阅读说明：本技术 一种亚波长光栅及其制备方法 (Sub-wavelength grating and preparation method thereof ) 是由 郝永芹 王凤玲 冯源 李辉 晏长岭 白雪梅 魏志鹏 于 2019-10-12 设计创作，主要内容包括：本申请属于光栅技术领域,特别是涉及一种亚波长光栅及其制备方法。目前用于VCSEL的HCG,其材料通常采用Si/SiO2等材料,可以在提供高反射率的同时达到很大的带宽,但因与广泛使用的GaAs基VCSEL的材料体系不同,需要额外通过PECVD等其他方式进行Si/SiO2等薄膜的制备,且存在由于不同材料体系之间热膨胀系数的差异大而导致材料之间的应力问题以及薄膜的牢固度问题,影响器件的稳定性。本申请提供了一种亚波长光栅,包括依次设置的低折射率亚层、应力缓冲层和高折射率亚波长光栅层。应力缓冲层可有效改善氧化过程产生的收缩应力,这些对提高HCG长期工作的稳定性具有重要意义。(The application belongs to the technical field of gratings, and particularly relates to a sub-wavelength grating and a preparation method thereof. At present, the HCG used for the VCSEL generally adopts Si/SiO2 and other materials, which can provide a high reflectivity and simultaneously achieve a large bandwidth, but different from the widely used GaAs-based VCSEL material system, it is necessary to additionally prepare Si/SiO2 and other films by PECVD and other methods, and there are problems of stress between materials and firmness of the films due to large difference in thermal expansion coefficients between different material systems, which affects stability of the device. The application provides a sub-wavelength grating, which comprises a low refractive index sub-layer, a stress buffer layer and a high refractive index sub-wavelength grating layer which are sequentially arranged. The stress buffer layer can effectively improve the shrinkage stress generated in the oxidation process, and the stress buffer layer has important significance for improving the stability of the HCG in long-term operation.)

1. A sub-wavelength grating, comprising: the device comprises a low-refractive-index sub-layer, a stress buffer layer and a high-refractive-index sub-wavelength grating layer which are sequentially arranged.

2. The sub-wavelength grating of claim 1, wherein: the low refractive index sub-layer, the stress buffer layer and the high refractive index sub-wavelength grating layer are sequentially arranged from bottom to top.

3. The sub-wavelength grating of claim 1, wherein: the stress buffer layer is made of the same material as the high-refractive-index sub-wavelength grating layer.

4. The sub-wavelength grating of claim 1, wherein: the sub-wavelength grating is a high refractive index contrast sub-wavelength grating.

5. A method for preparing a sub-wavelength grating is characterized by comprising the following steps: the method comprises the following steps:

step 1: growing a high-refractive-index material I and a high-refractive-index material II on the GaAs substrate in sequence;

step 2: etching the surface of the high-refractive-index material II to ensure that the side wall of the etching groove just completely exposes out of the high-refractive-index material I;

and step 3: after the high-refractive-index material I is completely exposed, oxidizing to form a low-refractive-index sub-layer of the high-refractive-index contrast sub-wavelength grating;

and 4, step 4: and (3) shallow etching is carried out on the high-refractive-index material II on the surface layer of the table top formed after etching in the step (2) to form a stress buffer layer and a high-refractive-index sub-wavelength grating layer.

6. The method of manufacturing a sub-wavelength grating of claim 5, wherein: the low refractive index sub-layer, the stress buffer layer and the high refractive index sub-wavelength grating layer are all completed by molecular beam epitaxial growth or metal organic chemical vapor deposition through one-time epitaxial growth.

7. The method of manufacturing a sub-wavelength grating of claim 5, wherein: the etching in the step 2 comprises photoetching and chemical corrosion.

8. The method of manufacturing a sub-wavelength grating of claim 5, wherein: and (3) forming the low-refractive-index sub-layer after the high-refractive-index material I is completely oxidized in the step 3.

9. The method of manufacturing a sub-wavelength grating of claim 5, wherein: the shallow etching of the step 4 comprises electron beam exposure and inductively coupled plasma etching.

10. The method of manufacturing a sub-wavelength grating of claim 5, wherein: the low refractive index sublayer is formed of an Al-rich AlGaAs or AlAs high refractive index material via an oxidation process.

Technical Field

The application belongs to the technical field of gratings, and particularly relates to a sub-wavelength grating and a preparation method thereof.

Background

In recent years, with the development of micromachining technology and theoretical research, subwavelength gratings have attracted more and more attention. The sub-wavelength grating is a grating with a relief structure, the grating period is less than the incident wavelength, only zero-order diffraction waves exist, and the high-order diffraction waves are evanescent waves. The optical diffraction element is an important research direction in diffraction optical devices, is widely applied as an optical diffraction element, and particularly shows a very good application prospect on a Vertical Cavity Surface Emitting Laser (VCSEL). The High-refractive-index Contrast sub-wavelength Grating (HCG) is characterized in that the stripes of a High-refractive-index Grating layer are completely surrounded by a low-refractive-index medium (usually air or silicon dioxide) to form a large refractive index difference, the reflectivity of incident light projected on the Grating can be almost 1 by adjusting the parameters of the material, the thickness, the duty ratio, the Grating period and the like of the Grating, and meanwhile, the High-refractive-index Contrast sub-wavelength Grating has a wide reflection band and can meet the requirement of a VCSEL High-reflection resonant cavity mirror. The HCG can be used for replacing a p-type DBR on the surface of the VCSEL, the purposes of reducing high series resistance and large absorption loss caused by a plurality of layers of DBRs are achieved, meanwhile, the output quality of laser can be improved, the polarization characteristic of the VCSEL is improved, and the development requirement of device miniaturization is met.

HCG currently used for VCSEL is made of Si/SiO₂The materials can achieve a large bandwidth while providing high reflectivity, but the materials are different from the widely used GaAs-based VCSEL material system, and need to additionally perform Si/SiO by other modes such as PECVD₂And the preparation of the thin film has the problems of stress among materials and firmness of the thin film due to large difference of thermal expansion coefficients among different material systems, and influences the stability of the device.

Content of application

1. Technical problem to be solved

HCG currently used for VCSEL is made of Si/SiO₂The materials can achieve a large bandwidth while providing high reflectivity, but the materials are different from the widely used GaAs-based VCSEL material system, and need to additionally perform Si/SiO by other modes such as PECVD₂And when the thin film is prepared, the problem of stress among materials and the problem of firmness of the thin film due to large difference of thermal expansion coefficients among different material systems exist, and the stability of the device is influenced.

2. Technical scheme

In order to solve the above technical problem, the present application provides a sub-wavelength grating, which includes a low refractive index sub-layer, a stress buffer layer, and a high refractive index sub-wavelength grating layer, which are sequentially disposed.

Another embodiment provided by the present application is: the low refractive index sub-layer, the stress buffer layer and the high refractive index sub-wavelength grating layer are sequentially arranged from bottom to top.

Another embodiment provided by the present application is: the stress buffer layer is made of the same material as the high-refractive-index sub-wavelength grating layer.

Furthermore, the stress buffer layer and the high-refractive-index sub-wavelength grating layer are both made of GaAs materials.

Another embodiment provided by the present application is: the sub-wavelength grating is a high refractive index contrast sub-wavelength grating.

The application also provides a preparation method of the sub-wavelength grating, which comprises the following steps:

step 1: growing a high-refractive-index material I and a high-refractive-index material II on the GaAs substrate in sequence;

step 2: etching the surface of the high-refractive-index material II to ensure that the side wall of the etching groove just completely exposes out of the high-refractive-index material I;

and step 3: after the high-refractive-index material I is completely exposed, oxidizing to form a low-refractive-index sub-layer of the high-refractive-index contrast sub-wavelength grating;

and 4, step 4: and (3) shallow etching is carried out on the high-refractive-index material II on the surface layer of the table top formed after etching in the step (2) to form a stress buffer layer and a high-refractive-index sub-wavelength grating layer.

Another embodiment provided by the present application is: the refractive index sub-layer, the stress buffer layer and the high refractive index sub-wavelength grating layer are all completed by molecular beam epitaxial growth or metal organic chemical vapor deposition through one-time epitaxial growth.

Another embodiment provided by the present application is: the etching in the step 2 comprises photoetching and chemical corrosion.

Another embodiment provided by the present application is: and (3) forming the low-refractive-index sub-layer after the high-refractive-index material I is completely oxidized in the step 3.

Another embodiment provided by the present application is: the shallow etching of the step 4 comprises electron beam exposure and inductively coupled plasma etching.

Another embodiment provided by the present application is: the low refractive index sublayer is formed of an Al-rich AlGaAs or AlAs high refractive index material via an oxidation process.

3. Advantageous effects

Compared with the prior art, the sub-wavelength grating and the preparation method thereof have the beneficial effects that:

the sub-wavelength grating provided by the application provides high reflectivity, wide bandwidth and good polarization selectivity by replacing a P-type distributed Bragg reflector in a GaAs-based VCSEL, reduces series resistance and power consumption of a device, and improves photoelectric characteristics of the device.

The application provides a high refractive index contrast subwavelength grating speculum only needs two layers of high refractive index material retes of epitaxial growth alright replace about 100P type DBRs about in the VCSEL, and thickness is only 400 ~ 600nm, and this makes the vertical size of speculum obviously reduce on the device, is favorable to the device miniaturization.

The high-refractive-index contrast sub-wavelength grating provided by the application has the same material system as the VCSEL, and the stress problem generated by different material systems can be greatly reduced.

The stress buffer layer in the high-refractive-index contrast subwavelength grating can effectively improve the shrinkage stress generated in the oxidation process, and the shrinkage stress has important significance for improving the stability of the HCG during long-term work.

By adopting the high-refractive-index contrast subwavelength grating provided by the application, the manufacture of the VCSEL epitaxial wafer of the integrated HCG can be completed through one-time epitaxial growth, the manufacture precision of the high-contrast subwavelength grating film thickness is improved, and the manufacture difficulty and the cost of a device are greatly reduced.

Drawings

FIG. 1 is a schematic diagram of a sub-wavelength grating structure of the present application;

FIG. 2 is a schematic view of a sub-wavelength grating epitaxial structure of the present application;

FIG. 3 is a reflection profile of a TM polarized sub-wavelength grating of the present application;

FIG. 4 is a reflection profile for a TM polarized sub-wavelength grating of the present application having a reflectivity greater than 99%;

FIG. 5 is a reflection profile for a TM polarized sub-wavelength grating of the present application having a reflectivity greater than 99.9%;

in the figure: 1-low refractive index sublayer, 2-stress buffer layer, 3-high refractive index sub-wavelength grating layer, 4-GaAs substrate, 5-high refractive index material layer I and 6-high refractive index material layer II.

Detailed Description

Hereinafter, specific embodiments of the present application will be described in detail with reference to the accompanying drawings, and it will be apparent to those skilled in the art from this detailed description that the present application can be practiced. Features from different embodiments may be combined to yield new embodiments, or certain features may be substituted for certain embodiments to yield yet further preferred embodiments, without departing from the principles of the present application.

PECVD: the gas containing film component atoms is ionized by means of microwave or radio frequency, etc. to form plasma locally, and the plasma has high chemical activity and easy reaction to deposit the required film on the substrate. In order to allow chemical reactions to proceed at lower temperatures, the reactivity of the plasma is exploited to promote the reactions, and thus such CVD is known as Plasma Enhanced Chemical Vapor Deposition (PECVD).

The TM mode (TM mode) refers to a propagation mode in which the longitudinal component of the magnetic field is zero and the longitudinal component of the electric field is non-zero in the waveguide.

The TM mode has an electric field component in the direction of propagation and no magnetic field component, called a transverse magnetic wave. In a planar optical waveguide (closed cavity structure), electromagnetic field components have Hy, Ex and Ez, and the propagation direction is the z direction.

Referring to fig. 1 to 5, the present application provides a sub-wavelength grating, which includes a low refractive index sublayer 1, a stress buffer layer 2, and a high refractive index sub-wavelength grating layer 3, which are sequentially disposed.

Further, the low refractive index sublayer 1, the stress buffer layer 2 and the high refractive index sub-wavelength grating layer 3 are sequentially arranged from bottom to top.

Further, the stress buffer layer 2 is made of the same material as the high-refractive-index sub-wavelength grating layer 3.

Furthermore, the stress buffer layer and the high-refractive-index sub-wavelength grating layer are both made of GaAs materials.

Further, the sub-wavelength grating is a high refractive index contrast sub-wavelength grating.

The application also provides a preparation method of the sub-wavelength grating, which comprises the following steps:

step 1: sequentially growing a high-refractive-index material I5 and a high-refractive-index material II6 on the GaAs substrate 4;

step 2: etching the surface of the high-refractive-index material II to ensure that the side wall of the etching groove just completely exposes the high-refractive-index material I5;

and step 3: after the high-refractive-index material I5 is completely exposed, oxidizing to form a low-refractive-index sub-layer 1 of the high-refractive-index contrast sub-wavelength grating;

and 4, step 4: shallow etching is carried out on the high-refractive-index material II6 on the surface layer of the table top formed after etching in the step 2, and a stress buffer layer 2 and a high-refractive-index sub-wavelength grating layer 3 are formed.

Further, the low refractive index sublayer 1, the stress buffer layer 2 and the high refractive index sub-wavelength grating layer 3 are all completed by molecular beam epitaxial growth or metal organic chemical vapor deposition through one-time epitaxial growth.

Further, the etching in step 2 includes photolithography and chemical etching.

Further, after the high refractive index material I5 is completely oxidized in step 3, the low refractive index sub-layer 1 is formed.

Further, the shallow etching of step 4 includes electron beam exposure and inductively coupled plasma etching.

Further, the low refractive index sublayer 1 is formed of an Al-rich AlGaAs or AlAs high refractive index material through an oxidation process.

In the application, the low refractive index sub-layer 1, the stress buffer layer 2 and the high refractive index sub-wavelength grating layer 3 form a high refractive index contrast sub-wavelength grating, which is used as an upper reflector of the VCSEL resonant cavity, that is, a high refractive index contrast sub-wavelength grating reflector having the same material system as the GaAs-based VCSEL, and has a higher reflectivity and a wider reflection bandwidth compared with a P-type DBR structure in the VCSEL. The HCG has high diffraction reflection effect, and outputs strong polarized light while realizing intracavity resonance.

Have in this application with GaAs base VCSEL with the high refractive index contrast subwavelength grating speculum of material system only need 2 retes alright replace P type DBR, thickness is 400 ~ 600nm, 1/5 left and right sides of original P type DBR thickness, this makes on the device the longitudinal dimension of speculum obviously reduce, and two-layer growth is simple, only need whole VCSEL once epitaxial growth can, the rete material is generally easily obtained, the cost of manufacture and the degree of difficulty of device have been reduced, the preparation quality obtains guaranteeing easily, be favorable to the device miniaturization and the stability of long-term work.

Stress buffer layer 2 in this application is the homogeneous material with high refracting index grating layer 3, and its existence has both alleviated the influence of stress release and stress to device stability that the oxidation in-process leads to because the low refracting index sublayer shrink, can adjust the high reflection bandwidth simultaneously, and through rationally setting up its value, the high reflection bandwidth can obviously improve.

The existence of the low-refractive-index sublayer 3 in the application obviously widens the bandwidth of high reflectivity, the change of the thickness of the sublayer has a non-negligible effect on the polarization, and the polarization selectivity of the reflector can be improved by reasonably setting the thickness of the sublayer.