Conductivity based on selective etch for GaN devices and applications thereof

• US 10,458,038 B2
• Filed: 10/30/2015
• Issued: 10/29/2019
• Est. Priority Date: 01/27/2010
• Status: Active Grant

• Current Assignee: Yale University
• Original Assignee: Yale University
• Inventors: Zhang, Yu, Sun, Qian, Han, Jung
• Primary Examiner(s): Reames, Matthew L
• Application Number:
  US14/929,015
• Publication Number:
  US 20160153113A1
• Time in Patent Office: 1,460 Days
• CPC Class Codes: C25B 1/04 by electrolysis of water
• CPC Class Codes: C25B 1/55 Photoelectrolysis
• CPC Class Codes: C25F 3/12 of semiconducting materials
• CPC Class Codes: C30B 23/025 characterised by the substrate
• CPC Class Codes: C30B 25/186 being specially pre-treated by, e.g. chemical or physical means
• CPC Class Codes: C30B 29/406 Gallium nitride
• CPC Class Codes: C30B 33/10 in solutions or melts
• CPC Class Codes: G02B 1/02 made of crystals, e.g. rock-salt, semi-conductors G02B1/08 takes precedence
• CPC Class Codes: G02B 1/118 having sub-optical wavelength surface structures designed to provide an enhanced transmittance, e.g. moth-eye structures
• CPC Class Codes: G02B 2207/107 Porous materials, e.g. for reducing the refractive index
• CPC Class Codes: G02B 5/1861 Reflection gratings characterised by their structure, e.g. step profile, contours of substrate or grooves, pitch variations, materials G02B5/1809, G02B5/1828, G02B5/1833, G02B5/1838 and G02B5/1847 take precedence
• CPC Class Codes: G02B 6/29356 Interference cavity within a single light guide, e.g. between two fibre gratings G02B6/29347 - G02B6/2935 take precedence; evanescent coupling to a resonator cavity G02B6/29335
• CPC Class Codes: G02B 6/29358 Multiple beam interferometer external to a light guide, e.g. Fabry-Pérot, etalon, VIPA plate, OTDL plate, continuous interferometer, parallel plate resonator G02B6/29347, G02B6/29349, G02B6/2935, G02B6/29361 take precedence; resonator evanescently coupled to light guide G02B6/29335
• CPC Class Codes: H01L 21/02002 Preparing wafers
• CPC Class Codes: H01L 21/02005 Preparing bulk and homogeneous wafers
• CPC Class Codes: H01L 21/0237 Materials
• CPC Class Codes: H01L 21/02458 Nitrides
• CPC Class Codes: H01L 21/02513 Microstructure
• CPC Class Codes: H01L 21/0254 Nitrides
• CPC Class Codes: H01L 21/0262 Reduction or decomposition of gaseous compounds, e.g. CVD
• CPC Class Codes: H01L 21/02631 : Physical deposition at reduced pressure, e.g. MBE, sputtering, evaporation
• CPC Class Codes: H01L 21/02658 : Pretreatments cleaning in general H01L21/02041
• CPC Class Codes: H01L 21/306 : Chemical or electrical treatment, e.g. electrolytic etching to form insulating layers H01L21/31
• CPC Class Codes: H01L 21/30612 : Etching of AIIIBV compounds
• CPC Class Codes: H01L 21/30625 : With simultaneous mechanical treatment, e.g. mechanico-chemical polishing
• CPC Class Codes: H01L 21/30635 : of AIIIBV compounds
• CPC Class Codes: H01L 21/326 : Application of electric currents or fields, e.g. for electroforming H01L21/20 - H01L21/288 and H01L21/302 - H01L21/324 take precedence
• CPC Class Codes: H01L 21/7813 : leaving a reusable substrate, e.g. epitaxial lift off
• CPC Class Codes: H01L 33/0025 : comprising only AIIIBV compounds
• CPC Class Codes: H01L 33/0062 : for devices with an active region comprising only III-V compounds
• CPC Class Codes: H01L 33/007 : comprising nitride compounds
• CPC Class Codes: H01L 33/0075 : comprising nitride compounds
• CPC Class Codes: H01L 33/0093 : Wafer bonding; Removal of the growth substrate
• CPC Class Codes: H01L 33/16 : with a particular crystal structure or orientation, e.g. polycrystalline, amorphous or porous
• CPC Class Codes: H01L 33/32 : containing nitrogen
• CPC Class Codes: Y02E 60/36 : Hydrogen production from non-carbon containing sources, e.g. by water electrolysis
• CPC Class Codes: Y10T 428/24997 : Of metal-containing material

Abstract

This invention relates to methods of generating NP gallium nitride (GaN) across large areas (>1 cm²) with controlled pore diameters, pore density, and porosity. Also disclosed are methods of generating novel optoelectronic devices based on porous GaN. Additionally a layer transfer scheme to separate and create free-standing crystalline GaN thin layers is disclosed that enables a new device manufacturing paradigm involving substrate recycling. Other disclosed embodiments of this invention relate to fabrication of GaN based nanocrystals and the use of NP GaN electrodes for electrolysis, water splitting, or photosynthetic process applications.

Claims

1. An integrated optoelectronic device comprising:

a first layer comprising gallium nitride located on a substrate;

a second layer comprising porous gallium nitride having an n-type conductivity located on a side of the first layer opposite the substrate and forming one layer of a distributed Bragg reflector; and

an active region formed on a side of the second layer opposite the substrate.

2. The integrated device of claim 1, wherein a refractive index of the second layer is less than a refractive index of the first layer.

3. The integrated device of claim 2, wherein the optoelectronic device is configured to emit in a direction away from the second layer.

4. The integrated device of claim 2, wherein the integrated optoelectronic device comprises a vertical-cavity surface-emitting laser or light-emitting diode.

5. The integrated device of claim 1, wherein the second layer has a dopant density greater than 2×

10¹⁸ cm³.

6. The integrated device of claim 1, further comprising a third layer comprising porous gallium nitride having an n-type conductivity located on a side of the first layer opposite the substrate.

7. The integrated device of claim 6, wherein the third layer has a conductivity and refractive index different from the second layer.

8. The integrated device of claim 7, wherein the integrated optoelectronic device is configured to emit light in a direction away from the second layer.

9. The integrated device of claim 7, wherein the integrated optoelectronic device comprises a vertical-cavity surface-emitting laser or light-emitting diode.

10. A method for making an integrated optoelectronic device, the method comprising:

forming a first layer comprising gallium nitride on a substrate;

forming a second layer comprising gallium nitride having an n-type conductivity on a side of the first layer opposite the substrate;

forming an active region on a side of the second layer opposite the first layer; and

electrochemically etching the second layer to form a first porous layer that is one layer of a distributed Bragg reflector.

11. The method of claim 10, wherein forming the second layer comprises doping the second layer to greater than 2×

10¹⁸ cm<sup>−

3</sup>.

12. The method of claim 11, wherein electrochemically etching comprises laterally etching the second layer in a direction parallel to a surface of the substrate with an etchant and without applying optical radiation for etching the second layer.

13. The method of claim 12, further comprising applying a bias voltage between the second layer and the etchant that is between 5 volts and 30 volts, and wherein the etchant comprises oxalic acid, hydrochloric acid, or potassium hydroxide.

14. The method of claim 11, wherein electrochemically etching comprises vertically etching the second layer in a direction perpendicular to a surface of the substrate with an etchant and without applying optical radiation for etching the second layer.

15. The method of claim 14, further comprising applying a bias voltage between the second layer and the etchant that is between 5 volts and 30 volts, and wherein the etchant comprises oxalic acid, hydrochloric acid, or potassium hydroxide.

16. The method of claim 14, further comprising applying a first bias voltage between the second layer and the etchant at a first time and a second bias voltage between the second layer and the etchant at a second time to form the first porous layer and a second porous layer having a different porosity than the first porous layer.

17. The method of claim 11, wherein the integrated optoelectronic device comprises a vertical-cavity surface-emitting laser or light-emitting diode.

18. The method of claim 10, further comprising:

forming a third layer comprising gallium nitride having an n-type conductivity that is different from the n-type conductivity of the second layer; and

electrochemically etching the third layer to form a second porous layer that is a second layer of the distributed Bragg reflector.

19. A method of lateral etching to form porous gallium nitride layers for optoelectronic devices, the method comprising:

forming a first layer comprising gallium nitride on a substrate;

forming a second layer comprising gallium nitride having an n-type conductivity on a side of the first layer opposite the substrate;

forming a third layer comprising gallium nitride having a first conductivity on a side of the second layer opposite the first layer;

exposing a side wall of the second layer; and

electrochemically and laterally etching the second layer between the first and third layers to form a first porous gallium nitride layer.

20. The method of claim 19, wherein forming the second layer comprises doping the second layer to greater than 2×

10¹⁸ cm<sup>−

3</sup>.

21. The method of claim 20, wherein electrochemically etching comprises etching the second layer using oxalic acid, hydrochloric acid, or potassium hydroxide.

22. The method of claim 21, wherein electrochemically etching comprises applying an electrical bias between the second layer and etchant and does not require optical radiation for the electrochemical etching.

23. The method of claim 22, wherein the bias is between 5 volts and 30 volts.

24. The method of claim 23, further comprising forming an active region on a side of the second layer opposite the substrate.