connected to the top VCSEL surface of the second set of semiconductor layers.

3. The SMI sensor of claim 2, wherein a reverse bias supply electrical contact is connected to a top RCPD surface of the first set of semiconductor layers.

4. The SMI sensor according to claim 1, further comprising a processing circuit, wherein the processing circuit is configured to: measuring the measurable parameter produced by the RCPD; and At least one of a displacement or a motion of the object is determined using at least the measured parameter. 5 . The SMI sensor of claim 1 , wherein the VCSEL diode is configured to emit the laser light having a native wavelength of 940 nanometers. 6 . The SMI sensor of claim 1 , wherein an active region layer within the RCPD is doped to have a narrower bandgap than an active region layer within the VCSEL diode.

7. A self-mixing interferometry (SMI) sensor, the SMI sensor comprising: A first vertical cavity surface emitting laser VCSEL diode; a second VCSEL diode, the second VCSEL diode being laterally adjacent to the first VCSEL diode; as well as Resonant Cavity Photodetector RCPD, where: The first VCSEL diode and the second VCSEL diode include a set of common semiconductor layers formed on a common substrate; The set of common semiconductor layers includes an active region layer, the active region layer including: a first active region layer; a second active region layer; and a tunnel junction layer between the first active region layer and the second active region layer; The first VCSEL diode and the second VCSEL diode are at least partially separated by a trench extending at least partially through the set of common semiconductor layers; and The RCPD is positioned vertically adjacent to the second VCSEL diode on a side of the second VCSEL diode opposite the common substrate.

8. The SMI sensor according to claim 7, wherein: The first VCSEL diode is configured to emit laser light when forward biased and to undergo self-mixing interference caused by receiving a first reflection or backscattering from an object, the self-mixing interference changing a characteristic of the emitted laser light; The RCPD and the second VCSEL diode are configured to be reverse biased during emission of the laser light by the first VCSEL diode; The RCPD is configured to receive a second reflection or backscatter of the emitted laser light from the object; as well as The altered properties of the emitted laser light can be detected using the measured parameters of the RCPD.

9. The SMI sensor of claim 7, wherein the RCPD comprises a junction layer comprising a first semiconductor material different from a second semiconductor material in the active region layer.

10. The SMI sensor of claim 9, wherein the first semiconductor material of the junction layer of the RCPD is InGaAs.

11. The SMI sensor of claim 7, wherein the first VCSEL diode is configured to emit laser light having a native wavelength of 940 nanometers. 12 . The SMI sensor of claim 7 , wherein the tunnel junction layer comprises a first sublayer and a second sublayer, the first sublayer comprising a highly doped n-type semiconductor, and the second sublayer comprising a highly doped p-type semiconductor.

13. The SMI sensor of claim 7, wherein the first VCSEL diode has an emission-side distributed Bragg reflector having a reflectivity less than 99.0%.

14. The SMI sensor according to claim 7, wherein: The RCPD includes a transmitter-side distributed Bragg reflector and a base-side distributed Bragg reflector; and The emitter-side distributed Bragg reflector has fewer Bragg pairs than the base-side distributed Bragg reflector.

15. A self-mixing interferometry (SMI) sensor, the SMI sensor comprising: Vertical Cavity Surface Emitting Laser VCSEL diode; as well as a resonant cavity photodetector, RCPD, the RCPD being vertically adjacent to the VCSEL diode, wherein: The RCPD includes a first set of semiconductor layers formed on a substrate; The VCSEL diode includes a second set of semiconductor layers formed on the first set of semiconductor layers opposite to the substrate; The VCSEL diode is configured to emit laser light when forward biased and to undergo self-mixing interference upon receiving reflection or backscatter of the emitted laser light from an object, the self-mixing interference changing a characteristic of the emitted laser light; as well as The RCPD is configured to be reverse biased during emission of the laser light by the VCSEL diode and to detect a change in the characteristic of the emitted laser light. 16 . The SMI sensor of claim 15 , further comprising an etch stop layer between the first set of semiconductor layers and the second set of semiconductor layers.

17. The SMI sensor of claim 15, wherein the VCSEL diode is configured to emit the laser light having a native wavelength of 940 nanometers.

18. The SMI sensor of claim 15, wherein the VCSEL diode additionally comprises a forward biased quantum well for emitting light.

19. The SMI sensor of claim 15, wherein the RCPD additionally comprises a reverse biased quantum well for absorbing light.

20. The SMI sensor of claim 15, wherein: at least one reverse bias power contact attached to a set of common semiconductor layers at a first topmost portion of the RCPD to provide a reverse bias voltage to the RCPD; and At least one forward bias power contact is attached to the second topmost layer of the additional semiconductor layer to provide a forward bias voltage to the VCSEL diode.

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