Vertical cavity surface emitting laser with planar surface oxidation grating

Abstract

A vertical cavity surface emitting laser (VCSEL) may include a first top mirror structure over a cavity region. The VCSEL may include a grating layer over the first top mirror structure. The grating layer may include a plurality of oxidized regions forming a grating structure in the grating layer. A grating structure may be associated with the polarization of the output light emitted by the VCSEL. The surface of the grating layer may be a planar surface.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This patent application claims priority to U.S. Provisional Patent Application No. 63 / 579,366, filed on August 29, 2023, and entitled “VERTICAL-CAVITY SURFACE-EMITTING LASER WITH APLANAR SURFACE OXIDIZED GRATING.” The disclosure of the prior application is considered a part of this patent application and is incorporated by reference into this patent application. Technical Field

[0003] The present disclosure relates generally to vertical cavity surface emitting lasers (VCSELs), and to VCSELs including planar surface oxide gratings. Background Art

[0004] A VCSEL is a semiconductor laser, more specifically a diode laser with a monolithic laser resonator, where light is emitted in a direction perpendicular to the chip surface. Typically, the laser resonator consists of two distributed Bragg reflector (DBR) mirror structures parallel to the chip surface, with a cavity region (consisting of one or more quantum wells) in between where the light is generated. The upper and lower mirror structures of the VCSEL are doped to form a diode junction, for example by p-doping the upper mirror structure of the VCSEL and n-doping the lower mirror structure of the VCSEL. Summary of the invention

[0005] In some embodiments, a VCSEL includes: a first top reflector structure above a cavity region; and a grating layer above the first top reflector structure, wherein the grating layer includes a plurality of oxidized regions forming a grating structure in the grating layer, the grating structure is associated with the polarization of output light emitted by the VCSEL, and wherein a surface of the grating layer is a planar surface.

[0006] In some embodiments, a VCSEL includes: a mirror structure over a cavity region; and a grating layer over the mirror structure, wherein the grating layer includes a plurality of oxidized regions defining the grating structure, and wherein a top surface of the grating layer is substantially planar.

[0007] In some embodiments, a VCSEL includes: a first top reflector structure above a cavity region; and a planar grating layer above the first top reflector structure, wherein the planar grating layer includes a plurality of oxidized regions forming a grating structure within the grating layer, and wherein the grating structure is associated with increased reflectivity on a side of the VCSEL including the first top reflector structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figure 1A and Figure 1B are diagrams associated with example implementations of a VCSEL including a planar surface oxide grating as described herein.

[0009] Figure 2A-2C is a diagram illustrating an example of process steps associated with forming a grating structure in a grating layer of a VCSEL as described herein.

[0010] Figure 3 is a diagram illustrating an alternative embodiment of a VCSEL including a planar surface oxide grating as described herein.

[0011] Figure 4A and Figure 4B is a graph illustrating a comparison of the oxidation profiles of the grating layer of a VCSEL for different grades of aluminum as described herein. DETAILED DESCRIPTION

[0012] The following detailed description of example embodiments refers to the accompanying drawings.The same reference numbers in different drawings may identify the same or similar elements.

[0013] Typically, gratings are formed on VCSELs by etching into the epitaxial surface or depositing additional material (e.g., dielectric or metal) and then etching the added material. However, this technique inevitably results in a non-planar surface at the grating. Non-planar surfaces are problematic in applications where the grating is not the final surface (i.e., when one or more other materials are to be deposited on top of the grating). An example where the grating is not the final surface is a bottom-emitting VCSEL. Ideally, the material formed on top of the grating needs to cover the grating in a consistent manner, ideally making the surface planar. For bottom-emitting VCSELs, the need to have additional reflectivity above the grating is critical because the top reflector of a bottom-emitting VCSEL needs to be very high. If the grating (e.g., for polarization control) is placed on top of a highly reflective mirror (e.g., a mirror with a reflectivity of at least 99.7%), then the effect of the grating on the laser mode will be low and will not effectively affect the polarization or other mode characteristics. For the grating to be effective, the grating needs to be closer to the active area of ​​the VCSEL and an additional pair of mirrors is needed above the grating to minimize the loss of light from the top of the bottom-emitting VCSEL.

[0014] Conventional techniques for achieving consistent coverage of such etched grating structures are very difficult. For example, thin films deposited by physical or chemical vapor deposition may leave gaps or bumps above the grating inconsistently (e.g., across wafers or run-to-run). Further, spin-on thin films (such as polyimide) or spin-on glass do not typically have a tightly controlled thickness, which is required in the case of VCSELs. It is worth noting that such films may have a planar surface, but if the viscosity of the film is very high, the film will not fill the grating and leave inconsistent gaps. Additionally, soft materials such as thin films may also have problems adhering to the grating surface.

[0015] Some embodiments described herein provide a VCSEL comprising a planar surface oxide grating. In some embodiments, the VCSEL comprises a first top reflector structure above a cavity region and a grating layer above the first top reflector structure. In some embodiments, the grating layer comprises a plurality of oxide regions forming a grating structure in the grating layer, wherein the surface of the grating layer is a planar surface. Thus, in some embodiments, the VCSEL comprises a surface grating formed by oxidation of an underlying material (i.e., the grating layer), which results in a substantially planar surface.

[0016] Figure 1A and Figure 1B is a diagram associated with an example implementation of a VCSEL 100 including a planar surface oxide grating as described herein. In some implementations, the VCSEL 100 can be included in an emitter array (e.g., an array of VCSELs 100). In some implementations, Figure 1A As illustrated, VCSEL 100 is a bottom emitting VCSEL (also known as a back side emitting (BSE) VCSEL), which means that VCSEL 100 emits light through a substrate 102 of VCSEL 100. In some embodiments, VCSEL 100 can be a single mode VCSEL. Alternatively, VCSEL 100 can be a multimode VCSEL.

[0017] like Figure 1A As shown, the VCSEL 100 may include a substrate 102, a bottom metal 104, a bottom reflector structure 106, a cavity including one or more active regions (referred to herein as (one or more) cavity regions 108), a confinement layer 110 forming a confining aperture 112, a first top reflector structure 114, a grating layer 116 including a grating structure 118 (including a plurality of oxidized regions 118o), a cap layer 120, a dielectric layer 122, a contact layer 124, a second top reflector structure 126, a top metal 128, and one or more isolation implants 132.

[0018] The substrate 102 includes a support material on which or within which one or more layers or features of the VCSEL 100 are grown or fabricated. In some embodiments, the substrate 102 includes an n-type material. In some embodiments, the substrate 102 includes a semi-insulating material. In some embodiments, when the VCSEL 100 includes one or more bottom-emitting emitters, the semi-insulating material can be used to reduce optical absorption from the substrate 102. In such embodiments, the VCSEL 100 can include a contact buffer in or near the bottom reflector structure 106. In some embodiments, the substrate 102 can include a semiconductor material such as gallium arsenide (GaAs), indium phosphide (InP), or another type of semiconductor material. In some embodiments, the bottom contact (e.g., bottom n-contact) of the VCSEL 100 can be formed from the back side of the substrate 102. In some embodiments, the bottom contact of the VCSEL 100 can be formed from the front side of the VCSEL 100. In some embodiments, the front side contact can be implemented by, for example, etching a mesa step or trench into the substrate 102 , or inserting a contact bumper in or near the bottom mirror structure 106 .

[0019] The bottom metal 104 includes a metal layer on the bottom surface of the substrate 102 (e.g., on the back side of the VCSEL 100). In some embodiments, the bottom metal 104 is an ohmic metal layer. In some embodiments, the bottom metal 104 is formed on an n-type semiconductor substrate 102 or an n-type semiconductor layer in the bottom reflector structure 106. Alternatively, in some embodiments, the bottom metal 104 can be formed from a p-type semiconductor substrate 104 or a p-type semiconductor layer in the bottom reflector structure 106. In some embodiments, the bottom metal 104 is a layer that is in electrical contact with the substrate 102. In some embodiments, the bottom metal 104 serves as an anode for the VCSEL 100. Alternatively, in some embodiments, the bottom metal 104 can serve as a cathode for the VCSEL 100. In some embodiments, the bottom metal 104 can include an annealed metallization layer, such as a gold germanium nickel (AuGeNi) layer, or a palladium germanium gold (PdGeAu) layer, among other examples. In some embodiments, as Figure 1A As shown, an anti-reflective (AR) coating 130 may be formed in the openings in the bottom metal 104 (eg, the openings through which the VCSEL 100 will emit light).

[0020] The bottom reflector structure 106 is a bottom reflector of an optical resonator of the VCSEL 100. For example, the bottom reflector structure 106 may include a plurality of distributed Bragg reflector (DBR) pairs or another type of reflector structure. In some embodiments, the bottom reflector structure 106 is formed of an n-type material. Therefore, in some embodiments, the bottom reflector structure 106 may include a plurality of n-type DBR pairs. Alternatively, in some embodiments, the bottom reflector structure 106 may be formed of a p-type material. In some embodiments, the bottom reflector structure 106 is on the (top) surface of the substrate 102. In some embodiments, the thickness of the bottom reflector structure 106 may be in a range from about 2.5 micrometers (μm) to about 9 μm, such as 5 μm. In some embodiments, the bottom reflector structure 106 includes a layer stack (e.g., aluminum gallium arsenide (AlGaAs) layer) grown using a metal organic chemical vapor deposition (MOCVD) technique, a molecular beam epitaxy (MBE) technique, or another technique.

[0021] The cavity region 108 includes one or more layers where electrons and holes recombine to emit light and define the emission wavelength range of the VCSEL 100. For example, the cavity region 108 can include one or more active regions in the form of quantum wells (QWs). In some embodiments, the cavity region 108 can include one or more cavity spacer layers (e.g., so that epitaxial growth can have sufficient space for ramping composition or temperature). In some embodiments, the one or more cavity spacer layers can reduce strain between active regions of the cavity region 108, and / or can alleviate thermal issues of laser operation of the VCSEL 100. In some embodiments, the one or more cavity spacer layers can include an oxide layer. The optical thickness of the cavity region 108 (including one or more active regions and any cavity spacer layers), the first top reflector structure 114, the second top reflector structure 126, and the bottom reflector structure 106 can define the resonant cavity wavelength of the VCSEL 100, which can be designed to be within the emission wavelength range of the cavity region 108 to achieve laser emission. The wavelength range of the VCSEL 100 can be in a range from about 800 nanometers (nm) to about 1550 nm in some embodiments. In some embodiments, the cavity region 108 can be formed on the bottom reflector structure 106. In some embodiments, the thickness of the cavity region 108 can be a positive integer multiple of half the wavelength, typically between 0.1 μm and 1.5 μm, such as 0.3 μm. In some embodiments, the cavity region 108 includes a layer set grown using MOCVD technology, MBE technology, or another technology.

[0022] The confinement layer 110 includes one or more layers that provide optical and / or electrical confinement for the VCSEL 100. In some embodiments, the confinement layer 110 enhances carrier and mode confinement of the VCSEL 100 and, therefore, can improve the performance of the VCSEL 100. In some embodiments, the confinement layer 110 is above the cavity region 108, below the cavity region 108, or in the cavity region 108. In some embodiments, one or more spacer layers or reflector layers (e.g., DBR) can be present between the confinement layer 110 and the cavity region 108. In some embodiments, as Figure 1A As shown, the confinement layer 110 is on a side of the cavity region 108 closer to the first top mirror structure 114 (i.e., on the non-substrate side of the cavity region 108). In some embodiments, the confinement layer 110 is on a side of the cavity region 108 closer to the bottom mirror structure 106 (i.e., on the substrate side of the cavity region 108).

[0023] In some embodiments, confinement layer 110 includes an oxide layer formed by oxidation of one or more epitaxial layers of VCSEL 100. For example, confinement layer 110 may be an aluminum oxide (Al2O3) layer formed by oxidation of an epitaxial layer (e.g., an AlGaAs layer, an AlAs layer, etc.). In some embodiments, confinement layer 110 may have a thickness in a range from about 0.007 μm to about 0.04 μm, such as 0.02 μm. In some embodiments, an oxide trench (e.g., a VCSEL 100) may be etched around the confinement layer 110 to form an oxide layer. Figure 1A ) may allow steam to enter the epitaxial layer(s) forming the confinement layer 110. In some embodiments, the oxidation trenches may not completely surround the confinement layer 110. For example, the oxidation trenches may follow the general shape of the confinement region, but there may be gaps between adjacent oxidation trenches. In some embodiments, the confinement layer 110 may follow a general geometry, but may have variations associated with the shape or position of the oxidation trenches and / or variations associated with the oxidation rate. In some embodiments, in addition to the confinement layer 110, the VCSEL 100 may also include one or more other types of structures or layers that provide current confinement, such as implant passivation structures, mesa isolation structures, moat trench isolation structures, buried tunnel junctions, etc. Additionally or alternatively, other types of structures or layers for providing current confinement may be included in the confinement layer 110 or integrated with the confinement layer 110.

[0024] In some embodiments, the confining layer 110 defines a confining aperture 112. Thus, in some embodiments, the confining aperture 112 is an optically active aperture defined by the confining layer 110. In some embodiments, the size of the confining aperture 112 (e.g., the width in a given direction) is in a range from about 1 μm to about 300 μm, such as 5 μm or 8 μm. In some embodiments, as described above, the confining aperture 112 can be formed by oxidation (e.g., when the confining layer 110 is an oxide layer). Additionally or alternatively, the confining aperture 112 can be formed by other means, such as by implantation, diffusion, regrowth (e.g., using a high resistance layer, a current blocking layer, a tunnel junction, etc.), or air gaps, among other examples. In some embodiments, the confining layer 110 can define a plurality of confining apertures 112 (e.g., such that the VCSEL 100 includes a plurality of confining apertures). In such embodiments, the sizes of the plurality of confining apertures can vary (e.g., as defined by oxidation among the layers of the confining layer 110).

[0025] The first top reflector structure 114 is a top reflector of an optical resonator of the VCSEL 100. For example, the first top reflector structure 114 may include a plurality of DBR pairs or another type of reflector structure. In some embodiments, the first top reflector structure 114 is formed of a p-type material. Therefore, in some embodiments, the first top reflector structure 114 may include a plurality of p-type DBR pairs. Alternatively, in some embodiments, the first top reflector structure 114 may be formed of an n-type material. In some embodiments, the thickness of the first top reflector structure 114 may be in a range from about 1 μm to about 4 μm, such as 2 μm. In some embodiments, the first top reflector structure 114 includes a layer set (e.g., AlGaAs layer) grown using MOCVD technology, MBE technology, or another technology. In some embodiments, the first top reflector structure 114 is grown on or above the cavity region 108.

[0026] The grating layer 116 is a layer that includes a grating structure 118. In some embodiments, the grating structure 118 can be associated with the polarization of light emitted by the VCSEL 100. For example, the grating structure 118 can introduce a polarization dependency to the reflectivity of the VCSEL 100, which has the effect of suppressing one of two orthogonal polarization orientations of the light (e.g., causing the light emitted by the VCSEL 100 to have a single polarization orientation). Additionally or alternatively, the grating structure 118 can be associated with increased reflectivity on a side of the VCSEL 100 that includes the first top reflector structure 114. In some embodiments, the grating structure 118 has a grating depth and a grating period that is approximately or less than the wavelength of the VCSEL 100. In some embodiments, as Figure 1AAs shown, the grating structure 118 is defined by a plurality of oxidized regions 118o.

[0027] In some embodiments, the grating layer 116 includes an AlGaAs layer. In some embodiments, the thickness of the grating layer 116 can be in a range from about 0.11×λ to about 0.26×λ, where λ is the wavelength of the VCSEL 100. In one example, for a wavelength of 940 nm (λ=940 nm), the thickness of the grating layer 116 can be in a range from about 100 nm to about 250 nm. In some embodiments, the aluminum content of the grating layer 116 can be in a range from about 20% to about 100%. More particularly, in some embodiments, the aluminum content of the grating layer 116 can be in a range from about 50% to about 80%, such as 75%. In some embodiments, oxidation of AlGaAs produces a material with a refractive index of about 1.6, which contrasts well with adjacent AlGaAs, which has a refractive index in a range from about 3.0 to about 3.4 (e.g., depending on composition and wavelength).

[0028] In some embodiments, the aluminum content in the grating layer 116 is within the thickness of the grating layer 116 (e.g., Figure 1A Alternatively, in some embodiments, the aluminum content in the grating layer can be graded over the thickness of the grating layer 116. In some embodiments, the level of aluminum content in the grating layer 116 can be selected to control the oxidation profile of the grating layer 116, as described below with respect to Figure 4A and Figure 4B described in further detail.

[0029] Figure 1B 1 is a diagram illustrating an example of a grating structure 118 defined by a plurality of oxidized regions 118o. Figure 1B As shown, in some embodiments, the plurality of oxidized regions 118o defining the grating structure 118 are planar with the surface of the grating layer 116. That is, selective surface oxidation on the epitaxial structure (grating layer 116) can be used to form an inherently planar grating (or photonic crystal structure). Such a grating structure 118 can be referred to as a planar surface oxidized grating. The grating structure 118 can have a pattern including, for example, a series of lines (e.g., from a top view of the VCSEL 100), or can be another type of pattern, such as an array of dots like a photonic crystal structure.

[0030] In some embodiments, Figure 1BAs illustrated, the width of a given oxidized region 118o can be greater than the depth of the given oxidized region 118o. In some embodiments, the depth of a given oxidized region 118o can be in a range from about 0.11×λ to about 0.26×λ, where λ is the wavelength of the VCSEL 100. In one example, for a wavelength of 940nm (λ=940nm), the thickness of a given oxidized region 118o can be in a range from about 100nm to about 250nm, such as 125nm. In some embodiments, the width of a given oxidized region 118o can be equal to the pitch p of the pattern of the grating structure multiplied by 1 minus the duty cycle DC of the pattern (width=p×(1-DC)). In some embodiments, the duty cycle DC can be in a range from about 0.4 to about 0.6, such as 0.5. As an example, for a duty cycle DC of 0.5 and a pitch p in the range from 0.20 μm to 0.45 μm, the width of a given oxidized region 118o can be in the range from about 0.11×λ to about 0.24×λ. In one example, for a wavelength of 940 nm (λ=940 nm), the width of a given oxidized region 118o can be in the range from about 0.10 μm to about 0.23 μm for a duty cycle DC of 0.5. In some embodiments, the pitch of the pattern of the grating structure 118 can be in the range from about 0.20 μm to about 0.45 μm. Additionally or alternatively, the pitch of the pattern can be in the range from about 0.21×λ to about 0.48×λ, where λ is the wavelength of the VCSEL 100.

[0031] Return to Figure 1A The cap layer 120 is a layer associated with covering or protecting one or more layers or features of the VCSEL. For example, the cap layer 120 can be used to protect some portions of the grating layer 116 (e.g., portions of the grating layer 116 that do not form an oxidized region) from oxidation. In some embodiments, as Figure 1A As shown, the cap layer 120 is on top of the first top reflector structure 114. In some embodiments, as Figure 1A As shown, the cap layer 120 is over the region of the grating layer 116 where the grating structure 118 is not present. In some embodiments, the cap layer 120 includes a semiconductor material, such as GaAs (e.g., highly doped GaAs). In some embodiments, the cap layer 118 has a thickness in a range from about 0.02 μm to about 0.05 μm, such as 0.04 μm.

[0032] The dielectric layer 122 is a layer that at least partially insulates the top metal 128 from one or more other layers or features (e.g., the sidewalls of the trench). Further, the dielectric layer 122 can be used to protect the grating layer 116. In some embodiments, the dielectric layer 122 can include, for example, silicon nitride (SiN X), silicon dioxide (SiO2), a polymer dielectric, or another type of insulating material. In some embodiments, a first portion of dielectric layer 122 can be formed before forming the plurality of oxidized regions 118o, and a second portion of dielectric layer 122 can be formed after forming the plurality of oxidized regions 118o. In some embodiments, a thickness t of dielectric layer 122 can be from about 0.92×(λ / n d ) to about 1.45×(λ / n d ), where λ is the wavelength of the VCSEL 100 and n d is the refractive index of the dielectric material. More generally, the thickness T of the dielectric layer 122 may be equal to the thickness t plus or minus a value corresponding to the wavelength of the VCSEL 100 divided by a multiple of two times the refractive index of the dielectric material (e.g., T = t ± X × λ / (2*n d ), where 0.92×(λ / n d )≤t≤1.45×(λ / n d ), and X is an integer value such as 0, 1, 2, etc.). In some embodiments, the thickness T of dielectric layer 122 can vary by some amount (e.g., ±10 nm, ±15 nm) depending on the VCSEL design. Thus, in some embodiments, the thickness T of dielectric layer 122 is within a value of about 15 nm, which is equal to a value from about 0.92×(λ / n d ) to about 1.45×(λ / n d ) plus or minus a value equal to X×λ / (2*n d ), where λ is the wavelength of the VCSEL, n d is the refractive index of the dielectric material, and X is an integer value.

[0033] The top contact layer 124 is a top contact layer of the VCSEL 100 that is in electrical contact with the first top reflector structure 114 through which current can flow. In some embodiments, the top contact layer 124 is formed of a material optimized for contacting a p-type semiconductor. Alternatively, in some embodiments, the contact layer 124 is formed of a material optimized for contacting an n-type semiconductor. In some embodiments, the thickness of the top contact layer 124 is in a range from about 0.2 μm to about 0.8 μm, such as 0.5 μm. In some embodiments, the top contact layer 124 has a ring shape, a slotted ring shape, a gear shape, or another type of circular or non-circular shape (e.g., depending on the design of the VCSEL 100). In some embodiments, in the case of a non-circular shape, the axis of the non-circular shape can be perpendicular to or parallel to the direction of a given oxidation region 118o.

[0034] In some embodiments, Figure 1AAs shown, the top contact layer 124 is above the grating layer 116 (e.g., on the cap layer 120). Alternatively, in some embodiments, the top contact layer 124 can be below the grating layer 116. Alternatively, in some embodiments, the top contact layer 124 can be in an opening in the grating layer 116 (e.g., examples of which are described below). Figure 3 (see figure in the figure).

[0035] The second top reflector structure 126 is a top reflector of the optical resonator of the VCSEL 100. In some embodiments, the second top reflector structure 126 is configured to increase the reflectivity on the side of the VCSEL 100 that includes the first top reflector structure 114 (e.g., the top side of the VCSEL 100). Without the top reflector structure 126, the efficiency of integrating optical elements (such as gratings) in the BSEVCSEL on top of the all-semiconductor DBR reflector is low (e.g., compared to top-emitting VCSELs) due to the required high reflectivity and the reduced interaction of the cavity mode with the optical element. Reducing the number of mirror pairs in the top reflector structure increases the coupling of the cavity mode with such an optical element. However, reducing the number of mirror pairs in the top reflector structure reduces the reflectivity in the side of the VCSEL that includes the top reflector structure. In the VCSEL 100, the second top reflector structure 126 is used to increase the reflectivity in the side of the VCSEL 100 that includes the first top reflector structure 114. Therefore, the number of mirror pairs in the first top reflector structure 114 can be reduced, and the second top reflector structure 126 can be designed to mitigate the reduction in reflectivity caused by the reduction in the number of mirror pairs in the first top reflector structure 114. In some embodiments, the second top reflector structure 126 can include a plurality of DBR pairs or another type of reflector structure. In some embodiments, the second top reflector structure 126 is formed of a dielectric material. Therefore, in some embodiments, the second top reflector structure 126 includes a plurality of dielectric DBR pairs. For example, the second top reflector structure 126 can include a plurality of SiO2 / SiNx mirror pairs, a plurality of SiO2 / titanium dioxide (TiO2) mirror pairs, or a plurality of Al2O3 / TiO2 mirror pairs, among other examples. In some embodiments, the thickness of the second top reflector structure 126 can be in a range from about 2.0 μm to about 4.0 μm, such as 2.5 μm. In some embodiments, the number of mirror pairs in the second top reflector structure 126 is in a range from three mirror pairs to eight mirror pairs.

[0036] Top metal 128 is a top metal layer at the front side of VCSEL 100. In some embodiments, top metal 128 can be a layer that is in electrical contact with top contact layer 124 (e.g., through vias in dielectric layer 122 and second top reflector structure 126). In some embodiments, top metal 128 can serve as a cathode for VCSEL 100. In some embodiments, top metal 128 can include an electroplating metal (e.g., gold (Au)) and / or a seed metal used in an electroplating process.

[0037] Isolation implants 132 are regions that prevent free carriers from reaching the edges of the trenches and / or isolate adjacent VCSELs 100 from each other (e.g., if the trenches do not completely surround the VCSELs of VCSEL 100). Isolation implants 132 may include, for example, ion implanted materials such as hydrogen / proton implanted materials or similar implanted elements to reduce conductivity.

[0038] Figure 1A and Figure 1B The number, arrangement, thickness, order, symmetry, etc. of the layers shown are provided as examples. Figure 1A and Figure 1B 12. The VCSEL 100 may include additional layers, fewer layers, different layers, differently constructed layers, or differently arranged layers than the layers shown. For example, in some embodiments, the VCSEL 100 may include a semiconductor layer (e.g., one or more p-type layers) above the grating layer 116 (e.g., instead of the dielectric layer 122). As another example, in some embodiments, the VCSEL may include an air interface above the grating layer 116 (e.g., instead of the dielectric layer 122 and the top metal 128). Additionally or alternatively, a set of layers (e.g., one or more layers) of the VCSEL 100 may perform one or more functions described as being performed by another set of layers of the VCSEL 100, and any layer may include more than one layer.

[0039] In some embodiments, to form the grating structure 118, an epitaxial layer is grown (as a single step) and then a grating pattern is etched into a sacrificial layer over the grating layer 116 to expose portions of the grating layer 116. The grating layer 116 is then oxidized to form a plurality of oxidized regions 118o. After oxidation, the sacrificial layer is removed, thereby leaving the grating structure 118 in the grating layer 116 while maintaining a substantially planar surface (e.g., compared to an etched grating). Figure 2A-2C is a diagram illustrating an example 200 of such process steps associated with forming a grating structure 118 in a grating layer 116 of a VCSEL 100 .

[0040] exist Figure 2AIn the example shown, a portion of the dielectric layer 122 (eg, SiN x ), and the portion of the dielectric layer 122 is patterned and etched together with the cap layer 120 (in the same pattern) to expose a portion of the grating layer 116. Here, the grating layer 116 has a higher aluminum content Al than the layer below the grating layer 116. x Ga 1- x In some embodiments, a selective wet etch or dry etch may be used to stop etching of the higher aluminum content grating layer 116 . Figure 2A The results of patterning and etching associated with forming the grating structure are shown, as well as etching of the (deeper) oxide trenches around the VCSEL 100 (which can be done as a step after high-resolution patterning of the surface). In some embodiments, the aluminum content in the AlGaAs grating layer 116 does not need to be very high, as only a shallow surface oxidation is required. For example, as mentioned above, a mole fraction (x) of aluminum in the range of from about 50% to about 80% can be used. In some embodiments, the mole fraction can be lower (e.g., as low as 20%) or higher (e.g., up to 100%).

[0041] In the next step, if Figure 2B As illustrated, exposed portions of the surface of the AlGaAs grating layer 116 are oxidized to form a plurality of oxidized regions 118o that define the grating structure 118. As shown, the confinement layer 110 may also be formed during this process step.

[0042] In the next step, if Figure 2C As shown, the remaining portion of the layer above the grating structure 118 can be removed by selective etching, where such selective etching stops at the AlGaAs grating layer 116 with a higher aluminum content. One or more other layers can then be formed on the grating layer 116. The one or more other layers can include, for example, another portion of the dielectric layer 122, and / or a second top reflector structure 126 (e.g., to enhance the top reflector reflectivity). Via and plating steps can then be performed, as well as forming an AR coating 130 to obtain a structure similar to Figure 1A The finished VCSEL 100 is shown.

[0043] As indicated above, Figure 2A-2C are provided as examples. Other examples may be related to Figure 2A-2C Different than described.

[0044] Figure 3 is a diagram illustrating an alternative embodiment of a VCSEL 100. Figure 3In the illustrated alternative embodiment, the VCSEL does not include the cap layer 120 (e.g., the VCSEL does not include the GaAs cap layer 120 on the AlGaAs grating layer 116). In some embodiments, when the aluminum content in the grating layer 116 is low enough that surface oxidation in air is tolerable, the VCSEL 100 can be formed without the cap layer 120. In such embodiments, the formation of the VCSEL 100 can be simplified because the selective removal of the cap layer 120 is not required, and the wet thermal oxidation can be selectively masked by only a portion of the dielectric layer 122 (e.g., rather than as shown in FIG. 1 ). Figure 2B As shown, masked by both the cap layer 120 and a portion of the dielectric layer 112).

[0045] It is worth noting that in Figure 3 In the illustrated embodiment of the VCSEL 100, an opening can be formed in the grating layer 116, and a contact layer 124 can be formed in the opening. In this way, a contact can be provided to a layer with a relatively low aluminum content (e.g., a GaAs layer below the grating layer 116). Alternatively, a contact can be made directly on the grating layer 116 with a higher aluminum content. That is, in some embodiments, a contact layer can be formed on the grating layer 116, and a contact can be provided through the grating layer 116.

[0046] As indicated above, Figure 3 are provided as examples. Other examples may be related to Figure 3 Different than described.

[0047] In some embodiments, as mentioned above, the aluminum composition within the grating layer 116 can be designed to control the oxidation profile of the grating layer 116 . Figure 4A and Figure 4B is a graph illustrating a comparison of oxidation profiles for different grades of aluminum and the grating layer 116 .

[0048] In some embodiments, the aluminum composition within the grating layer 116 can be uniform across the thickness of the grating layer 116 (i.e., the aluminum content can be substantially unchanged across the thickness of the grating layer 116). In some embodiments, the uniform aluminum composition can result in the same oxidation rate in the vertical and lateral directions, and thus will provide a wider oxidation distribution (e.g., a wider oxidized region 118o) in the grating layer 116, such as Figure 4A As shown.

[0049] Alternatively, the aluminum composition within the grating layer 116 may be graded across the thickness of the grating layer 116. For example, the aluminum content of the grating layer 116 closer to the bottom of the grating layer 116 may be higher than the aluminum content of the grating layer 116 closer to the top of the grating layer 116. In such an embodiment, oxidation in the lateral direction is reduced, and thus a narrower oxidation profile (e.g., a narrower oxidized region 118o) is formed.

[0050] The foregoing disclosure provides illustrations and descriptions, but is not intended to be exhaustive of embodiments or to limit the embodiments to the precise forms disclosed. Modifications and variations may be made in light of the foregoing disclosure or may be acquired from the practice of the embodiments. In addition, any embodiments described herein may be combined, unless the foregoing disclosure explicitly provides reasons why one or more embodiments may not be combined.

[0051] Even though specific combinations of features are listed in the claims and / or disclosed in the specification, these combinations are not intended to limit the disclosure of the various embodiments. In fact, many of these features can be combined in ways that are not specifically listed in the claims and / or disclosed in the specification. Although each dependent claim listed below can directly depend on only one claim, the disclosure of the various embodiments includes each dependent claim combined with each other claim in the claim set. As used herein, a phrase referring to "at least one of" a list of items refers to any combination of these items, including single members. As an example, "at least one of: a, b, or c" is intended to cover a, b, c, ab, ac, bc, and abc, as well as any combination with multiple identical items.

[0052] When a component or one or more components (e.g., a laser emitter or one or more laser emitters) is described or claimed (within a single claim or across multiple claims) as performing multiple operations or being configured to perform multiple operations, such language is intended to broadly cover a variety of architectures and environments. For example, unless otherwise expressly required (e.g., via the use of "first component" and "second component" or other language that distinguishes components in a claim), the language is intended to cover a single component that performs or is configured to perform all operations, a group of components that collectively perform or are configured to perform all operations, a first component that performs or is configured to perform a first operation and a second component that performs or is configured to perform a second operation, or any combination of components that perform or are configured to perform operations. For example, when a claim is of the form "one or more components are configured to: perform X; perform Y; and perform Z", the claim should be interpreted to mean "one or more components are configured to perform X; one or more (possibly different) components are configured to perform Y; and one or more (possibly different) components are configured to perform Z".

[0053] The elements, actions, or instructions used herein should not be interpreted as key or necessary unless explicitly described as such. In addition, as used herein, the articles "one" and "an" are intended to include one or more items, and can be used interchangeably with "one or more". Further, as used herein, the article "the" is intended to include one or more items quoted in conjunction with the article "the", and can be used interchangeably with "the one or more". In addition, as used herein, the term "set" is intended to include one or more items (e.g., a combination of related items, unrelated items, or related items and unrelated items), and can be used interchangeably with "one or more". In the case of being intended to only one item, the phrase "only one" or similar language is used. In addition, as used herein, the terms "having", "containing", "with", etc. are intended to be open terms. Further, unless otherwise expressly stated, the phrase "based on" is intended to mean "based at least in part on". In addition, as used herein, unless otherwise expressly stated (e.g., if used in combination with "either" or "only one of"), the term "or" when used in series is intended to be inclusive and may be used interchangeably with "and / or". Further, for ease of description, spatially relative terms such as "below," "lower," "above," "upper," etc. may be used herein to describe the relationship of one element or feature to another (one or more) element or (one or more) features illustrated in the accompanying drawings. Spatially relative terms are intended to cover different orientations of devices, equipment, and / or elements in use or operation in addition to the orientations depicted in the accompanying drawings. The device may be oriented in other ways (rotated 90 degrees or in other orientations), and the spatially relative descriptors used herein may likewise be interpreted accordingly.

Claims

1. A vertical cavity surface emitting laser (VCSEL), comprising: a first top reflector structure over the cavity region; as well as a grating layer, above the first top reflector structure, wherein the grating layer comprises a plurality of oxidized regions forming a grating structure in the grating layer, the grating structure being associated with the polarization of output light emitted by the VCSEL, and The surface of the grating layer is a planar surface.

2. The VCSEL of claim 1, wherein the grating layer comprises aluminum gallium arsenide (AlGaAs).

3. The VCSEL of claim 1, further comprising a dielectric layer above the grating layer.

4. The VCSEL of claim 3, wherein the VCSEL comprises a second top reflector structure above the dielectric layer. 5 . The VCSEL of claim 1 , wherein the VCSEL comprises a cap layer over a region of the grating layer where the grating structure is not present.

6. The VCSEL of claim 1, wherein the VCSEL comprises a contact layer above the grating layer.

7. The VCSEL of claim 1, wherein the VCSEL comprises a contact layer below the grating layer.

8. The VCSEL of claim 1, wherein the VCSEL comprises a contact layer in the opening in the grating layer.

9. The VCSEL of claim 1, wherein the grating structure has a grating depth and a grating period that are approximately or less than a wavelength of the VCSEL. 10 . The VCSEL of claim 1 , wherein a width of an oxidized region of the plurality of oxidized regions is greater than a depth of the oxidized region.

11. The VCSEL of claim 1, wherein a depth of an oxidized region of the plurality of oxidized regions is in a range from about 0.11 x λ to about 0.26 x λ, where λ is a wavelength of the VCSEL.

12. The VCSEL of claim 1, wherein a width of an oxidized region of the plurality of oxidized regions is in a range from about 0.10 x λ to about 0.23 x λ, where λ is a wavelength of the VCSEL.

13. The VCSEL of claim 1, wherein the aluminum content of the grating layer is in a range from about 50% to about 80%.

14. The VCSEL of claim 1, wherein the aluminum content within the grating layer is uniform across the thickness of the grating layer.

15. The VCSEL of claim 1, wherein the aluminum composition within the grating layer is graded across the thickness of the grating layer.

16. A vertical cavity surface emitting laser (VCSEL), comprising: a reflector structure, above the cavity region; as well as a grating layer, above the reflector structure, wherein the grating layer comprises a plurality of oxidized regions defining a grating structure, and The top surface of the grating layer is substantially planar.

17. The VCSEL of claim 16, wherein the VCSEL comprises a second top reflector structure above the dielectric layer.

18. The VCSEL of claim 16, wherein the grating structure has a grating depth and a grating period that are approximately or less than a wavelength of the VCSEL.

19. A vertical cavity surface emitting laser (VCSEL), comprising: a first top reflector structure over the cavity region; as well as a planar grating layer, above the first top reflector structure, wherein the planar grating layer comprises a plurality of oxidized regions forming a grating structure within the grating layer, and Wherein the grating structure is associated with increased reflectivity on a side of the VCSEL including the first top reflector structure.

20. The VCSEL of claim 19, wherein the grating structure has a grating depth and a grating period that are approximately or less than a wavelength of the VCSEL.

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