Group iii-nitride distributed feedback laser utilizing both a surface grating and a lateral grating, and a method of manufacture

Abstract

A diode laser utilizing distributed feedback (DFB) and / or distributed Bragg reflector (DBR) gratings to provide single wavelength operation, primarily for Group III-nitride diode lasers operating at visible or ultraviolet wavelengths. The diode lasers utilize both surface and / or lateral gratings.

Description

[0001] GROUP III-NITRIDE DISTRIBUTED FEEDBACK LASER UTILIZING BOTH A SURFACE GRATING AND A LATERAL GRATING,

[0002] AND A METHOD OF MANUFACTURE

[0003] CROSS REFERENCE TO RELATED APPLICATIONS

[0004] This application claims the benefit under 35 U.S.C. Section 119(e) of the following co-pending and commonly-assigned applications:

[0005] U.S. Provisional Application Serial No. 63 / 595,880. filed on November 3, 2023, by Emily Trageser, Ryan Anderson, Daniel A. Cohen, Shuji Nakamura and Steven P. DenBaars, entitled “GROUP III-NITRIDE DISTRIBUTED FEEDBACK LASER UTILIZING BOTH A SURFACE GRATING AND LATERAL GRATING, AND A METHOD OF MANUFACTURE,” attorneys’ docket number G&C 30794.0850USP1 (UC-2024-864-1); and

[0006] U.S. Provisional Application Serial No. 63 / 565,140, filed on March 14, 2024, by Emily Trageser, Ryan Anderson, Daniel A. Cohen, Shuji Nakamura and Steven P. DenBaars, entitled “GROUP III-NITRIDE DISTRIBUTED FEEDBACK LASER UTILIZING BOTH A SURFACE GRATING AND LATERAL GRATING, AND A METHOD OF MANUFACTURE,” attorneys’ docket number G&C 30794.0850USP2 (UC-2024-864-2); and both of which applications are incorporated by reference herein.

[0007] BACKGROUND OF THE INVENTION

[0008] 1. Field of the Invention.

[0009] This invention relates generally to diode lasers and methods of fabrication of diode lasers.

[0010] 2. Description of the Related Art.

[0011] (Note: This application references a number of different patents and publications as indicated throughout the specification by one or more reference numbers within brackets [x] . A list of these different patents and publications ordered according to these reference numbers can be found below in the section entitled “References."’ Each of these patents and publications is incorporated by reference herein.)

[0012] Injection lasers, also known as laser diodes or diode lasers, comprise a semiconductor active region in which electrically injected electrons and holes recombine to generate light, with the active region usually disposed within or nearby the depletion region of a p-n junction, and all embedded within a semiconductor waveguide in which the generated light propagates. The waveguide often includes n- type and p-type optical confinement layers surrounding the active region and with refractive indices slightly lower than the active region, and these are generally surrounded by n-type and p-type optical cladding layers of yet lower refractive indices. The thickness of these layers depends on the properties of the material and the wavelength of the light; for lasers operating in the visible or near infrared range the optical confinement layers are generally 30-200 nm thick, and the cladding layers are 500-2000 nm thick.

[0013] In some cases, it may be advantageous to substitute all or part of one or more epitaxial cladding layers with a transparent, electrically conducting layer made from a material system other than that of the laser active region, such as an indium tin oxide (ITO) cladding layer on an AlGalnN based diode laser. [1,2,3] In such a case, the native semiconductor cladding layer may be much thinner than 500 nm. Transparent conducting oxides (TCO) are the most common “foreign” transparent conductors that may be used with the important cubic or wurtzite III-V “native” semiconductors, and throughout this disclosure, all foreign transparent conductors will simply be referred to as TCOs.

[0014] The waveguide may terminate in reflective facets to form an optical resonator, in which case a number of longitudinal optical modes may oscillate during laser operation. Alternatively, diffraction gratings may be disposed within or near the waveguide to provide wavelength selective optical feedback to preferentially select a single resonator mode during laser operation, with mode selectivity often exceeding a 103(30 dB). Such gratings can be coupled to the optical mode using periodic changes in refractive index (index coupled), material gain (gain coupled), or both (complex coupled).

[0015] If the grating extends along the majority of the active region length, the laser is called a distributed feedback (DFB) laser. If the grating extends over waveguide regions in which there is no active region, the laser is called a distributed Bragg reflector (DBR) laser. DFB and DBR lasers are manufactured in similar ways, and through the remainder of this disclosure, all such DFB and DBR lasers will be called simply DFB lasers. Such lasers are manufactured in a variety of material systems to operate at wavelengths from below 400 nm to above 10,000 nm, and are widely used for optical communications, spectroscopy, chemical sensing, and environmental monitoring.

[0016] The gratings for index coupled DFB lasers are frequently formed by first etching a surface relief grating into waveguide layers above or below the active region, followed by epitaxial growth of the remainder of the structure in the native material system. [4] The crystal regrowth is a difficult and expensive step, often with low yield, particularly if aluminum-containing layers are exposed.

[0017] Occasionally, a dielectric layer is deposited above or below the active region, patterned with a surface grating, and then buried with the remainder of the native semiconductor structure using a lateral epitaxial overgrowth process. [5] This is also a difficult process, and not technologically available in all material systems.

[0018] A third known approach for index coupled gratings is to etch from the surface of the structure to a depth sufficient to interact with the optical field of the waveguide mode. [6] This depth is typically between tens and hundreds of nanometers. This approach suffers from potential damage to the active region by the etching process, and increased operating voltage because the etched contact layer may be damaged or the effective contact area is reduced by the grating duty cycle. In laser designs with thin cladding layers and poor carrier mobility', the periodic contact area may lead to nonuniform carrier injection and a diffraction coupling constant that varies with electrical injection level.

[0019] Similar methods are used for gain and loss coupled DFB lasers. Gain coupled lasers have been built by forming a periodic grating directly in the active region. [7] Loss coupled DFBs have been built by etching gratings into absorptive semiconductor layers above the active region [8], followed by regrowth, again a difficult process compounded by potential etching damage to the active gain material. Loss coupled or complex coupled DFB lasers may be built by fabricating absorptive gratings on the surface or alongside a ridge waveguide. [9,10] While this avoids damage to the active region, the additional optical loss limits laser performance by increasing the threshold current and reducing the external differential efficiency. As with index coupled surface gratings, the reduced contact area of loss coupled surface gratings can lead to reduced power efficiency and problems arising from nonuniform carrier injection. Complex coupled lasers utilize some combination of these approaches, and suffer from some combination of these problems.

[0020] Thus, there is a need in the art for improvements of the fabrication methods of distributed feedback lasers from the Group Ill-nitride material system. The present invention satisfies this need.

[0021] SUMMARY OF THE INVENTION

[0022] The present invention discloses improved diode lasers and methods of fabrication of diode lasers. Specifically, this invention comprises a diode laser utilizing distributed feedback (DFB) and / or distributed Bragg reflector (DBR) gratings to provide single wavelength operation, primarily for Group Ill-nitride lasers operating at visible or ultraviolet (UV) wavelengths. The novel and inventive features include the use of surface and / or lateral gratings.

[0023] This invention is expected to provide a significant improvement in performance and reduction in manufacturing cost, and may enable fabrication of DFB and / or DBR diode lasers that operate at wavelengths inaccessible with other grating fabrication methods.

[0024] This invention is of interest for diode lasers emitting visible light for data communication, light detection and ranging (LIDAR), biochemical and environmental sensing, scientific instrumentation, holographic data storage, displays, and illumination.

[0025] Since cleaved or etched facets are not necessary to provide optical feedback for laser operation, this invention is useful for monolithic or hybrid integration with other optoelectronic components such as amplifiers, detectors, modulators, filters, routers and switches commonly employed in photonic integrated circuits.

[0026] This invention is also of interest for use in the ultraviolet where high aluminum content AlGaN layers are needed and upon which the commonly used etch and regrowth techniques become exceedingly costly and of low yield.

[0027] BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Referring now to the drawings in which like reference numbers represent corresponding parts throughout:

[0029] FIGS. 1A, IB, 1C, ID, IE and IF provide schematic representations of various diode laser designs.

[0030] FIGS. 2A and 2B) are an edge view and facet view, respectively, of a diode laser implemented in the Group Ill-nitride material system for visible light emission.

[0031] FIGS. 3 A, 3B, 3C, 3D and 3E illustrate the results of a process flow for fabrication of the diode laser.

[0032] FIGS. 4A, 4B, 4C, 4D, 4E and 4F illustrate the steps involved in the grating fabrication process.

[0033] FIGS. 5A, 5B, 5C, 5D and 5E illustrate a Group Ill-nitride diode laser with an embedded first order hydrogen silsesqui oxane (HSQ) grating, wherein: FIG. 5 A is a graph of LIV characteristics including Voltage (V) vs. Injection current (mA) and Power (mW) vs. Injection current (mA), for the Group Ill-nitride diode laser with dimensions 900 pm x 8 pm; FIG. 5B is a graph of Power (10 dB per division) vs. Wavelength (nm); FIG. 5C is an image of the far-field pattern for the Group III- nitride diode laser; FIG. 5D is an image of the lasing operation for the Group III- nitride diode laser; and FIG. 5E is an image of the packaged chip for the Group III- nitride diode laser.

[0034] FIGS. 6A and 6B illustrate the measured Lorentzian linewidth calculated from the phase noise of a correlated self heterodyne, wherein FIG. 6A is a graph of calculated Frequency Noise (Hz2 / Hz) vs. Frequency Offset (Hz) at a drive current of 185 mA; and FIG. 6B is a graph of Linewidth (kHz) vs. Laser Drive Current (mA).

[0035] FIGS. 7A and 7B illustrate c-plane Group Ill-nitride diode lasers fabricated on 2 inch GaN c-plane wafers, having 1stand 3rdorder gratings and cleaved facets, wherein FIG. 7A is a graph of Voltage (V) vs. Current Density J (kA / cm2) and Power (mW) (single facet) vs. Current Density J (kA / cm2) for the Group 111-nitride diode laser having dimensions of 900 x 1.5 pm and a reference Fabiy-Perot (FP) Group III- nitride diode laser having dimensions of 900 x 1.5 pm; FIG. 7B is a graph of Intensity (dB) vs. Wavelength (nm) showing a 41.0 dB SMSR (side mode suppression ratio); and FIG. 7C is a scanning electron microscopy (SEM) image showing the misalignment of the grating to the ridge.

[0036] FIG. 8 illustrates the steps for improved grating fabrication, showing top, facet and side views, with narrow and wide gratings, wherein the first column shows HSQ gratings deposited on GaN, the second column shows a ridge photoresist deposited on the HSQ gratings, and the third column shows the resulting ridge structure.

[0037] FIGS. 9A and 9B are top and side view SEM images of narrow gratings and FIGS. 9C and 9D are top and side view SEM images of wide gratings, according to one embodiment of the invention, wherein FIGS. 9B and 9D are SEM images of cross-sections of the narrow and wide gratings, respectively, prepared using a focused ion beam (FIB).

[0038] FIGS. 10A, 10B, 10C, 10D and 10E illustrate how the wide grating improves single frequency stability for a first-order grating. FIGS. 11 A, 1 IB, 11C, 1 ID and 1 IE illustrate how the wide grating improves single frequency stability for a third-order grating.

[0039] DETAILED DESCRIPTION OF THE INVENTION

[0040] 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.

[0041] Overview

[0042] This invention describes innovations to Group Ill-nitride diode laser designs, as well as methods to manufacture surface and / or lateral gratings for Group 111-nitride diode lasers. Specifically, this invention describes Group Ill-nitride diode lasers utilizing distributed feedback (DFB) and / or distributed Bragg reflector (DBR) gratings to provide single wavelength operation, wherein the gratings include surface and / or lateral gratings. The proposed designs improve the grating effectiveness and manufacturability, and result in improved current and temperature stability.

[0043] This invention also improves the process tolerance during manufacturing of Group Ill-nitride diode lasers and is advantageous for wafer-scale manufacturing. Devices manufactured using this invention exhibit more robust current stability, which allows for a larger range of wavelength tunability to meet targeted wavelength specifications.

[0044] Various Diode Laser Designs

[0045] FIGS. 1A, IB, 1C, ID. IE and IF provide schematic representations of various diode laser designs, each of which include: a substrate 100, cladding layer 101, waveguide layer 102, active region 103, waveguide layer 104, cladding layer 105 and contact layer 106. More specifically, FIG. 1 A shows an etched and regrown index coupled grating in cladding layer 101 and waveguide layer 102; FIG. IB shows an index coupled surface grating etched through the cladding layer 105 and contact layer 106; FIG. 1C shows a gain coupled grating formed in the active region 103 prior to regrowth; FIG. 1 D shows a side view and FIG. 1 E show s an end view of a lateral index or loss coupled grating adjacent the waveguide layer 104; and FIG. IF shows a TCO grating with embedded TCO or dielectric grating teeth in cladding layer 105.

[0046] Laser Diode with Embedded Gratings

[0047] One embodiment of the present invention includes surface and / or lateral gratings formed in a transparent conductor foreign to the material system of the epitaxial stack forming the laser active region, wherein a thin layer of TCO is deposited on an epitaxial stack for the Group 111-nitride diode laser, and wherein the gratings are formed without etching the epitaxial stack for the Group Ill-nitride diode laser and the gratings are formed without epitaxial regrow th on the epitaxial stack for the Group Ill-nitride diode laser. These innovations avoid the difficulties of epitaxial regrowth, do not damage the native semiconductor layers, do not introduce excessive optical loss, and maintain the full contact area for low voltage operation and uniform electrical injection under all injection conditions.

[0048] A variety of designs may be used to implement this invention, dependent to some extent on the semiconductor material system used. For laser operation in the visible and ultraviolet spectrum, diode lasers based on Group III-mtride are known to be useful.

[0049] The implementation of this embodiment for a visible light emitting diode laser in the Group Ill-nitride material system is shown in FIGS. 2A and 2B, with the manufacturing process shown in FIGS. 3A, 3B, 3C, 3D and 3E.

[0050] FIGS. 2A and 2B, which are edge and facet views of the Group Ill-nitride diode laser, respectively, illustrate how fabrication begins with epitaxial crystal growth on a bulk GaN substrate 200. upon which is grown sequentially, a GaN buffer 201, an (optional) n-AlGaN / GaN superlattice (SL) cladding layer 202, an n-InGaN (or n-GaN) optical confinement layer 203, an active region 204 comprised of InGaN multiple quantum wells (MQWs) separated by GaN or InGaN barriers, a p-AlGaN electron blocking layer (EBL) 205, a p-InGaN (or p-GaN) optical confinement layer 206, an (optional) p-GaN (or p-AlGaN) cladding 207, and a p+ GaN (or p+ InGaN) contact 208. This is followed by deposition of a first TCO layer, e.g., an ITO current spreading layer 209; a dielectric layer, e.g., an SiO2 grating layer 210; a second TCO layer, e.g., an ITO cladding 211 ; a metallic anode contact 212; and a metallic cathode contact 213.

[0051] FIG. 3A shows the p-InGaN optical confinement layer 206, p-GaN cladding 207 and p+ GaN contact 208, and illustrates the results of physical vapor deposition of the ITO current spreading layer 209 upon the p+ type contact 208. The ITO cunent spreading layer 209 is typically 10-50 nm thick; the refractive index of ITO is generally between 1.8-2.2 in the visible spectrum; and the absorption loss of ITO is below 3000 cm'1(by comparison, the absorption loss in metals is above 106cm'1).

[0052] FIG. 3B illustrates the results of a grating resist layer 300 deposited on the ITO current spreading layer 209. The grating resist layer 300 is patterned into a grating of a desired pitch using known techniques, such as interference lithography or electron beam lithography. The resist grating layer 300 is developed, leaving the surface of the underlying ITO current spreading layer 209 exposed between the lines of the resist grating layer 300.

[0053] FIG. 3C illustrates the results of embedded material, e.g., the SiO2 grating layer 210, deposited on the resist grating layer 300, at an angle relative to a surface normal, leaving one edge of each line of the resist grating layer 300 uncoated by the embedded material. The SiO2 grating layer 210 or other embedded material possesses a different refractive index than the ITO current spreading layer 209, either higher or lower, and with an optical loss also below 3000 cm'1. Alternatives to SiO2 for the grating layer 210 may include ITO deposited under different conditions than the ITO current spreading layer 209, other conducting oxides such as gallium indium oxide or zinc oxide, other TCOs, nonconducting transparent dielectrics, optically absorbing dielectrics, metals or air, etc. The thickness of the SiCh grating layer 210 is typically between 1-50 nm, depending on the refractive index difference as compared to the ITO current spreading layer 209. the thicknesses of the semiconductor layers in the epitaxial stack, and the intended laser wavelength.

[0054] FIG. 3D illustrates the results of a lift-off where the resist grating layer 300 is dissolved in a suitable stripper, also a lift-off of a thin coating of the SiO2 grating layer 210 on the resist grating layer 300. results in only a portion of the SiO2 grating layer 210 remaining on a surface of the underlying ITO current spreading layer 209, thereby forming a refractive index grating of a desired pitch and depth without an etching step.

[0055] FIG. 3E illustrates the results of physical vapor deposition of the ITO cladding layer 211, making electrical contact with both the ITO current spreading layer 209 and the SiO2 grating layer 210, wherein the ITO cladding layer 211 is typically ITO identical to the ITO current spreading layer 209. The ITO cladding layer 211 is typically at least 100 nm thick, sufficient to prevent the guided optical field from interacting with the metallic anode contact 212.

[0056] Subsequent steps (not shown) may include ridge formation, deposition of sidewall dielectric, deposition of anode and cathode metal contacts 212, 213, etc. The waveguide ridges are formed by conventional lithographic and etching techniques, and optionally the now exposed embedded grating teeth formed in the SiCh grating layer 210 may be selectively etched, leaving an air gap in their place to form a grating with a higher refractive index contrast. Moreover, the gaps between the teeth of the gratings may be filled with other materials with a refractive index different from the SiCh grating layer 210.

[0057] The result is an embedded diffraction grating formed in relatively low loss electrically conductive materials of the SiCh grating layer 211 deposited without etching and at temperatures lower than epitaxial growth temperatures for the epitaxial stack for the Group Ill-nitride diode laser. Diode Lasers with Embedded Surface Gratings using HSQ

[0058] FIGS. 4A, 4B, 4C, 4D, 4E and 4F illustrate a grating process using HSQ. The steps of the process include: a GaN substrate 400 upon which is deposited an ITO contact layer 401, as shown in FIG. 4A; an HSQ photoresist 402 spin coated on the ITO contact layer 401, as shown in FIG. 4B; electron beam lithography to pattern the HSQ photoresist 402, as shown in FIG. 4C; and ITO cladding 403 deposited on the patterned HSQ photoresist 402, as shown in FIG. 4D. The final step is p-metal 404 deposition on the ITO cladding 403, as shown in FIG. 4E. An SEM image of a crosssection of the resulting structure performed using an FIB is shown in FIG. 4F.

[0059] FIGS. 5A, 5B, 5C, 5D and 5E illustrate a Group Ill-nitride diode laser with an embedded first order HSQ grating, wherein: FIG. 5 A is a graph of LIV characteristics including Voltage (V) vs. Injection current (mA) and Power (mW) vs. Injection current (mA), for the Group Ill-nitride diode laser with dimensions 900 pm x 8 pm; FIG. 5B is a graph of Power (10 dB per division) vs. Wavelength (nm); FIG. 5C is an image of the far-field pattern for the Group III -nitride diode laser; FIG. 5D is an image of the lasing operation for the Group Ill-nitride diode laser; and FIG. 5E is an image of the packaged chip for the Group Ill-nitride diode laser.

[0060] FIGS. 6 A and 6B illustrate the measured Lorentzian linewidth of the Group Ill-nitride diode laser with the embedded first order HSQ grating using, for example, a correlated self-heterodyne method, as described in

[0011] , wherein FIG. 6 A is a graph of calculated Frequency Noise (Hz2 / Hz) vs. Frequency Offset (Hz) measured at a laser drive current of 185 mA and showing a measured linewidth at 684.656 kHz, which is the lowest reported linewidth for an InGaN-based DFB diode laser; and FIG. 6B is a graph of Lorentzian Linewidth (kHz) vs. Laser Drive Current (mA) using an LDX-3620B™ battery-powered, ultra-low-noise current source, optimized for narrow linewidth or stable wavelength laser diode applications. Diode Lasers with Surface and / or Lateral Gratings using HSQ

[0061] FIGS. 7A, 7B and 7C illustrate c-plane Group Ill-nitride diode lasers (created in collaboration with Bluglass Ltd.™ and described in

[0013] ) fabricated on 2 inch GaN c-plane wafers, having 1stand 3rdorder gratings and cleaved facets, wherein FIG. 7A is a graph of Voltage (V) vs. Current Density J (kA / cm2) and Power (mW) (single facet) vs. Current Density J (kA / cm2) for the Group Ill-nitride diode laser having dimensions of 900 x 1.5 pm and a reference Fabry-Perot (FP) Group Ill-nitride diode laser having dimensions of 900 x 1.5 pm; FIG. 7B is a graph of Intensity (dB) vs. Wavelength (nm) with a peak intensity at a wavelength of 448.5 nm with a 41.0 dB SMSR; and FIG. 7C is a SEM image showing the misalignment of the grating to the ridge.

[0062] FIG. 8 illustrates the steps of a method for improved grating fabrication, wherein gratings are formed in an HSQ photoresist layer spin coated on an epitaxial stack for the Group Ill-nitride diode laser, the HSQ photoresist layer acts as a hard mask during an etch of a ridge structure in the epitaxial stack of the Group Ill-nitride diode laser, the gratings are wide gratings wider than the ridge structure to form the surface gratings on the ridge structure and the lateral gratings adjacent the ridge structure, a portion of the lateral grating is removed to maintain a self-aligned surface grating during the etch of the ridge structure, and the wide gratings improve single frequency stability.

[0063] Specifically, FIG. 8 showing rows of top, facet and side views, with columns of both narrow and wide gratings, wherein 800, 801, 802 in the first column show HSQ gratings deposited on GaN in top, facet and side views; 803, 804, 805 in the second column show a ridge photoresist deposited on the HSQ gratings in top, facet and side views; and 806, 807, 808 in the third column show the resulting ridge structure in top, facet and side views. Specifically, 808 in the third column is a side view showing how the narrow and wide gratings result in both surface gratings on the resulting ridge structure and lateral gratings adjacent the ridge structure, which may be used to provide a Group Ill-nitride diode laser utilizing distributed feedback (DFB) and / or distributed Bragg reflector (DBR) gratings to provide single wavelength operation, wherein the gratings include surface and / or lateral gratings.

[0064] FIGS. 9A and 9B are top and side view SEM images of narrow gratings and FIGS. 9C and 9D are top and side view SEM images of wide gratings, wherein FIGS. 9B and 9D are SEM images of cross-sections of the narrow and wide gratings, respectively, prepared using a FIB. The images of the wide gratings confirm nanomasking has occurred, namely, the HSQ grating acts as a hard mask during the ridge etch.

[0065] FIGS. 10A, 10B, IOC, 10D and 10E illustrate how the wide grating improves single frequency stability for a first-order grating, wherein FIG. 1 OA is a graph of Intensity (10 dB per division) vs. Wavelength (nm) and Current (mA) vs. Wavelength (nm) for a first-order narrow grating shown in FIG. 10B; FIG. 10C is a graph of Intensity (10 dB per division) vs. Wavelength (nm) and Current (mA) vs. Wavelength (nm) for a first-order wide grating shown in FIG. 10D; and FIG. 10E is a graph of the SMSR (dB) vs. Current (mA) for both the wide and narrow gratings.

[0066] FIGS. 11A, 11B, 11C, 11D and HE illustrate how the wide grating also improves single frequency stability' for a third-order grating, wherein FIG. 11 A is a graph of Intensity (10 dB per division) vs. Wavelength (nm) and Current (mA) vs. Wavelength (nm) for a third-order narrow grating shown in FIG. 1 IB; FIG. 11C is a graph of Intensity (10 dB per division) vs. Wavelength (nm) and Current (mA) vs. Wavelength (nm) for a third-order wide grating shown in FIG. 1 ID; and FIG. 1 IE is a graph of SMSR (dB) vs. Current (mA) for both the wide and narrow gratings. Specifically, FIG. 1 ID is a top image showing the third-order wide grating comprises both surface gratings on the resulting ridge structure, and lateral gratings adjacent the ridge structure.

[0067] Modifications and Variations

[0068] Many modifications and variations of the present invention are possible, including but not limited to the following: • Application to other material systems than Group Ill-nitrides.

[0069] • Use of transparent conducting oxides other than ITO, including but not limited to zinc oxide, gallium oxide, indium oxide, alloys of these with or without additional doping compounds.

[0070] • The use of selective wet or dry etching to maintain a self-aligned wide grating during the ridge formation.

[0071] References

[0072] The following patents and publications are incorporated by reference herein:

[0073] [1] U.S. Patent No. 8.254,423, issued August 28, 2012, to Daniel A. Cohen.

[0074] Steven P. DenBaars, and Shuji Nakamura, entitled ' (AI.Ga.In)N diode laser fabricated at reduced temperature.”

[0075] [2] M. T. Hardy, Appl. Phys. Lett. 103, 081103 (2013).

[0076] [3] S. Mehari, Optics Express 26, 1564 (2018).

[0077] [4] S. Masui, Jpn. J. Appl. Phys. 45, L1223 (2006).

[0078] [5] A. Abare. IEICE Trans. Electron. E83-C. 560 (2000).

[0079] [6] H. S. Djie, Opt. Eng. 41 , 2345 (2002).

[0080] [7] Y. Luo, Appl. Phys. Lett. 56, 1620 (1990).

[0081] [8] Y. Nakano, Jpn. J. Appl. Phys. 32, 825 (1993).

[0082] [9] M. L. Osowski, IEEE Photon. Technol. Lett. 9, 1460 (1997).

[0083]

[0010] M. Kamp, Appl. Phys. Lett. 74, 483 (1999).

[0084]

[0011] Z. Yuan, P. Liu, B. Li, B. Shen, M. Gao, L. Chang, W. Jin, A. Feshali, M. Paniccia, J. Bowers, K. Vahala, Opt. Express, 30 14 (2022).

[0085]

[0012] Coldren, L., Corzine, S.. & Masanovic, M. (2012). Diode Lasers and Photonic Integrated Circuits (2nd ed.). John Wiley & Sons, Inc.

[0086]

[0013] R. Anderson et al., “Single-frequency DFB laser diodes at visible wavelengths grown with low temperature remote plasma chemical vapor deposition p- AlGaN,” Proceedings of SPIE, 15 March 2023. Nomenclature

[0087] The terms “Group-Ill nitride’’ or “III-nitride” or “Group III-N” or “III-N” or “nitride” as used herein refer to any composition or material related to (B,Al,Ga,In,Tl)N semiconductors having the formula BvAlxGayInzTlwN where 0<v<l, 0<w<l , 0<x<l , 0<y<l , 0<z<l , and v+w+x+y+z=l . These terms as used herein are intended to be broadly construed to include respective nitrides of the single species, B, Al, Ga, In, and Tl, as well as binary, ternary and higher mixed compositions of such Group III metal species. Accordingly, these terms include, but are not limited to, the compounds of AIN, GaN, InN, AlGaN, AllnN, InGaN, and AlGalnN. When two or more of the (B, Al, Ga, In, T1)N component species are present, all possible compositions, including stoichiometric proportions as well as off-stoichiometric proportions (with respect to the relative mole fractions present of each of the (Al. Ga, In)N component species that are present in the composition), can be employed within the broad scope of this invention. Further, compositions and materials within the scope of the invention may further include quantities of dopants and / or other impurity materials and / or other inclusional materials and / or trace amounts of other elements. Moreover, the present invention might be useful in other material systems, such as cubic III-V or II-VI material systems.

[0088] Conclusion

[0089] 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 Group Ill-nitride diode laser utilizing distributed feedback (DFB) and / or distributed Bragg reflector (DBR) gratings to provide single wavelength operation, wherein the gratings include surface and / or lateral gratings.

2. The device of claim 1, wherein the gratings are formed in a transparent conducting oxide (TCO) layer deposited on an epitaxial stack for the Group Ill-nitride diode laser.

3. The device of claim 2, wherein the gratings are formed without etching the epitaxial stack for the Group Ill-nitride diode laser.

4. The device of claim 2, wherein the gratings are formed without epitaxial regrowth on the epitaxial stack for the Group Ill-nitride diode laser.

5. The device of claim 2, wherein the gratings are formed at temperatures lower than epitaxial grow th temperatures for the epitaxial stack for the Group III- nitride diode laser.

6. The device of claim 2, further comprising other TCOs, nonconducting transparent dielectrics, optically absorbing dielectrics, metals or air, fill gaps between teeth of the gratings formed in the TCO layer, with a refractive index different from the TCO layer.

7. The device of claim 2, wherein a grating resist layer is deposited on the TCO layer, the grating resist layer is patterned into the grating of a desired pitch, embedded material is deposited on the resist grating layer, at an angle relative to asurface normal, leaving one edge of each line of the resist grating layer uncoated by the embedded material.

8. The device of claim 7, wherein a liftoff of the grating resist layer and a thin coating of the embedded material results in only a portion of the embedded material remaining on a surface of the TCO layer, thereby forming a refractive index grating of a desired pitch and depth.

9. The device of claim 8, wherein the embedded material possesses a different refractive index than the TCO layer.

10. The device of claim 8, wherein exposed grating teeth formed in the embedded material is selectively etched, leaving an air gap in their place to form the grating with a higher refractive index contrast.

11. The device of claim 10. wherein the embedded material comprises SiCh.

12. The device of claim 1, wherein the gratings are formed in a hydrogen silsesquioxane (HSQ) photoresist layer spin coated on an epitaxial stack for the Group Ill-nitride diode laser.

13. The device of claim 12, wherein the HSQ photoresist layer acts as a hard mask during an etch of a ridge structure in the epitaxial stack of the Group III- nitride diode laser.

14. The device of claim 13, wherein the gratings are wide gratings wider than the ridge structure to form the surface gratings on the ridge structure and the lateral gratings adjacent the ridge structure.

15. The device of claim 14, wherein a portion of the lateral grating is removed to maintain a self-aligned surface grating during the etch of the ridge structure.

16. The device of claim 14, wherein the wide gratings improve single frequency stability.

17. A method, comprising: fabricating a Group Ill-nitride diode laser utilizing distributed feedback (DFB) and / or distributed Bragg reflector (DBR) gratings to provide single wavelength operation, wherein the gratings include surface and / or lateral gratings.

18. A device fabricated by the method of claim 17.

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