Superlattice epitaxial structure for laser

Abstract

The utility model relates to the technical field of quantum communication. The superlattice epitaxial structure comprises a GaAs substrate, a GaAs buffer layer, a first limiting unit, a second limiting unit, a third limiting unit, a fourth limiting unit, a contact unit, a first GaAs spacer layer, a first InAs quantum dot, a first stress release layer, a second GaAs spacer layer, a second InAs quantum dot, a second stress release layer and a third GaAs spacer layer. An optimized InAs / GaAs high-density quantum dot is grown through molecular beam epitaxy, a monolithic integrated mode mode-locking ultrashort pulse laser with the light emitting wavelength of 1.3 microns is successfully developed, multi-path space technology integration is achieved, and the method can be used for an efficient and practical lower parametric conversion room temperature single photon source.

Description

Technical Field

[0001] The utility model relates to the technical field of quantum communication, in particular to a superlattice epitaxial structure for lasers. Background Art

[0002] At present, InAs / GaAs single quantum dot single photon sources generally require liquid nitrogen or liquid helium refrigeration. This is because InAs / GaAs quantum dots have a small conduction band order and a weak quantum confinement effect on electrons. When the operating temperature rises, the thermal electron emission is significantly enhanced, and the carriers can easily transition to the wetting layer, reducing the light emission efficiency. Compared with electrons, holes have more split energy levels (light and heavy holes, spin-orbit coupling energy levels). As the temperature rises, the inter-band transition between holes intensifies, causing the luminescence peak of the biexciton of the quantum dot to overlap with the peak of the single exciton, thereby greatly increasing the probability of multi-photon emission in the biexciton-exciton cascade radiation process. As the temperature rises, the scattering phenomenon of phonon-assisted transitions increases greatly, and the original electron-hole two-level system becomes a three-level system. According to Loudon's quantum optics theory, this process can increase the probability of multi-photon emission by up to two times. In addition, the output wavelength adjustment range of the single quantum dot single photon source is limited, mostly concentrated around 900nm, and the single-mode coupling efficiency is very low. These all limit the practical application of single quantum dot single photon sources. Currently, the light sources used in most quantum communication experiments are still weak laser pulses that have undergone strong attenuation.

[0003] In recent years, the research on semiconductor ultrashort pulse lasers has developed rapidly, making it possible to replace traditional titanium sapphire femtosecond lasers with picosecond or sub-picosecond semiconductor lasers. Not only can miniaturization be achieved, but semiconductor ultrashort pulse lasers are also easy to integrate and low in cost. The most critical issue is the device preparation and performance of semiconductor ultrashort pulse semiconductor lasers. The wide gain of InAs quantum dots gives them a very narrow pulse width. At the same time, the ultrafast gain dynamic characteristics of InAs quantum dots and their easier gain saturation and absorption saturation make InAs quantum dots the only choice for mode-locked lasers in monolithic integrated gain regions and saturable absorption regions. Utility Model Content

[0004] The utility model aims to provide a superlattice epitaxial structure for lasers, which solves the problem of low efficiency of parameter conversion room temperature single photon source.

[0005] To achieve the above-mentioned purpose, the utility model adopts a superlattice epitaxial structure for a laser, comprising a GaAs substrate, a GaAs buffer layer, a first restriction unit, a second restriction unit, a third restriction unit, a fourth restriction unit, a contact unit, a first GaAs spacer layer, a first InAs quantum dot, a first stress release layer, a second GaAs spacer layer, a second InAs quantum dot, a second stress release layer and a third GaAs spacer layer, wherein the GaAs buffer layer is grown on the upper surface of the GaAs substrate, the fourth restriction unit is grown on the upper surface of the GaAs buffer layer, the first restriction unit is grown on the upper surface of the fourth restriction unit, the third restriction unit is grown on the upper surface of the first restriction unit, and the first GaAs spacer layer is grown on the upper surface of the third restriction unit The first InAs quantum dots are grown on the upper surface of the first GaAs spacer layer, the first stress release layer is grown on the upper surface of the first InAs quantum dots, the second GaAs spacer is grown on the upper surface of the first stress release layer, the second InAs quantum dots are grown on the upper surface of the second GaAs spacer layer, the second stress release layer is grown on the upper surface of the second InAs quantum dots, the third GaAs spacer is grown on the upper surface of the second stress release layer, the third restriction unit is grown on the upper surface of the third GaAs spacer layer, the second restriction unit is grown on the upper surface of the third restriction unit, the fourth restriction unit is grown on the upper surface of the second restriction unit, and the contact unit is grown on the upper surface of the fourth restriction unit.

[0006] The first confinement unit includes a first AlGaAs confinement layer and a second AlGaAs confinement layer, the first AlGaAs confinement layer is grown on the upper surface of the fourth confinement unit, and the second AlGaAs confinement layer is grown on the upper surface of the first AlGaAs confinement layer.

[0007] The second confinement unit includes a third AlGaAs confinement layer and a fourth AlGaAs confinement layer. The third AlGaAs confinement layer is grown on the upper surface of the third confinement unit, and the fourth AlGaAs confinement layer is grown on the upper surface of the third AlGaAs confinement layer.

[0008] The third confinement unit includes a fifth AlGaAs confinement layer and a sixth AlGaAs confinement layer, the fifth AlGaAs confinement layer is grown on the upper surface of the second AlGaAs confinement layer, the first GaAs spacer layer is grown on the upper surface of the fifth AlGaAs confinement layer, the sixth AlGaAs confinement layer is grown on the upper surface of the third GaAs spacer layer, and the third AlGaAs confinement layer is grown on the upper surface of the sixth AlGaAs confinement layer.

[0009] The fourth restriction unit includes a seventh AlGaAs restriction layer and an eighth AlGaAs restriction layer, the seventh AlGaAs restriction layer is grown on the upper surface of the GaAs buffer layer, the first AlGaAs restriction layer is grown on the upper surface of the seventh AlGaAs restriction layer, the eighth AlGaAs restriction layer is grown on the upper surface of the fourth AlGaAs restriction layer, and the contact unit is grown on the upper surface of the eighth AlGaAs restriction layer.

[0010] The contact unit includes a first GaAs contact layer and a second GaAs contact layer. The first GaAs contact layer is grown on the upper surface of the eighth AlGaAs confinement layer, and the second GaAs contact layer is grown on the upper surface of the first GaAs contact layer.

[0011] The utility model discloses a superlattice epitaxial structure for lasers. The GaAs substrate is an N+ doped 2-inch wafer, which is placed in a growth chamber after being baked at 190°C for 2 hours in a sample injection chamber and degassed at 420°C in a preparation chamber. The GaAs substrate heater is heated to 400°C, the As baffle is opened, and the As beam current is opened to 1×10 -6 ~7×10 -6 Torr, the temperature was raised to 670°C and maintained for 10 minutes for deoxidation treatment, and then the temperature was lowered to 620°C to grow the GaAs buffer layer of 300 nm, and Si doped 3×10 18 / cm 3 The first limiting unit, the second limiting unit, the third limiting unit and the fourth limiting unit are doped with Si and Be respectively. In order to reduce carrier absorption, there are 150nm of no doping above and below. The first InAs quantum dot is composed of five layers of InAs quantum dots. The quantum dots are surrounded by 5nm of InAs. 0.15 Ga 0.85 As the first stress release layer covers, the emission wavelength is extended to around 1300nm, each layer of quantum dots is separated by 50nm GaAs, and a 150nm GaAs contact unit is grown on the surface of the sample, and the P-type high doping 10 19The growth temperature of the GaAs buffer layer, the contact unit, the first restriction unit, the second restriction unit, the third restriction unit and the fourth restriction unit is 620°C, the growth temperature of the first InAs quantum dot, the second InAs quantum dot, the first stress release layer, the second stress release layer, the first GaAs spacer layer and the second GaAs spacer layer is 490°C, and the optimized InAs / GaAs high-density quantum dots are grown by molecular beam epitaxy. A monolithic integrated mode-locked ultrashort pulse laser with a light emission wavelength of 1.3μm is successfully developed, realizing multi-path spatial technology integration, which can be used for an efficient and practical lower parametric conversion room-temperature single-photon source. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] In order to more clearly illustrate the embodiments of the utility model or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the utility model. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0013] Figure 1 It is a schematic diagram of the principle of the superlattice epitaxial structure for laser of the utility model.

[0014] 1-GaAs substrate, 2-GaAs buffer layer, 3-first AlGaAs confinement layer, 4-second AlGaAs confinement layer, 5-third AlGaAs confinement layer, 6-fourth AlGaAs confinement layer, 7-fifth AlGaAs confinement layer, 8-sixth AlGaAs confinement layer, 9-first InAs quantum dot, 10-second InAs quantum dot, 11-first stress release layer, 12-second stress release layer, 13-first GaAs spacer layer, 14-second GaAs spacer layer, 15-seventh AlGaAs confinement layer, 16-eighth AlGaAs confinement layer, 17-third GaAs spacer layer, 18-first GaAs contact layer, 19-second GaAs contact layer. DETAILED DESCRIPTION

[0015] See also Figure 1 ,in Figure 1 This is a schematic diagram of the principle of superlattice epitaxial structure for lasers.

[0016] The utility model provides a super lattice epitaxial structure for a laser, comprising a GaAs substrate 1, a GaAs buffer layer 2, a first limiting unit, a second limiting unit, a third limiting unit, a fourth limiting unit, a contact unit, a first GaAs spacer layer 13, a first InAs quantum dot 9, a first stress release layer 11, a second GaAs spacer layer 14, a second InAs quantum dot 10, a second stress release layer 12 and a third GaAs spacer layer 17, wherein the first limiting unit comprises a first AlGaAs limiting layer 3 and a second AlGaAs limiting layer 4, the second limiting unit comprises a third AlGaAs limiting layer 5 and a fourth AlGaAs limiting layer 6, the third limiting unit comprises a fifth AlGaAs limiting layer 7 and a sixth AlGaAs limiting layer 8, the fourth limiting unit comprises a seventh AlGaAs limiting layer 15 and an eighth AlGaAs limiting layer 16, and the contact unit comprises a first GaAs contact layer 18 and a second GaAs contact layer 19.

[0017] The GaAs buffer layer 2 is grown on the upper surface of the GaAs substrate 1, the fourth restriction unit is grown on the upper surface of the GaAs buffer layer 2, the first restriction unit is grown on the upper surface of the fourth restriction unit, the third restriction unit is grown on the upper surface of the first restriction unit, the first GaAs spacer layer 13 is grown on the upper surface of the third restriction unit, the first InAs quantum dots 9 are grown on the upper surface of the first GaAs spacer layer 13, the first stress release layer 11 is grown on the upper surface of the first InAs quantum dots 9, and the first stress release layer 11 is grown on the upper surface of the first stress release layer 11. There is a second GaAs spacer layer 14, the second InAs quantum dots 10 are grown on the upper surface of the second GaAs spacer layer 14, the second stress release layer 12 is grown on the upper surface of the second InAs quantum dots 10, the third GaAs spacer layer 17 is grown on the upper surface of the second stress release layer 12, the third restriction unit is grown on the upper surface of the third GaAs spacer layer 17, the second restriction unit is grown on the upper surface of the third restriction unit, the fourth restriction unit is grown on the upper surface of the second restriction unit, and the contact unit is grown on the upper surface of the fourth restriction unit.

[0018] In this embodiment, the GaAs substrate 1 is an N+ doped 2-inch wafer, which is placed in the growth chamber after being baked at 190°C for 2 hours in the injection chamber and degassed at 420°C in the preparation chamber. The GaAs substrate 1 heater is heated to 400°C, the As baffle is opened, and the As beam current is opened to 1×10 -6 ~7×10 -6 Torr, continue to heat up to 670 ° C and maintain for 10 minutes for deoxidation treatment, then cool down to 620 ° C to grow the GaAs buffer layer 2 to 300 nm, Si doping 3×1018 / cm 3 The first limiting unit, the second limiting unit, the third limiting unit and the fourth limiting unit are doped with Si and Be respectively. In order to reduce carrier absorption, there are 150nm of no doping above and below. The first InAs quantum dot 9 is composed of five layers of InAs quantum dots. The quantum dots are surrounded by 5nm of InAs. 0.15 Ga 0.85 As the first stress release layer 11 covers, the emission wavelength is extended to about 1300nm, each layer of quantum dots is 50nm GaAs apart, and a 150nm GaAs contact unit is grown on the surface of the sample, and the P-type high doping 10 19 The growth temperature of the GaAs buffer layer 2, the contact unit, the first restriction unit, the second restriction unit, the third restriction unit and the fourth restriction unit is 620°C, the growth temperature of the first InAs quantum dot 9, the second InAs quantum dot 10, the first stress release layer 11, the second stress release layer 12, the first GaAs spacer layer 13 and the second GaAs spacer layer 14 is 490°C, and the optimized InAs / GaAs high-density quantum dots are grown by molecular beam epitaxy, and a monolithic integrated mode-locked ultrashort pulse laser with a light emission wavelength of 1.3μm is successfully developed, realizing multi-channel spatial technology integration, which can be used for an efficient and practical lower parametric conversion room temperature single-photon source.

[0019] The first GaAs spacer layer 13, the first InAs quantum dot 9, the first stress release layer 11, the second GaAs spacer layer 14, the second InAs quantum dot 10, the second stress release layer 12, and the third GaAs spacer layer 17 constitute an active area. The upper layer and the lower layer of the active area are each 1.5 μm AlGaAs confinement layer. The upper layer of the active area includes the seventh AlGaAs confinement layer 15, the first AlGaAs confinement layer 3, the second AlGaAs confinement layer 4, and the fifth AlGaAs confinement layer 7. The lower layer of the active area includes the sixth AlGaAs confinement layer 8, the third AlGaAs confinement layer 5, the fourth AlGaAs confinement layer 6, and the eighth AlGaAs confinement layer 16.

[0020] Furthermore, the first AlGaAs confinement layer 3 is grown on the upper surface of the fourth confinement unit, and the second AlGaAs confinement layer 4 is grown on the upper surface of the first AlGaAs confinement layer 3 .

[0021] In this embodiment, the first AlGaAs confinement layer 3 and the second AlGaAs confinement layer 4 are doped with Si.

[0022] Furthermore, the third AlGaAs confinement layer 5 is grown on the upper surface of the third confinement unit, and the fourth AlGaAs confinement layer 6 is grown on the upper surface of the third AlGaAs confinement layer 5 .

[0023] In this embodiment, the third AlGaAs confinement layer 5 and the fourth AlGaAs confinement layer 6 are doped with Be.

[0024] Furthermore, the fifth AlGaAs confinement layer 7 is grown on the upper surface of the second AlGaAs confinement layer 4, the first GaAs spacer layer 13 is grown on the upper surface of the fifth AlGaAs confinement layer 7, the sixth AlGaAs confinement layer 8 is grown on the upper surface of the third GaAs spacer layer 17, and the third AlGaAs confinement layer 5 is grown on the upper surface of the sixth AlGaAs confinement layer 8.

[0025] In this embodiment, the fifth AlGaAs confinement layer 7 and the sixth AlGaAs confinement layer 8 are non-doped in order to reduce carrier absorption.

[0026] Furthermore, the seventh AlGaAs confinement layer 15 is grown on the upper surface of the GaAs buffer layer 2, the first AlGaAs confinement layer 3 is grown on the upper surface of the seventh AlGaAs confinement layer 15, the eighth AlGaAs confinement layer 16 is grown on the upper surface of the fourth AlGaAs confinement layer 6, and the contact unit is grown on the upper surface of the eighth AlGaAs confinement layer 16.

[0027] In this embodiment, the seventh AlGaAs confinement layer 15 and the eighth AlGaAs confinement layer 16 are doped with Si and Be, respectively.

[0028] Furthermore, the first GaAs contact layer 18 is grown on the upper surface of the eighth AlGaAs confinement layer 16 , and the second GaAs contact layer 19 is grown on the upper surface of the first GaAs contact layer 18 .

[0029] In this embodiment, the first GaAs contact layer 18 and the second GaAs contact layer 19 are grown on the surface of the sample with a thickness of 150 nm, and the P-type highly doped layer 10 19The growth temperature of the GaAs buffer layer 2, the first GaAs contact layer 18, the second GaAs contact layer 19, the first layer restriction unit, the second layer restriction unit, the third layer restriction unit and the fourth layer restriction unit is 620°C, and the growth temperature of the first InAs quantum dot 9, the second InAs quantum dot 10, the first stress release layer 11, the second stress release layer 12, the first GaAs spacer layer 13 and the second GaAs spacer layer 14 is 490°C.

[0030] InAs quantum dot ultrashort pulse laser process preparation method:

[0031] (1) Cleaning the epitaxial wafer: In order to ensure that the device manufacturing process is not affected by the surface contaminants of the epitaxial wafer, this device is cleaned three times using trichloroethylene, acetone and ethanol. The specific steps are as follows: boil the trichloroethylene water bath for 10 minutes; boil the acetone water bath for 5 minutes; boil the ethanol water bath for 5 minutes; repeat the above steps for a total of three cycles, and finally rinse with deionized water for 1 minute, blow dry with a nitrogen gun, bake in an oven at 120°C for 10 minutes, and store in a nitrogen cabinet for later use.

[0032] (2) Photolithography and etching of strip mesas: Strip structures are widely used in laser structures and can effectively limit the area of ​​injected current to obtain higher current injection density. This device uses a strip width of 20μm and a strip length of 2150μm, including an InAs quantum dot ultrashort pulse laser gain region of 1800μm, an InAs quantum dot saturable absorption region of 300μm, and a 50μm isolation groove that isolates the two. Each device is vertically spaced 300nm, which is the width of the final cleaved device. The mesa is etched using wet etching, and the etching solution formula is H3PO3:H2O2:H2O=1:1:38 volume ratio. The etching rate is about 1.3nm / s at room temperature.

[0033] (3) Deposition of SiO2: SiO2 is deposited by PECVD to form a protective film, which also serves as an electrical insulating medium to prepare for the P-type electrode. The deposition thickness is 300nm.

[0034] (4) Photolithography of the upper electrode window: The silicon dioxide at the electrode window is removed by photolithography etching, and the silicon dioxide in other areas is retained. The etching solution is a buffered solution of hydrofluoric acid (BOE).

[0035] (5) Electron beam evaporation P electrode: The upper electrode of this device is a P-type electrode, made of Ti / Au alloy with a ratio of Large area evaporation electrode.

[0036] (6) Photolithography and etching of isolation grooves: The isolation grooves serve to isolate the gain region and saturable absorption region of the ultrashort pulse laser and must have good electrical insulation. Therefore, after making the P-type upper electrode, the metal electrode at the isolation groove needs to be etched away. A separate photolithography board with a width slightly larger than the design size is used to ensure that the metal electrode at the isolation groove is completely etched away.

[0037] (7) Substrate thinning and polishing: Since the substrate used for epitaxial growth is relatively thick (generally, the thickness of a GaAs substrate is about 350 μm), it is very difficult to obtain a single device of relatively small size through ordinary cleavage methods. Therefore, the substrate needs to be thinned. After thinning, the thickness of the epitaxial wafer is about 120 μm.

[0038] (8) Cleaning the epitaxial wafer: During the thinning and polishing process, the epitaxial wafer needs to be glued to the grinding tool with wax. The grinding process will cause contamination to the epitaxial wafer. After the grinding is completed, the epitaxial wafer is cleaned in three cycles using three organic solutions: trichloroethylene, acetone and anhydrous ethanol.

[0039] (9) Thermal evaporation N-type electrode: The N-type electrode is made by thermal evaporation method and is a mixture of Au / Ge / Ni with a thickness of about After the N-type click is made, the sample is placed in a N2 / H2 mixed atmosphere and alloyed at 445℃ for 1 minute.

[0040] (10) Cleavage packaging: Direct cleavage produces a natural cleavage surface to provide the laser's resonant cavity surface. Both sections are not coated with a reflective film. The final size of the cleaved laser is 2150μm long and 300μm wide. A single laser is sintered on a copper heat sink with the P-type electrode facing upward, and the electrode is led out by welding and set aside for testing.

[0041] The above disclosure is only a preferred embodiment of the present invention, and certainly cannot be used to limit the scope of rights of the present invention. Ordinary technicians in this field can understand that all or part of the processes of the above embodiment and equivalent changes made according to the claims of the present invention still fall within the scope covered by the utility model.

Claims

1. A superlattice epitaxial structure for a laser, characterized in that: The invention comprises a GaAs substrate, a GaAs buffer layer, a first limiting unit, a second limiting unit, a third limiting unit, a fourth limiting unit, a contact unit, a first GaAs spacer, a first InAs quantum dot, a first stress release layer, a second GaAs spacer, a second InAs quantum dot, a second stress release layer and a third GaAs spacer, wherein the GaAs buffer layer is grown on the upper surface of the GaAs substrate, the fourth limiting unit is grown on the upper surface of the GaAs buffer layer, the first limiting unit is grown on the upper surface of the fourth limiting unit, the third limiting unit is grown on the upper surface of the first limiting unit, the first GaAs spacer is grown on the upper surface of the third limiting unit, and the first GaAs spacer is grown on the upper surface of the first GaAs spacer. The first InAs quantum dots are grown on the upper surface of the first InAs quantum dots, the first stress release layer is grown on the upper surface of the first InAs quantum dots, the second GaAs spacer is grown on the upper surface of the first stress release layer, the second InAs quantum dots are grown on the upper surface of the second GaAs spacer, the second stress release layer is grown on the upper surface of the second InAs quantum dots, the third GaAs spacer is grown on the upper surface of the second stress release layer, the third restriction unit is grown on the upper surface of the third GaAs spacer, the second restriction unit is grown on the upper surface of the third restriction unit, the fourth restriction unit is grown on the upper surface of the second restriction unit, and the contact unit is grown on the upper surface of the fourth restriction unit.

2. The superlattice epitaxial structure for laser according to claim 1, characterized in that: The first confinement unit includes a first AlGaAs confinement layer and a second AlGaAs confinement layer. The first AlGaAs confinement layer is grown on the upper surface of the fourth confinement unit, and the second AlGaAs confinement layer is grown on the upper surface of the first AlGaAs confinement layer.

3. The superlattice epitaxial structure for laser according to claim 2, characterized in that: The second confinement unit includes a third AlGaAs confinement layer and a fourth AlGaAs confinement layer. The third AlGaAs confinement layer is grown on an upper surface of the third confinement unit, and the fourth AlGaAs confinement layer is grown on an upper surface of the third AlGaAs confinement layer.

4. The superlattice epitaxial structure for laser according to claim 3, characterized in that: The third confinement unit includes a fifth AlGaAs confinement layer and a sixth AlGaAs confinement layer, the fifth AlGaAs confinement layer is grown on the upper surface of the second AlGaAs confinement layer, the first GaAs spacer layer is grown on the upper surface of the fifth AlGaAs confinement layer, the sixth AlGaAs confinement layer is grown on the upper surface of the third GaAs spacer layer, and the third AlGaAs confinement layer is grown on the upper surface of the sixth AlGaAs confinement layer.

5. The superlattice epitaxial structure for laser according to claim 4, characterized in that: The fourth confinement unit includes a seventh AlGaAs confinement layer and an eighth AlGaAs confinement layer, the seventh AlGaAs confinement layer is grown on the upper surface of the GaAs buffer layer, the first AlGaAs confinement layer is grown on the upper surface of the seventh AlGaAs confinement layer, the eighth AlGaAs confinement layer is grown on the upper surface of the fourth AlGaAs confinement layer, and the contact unit is grown on the upper surface of the eighth AlGaAs confinement layer.

6. The superlattice epitaxial structure for laser according to claim 5, characterized in that: The contact unit includes a first GaAs contact layer and a second GaAs contact layer. The first GaAs contact layer is grown on the upper surface of the eighth AlGaAs confinement layer, and the second GaAs contact layer is grown on the upper surface of the first GaAs contact layer.

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