Iii-nitride-based vertical cavity surface emitting laser (VCSEL) with modified emission properties

Abstract

A III-nitride-based vertical cavity surface emitting laser (VCSEL) includes at least an active region between a hole-injecting region and an electron-injecting region; and one or more shapes etched into the hole-injecting, active and / or electron-injecting regions, wherein the shapes comprise holes or grooves. The shapes provide optical guiding and selection of a single higher order mode or a selection of a plurality of higher order modes, as well as provide for lateral activation of the hole-injecting region.

Description

[0001] III-NITRIDE-BASED VERTICAL CAVITY SURFACE EMITTING LASER (VCSEL) WITH MODIFIED EMISSION PROPERTIES

[0002] CROSS REFERENCE TO RELATED APPLICATIONS

[0003] This application claims the benefit under 35 U.S.C. Section 119(e) of the following co-pending and commonly-assigned application:

[0004] U.S. Provisional Application Serial No. 63 / 558,727, filed on February 28, 2024, by Nathan Palmquist and Shuji Nakamura, entitled “III-NITRIDE-BASED VERTICAL CAVITY SURFACE EMITTING LASER (VCSEL) WITH MODIFIED EMISSION PROPERTIES,” attorneys’ docket number G&C 30794.0856USP1 (UC- 2024-884-1); which application is incorporated by reference herein.

[0005] This application is related to the following co-pending and commonly- assigned applications:

[0006] U.S. Utility Patent Application No. 17 / 613,659, filed November 23, 2021, by Jared Kearns, Daniel Cohen, Joonho Back, Nathan Palmquist, Tai Margalith, Steven P. DenBaars and Shuji Nakamura, entitled “III-NITRIDE-BASED VERTICAL CAVITY SURFACE EMITTING LASER (VCSEL) CONFIGURATIONS,” attorney’s docket no. 30794.0728USWO (UC 2019-934-2); which application claims the benefit under 35 U.S.C. Section 365(c) of the following co-pending and commonly-assigned application:

[0007] PCT International Patent Application Serial No. PCT / US2020 / 034955, filed May 28, 2020, by Jared Kearns, Daniel Cohen, Joonho Back, Nathan Palmquist, Tai Margalith, Steven P. DenBaars and Shuji Nakamura, entitled “ III-NITRIDE-BASED VERTICAL CAVITY SURFACE EMITTING LASER (VCSEL) CONFIGURATIONS,” attorney’s docket no. 30794.0728WOU1 (UC 2019-934-2); which application claims the benefit under 35 U.S.C. Section 119(e) of the following co-pending and commonly-assigned applications: U.S. Provisional Patent Application No. 62 / 854,046 filed May 29, 2019, by Jared Kearns, Daniel Cohen, Joonho Back, and Shuji Nakamura, entitled “III- NITRIDE-BASED VERTICAL CAVITY SURFACE EMITTING LASER(VCSEL) WITH CURVED MIRROR ON P-SIDE OF THE APERTURE” Attorney’s Docket No. 30794.0728USP1 (2019-934-1); and

[0008] U.S. Provisional Patent Application No. 62 / 866,183, filed June 25, 2019, by Nathan Palmquist, Jared Kearns, and Shuji Nakamura, entitled “III-NITRIDE VERTICAL-CAVITY SURFACE EMITTING LASERS WITH A HIGH INDIUM CONTENT ACTIVE REGION” Attorney’s Docket No. 30794.730-US-P1 (2019- 935); all of which applications are incorporated by reference herein.

[0009] BACKGROUND OF THE INVENTION

[0010] 1. Field of the Invention.

[0011] This invention relates to a Ill-nitride vertical cavity surface emitting laser (VCSEL) with modified emission properties.

[0012] 2. Description of the Related Art.

[0013] (This application references a number of different publications as indicated throughout the specification by one or more reference numbers in brackets, e.g., [x] . A list of these different publications ordered according to these reference numbers can be found below in the section entitled “References.” Each of these publications is incorporated by reference herein.)

[0014] Vertical cavity surface emitting lasers (VCSELs) have a number of advantages over edge emitting lasers (EELDs) and light emitting diodes (LEDs), including a focused output beam with low divergence, a low threshold current and high output power with a narrow spectrum, and the ability to be processed in dense, two- dimensional arrays [1], Infrared phosphide and arsenide VCSELs are currently used in a variety of applications, including optical communications, sensing, and high-power arrays, and experience a yearly production volume of approximately 100 million units.

[0015] Gallium nitride (GaN) VCSELs have recently been receiving increasing research attention due to their ability to emit in the visible and ultraviolet (UV) regions. As used herein, the terms “GaN”, “Ill-nitride”, “nitride” and “III-N”, refer to any alloy of Group-Ill nitride semiconductors that are described by (BwAlxGayInz)N, where 0<w<l, 0<x<l, 0<y<l, 0<z<l, and w+x+y+z=l. Compositions can range from containing a single Group-Ill element to all four Group-Ill elements. These materials can, and often, include dopants and impurities including scandium (Sc) to make the alloy.

[0016] GaN VCSELs open up a variety of exciting new applications in displays, solid state lighting, sensing, and communications. One particularly exciting application is visible light communications (VLC), wherein a GaN VCSEL could couple with a phosphor to act as both a natural light source and data transmission device simultaneously. With the increasing proliferation of devices that can access networks, bandwidths are becoming overly crowded. Gaining the ability to transmit certain data via visible wavelengths would greatly expand current bandwidth capabilities.

[0017] Continuous-wave (CW) lasing at 462 nm of an electrically injected GaN VCSEL was first demonstrated in 2008 at a temperature of 77K [2], Since then, considerable progress has been made in terms of output power, efficiency, threshold current, lasing wavelength, and room temperature (RT) stability. Despite over a decade of research, GaN VCSELs are maturing slower than other IILV VCSEL platforms. This is primarily from issues with thermal management due to self-heating from higher input power requirements, high optical losses from p-GaN and current spreaders [3], and poor heatsinking from the typically low thermal conductivities of the bottom-side distributed Bragg reflectors (DBRs) [4],

[0018] Recently, long GaN VCSEL cavities (Leff > 10 pm) have shown significant promise towards addressing the issues of thermal stability and cavity length control [5,6], Lateral mode confinement was achieved by incorporating a curved Ill-nitride lens which minimized the diffraction loss that would otherwise occur in long planar cavities [7,8], The two previously reported methods are mainly differentiated by the fabrication and location of the lens, either etching the lens into the bottom of the substrate (bottom-side lens) or performing a regrowth of the lens above the epitaxial layers (top-side lens). The first method requires substrate polishing down to 28 pm and increases the risk of cracking, and the second method requires a high temperature regrowth that damages the active region.

[0019] Recently, the inventors demonstrated a GaN VCSEL with a top-side dielectric lens that could be processed with standard microfabrication techniques at room temperature, providing greater design flexibility over the prior methods [9], However, the device performance was impacted by the presence of 300 nm wide pits across the lens surface that were introduced during the lens processing, prohibiting CW operation and generating higher order transverse modes

[0010] ,

[0020] In general, GaN-based VCSEL designs, whether planar or with a curved lens, have struggled to realize single transverse mode operation for current apertures wider than 4 pm, mainly for two reasons. First, GaN VCSEL transverse mode control has struggled with filamentary lasing, defined as non-uniform emission across the current aperture

[0011] , The exact cause of filamentary lasing is unknown, but is believed to be partly due to non-uniformities or interfacial effects between the p-GaN and current spreading layer, or inefficiencies in the thermal activation process for p-GaN. This non-uniformity issue is worse for MOCVD-grown tunnel junctions, where hydrogen passivates Mg in the p++-layer (and underlying p-type layer), requiring a thermal activation post-growth. Hydrogen cannot diffuse through n-type GaN, so for tunnel junction (TJ) devices, the hydrogen must move laterally out through the device sidewalls

[0012] , This results in incomplete activation, where Mg at the center remains passivated, and in general, activation is less efficient compared to top-side activation, introducing an additional resistance-related voltage penalty and impacting light uniformity. Filamentary lasing has been observed in a variety of VCSEL architectures, including an indium-tin-oxide (ITO) current spreader

[0013] , tunnel junction

[0014] , and in both planar and non-planar demonstrations

[0015] , and the effect gets worse for wider apertures. In practice, the filamentary lasing leads to messy mode behavior that is difficult to manipulate, including coupling into optic fiber, beam steering, and directional illumination

[0016] , Certain structures, such as mode posts or curved lens, appear to generate more symmetric and ordered modes

[0017] , and in some cases, generate clean higher order transverse modes and even the fundamental transverse mode [15,18], However, the control over the generation of either the fundamental mode or higher order modes using larger apertures has been inconsistent. Recently, the use of lenses with an ultra-wide radius-of-curvature (ROC) has shown single transverse mode operation for an 8 pm aperture, but the large size of the lens limits VCSEL packing density and applicability to commercial products which require dense two-dimensional (2D) arrays

[0019] ,

[0021] The second reason that mode control for GaN VCSELs apertures wider than 4 pm is difficult is that, for wider apertures, the overlap with higher order modes and the current aperture becomes higher, leading to laser output beams that are multi- lobed and multi -wavelength. This issue is material system agnostic, and is instead a symptom of current crowding, spatial hole burning, and thermal lensing, all of which are exacerbated for large VCSEL apertures. A particular transverse linearly polarized (LPij) cavity mode is excited in a laser cavity when its modal gain becomes equal to its modal losses. In the case of the fundamental mode, the intensity profile is in the form of a single central peak, and the intensity area is minimized. All other organized higher order modes contain more peaks where at least some of them are shifted from the central active region position. To enhance stable single mode operation, modal gain of the fundamental mode and / or modal losses of all higher order modes should be as high as possible. This means that the radial profile of the optical gain should be approximately Gaussian, and the optical losses should be radially shifted from the central position. This is a fundamental challenge for wider aperture VCSELs, since current crowding around the edge of the aperture leads to the opposite of the desired effect. Fortunately, there are some applications which would prefer an organized higher order mode, such as in spatiotemporal mode locking, where higher order modes have a higher effective area compared to single modes, leading to higher and tighter energy per pulse

[0020] , Regardless, it is preferable to generate only one single mode, be it the fundamental spatial mode, or a selected higher order mode. Focusing back on generating the fundamental spatial mode, and suppressing all higher order modes, a variety of techniques have been developed in the more mature gallium arsenide (GaAs) based VCSEL system as reviewed extensively by

[0021] , Each technique either increases the modal gain of the fundamental mode or increases the modal loss for all higher order modes, and they will be summarized here.

[0022] To increase the modal gain of the fundamental mode, the most efficient method is to improve the uniformity of the current injection into the VCSEL active region

[0022] , However, this method alone is limited, as increasing current injection above threshold will lead to spatial hole burning, wherein stimulated carrier recombination in places of high mode intensity (the center of the active region) leads to lower carrier concentration in the center. Over time, this will lower the modal gain of the fundamental mode, and increase the modal gains of the higher order modes. Additionally, as mentioned previously, uniform current injection is a general challenge for larger apertures. Alternatively, the radial absorption loss can be adjusted using ion implantation. In this method, ions are implanted which heavily absorb incident light

[0023] , This approach relies on the fact that higher order modes have a wider distribution of light intensity compared to the fundamental mode, so they will interact more with the implanted region and experience higher absorption loss. The main limitation with this is that there is a tradeoff between higher mode selectivity and performance, since the fundamental mode will still have some overlap with the implanted region.

[0023] To increase the modal loss of higher order modes, one popular method is to use spatial mode filtering by modifying the reflectivity of the DBR. By taking advantage of the central confinement of the fundamental mode, the DBR can be designed to have higher reflectivity in the center, but lower outside, leading to exorbitant mirror losses for the higher order modes

[0024] . Another simple method is to increase the cavity length, as diffraction loss increases with cavity length and higher order modes suffer from higher diffraction losses compared to the fundamental mode

[0025] , However, this option is not available for VCSELs with a curved lens, as diffraction loss is prevented. Another option is to use a passive-antiguide-region, wherein the central VCSEL aperture is surrounded by a material with a higher index of refraction, again leading to higher diffraction losses of the higher order mode

[0026] , Finally, scattering loss can be radially introduced into the structure that interact with the higher order mode. In this method, the central aperture is surrounded by, or partly intersected by, a row of hole structures that selectively introduce loss. For GaAs- based VCSELs, the hole structure has been used to great effect, generating near record high output power and low divergence of the output beam [27,28],

[0024] Many of these methods, such as passive anti-guiding

[0029] , long monolithic cavities [7], spatial mirror filtering

[0018] , and ion implantation

[0030] , have been employed in GaN VCSELs, some with the explicit goal of mode control. However, there is no report of introducing hole shapes or structures into the vicinity of the VCSEL cavity. Thus, there is a need in the art for additional tools for mode control in Ill-nitride VCSELs, ideally one that can provide increased current injection uniformity, and one that can provide consistent mode control. This invention satisfies that need.

[0025] SUMMARY OF THE INVENTION

[0026] To overcome the limitations of the prior art described above, the present invention discloses a device comprising a Ill-nitride-based vertical cavity surface emitting laser (VCSEL), and a method of fabricating the device, wherein the device includes at least an active region between a hole-injecting (p-type) region and an electron -injecting (n-type) region; and one or more shapes etched into the holeinjecting, active and / or electron -injecting regions, wherein the shapes comprise holes or grooves. The shapes provide optical confinement or guiding in a lateral direction, and selection of a single higher order mode or a selection of a plurality of higher order modes, as well as provide for lateral activation of the hole-injecting region.

[0027] BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Referring now to the drawings in which like labels represent corresponding components throughout:

[0029] Fig. 1(a) is a schematic of a conventional VCSEL with a top-side lens, Fig. 1(b) is a schematic of a VCSEL with a top-side lens with shapes etched around the current aperture according to this invention, with the shape spacing parameter denoted by a set of dashed lines, Fig. 1(c) is a top-down schematic of the conventional VCSEL with a top-side lens, and Fig. 1(d) is a top-down schematic of the VCSEL with a topside lens with shapes etched around the current aperture according to this invention with a dashed arrow representing the shape spacing parameter.

[0030] Fig. 2(a) is a scanning electron microscopy (SEM) image of a top-down view of a conventional planar VCSEL, Fig. 2(b) is an SEM image of a planar VCSEL with shapes etched around the current aperture according to this invention, Fig. 2(c) is an SEM image of a top-down view of a conventional VCSEL with a top-side lens, and Fig. 2(d) is an SEM image of a VCSEL with a top-side lens with shapes etched far from the edge of the current aperture according to this invention.

[0031] Fig. 3(a) shows current-density -voltage data comparing a 10 pm current aperture VCSEL fabricated using the conventional method and a 10pm current aperture VCSEL fabricated using this invention, and Fig. 3(b) shows the current- density-light data from the same two devices.

[0032] Figs. 4(a), 4(b) and 4(c) show far field pattern (FFP) images of VCSELs fabricated using this invention where the hole shapes are separated by an distance of 9 pm, 10 pm, and 12 pm, respectively, and Fig. 4(d) shows the dependence of mode order on the hole shape separation. DETAILED DESCRIPTION OF THE INVENTION

[0033] In the following description of the preferred embodiment, reference is made to the accompanying drawings which form a part hereof, and in which is shown by way of illustration a specific embodiment in which the invention may be practiced. It is to be understood that other embodiments may be utilized and structural changes may be made without departing from the scope of the present invention.

[0034] Overview

[0035] The use of hole shapes or structures in a Ill-nitride-based VCSEL has been shown to be a viable way to scatter and influence transverse mode behavior. Additionally, the use of hole shapes or structures enables more efficient p-type GaN activation, improving device performance by improving current injection uniformity and reducing threshold current density. One or more embodiments of this invention comprise a Ill-nitride VCSEL with shapes comprising holes or grooves etched partially over the optical aperture or over the current aperture as an active or passive optic component.

[0036] Technical Disclosure

[0037] The following disclosure is divided into two sections. The first section will discuss the fabrication method for the conventional method and for one sample embodiment of this invention. The second section will provide an overview of experimental results.

[0038] Fabrication Methods

[0039] Figs. 1(a), 1(b), 1(c) and 1(d) illustrate two samples of epitaxial device structures grown using atmospheric metalorganic chemical-vapor deposition (MOCVD).

[0040] Fig. 1(a) is a cross-sectional schematic of a conventional method VCSEL (referred to herein as a C-VCSEL), while Fig. 1(b) is a cross-sectional schematic of a VCSEL according to the present invention (referred to herein as a P-VCSEL). The epitaxial layers of the C-VCSEL and P-VCSEL were grown on freestanding double- side-polished m-plane (10-10) GaN substrates 100 as follows: a 22-period superlattice of unintentionally doped (LTD) GaN and n+-GaN ([Si] = 5* 1019cm’3) 101; 8,000 nm of LTD GaN 102; 1,000 nm of n-GaN ([Si] = 8* 1018cm’3) 103; an active region 104 comprised of 2x 8 nm InGaN quantum wells with 3 nm UID GaN barriers; a 10 nm graded p- Al GaN electron blocking layer (EBL) 105 graded from 35% to 0%; 80 nm p-GaN ([Mg] = l * 1019cm’3) 106; and 12.5 nm p++-GaN ([Mg] = 3 x io20cm’3) 107.

[0041] After this first growth, the samples were treated with concentrated hydrofluoric (HF) acid and ozone before regrowing a 10 nm n++-GaN([Si] = 1.5* IO20cm’3) TJ layer 108. Buried tunnel junction (BTJ) current apertures were then defined by etching 35 nm through the n++ / p++-GaN layers 107, 108 using reactive ion etching (RIE). Next, 300 nm n-GaN ([Si] = 8* 1018cm’3) 109 as a current spreader was regrown by MOCVD.

[0042] In the P-VCSEL, 2,200 nm SiCL 110 was deposited via ion beam deposition (IBD). In both the C-VCSEL and P-VCSEL, photoresist lenses with a radius-of- curvature of 45 pm were formed via photoresist reflow and transferred either into the n-GaN 109 of the C-VCSEL or the SiCL 110 of P-VCSEL by inductively coupled plasma etching (ICP) using a CF^CL CHFs gas mixture of 3: 1 : 1

[0010] ,

[0043] Thereafter, a nanoporous (NP) DBR 111 was electrochemically etched in the 22-period superlattice 101 with an average porosity of 35%, followed by deposition of Ti / Au metal contacts 112 and a 16-period dielectric SiCL / Ta?!); DBR 113 on top of the n-GaN 109 of the C-VCSEL or the SiCL 110 of the P-VCSEL. Finally, the back surface of the substrate was coated with a A / 4-thick SiCh as an antireflection (AR) coating (not shown). The total cavity length was approximately 70 , and the active region 104 was placed approximately 8 pm from the beam waist. The reflectivity of the 16-period dielectric DBR 113 was calculated to be 99.99% at 410 nm, and the reflectivity of the 22-period NP DBR 111 was calculated to be 99.9% at 410 nm.

[0044] Mesa structures and trenches were dry etched by RIE. Thereafter, the sample comprising the C-VCSEL was put aside and shapes 114 comprising circular holes with a diameter of 1.5 pm and a depth of 450 nm were dry-etched in a circle at a set distance comprising a shape spacing 115 from the center of the current aperture on the sample comprising the P-VCSEL. The distance 115 between two holes opposite the aperture was varied from 9 pm to 12 pm, and the number of holes was 8 for all distances 115.

[0045] Fig. 1(c) is a top-down schematic of the C-VCSEL showing a device mesa 116 with a top-side lens 109, and Fig. 1(d) is a top-down schematic of the P-VCSEL showing a device mesa 116 with a top-side lens 110 with etched shapes 114 etched around the current aperture 117 according to this invention with a dashed arrow extending across the top-side lens 110 and through the device aperture 117 representing the shape spacing 115 parameter.

[0046] In this and other embodiments, a number of alternatives and modifications are available for the P-VCSEL, including:

[0047] • in addition to holes or grooves, the shapes 114 may have any number of sides, and comprise any geometry;

[0048] • the shapes 114 may not overlap with an optical or current aperture of the P-VCSEL;

[0049] • the shapes 114 may at least partially overlap an optical and / or current aperture of the P-VCSEL;

[0050] • the shapes 114 may be etched around the optical and / or current aperture of the P-VCSEL;

[0051] • the shapes 114 may be etched away from an edge of an optical and / or current aperture of the P-VCSEL;

[0052] • the shapes 114 may be comprised of and / or arranged in an arbitrary geometry surrounding an optical and / or current aperture of the P-VCSEL;

[0053] • the shapes 114 may be comprised of and / or arranged in one or more patterns surrounding an optical and / or current aperture of the P-VCSEL;

[0054] • the shapes 114 may be at least partially filled with a dielectric material; • the shapes 114 may control a transverse mode profile of the P-VCSEL;

[0055] • the shapes 114 may reduce threshold current density in the P-VCSEL as compared to a C-VCSEL without the shapes 114;

[0056] • the shapes 114 may be etched onto a flat surface of the P-VCSEL;

[0057] • there may be a curved surface on or above the hole-injecting (p-type) region such that the hole-injecting region is between the active region and the curved surface, wherein the curved surface comprises a curved mirror or top-side lens, and the shapes 114 are etched into the curved surface; and

[0058] • there may be an electron blocking layer and / or one or more tunnel junction layers present, wherein the shapes 114 are etched into the electron blocking layer and / or the tunnel junction layers.

[0059] Fig. 2(a) shows a top-down SEM image of the C-VCSEL, and Fig. 2(b) shows a top-down SEM image of the P-VCSEL, prior to the etch of the lenses 109, 110. Fig. 2(c) shows the C-VCSEL after the lens 109 etch, and Fig. 2(d) shows one embodiment of the P-VCSEL after the lens 110 etch, with the hole shapes 1 pm away from both the optical and current aperture.

[0060] Electrical characteristics were analyzed under CW operation at RT (e.g., 20°C). Optical power measurements were taken by placing the sample 25 mm above an integrating sphere with a 11.5 mm input port diameter. Spectrum data was acquired with an Ocean Insight HR4Pro ™ spectrometer with a spectral resolution of 0.2 nm. Top-side nearfield patterns (NFPs) were taken using an optical microscope with a 20x objective lens, and bottom-side far field patterns (FFPs) were taken by either placing a piece of fluorescent paper 25 mm below the device and imaging the resulting mode with a camera mounted at 35° or with a Thorlabs ™ goniometric stage with a 2.54 cm point to rotation.

[0061] It was noted that, after processing of the lens, the hole depression expanded by 33% from 1.5 pm to 2 pm, likely due to the conformal nature of the SiCL deposition. The expansion was uniform around the hole. The Gaussian beam diameter, 2coz, at the active region can be calculated using the following equation

[0031] : where z describes the position of the beam within the cavity and n describes the effective refractive index of the cavity. For this cavity design, 99.7% of the Gaussian profile is contained in a 7.3 pm diameter, and 99.9% of the Gaussian profile is contained in an 8.8 pm diameter.

[0062] Fig. 3(a) shows current-density-voltage data comparing a 10 pm aperture C- VCSEL, and a 10 pm aperture P-VCSEL with a hole spacing of 12 pm, meaning the distance from the edge of the current aperture to the edge of the hole was 1 pm. The P-VCSEL has a significantly higher series resistance compared to the C-VCSEL, with a voltage penalty of approximately 5 V at 10 kA / cm2. The suspected reason for this is that the hole etch removed a significant portion of the top-side n-GaN current spreader, reducing the pathway for current to flow by 31%. However, despite the higher series resistance, the Jth is significantly reduced, as can be seen in Fig. 3(b). The C-VCSEL begins lasing at 14 kA / cm2, whereas the P-VCSEL reaches threshold at 1.4 kA / cm2, a 90% reduction. This reduction is again partly attributed to the hole etch, as the diffusion pathway for hydrogen to laterally diffuse was reduced from 15 pm (the edge of the C-VCSEL mesa) to 1 pm (the edge of the P-VCSEL hole). The more uniform current spreading leads to an effective increase of the current injection into the center of the aperture, providing improved overlap with the transverse mode. The holes also increase the lateral confinement by reducing the effective refractive index in the hole regions to reduce the threshold current density as shown in Figs. 3(a) and 3(b). This implies a tradeoff between the ability of holes to improve the lateral current spreading for improved Jth, and the negative impact on series resistance. Future improvements to the hole design will focus on minimizing the negative impact on device performance while still retaining the spreading characteristic.

[0063] Figs. 4(a), 4(b) and 4(c) show FFP images of P-VCSELs fabricated using this invention, where the hole shapes are separated by a distance of 9 pm, 10 pm, and 12 pm, respectively. Fig. 4(d) shows the dependence of mode order on the hole shape separation. Fig. 4(d) shows that the mode order increases as the hole separation is reduced. Thus, the holes increase the lateral confinement by reducing the effective refractive index in the hole regions to reduce the threshold current density. Thus, by forming the holes or grooves with any shape surrounding the aperture, the transverse mode and threshold current density can be controlled effectively. Using this invention, the threshold current density is reduced by almost one order of magnitude, as shown in Fig. 3(b). Also, the transverse mode is also drastically changed by using this invention, as shown in Fig. 4(d).

[0064] References

[0065] The following references are incorporated by reference herein.

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[0089] 25. Wong, M. S. et al. Effects of activation method and temperature to III- nitride micro-light-emitting diodes with tunnel junction contacts grown by metalorganic chemical vapor deposition. Appl. Phys. Lett. 119, 202102 (2021).

[0090] 26. Wong, M. S. et al. High efficiency of Ill-nitride micro-light-emitting diodes by sidewall passivation using atomic layer deposition. Opt. Express 26, 21324-21331 (2018). Conclusion

[0091] This concludes the description of the preferred embodiment of the present invention. The foregoing description of one or more embodiments of the invention has been presented for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed. Many modifications and variations are possible in light of the above teaching. It is intended that the scope of the invention be limited not by this detailed description, but rather by the claims appended hereto.

Claims

WHAT IS CLAIMED IS:

1. A device, comprising: a Ill-nitride-based vertical cavity surface emitting laser (VCSEL) including at least an active region between a hole-injecting region and an electron -injecting region; and one or more shapes etched into the hole-injecting, active and / or electron -injecting regions.

2. The device of claim 1, wherein the shapes comprise holes or grooves.

3. The device of claim 1, wherein the shapes provide optical confinement in a lateral direction and selection of a single mode or selection of a plurality of modes.

4. The device of claim 1, wherein the shapes provide for lateral activation of the hole-injecting region.

5. The device of claim 1, wherein the shapes may have any number of sides, and comprise any geometry.

6. The device of claim 1, wherein the shapes do not overlap with an optical or current aperture of the VCSEL.

7. The device of claim 1, wherein the shapes at least partially overlap an optical and / or current aperture of the VCSEL.

8. The device of claim 1, wherein the shapes are etched around an optical and / or current aperture of the VCSEL.

9. The device of claim 1, wherein the shapes are etched away from an edge of an optical and / or current aperture of the VCSEL.

10. The device of claim 1 , wherein the shapes are comprised of an arbitrary geometry surrounding an optical and / or current aperture of the VCSEL.

11. The device of claim 1, wherein the shapes are comprised of one or more patterns surrounding an optical and / or current aperture of the VCSEL.

12. The device of claim 1, wherein the shapes are at least partially filled with a dielectric material.

13. The device of claim 1, wherein the shapes control a transverse mode profile of the VCSEL.

14. The device of claim 1, wherein the shapes reduce threshold current density in the VCSEL as compared to a VCSEL without the shapes.

15. The device of claim 1, wherein the shapes are etched onto a flat surface of the VCSEL.

16. The device of claim 1, further comprising a curved surface on or above the holeinjecting region such that the hole-injecting region is between the active region and the curved surface, wherein the curved surface comprises a curved mirror or top-side lens, and the shapes are etched into the curved surface.

17. The device of claim 1, further comprising an electron blocking layer and / or one or more tunnel junction layers, wherein the shapes are etched into the electron blocking layer and / or the tunnel junction layers.

18. A method, comprising: fabricating a Ill-nitride-based vertical cavity surface emitting laser (VCSEL) including an active region between a hole-injecting region and an electron -injecting region; and etching one or more shapes into the hole-injecting, active and / or electron-injecting regions.

19. The method of claim 18, wherein the shapes comprise holes or grooves.

20. The method of claim 18, wherein the shapes provide optical confinement in a lateral direction and selection of a single mode or selection of a plurality of modes.

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