CN110768104A

CN110768104A - Long wavelength GaInNAs/InGaAs composite quantum dot vertical cavity surface emitting laser

Info

Publication number: CN110768104A
Application number: CN201911212035.0A
Authority: CN
Inventors: 黄珊珊; 黄辉廉; 文宏; 叶旺; 刘建庆
Original assignee: Zhongshan Dehua Chip Technology Co Ltd
Current assignee: Zhongshan Dehua Chip Technology Co Ltd
Priority date: 2019-12-02
Filing date: 2019-12-02
Publication date: 2020-02-07

Abstract

The invention discloses a long-wavelength GaInNAs/InGaAs composite quantum dot vertical cavity surface emitting laser, which comprises an n-type GaAs substrate, wherein an n-type GaAs buffer layer, an n-type DBR, a non-doped quantum dot active layer and a p-type DBR are sequentially arranged on the upper surface of the n-type GaAs substrate from bottom to top; the undoped GaInNAs/InGaAs composite quantum dot is internally provided with a GaInNAs quantum dot in a 3D island-shaped structure, the outer part of the undoped GaInNAs/InGaAs composite quantum dot is provided with an InGaAs coating layer, the stress between the GaInNAs quantum dot and the undoped GaAs barrier layer caused by lattice constant difference is buffered by adjusting the content of indium in the InGaAs coating layer, and the emission wavelength of the laser is controlled to reach 1.31-1.55 mu m by adjusting the content of nitrogen and indium in the GaInNAs quantum dot. The invention has the characteristics of lower threshold current, narrower spectral line width, higher power output and the like.

Description

Long wavelength GaInNAs/InGaAs composite quantum dot vertical cavity surface emitting laser

Technical Field

The invention relates to the technical field of semiconductor lasers, in particular to a long-wavelength GaInNAs/InGaAs composite quantum dot vertical cavity surface emitting laser.

Background

With the rapid development of the optical communication field, new optical active devices with low cost, high speed and low power consumption are being searched internationally. Among them, a light source having a lasing wavelength of 1.31/1.55 μm has become an important light source for medium-long distance and high-speed optical communication. Long wavelength Vertical Cavity Surface Emitting Lasers (VCSELs) have the advantages of occasional high efficiency with optical fibers, high modulation rates, and low power consumption. However, the development of GaInAsP/InP VCSELs has not progressed much in recent years, mainly because: 1) the conduction band edge deviation of the GaInAsP/InP material is small, the electronic limiting capability is poor, so that serious carrier leakage is caused, and the characteristic temperature of the device is only 50K; 2) the refractive index difference of GaInAsP/InP series materials is small, and the manufacture of a Distributed Bragg Reflector (DBR) with high reflectivity is very difficult; 3) there is severe non-radiative recombination and the current confinement structure is poorly capable.

Currently, the most practical long wavelength VCSEL is GaInNAs/GaAs VCESL, which has the following characteristics: 1) the characteristic temperature can reach 180-200K, and the high-temperature stability is achieved; 2) can be integrated with high-reflectivity AlAs/GaAs DBR; 3) GaAs is used as a substrate, the crystal quality, the processing technology of devices and integrated circuits are superior to that of InP, and the cost is low. By introducing N into InGaAs, the band gap of the GaInNAs can be expanded to a region of 1.3-1.55 μm corresponding to the wavelength. However, the difficulty in fabricating the GaInNAs/GaAs VCSEL is: when the gain wavelength of GaInNAs/GaAs is close to 1310 nm or 1550nm, the content of N in the material is increased, GaInNAs can not form mixed crystal with complete crystal form, phase splitting can occur, or other non-radiative trapping centers and defects can be formed, the quality of the material is greatly reduced, and the laser shows a threshold current density much higher than that of the traditional laser; therefore, to obtain high quality quantum hydrazine, it is better to select the content of N to be low, but to increase the peak wavelength of gain, the content of In must be increased, which results In the increase of the strain amount of quantum hydrazine, and the high strain GaInNAs/GaAs quantum hydrazine affects the reliability of the laser.

Disclosure of Invention

The invention aims to overcome the defects of the prior art and provide a long-wavelength GaInNAs/InGaAs composite quantum dot vertical cavity surface emitting laser, which adopts a GaInNAs/InGaAs composite quantum dot structure, can control the emitting wavelength of the laser to reach 1.31-1.55 mu m by changing the content of nitrogen and indium in the GaInNAs quantum dots, combines the advantages of a quantum dot superlattice structure, and obtains a high-quality undoped quantum dot active layer with GaInNAs/InGaAs composite quantum dots and a GaAs barrier layer by controlling the growth conditions. Compared with the traditional quantum hydrazine structure, the quantum dot active material enables the VCSEL to obtain excellent characteristics of lower threshold current, narrower spectral line width, higher power output and the like. Meanwhile, the optical quality degradation in the long wave range generated in the conventional quantum well structure can be prevented, and the emission wavelength generated when the GaInNAs quantum dots are subjected to heat treatment is prevented from moving toward the shorter wavelength range.

In order to achieve the purpose, the technical scheme provided by the invention is as follows: the long-wavelength GaInNAs/InGaAs composite quantum dot vertical cavity surface emitting laser comprises a GaAs substrate, wherein the GaAs substrate is an n-type single wafer, namely an n-type GaAs substrate, an n-type GaAs buffer layer, an n-type DBR, a non-doped quantum dot active layer and a p-type DBR are sequentially arranged on the upper surface of the n-type GaAs substrate from bottom to top according to a layered stack structure, an upper electrode is prepared on the p-type DBR, and a lower electrode is prepared on the lower surface of the n-type GaAs substrate; the undoped GaInNAs/InGaAs composite quantum dot is divided into an inner part and an outer part, the inner part of the undoped GaInNAs/InGaAs composite quantum dot is a GaInNAs quantum dot with a 3D island-shaped structure, the outer part of the undoped GaInNAs/InGaAs composite quantum dot is an InGaAs cladding layer, the InGaAs cladding layer wraps the GaInNAs quantum dot, stress caused by lattice constant difference between the GaInNAs quantum dot and the undoped GaAs barrier layer is buffered by adjusting the content of indium in the InGaAs cladding layer, and the emission wavelength of the laser is controlled to reach 1.31-1.55 mu m by adjusting the content of nitrogen and indium in the GaInNAs quantum dot.

Further, the GaInNAs quantum dots are grown by a strain self-assembly method, and a layer-island growth mode, namely an SK mode: when the band gap of the epitaxial layer is lower than the substrate, the epitaxial layer has large positive mismatch with the crystal lattice of the substrate and has small interface energy, the two-dimensional layer growth is carried out at the initial stage of the epitaxial layer, the two-dimensional layer is called as an infiltration layer, the epitaxial growth is changed from the two-dimensional layer growth into the three-dimensional island growth along with the increase of the thickness of the infiltration layer and the continuous accumulation of strain energy when the critical thickness is reached, the strain energy is partially released in a form of forming a 3D island, the islands do not contain dislocation, the size of the islands is regularly distributed, the diameter of the bottom is dozens of nanometers and is higher than a few nanometers, when the islands are surrounded by a material with large forbidden band width, current carriers in the islands are limited in three dimensions to form quantum dots, and the defect-free quantum dot material with uniform size and space distribution can.

Furthermore, the growth temperature of the GaInNAs quantum dots is 480-520 ℃, and the diameter of the GaInNAs quantum dots is 3-30 nm.

Furthermore, the growth temperature of the InGaAs coating layer is 480-520 ℃, and the thickness of the InGaAs coating layer is 3-30 nm.

Further, the undoped GaAs barrier layer has a thickness of 5nm to 50 nm.

Compared with the prior art, the invention has the following advantages and beneficial effects:

1) compared with a quantum hydrazine structure, the quantum dot and the quantum hydrazine structure have the advantage that the electron free movement dimension is reduced, so that the laser can obtain excellent characteristics of lower threshold current, narrower spectral line width, higher power output and the like.

2) The strain self-assembly technology can be used for preparing defect-free quantum dot materials with relatively uniform size and spatial distribution. The strain energy is partially released in a form of forming a 3D island, and the islands do not contain dislocation, so that the material quality problem and lattice mismatch defects brought by the traditional GaInNAs/GaAs quantum well structure are avoided.

3) GaInNAs requires low growth temperatures to enhance nitrogen incorporation, but low temperature growth will cause GaInNAs material to enter 3D growth mode, which is not good for the growth of quantum well structures, whereas the growth of quantum dot structures requires just low growth temperatures.

4) The InGaAs cladding layer is added on the quantum dot, so that the problem that the emission wavelength is shifted to a short wavelength range when the quantum dot is subjected to heat treatment can be prevented, and the InGaAs serving as a transition layer can improve the interface quality between the GaInNAs quantum dot and the undoped GaAs barrier layer.

Drawings

FIG. 1 is a schematic structural diagram of a long wavelength GaInNAs/InGaAs composite quantum dot VCSEL.

Detailed Description

The present invention will be further described with reference to the following specific examples.

As shown in fig. 1, the long wavelength GaInNAs/InGaAs composite quantum dot vertical cavity surface emitting laser according to the present embodiment includes an n-type GaAs substrate 1, an n-type GaAs buffer layer 2, an n-type DBR 3, an undoped quantum dot active layer 4, and a p-type DBR 5 are sequentially disposed on an upper surface of the n-type GaAs substrate 1 from bottom to top in a layered stacked structure, an upper electrode 6 is disposed on the p-type DBR 5, and a lower electrode 7 is disposed on a lower surface of the n-type GaAs substrate 1; wherein the non-doped quantum dot active layer 4 is formed by mixing non-doped GaInNAs/InGaAs composite quantum dots 41 and a non-doped GaAs barrier layer 42, the thickness of the non-doped GaAs barrier layer is about 5nm to 50nm, the non-doped GaInNAs/InGaAs composite quantum dot 41 is divided into an inner part and an outer part, inside the quantum dots 411 of GaInNAs in 3D island structure, outside the quantum dots 412 of InGaAs cladding layer, the growth temperature of the GaInNAs quantum dots 411 is 480-520 ℃, the diameter is about 3-30 nm, the growth temperature of the InGaAs coating layer is 480-520 ℃, the thickness is about 3-30 nm, the InGaAs cladding layer 412 cladds the GaInNAs quantum dots 411, the stress caused by the difference in lattice constant between the GaInNAs quantum dots 411 and the undoped GaAs barrier layer 42 is buffered by adjusting the indium content in the InGaAs cladding layer 412, the emission wavelength of the laser is controlled to reach 1.31 to 1.55 μm by adjusting the content of nitrogen and indium in the GaInNAs quantum dots 411.

The GaInNAs quantum dots 411 are grown by a strain self-assembly method, and a layer-island (SK) growth mode is utilized: when the band gap of the epitaxial layer is lower than the substrate, and has larger positive mismatch with the substrate crystal lattice, and has smaller interface energy, the two-dimensional layer growth is carried out at the initial stage of the epitaxial layer, the two-dimensional layer is called as an infiltration layer, the epitaxial growth is changed from the two-dimensional layer growth into the three-dimensional island growth when the critical thickness (usually only a few molecular layers) is reached along with the increase of the thickness of the infiltration layer and the continuous accumulation of strain energy, because the strain energy is partially released in the form of forming 3D islands, the islands do not contain dislocation, the size of the islands has certain distribution, the diameter of the bottom is generally dozens of nanometers and about a few nanometers, when the islands are surrounded by the material with large forbidden band width, the current carriers in the islands are limited in three dimensions to form quantum dots, and the defect-free quantum dot material with uniform size and spatial distribution can be prepared by utilizing the strain self-, lowering the growth temperature, increasing the growth rate and lowering the V/III ratio allows the growth mode to occur earlier, favoring the growth of quantum dots, and in addition, lowering the growth temperature of GaInNAs favors the incorporation of N.

Generally, an upper cover layer needs to be grown on the quantum dots at a temperature higher than 650 ℃, and an annealing effect with adverse effect is generated on the quantum dots, so that severe blue shift and spectral line broadening are caused, and the device is difficult to operate under a long wave. Growing a thin InGaAs cladding layer on the GaInNAs island structure at the same temperature can prevent the problem of the emission wavelength shifting to the short wavelength range that occurs when being thermally treated, and InGaAs as a transition layer can improve the interface quality between the GaInNAs quantum dots and the undoped GaAs barrier layer.

The following is a specific process for fabricating the long wavelength GaInNAs/InGaAs composite quantum dot vertical cavity surface emitting laser in this embodiment, and the case is as follows:

firstly, a 4-inch n-type GaAs single chip is taken as a substrate, then an n-type GaAs buffer layer, an n-type DBR and an undoped GaAs barrier layer are sequentially grown on the upper surface of the GaAs substrate by adopting a Metal Organic Chemical Vapor Deposition (MOCVD) technology or a Molecular Beam Epitaxy (MBE) technology, then an undoped GaInNAs/InGaAs composite quantum dot is manufactured by using a layer-island (SK) growth mode strain self-assembly growth quantum dot method, then a p-type DBR is grown, and finally contact electrodes are prepared at two ends of a laser, so that the preparation of the long-wavelength GaInNAs/InGaAs composite quantum dot vertical cavity surface emitting laser can be completed.

In summary, the invention fully combines the characteristics of the GaInNAs material and the quantum dot structure, not only can avoid the material quality problem and the lattice mismatch defect brought by the traditional GaInNAs/GaAs quantum well structure, but also can prevent the problem that the emission wavelength moves to a short wavelength range when the GaInNAs material is thermally treated, and the InGaAs is taken as a transition layer can improve the interface quality between the GaInNAs quantum dot and the non-doped GaAs barrier layer, thereby obtaining excellent characteristics of lower threshold current, narrower spectral line width, higher power output and the like, and being worthy of popularization.

The above-mentioned embodiments are merely preferred embodiments of the present invention, and the scope of the present invention is not limited thereto, so that the changes in the shape and principle of the present invention should be covered within the protection scope of the present invention.

Claims

1. The long wavelength GaInNAs/InGaAs composite quantum dot vertical cavity surface emitting laser comprises a GaAs substrate and is characterized in that: the GaAs substrate is an n-type single chip, namely an n-type GaAs substrate, an n-type GaAs buffer layer, an n-type DBR, a non-doped quantum dot active layer and a p-type DBR are sequentially arranged on the upper surface of the n-type GaAs substrate from bottom to top according to a layered superposed structure, an upper electrode is prepared on the p-type DBR, and a lower electrode is prepared on the lower surface of the n-type GaAs substrate; the undoped GaInNAs/InGaAs composite quantum dot is divided into an inner part and an outer part, the inner part of the undoped GaInNAs/InGaAs composite quantum dot is a GaInNAs quantum dot with a 3D island-shaped structure, the outer part of the undoped GaInNAs/InGaAs composite quantum dot is an InGaAs cladding layer, the InGaAs cladding layer wraps the GaInNAs quantum dot, stress caused by lattice constant difference between the GaInNAs quantum dot and the undoped GaAs barrier layer is buffered by adjusting the content of indium in the InGaAs cladding layer, and the emission wavelength of the laser is controlled to reach 1.31-1.55 mu m by adjusting the content of nitrogen and indium in the GaInNAs quantum dot.

2. The long wavelength GaInNAs/InGaAs composite quantum dot vertical cavity surface emitting laser of claim 1, wherein: the GaInNAs quantum dots are grown by adopting a strain self-assembly method, and a layer-island growth mode, namely an SK mode is utilized: when the band gap of the epitaxial layer is lower than the substrate, the epitaxial layer has large positive mismatch with the crystal lattice of the substrate and has small interface energy, the two-dimensional layer growth is carried out at the initial stage of the epitaxial layer, the two-dimensional layer is called as an infiltration layer, the epitaxial growth is changed from the two-dimensional layer growth into the three-dimensional island growth along with the increase of the thickness of the infiltration layer and the continuous accumulation of strain energy when the critical thickness is reached, the strain energy is partially released in a form of forming a 3D island, the islands do not contain dislocation, the size of the islands is regularly distributed, the diameter of the bottom is dozens of nanometers and is higher than a few nanometers, when the islands are surrounded by a material with large forbidden band width, current carriers in the islands are limited in three dimensions to form quantum dots, and the defect-free quantum dot material with uniform size and space distribution can.

3. The long wavelength GaInNAs/InGaAs composite quantum dot vertical cavity surface emitting laser of claim 1, wherein: the growth temperature of the GaInNAs quantum dots is 480-520 ℃, and the diameter of the GaInNAs quantum dots is 3-30 nm.

4. The long wavelength GaInNAs/InGaAs composite quantum dot vertical cavity surface emitting laser of claim 1, wherein: the growth temperature of the InGaAs coating layer is 480-520 ℃, and the thickness of the InGaAs coating layer is 3-30 nm.

5. The long wavelength GaInNAs/InGaAs composite quantum dot vertical cavity surface emitting laser of claim 1, wherein: the thickness of the non-doped GaAs barrier layer is 5nm to 50 nm.