CN109713091B

CN109713091B - Method for improving optical coupling efficiency of GaN-based integrated waveguide by adopting high-reflection film

Info

Publication number: CN109713091B
Application number: CN201811634478.4A
Authority: CN
Inventors: 黎大兵; 程东碧; 孙晓娟; 贾玉萍; 石芝铭
Original assignee: Changchun Institute of Optics Fine Mechanics and Physics of CAS
Current assignee: Changchun Institute of Optics Fine Mechanics and Physics of CAS
Priority date: 2018-12-29
Filing date: 2018-12-29
Publication date: 2020-06-26
Anticipated expiration: 2038-12-29
Also published as: CN109713091A

Abstract

The invention discloses a method for improving optical coupling efficiency of a GaN-based integrated waveguide by adopting a high-reflectivity film, belonging to the technical field of semiconductors. The method mainly aims at the problem of light loss of the GaN-based integrated waveguide, and the high-reflection film is adopted to improve the light coupling efficiency of the GaN-based integrated waveguide. The method comprises the following key steps: the method comprises the key technologies of multi-quantum well ridge optical waveguide structure design, GaN material growth, multi-quantum well InGaN/GaN structure growth, electrode sheathing technology, multi-quantum well LED side surface plating high reflection film and the like. The invention can effectively improve the optical coupling efficiency of the integrated waveguide and provides an effective way for improving the optical coupling efficiency of the GaN-based integrated waveguide. The invention has simple process, low cost and wide application prospect.

Description

Method for improving optical coupling efficiency of GaN-based integrated waveguide by adopting high-reflection film

Technical Field

The invention belongs to the technical field of semiconductors, and particularly relates to a method for improving optical coupling efficiency of a GaN-based integrated waveguide by using a high-reflection film.

Background

With the increasing demand of people for information dissemination technologies with high capacity, high speed and low cost, silicon-based optoelectronics has been developed vigorously in recent years, and is applied to information communication, multimedia, personal consumption, measurement sensing, biosensing and military applications.

Since silicon (Si) is an indirect bandgap semiconductor material, the problem of silicon (Si) -based light sources has been the core that has restricted the development and application of silicon (Si) -based photoelectrons. From the waveguide material point of view, the conventional silicon (Si) material has strong absorption of visible light, which is not favorable for light transmission in the optical waveguide. The refractive index of silicon (Si) material is small, the optical field constraint effect is poor, and the GaN material can not only meet the condition of no absorption of visible light, but also has a large refractive index, thus becoming an excellent material for preparing visible light waveguide and planar integrated photonic devices.

With the development and breakthrough of the third generation semiconductor materials and devices represented by GaN, GaN-based optoelectronic devices will possibly lead to the rapid development of the future optoelectronic field. Compared with silicon-based photons, the GaN-based material is a direct wide-band-gap semiconductor material, has excellent luminescence and detection performances, is expected to solve the problems of high power consumption of electrical interconnection transmission, serious electromagnetic interference, low transmission capacity and the like of the GaN-based integrated waveguide device, and has made some breakthroughs in the GaN-based integrated waveguide structure. For example, professor huilongqing, the american university of kansasi, prepares a planar Wavelength Division Multiplexer (WDM) for optical fiber communication using GaN material, and professor yankee peak, the american university of sickladen, prepares a GaN planar waveguide device for 850 nm. Domestic GaN-based integrated waveguide devices have also achieved simple communication functions. However, the efficiency of optical coupling between the LED and the optical waveguide in the GaN-based integrated waveguide is low, about 10%, which greatly degrades other properties of the GaN-based integrated waveguide. How to improve the optical coupling efficiency of the GaN-based integrated waveguide and realize the improvement of the overall performance of the integrated waveguide is not yet solved.

Disclosure of Invention

Aiming at the technical problem, the invention provides a method for improving the optical coupling efficiency of a GaN-based integrated waveguide by adopting a high-reflection film, which improves the optical coupling efficiency between an LED and an optical waveguide by plating a high-reflection film DBR (distributed Bragg reflection) on a multi-quantum well LED side wall and reflecting LED light, thereby solving the problem of low coupling efficiency of a GaN-based waveguide device.

The GaN-based integrated waveguide mainly comprises the following three parts: multiple quantum well Light Emitting Diodes (LEDs), multiple quantum well optical waveguides, multiple quantum well detectors (PDs). The invention provides a method for improving the coupling efficiency of light by using a DBR high-reflection film, thereby improving the overall performance of a GaN-based integrated waveguide.

In order to achieve the purpose, the technical scheme provided by the invention is as follows:

a method for improving the optical coupling efficiency of a GaN-based integrated waveguide by adopting a high-reflection film comprises the following steps:

the method for improving the optical coupling efficiency of the GaN-based integrated waveguide by adopting the high-reflection film comprises the following steps:

growing a GaN epitaxial layer on the surface of a substrate;

preparing a multi-quantum well structure on the surface of the GaN epitaxial layer, wherein the multi-quantum well structure sequentially comprises an n-GaN layer, an MQWs layer and a p-GaN layer from bottom to top, and photoresist is spin-coated on the surface layer of the multi-quantum well structure;

transferring the pattern on the mask plate to a substrate by utilizing photoetching development and nitride etching to obtain a GaN-based integrated waveguide structure, wherein the GaN-based integrated waveguide structure sequentially comprises a multi-quantum well light-emitting diode, a multi-quantum well optical waveguide and a multi-quantum well detector which have the same structure from left to right;

plating a DBR high-reflection film on the side surface of the multi-quantum well light-emitting diode, and plating positive and negative metal electrodes on the multi-quantum well light-emitting diode and the multi-quantum well detector respectively;

and step five, sleeving an electrode and packaging a lead.

Preferably, the substrate material used in step one is sapphire, silicon, SiC or GaN.

Preferably, in the step one, a Metal Organic Chemical Vapor Deposition (MOCVD) method is adopted to grow the GaN base on the surface of the substrate.

Preferably, step one is to grow GaN base on the surface of the substrate by high temperature metal organic compound vapor deposition.

Preferably, in the second step, a metal organic chemical vapor deposition (PECVD) or a Molecular Beam Epitaxy (MBE) method is used to prepare the multiple quantum well structure on the GaN-based surface.

Preferably, the photoresist used in step three is a positive photoresist AZ5412 having an inversion characteristic. The light emitting diode, the detector and the waveguide window are obtained by using a traditional photoetching process. The photoetching process comprises photoresist homogenizing, prebaking, exposing, developing and postbaking.

Preferably, the nitride etching in step three adopts a coupled plasma etching process. And etching to the n-GaN layer to obtain a mesa structure of the light-emitting diode and the detector and a ridge structure of the waveguide.

Preferably, the method for preparing the electrode in the fourth step is an electron beam evaporation method or a thermal evaporation method.

Preferably, the GaN Schottky contact electrode in the fourth step is Ni, Au, Pt or Ni/Au, and the ohmic contact electrode material is Ti/Al or Ti/Al/Ti/Au. Alternatively, the electrode material may be a same kind of metal or a different kind of metal capable of forming a schottky or ohmic gold half contact with GaN, such as Ni/Au, Pt, Ti/Al/Ni/Au, or the like.

Preferably, the DBR high-reflection film material of the four steps is a multi-period high-refractive-index Si/SiC material.

Preferably, the electrode annealing conditions in the fifth step are determined according to specific metal electrode types. For the Ni/Au composite electrode, the annealing temperature of the electrode sheath is 400-600 ℃, and the time is 3-15 minutes.

Compared with the prior art, the invention has the beneficial effects that:

the invention provides a method for improving the optical coupling efficiency of a GaN-based integrated waveguide by utilizing a high-reflectivity film (DBR), wherein the DBR is a periodic structure formed by alternately arranging two materials with different refractive indexes in an ABAB mode, the optical thickness of each layer of material is 1/4 of the central reflection wavelength, the DBR is equivalent to a group of photonic crystals, and the reflectivity of the DBR can reach more than 99 percent because electromagnetic waves with the frequency within the range of energy gaps cannot penetrate through the DBR. The DBR high-reflection film is not absorbed by a metal high-reflection film, and the position of an energy gap can be adjusted by changing the refractive index or the thickness of the material, so that the DBR high-reflection film is selected as a material for improving optical coupling. The invention designs the GaN-based integrated waveguide device on the basis of the traditional semiconductor process. Since the structure has the advantages that the structures of the light emitting diode LED, the multi-quantum well optical waveguide and the PD are the same, forward bias is applied to the structure, and the structure is in a light emitting mode. The reverse bias is applied, i.e. the photo-detection mode. The multiple quantum well detector needs a certain amount of photon excitation to generate a hole and electron pair to form a photocurrent, and due to the large scattering loss of the LED with the structure, a DBR high-reflection film needs to be added on the side surface to enable more optical energy to be coupled into the multiple quantum well waveguide, so that the sensitivity of the detector is improved. The invention has the advantages of simple process, obvious effect and wide application prospect, and provides an effective way for improving the optical coupling efficiency of the GaN-based integrated waveguide.

Drawings

In order to more clearly illustrate the embodiments of the present application or technical solutions in the prior art, the drawings needed to be used in the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments described in the present invention, and other drawings can be obtained by those skilled in the art according to the drawings.

Fig. 1 is a flowchart of a method for improving optical coupling efficiency of a GaN-based integrated waveguide by using a DBR high reflectivity film according to embodiment 1 of the present invention;

fig. 2 is a schematic structural diagram of a GaN-based integrated waveguide prepared by using a DBR high reflection film according to embodiment 2 of the present invention.

Description of the drawings:

1. a substrate; 2. a GaN epitaxial layer; 3. an n-GaN layer; 4. an MQWs layer; 5. a p-GaN layer; 6. an LED; 7. a waveguide; 8. PD; 9. DBR high reflection film.

Detailed Description

In order to make those skilled in the art better understand the technical solution of the present invention, the present invention will be further described in detail with reference to the accompanying drawings and examples, but the present invention is not limited to these examples.

Example 1

Referring to fig. 1, the method for improving the optical coupling efficiency of the GaN-based integrated waveguide by using the DBR high-reflection film provided by the present invention comprises the following steps:

(1) cleaning the wafer required by processing, and drying by using nitrogen. And growing the n-GaN layer, the MQWs layer and the p-GaN layer thin film layer of the device by using MOCVD.

(2) And spin-coating a layer of photoresist on the GaN surface layer of the wafer. In order to make the glue spin coating uniform and control the thickness of the glue, a rotation speed of 4000 revolutions per minute is selected, the rotation time is 90s, and the thickness is about 350 nm. Then, the wafer coated with the paste is baked for about 90 seconds by a hot plate at 180 ℃. Thus, the first step of photoresist spin coating is completed, and a thin photoresist material layer is formed on the surface layer of the wafer after spin coating.

(3) And 2, carrying out photoetching development on the wafer coated with the photoresist, using a customized mask plate in the exposure process, completely arranging a pattern region on the mask plate above the wafer, setting the exposure time of 7s, and transferring the waveguide structure designed on the mask plate to the photoresist layer by using an exposure technology. The exposed wafer needs to be developed to display a pattern. And (3) mainly using 3038 developing solution for developing, cleaning with clear water and drying with nitrogen after developing, and drying water vapor on a hot plate, so that the process of the step 2 is finished.

(4) After lithographic development, the wafer needs to be nitride etched to obtain the desired ridge structure. Ion beam etching of Ar ions is used in the etching, and the etching height is the ridge height of the ridge waveguide. After etching, the wafer needs to be cleaned, and the photoresist on the wafer needs to be cleaned. The waveguide structure on the wafer can be clearly observed under a microscope. And cleaning and drying the etched wafer to obtain the InGaN/GaN multi-quantum well optical waveguide device.

(5) And plating a high-reflection film (DBR) on the side surface of the multi-quantum well LED. And respectively plating positive and negative electrodes on the LED and the PD structures.

(6) And (4) sleeving the electrodes and packaging the leads.

Example 2

Referring to fig. 2, the present invention provides a method for enhancing GaN-based integrated waveguides using a high-reflectivity film (DBR), which is further described in detail as follows:

the desired substrate 1 of GaN material is selected, and we select a sapphire substrate.

The GaN layer 2 is grown by a multi-step growth method and a high-temperature MOCVD technology, the n-GaN layer 3, the MQWs layer 4 and the p-GaN layer 5 of a device are grown on the GaN layer 2 by MOCVD, the n-GaN layer 3 is formed by doping Si in a GaN material, the MQWs layer 4 is a structure formed by growing InGaN and GaN according to a certain proportion of components, and the p-GaN layer 5 is formed by doping Mg in the GaN material.

By using photoetching technology, an integrated waveguide design pattern on a mask plate is etched to the n-GaN layer 3, and a mesa structure of the LED6 and the detector PD8 and a ridge structure of the waveguide 7 are obtained

The DBR high-reflection film 9 is plated on the side face of the multiple quantum well light emitting diode LED6, and the positive and negative metal electrodes are respectively plated on the multiple quantum well light emitting diode and the multiple quantum well detector.

And evaporating a Schottky contact electrode Ni/Au composite layer on the photoresist mask pattern by using an electron beam evaporation technology, wherein the thickness of the Schottky contact electrode Ni/Au composite layer is 10-300 nanometers, so that the GaN epitaxial layer is directly contacted with Ni/Au at the position of a photoresist mask pattern window, and the photoresist is contacted with metal Ni/Au at the position shielded by the photoresist.

And (3) annealing the Ni/Au Schottky contact electrode by using a rapid annealing furnace in a nitrogen atmosphere, wherein the annealing temperature is 400-600 ℃, and the annealing time is 3-15 minutes.

The method is not limited to the embodiment, and the method can also effectively improve the performance of the multi-quantum well LED structure and the multi-quantum well detector. On the basis of the traditional structure, the method increases the light energy coupled to the optical waveguide by adding the high-reflection film DBR and reflecting, thereby improving the performance of the sensitivity of the detector.

While certain exemplary embodiments of the present invention have been described above by way of illustration only, it will be apparent to those of ordinary skill in the art that the described embodiments may be modified in various different ways without departing from the spirit and scope of the invention. Accordingly, the drawings and description are illustrative in nature and should not be construed as limiting the scope of the invention.

Claims

1. A method for improving the optical coupling efficiency of a GaN-based integrated waveguide by using a high-reflectivity film is characterized by comprising the following steps:

growing a GaN epitaxial layer on the surface of a substrate;

plating a DBR high-reflection film on the side surface of the multi-quantum well light-emitting diode, wherein the DBR high-reflection film is made of a multi-period high-refractive-index Si/SiC material, and plating positive and negative metal electrodes on the multi-quantum well light-emitting diode and the multi-quantum well detector respectively;

and step five, sleeving an electrode and packaging a lead.

2. The method of claim 1, wherein the substrate material used in step one is sapphire, silicon, SiC or GaN.

3. The method of claim 1, wherein in step one, GaN-based material is grown on the surface of the substrate by MOCVD.

4. The method of claim 3, wherein the step one comprises growing GaN-based material on the surface of the substrate by high temperature metal organic compound vapor deposition.

5. The method of claim 1, wherein in step two, the multiple quantum well structure is formed on the GaN-based surface by MOCVD or MOepitaxy.

6. The method of claim 1, wherein the photoresist used in step three is positive photoresist AZ5412 with inversion property.

7. The method of claim 1, wherein the nitride etching in step three is performed by a coupled plasma etching process.

8. The method of claim 1, wherein the step four is performed by electron beam evaporation or thermal evaporation.

9. The method of claim 1, wherein in the fourth step, the GaN Schottky contact electrode is Ni, Au, Pt or Ni/Au, and the ohmic contact electrode is Ti/Al or Ti/Al/Ti/Au.

10. The method of claim 1, wherein in step five, the annealing temperature of the electrode sheath is 400-600 ℃ and the annealing time is 3-15 minutes for the Ni/Au composite electrode.