WO2021212597A1 - Quaternary system tensile strain semiconductor laser epitaxial wafer and preparation method therefor - Google Patents

Abstract

Provided are a quaternary system tensile strain semiconductor laser epitaxial wafer and a preparation method therefor. The preparation method comprises the following steps: step 1: selecting an InP substrate (1); step 2: sequentially depositing, on the substrate (1), a cushion layer (2), a grating layer (3), and an InP cover layer (4); step 3: preparing a grating pattern on the grating layer (3) and the InP cover layer (4); and step 4: after completing preparing the grating pattern, continuing to grow, on the grating layer (3) and the InP cover layer (4), a coverage layer (5), an isolation layer (6), a lower limiting layer (7), a lower gradient waveguide layer (8), a multi-quantum well layer (9), an upper gradient waveguide layer (10), an upper limiting layer (11), an upper cladding layer (12), an upper gradient layer (13), and a contact layer (14) in sequence for completing preparation. The laser epitaxial wafer prepared by the preparation method increases the transport speed of a carrier, and the optical gain and the reliability of a semiconductor laser.

Description

Quaternary system tensile strain semiconductor laser epitaxial wafer and preparation method thereof Technical field

The present invention relates to the field of semiconductor technology, in particular to a quaternary system tensile strain semiconductor laser epitaxial wafer and a preparation method thereof.

Background technique

Since the advent of semiconductor lasers in the early 1960s, due to its wide wavelength coverage, compact structure, high reliability and easy integration, it has been used in people’s daily life, industrial, agricultural production, national defense and military fields. It is widely used. The performance of semiconductor lasers largely depends on the quality of semiconductor epitaxial wafers, so the preparation of high-quality epitaxial wafers is the key to the preparation of high-performance semiconductor lasers. Especially in the 1980s, the emergence of quantum well structures made a big leap in semiconductor lasers. In the quantum well structure, when the thickness of the ultra-thin active layer material is less than the de Broglie wavelength of electrons, the active region becomes a potential well region, and the broadband materials on both sides become barrier regions, along with electrons and holes. The movement in the direction perpendicular to the well wall appears quantized. The emergence of strained quantum wells fundamentally changed the energy band structure of semiconductor materials. Just by adjusting the type of strain and the magnitude of the amount of strain, it is possible to obtain the band structure we need. So far, the performance of semiconductor devices has taken a big leap, and the application of semiconductor lasers in many fields has become a reality. At present, as a light source, quantum well semiconductor lasers have the advantages of small size, low threshold current density, good temperature characteristics, high output power, good dynamic characteristics, and can be directly modulated. Then the grating is introduced for distributed feedback (DFB), and the quantum well DFB laser becomes The most ideal light source in high-speed communication. However, due to its different energy band structure and carrier transport characteristics, tensile stress quantum wells have brought new opportunities to high-speed laser applications. But at present, in communication applications, the most commonly used light sources are based on compressive strain quantum wells. In order to meet the needs of high-speed applications above 25G, people usually increase the stress of the quantum wells and the number of quantum wells to increase the differential gain of the laser's active region. , But the excessive stress and the number of quantum wells bring great challenges to the reliability of the device.

In view of this, in order to overcome the above technical defects, providing a quaternary system tensile strain semiconductor laser epitaxial wafer and a preparation method thereof has become an urgent problem to be solved in this field.

Summary of the invention

The purpose of the present invention is to overcome the shortcomings of the prior art and provide a quaternary system tensile strain semiconductor laser epitaxial wafer and a preparation method thereof, which improve the carrier transport speed and the optical gain and reliability of the semiconductor laser.

In order to solve the above technical problems, the technical solution of the present invention is: a preparation method of a quaternary system tensile strain semiconductor laser epitaxial wafer, the difference lies in that it includes the following steps:

Step 1: Choose an InP substrate;

Step 2: Depositing a buffer layer, a grating layer and an InP cap layer on the substrate in sequence;

Step 3: Prepare grating patterns on the grating layer and the InP cover layer;

Step 4: After the preparation of the grating pattern is completed, the cover layer, the isolation layer, the lower confinement layer, the lower graded waveguide layer, the multiple quantum well layer, the upper graded waveguide layer, the upper confinement layer, and the upper The cladding layer, the upper gradient layer and the contact layer are prepared.

According to the above technical scheme, the material of the buffer layer is InP, the thickness is 500-1000nm, the doping concentration is between 1×10 ¹⁸ ～3×10 ¹⁸ cm ^-3 , and the growth rate is between 0.4 and 0.6 nm/s. between.

According to the above technical solution, the material of the grating layer is InGaAsP, the thickness is 10-50nm, and the band gap wavelength is between 1000-1300nm.

According to the above technical solution, the grating duty ratio of the grating layer ranges from 20% to 80%.

According to the above technical solution, the multiple quantum well layer is composed of a plurality of In _x (Al _y Ga _1-y ) _1-x As quantum wells, the quantum well material has a tensile strain relative to the substrate, and the strain is between -0.5% ～-2.0%.

According to the above technical solution, the barrier layer between the plurality of quantum wells is composed of compressive stress In _x (Al _y Ga _1-y ) _1-x As, and the amount of strain is between +0.3% and +1.5%.

According to the above technical solution, the logarithm of the quantum well is between 1 and 20, the thickness of the quantum well is between 5 and 15 nm, and the thickness of the barrier is between 5 and 20 nm.

According to the above technical solution, the lower graded waveguide layer and the upper graded waveguide layer are composition graded In _x (Al _y Ga _1-y ) _1-x As, the Al composition content y is gradually changed from 0.8 to 0.5, and the range of x Between 0.4 and 0.6.

According to the above technical solution, the material of the lower confinement layer and the upper confinement layer is In _x (Al _y Ga _1-y ) _1-x As, the Al component content y is between 0.6 and 1, and the range of x is between Between 0.4 and 0.7.

A quaternary system tensile strain semiconductor laser epitaxial wafer prepared according to the above-mentioned preparation method. The difference is that it includes a substrate, a buffer layer, a grating layer, an InP cover layer, a cover layer, an isolation layer, and a bottom layer in order from bottom to top. Confinement layer, lower graded waveguide layer, multiple quantum well layer, upper graded waveguide layer, upper confinement layer, upper cladding layer, upper graded layer and contact layer.

Based on the above solution, the present invention discloses a quaternary tensile strain semiconductor laser epitaxial wafer and a preparation method thereof, which design multiple pairs of quaternary tensile strain InAlGaAs quantum well active regions through band structure tailoring to improve the optical gain of the semiconductor laser And reliability; through the design of the N-face grating to reduce the impedance of the carrier when passing through the Bragg reflector, and improve the carrier transport speed; through the isolation layer structure parameters and the quantum well layer optical field distribution theoretical model matching, design high coupling efficiency Epitaxial wafer structure. The high-speed laser prepared by the epitaxial wafer is very suitable for the needs of high-speed optical transmission applications such as 5G communications.

Description of the drawings

Figure 1 is a schematic flow diagram of a preparation method according to an embodiment of the present invention;

2 is a schematic diagram of the overall structure of a laser epitaxial wafer according to an embodiment of the present invention;

3 is a schematic diagram of the structure of the laser epitaxial wafer before the grating is prepared according to the embodiment of the present invention;

4 is a schematic diagram of the structure of the laser epitaxial wafer after preparing the grating according to the embodiment of the present invention;

Among them: 1-substrate; 2-buffer layer; 3-grating layer; 4-InP cover layer, 5-cover layer, 6-isolation layer; 7-lower confinement layer; 8-lower graded waveguide layer; 9-multi-quantum Well layer; 10-upper graded waveguide layer; 11-upper confinement layer; 12-upper cladding layer; 13-upper graded layer; 14-contact layer.

Detailed ways

In order to make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described here are only used to explain the present invention, but not used to limit the present invention.

In the following, many aspects of the present invention will be better understood with reference to the drawings. The parts in the drawings are not necessarily drawn to scale. Instead, the focus is on clearly describing the components of the invention. In addition, in several views in the drawings, the same reference numerals indicate corresponding parts.

The word "exemplary" or "illustrative" as used herein means serving as an example, instance, or illustration. Any embodiment described herein as "exemplary" or "illustrative" is not necessarily construed as being preferred or advantageous over other embodiments. All the embodiments described below are exemplary embodiments. These exemplary embodiments are provided to enable those skilled in the art to make and use the embodiments of the present disclosure and are not intended to limit the scope of the present disclosure. The scope of the present disclosure is determined by Claims are defined. In other embodiments, well-known features and methods are described in detail so as not to obscure the present invention. For the purpose of the description herein, the terms "upper", "lower", "left", "right", "front", "rear", "vertical", "horizontal" and their derivatives will be oriented as shown in Figure 1. The invention is related. Moreover, there is no intention to be limited by any expressed or implied theory given in the foregoing technical field, background technology, summary of the invention or the following detailed description. It should also be understood that the specific devices and processes shown in the drawings and described in the following specification are simple exemplary embodiments of the inventive concept defined in the appended claims. Therefore, the specific dimensions and other physical features related to the embodiments disclosed herein should not be construed as restrictive unless the claims expressly state otherwise.

Please refer to Fig. 1 and Fig. 2, a method for preparing a quaternary system tensile strain semiconductor laser epitaxial wafer according to the present invention, the difference lies in that it includes the following steps:

Step 1: Choose an InP substrate 1, where the InP substrate 1 is an InP single wafer, the crystal orientation is (001), the off angle is within ±0.5°, the thickness is 325-375μm, and the doping concentration is (2-8) ×10 ¹⁸ cm ^-3 ;

Step 2: Deposit an InP buffer layer 2, a grating layer 3, and an InP cap layer 4 on the substrate 1 in sequence; the InP buffer layer 2 has a thickness of 500-1000 nm, a growth temperature between 630 and 680°C, and SiH _{4 is} used as Dopant, the doping concentration is between 1×10 ¹⁸ to 3×10 ¹⁸ cm ^-3 , the growth rate is about 0.4-0.6 nm/s, too fast growth rate is not conducive to the formation of high-quality buffer layer; grating layer 3 is InGaAsP material, the band gap wavelength is between 1100-1200nm, the lattice mismatch is less than ±500ppm, and the total thickness is 20-40nm. The thickness of the InP cap layer 4 is 5-20 nm.

Step 3: Make a grating pattern on the above-mentioned epitaxial substrate. Specifically, the above-mentioned substrate is cleaned with an organic solvent, rinsed with a large amount of deionized water, and dried. After pre-baking, homogenizing, post-baking, electron beam exposure, development, hardening, etching, and debinding, the first-order Bragg grating required for the production of DFB semiconductor laser epitaxial wafers is obtained. A duty ratio of 0.5 is obtained through the combination of exposure time and development time. The grating period is between 195 and 210 nm, and the depth is set to 60 nm. After the production is completed, the surface morphology, period and depth of the grating are tested by atomic force microscope (AFM) and scanning electron microscope (SEM) to ensure that the produced graphics meet the design requirements. In this step, the grating layer 3 and the InP capping layer 4 will be partially etched away, and then the capping layer 5 and subsequent layers will be grown in the etched trench.

Step 4: Continue to grow the cover layer 5, the isolation layer 6, the lower confinement layer 7, the lower graded waveguide layer 8, the multiple quantum well layer 9, the upper graded waveguide layer 10, the upper confinement layer 11, and the upper The cladding layer 12, the upper gradient layer 13, and the contact layer 14; specifically, the substrate produced in step 3 is cleaned with a solvent to clean the remaining photoresist, rinsed with a large amount of deionized water, and dried. Then it is put into the MOCVD growth reaction chamber, and the surface oxide layer is fully desorbed after raising the temperature. Wherein, the covering layer 5 is made of InP material with a growth thickness of 50-100 nm, which ensures that the grating layer is fully covered. The isolation layer 6 is made of InP material, and the thickness is between 50-150 nm. The lower confinement layer 7 is matched In _x (Al _y Ga _1-y ) _1-x As, the Al composition y is 0.9, the thickness is 10-30 nm, the lower graded waveguide layer 8 and the upper graded waveguide layer 10 are composition graded In _x (Al _y Ga _1-y ) _1-x As, the Al composition is gradually changed from 0.8 to 0.5, and the range of x is between 0.4 and 0.6. The multiple quantum well layer 9 is composed of a plurality of In _x (Al _y Ga _1-y ) _1-x As quantum wells. The range of y is between 0 and 0.6, and the range of x is between 0 and 0.6. The quantum well The material has a tensile strain relative to the substrate, and the amount of strain is between -0.5% and -2.0%. The barrier layer is composed of compressive stress In _x (Al _y Ga _1-y ) _1-x As, the amount of strain is between +0.3% and +1.5%, and the number of pairs of quantum wells is between 4 and 10. The thickness of the quantum well is between 5 and 15 nm; the thickness of the barrier is between 5 and 15 nm. The upper confinement layer 11 is made of InAlAs material with a thickness of 10-30 nm. The upper cladding layer 12 is made of InP material, and the P doping concentration is gradually changed ^{from 8×10 17} to 2.5×10 ¹⁸ cm ^-3. The upper graded layer 13 is made of InGaAsP material, the band gap wavelength is 1100-1500nm, the doping concentration is 3×10 ¹⁸ cm ^-3 , the contact layer 14 is made of InGaAs material, the doping concentration is greater than 5E18 cm ^-3 , and the growth temperature is lower than 650°C. In this embodiment, we used a doping concentration of 2.5E19cm ^-3 and a growth temperature of 600°C. Too high a growth temperature will cause Zn to diffuse out and escape, thereby reducing the doping concentration of the contact layer and increasing the contact resistance.

The quaternary system tensile strain semiconductor laser epitaxial wafer prepared according to the above preparation method is different in that it includes an InP substrate, a buffer layer, a grating layer, an InP cover layer, a cover layer, an isolation layer, and a lower limit in order from bottom to top. Layer, lower graded waveguide layer, multiple quantum well layer, upper graded waveguide layer, upper confinement layer, upper cladding layer, upper graded layer and contact layer. N-face grating patterns are prepared on the grating layer and the InP cover layer.

The above-mentioned epitaxial material growth equipment is MOCVD, and the sources used in the epitaxial growth process are trimethylindium (TMIn), trimethylgallium (TMGa), triethylgallium (TEGa), arsine (AsH3), and phosphorus. Alkane (PH3), silane (SiH4), diethyl zinc (DEZn).

The embodiment of the present invention is based on the energy band structure design and grows InP-based semiconductor laser epitaxial substrates and secondary epitaxial materials through MOCVD. Growth of quaternary system tensile strain semiconductor laser epitaxial materials by molecular beam epitaxy (MBE) or metal organic chemical vapor deposition (MOCVD), combined with holographic and electron beam exposure technology to make grating microstructures, to achieve a high-speed and low-power semiconductor laser epitaxial wafer .

The above content is a further detailed description of the present invention in combination with specific implementations, and it cannot be considered that the specific implementations of the present invention are limited to these descriptions. For those of ordinary skill in the technical field to which the present invention belongs, several simple deductions or substitutions can be made without departing from the concept of the present invention, which should be regarded as belonging to the protection scope of the present invention.

Claims (10)

1. A method for preparing a quaternary system tensile strain semiconductor laser epitaxial wafer is characterized in that it comprises the following steps:

   Step 1: Choose an InP substrate;

   Step 2: Depositing a buffer layer, a grating layer and an InP cap layer on the substrate in sequence;

   Step 3: Prepare grating patterns on the grating layer and the InP cover layer;

   Step 4: After the preparation of the grating pattern is completed, the cover layer, the isolation layer, the lower confinement layer, the lower graded waveguide layer, the multiple quantum well layer, the upper graded waveguide layer, the upper confinement layer, and the upper The cladding layer, the upper gradient layer and the contact layer are prepared.
2. The method for preparing a quaternary system tensile strain semiconductor laser epitaxial wafer according to claim 1, wherein the material of the buffer layer is InP, the thickness is 500-1000 nm, and the doping concentration is between 1×10 ¹⁸ ～3 ×10 ¹⁸ cm ^-3 , the growth rate is between 0.4 and 0.6 nm/s.
3. The method for preparing a quaternary tensile strain semiconductor laser epitaxial wafer according to claim 1, wherein the grating layer is made of InGaAsP, has a thickness of 10-50 nm, and a band gap wavelength between 1000-1300 nm.
4. The method for preparing a quaternary system tensile strain semiconductor laser epitaxial wafer according to claim 3, wherein the grating duty ratio of the grating layer is in the range of 20% to 80%.
5. The method for preparing a quaternary system tensile strain semiconductor laser epitaxial wafer according to claim 1, wherein the multi-quantum well layer is composed of a plurality of In _x (Al _y Ga _1-y ) _1-x As quantum wells , The quantum well material has a tensile strain relative to the substrate, and the amount of strain is between -0.5% and -2.0%.
6. The method for preparing a quaternary system tensile strain semiconductor laser epitaxial wafer according to claim 5, wherein the barrier layer between the plurality of quantum wells is composed of compressive stress In _x (Al _y Ga _1-y ) _{1 -x} As composition, the strain is between +0.3%~+1.5%.
7. The method for preparing a quaternary system tensile strain semiconductor laser epitaxial wafer according to claim 6, wherein the logarithm of the quantum well is between 1 and 20, and the thickness of the quantum well is between 5 and 15 nm. The thickness of the barrier is between 5 and 20 nm.
8. The method for preparing a quaternary system tensile strain semiconductor laser epitaxial wafer according to claim 1, wherein the lower graded waveguide layer and the upper graded waveguide layer are composition graded In _x (Al _y Ga _1-y ) _{1 -x} As, the content of Al component y is gradually changed from 0.8 to 0.5, and the range of x is between 0.4 and 0.6.
9. The method for preparing a quaternary system tensile strain semiconductor laser epitaxial wafer according to claim 1, wherein the material of the lower confinement layer and the upper confinement layer is In _x (Al _y Ga _1-y ) _1-x As , The content of Al component y is between 0.6 and 1, and the range of x is between 0.4 and 0.7.
10. A quaternary system tensile strain semiconductor laser epitaxial wafer prepared according to the method of any one of claims 1 to 9, characterized in that it includes a substrate, a buffer layer, a grating layer, an InP cover layer, from bottom to top, Cover layer, isolation layer, lower confinement layer, lower graded waveguide layer, multiple quantum well layer, upper graded waveguide layer, upper confinement layer, upper cladding layer, upper graded layer and contact layer.

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