A high-power high-speed direct modulation quantum dot laser and a preparation method thereof

Abstract

The application discloses a kind of high-power high-speed direct modulation quantum dot laser and preparation method thereof, N-type GaAs substrate is sent into MBE chamber to remove the surface oxidation layer, N-type GaAs contact layer is sequentially grown on the N-type GaAs substrate of surface oxidation layer removal, N-type AlGaAs restriction layer, first undoped GaAs waveguide layer, multilayer quantum dot active region, second undoped GaAs waveguide layer, P-type AlGaAs restriction layer, P-type GaAs contact layer, to obtain high-power high-speed direct modulation quantum dot laser from this. The method greatly improves the number of quantum dot layers by precisely controlling the growth conditions of quantum dots and the thickness of the spacer layer, while controlling the thickness of the quantum dot active region, thereby increasing the differential gain of quantum dots, carrier injection efficiency and greatly improving the direct modulation rate and light output power of quantum dot laser.

Description

Technical Field

[0001] This invention relates to the field of semiconductor material epitaxial growth technology, and in particular to a high-power, high-speed, directly modulated quantum dot laser and its fabrication method. Background Technology

[0002] With the rapid development of 5G / 6G communication and data center optical interconnect technologies, optical communication systems have placed urgent demands on their core light source, namely lasers, for higher bandwidth, lower power consumption, stronger temperature stability, and lower noise. These performance indicators directly determine the transmission rate, noise margin, and energy efficiency of optical communication systems. Among them, the O-band (1260-1360nm), with its low dispersion characteristics, has become the preferred band for short-distance high-speed optical interconnects.

[0003] InAs (Indium Arsenide) quantum dot lasers exhibit significant advantages due to their three-dimensional quantum confinement effect: ultra-low threshold current density, high differential gain, wide gain spectrum, and excellent high-temperature stability. These characteristics make them highly promising for high-efficiency optical communication, silicon-based photonics integration, and high-temperature applications. Compared to solutions requiring external modulators, high-power, directly modulated lasers are particularly suitable for mass production and short-distance optical communication applications due to their low cost, small size, and low power consumption. However, the current direct modulation bandwidth of quantum dot lasers still falls short of the stringent requirements for ultra-high-speed modulation in 5G / 6G communication and data centers, becoming a key bottleneck limiting their widespread application.

[0004] The modulation rate bottleneck of quantum dot lasers mainly stems from limitations in material growth kinetics and carrier transport mechanisms:

[0005] (1) Material growth uniformity challenge: During the growth of MBE (Molecular Beam Epitaxy) or MOCVD (Metal-organic Chemical Vapor Deposition), the size uniformity and density of quantum dots are difficult to control precisely, which leads to uneven distribution of local state density, causing thermal escape of charge carriers and nonradiative recombination assisted by wet layer, reducing device efficiency;

[0006] (2) Carrier transport problem in multilayer structures: The modulation rate of quantum dot lasers is closely related to the differential gain of the active region. Traditionally, the differential gain and total gain are improved by increasing the number of quantum dot layers. However, in order to isolate the interlayer stress transmission, multilayer quantum dot structures require a thick GaAs (gallium arsenide) spacer layer. A thick spacer layer will seriously hinder the longitudinal transport efficiency of carriers, which will limit the improvement of the direct modulation rate.

[0007] Therefore, by using innovative quantum dot epitaxial growth technology to systematically solve the problems of quantum dot size / density uniformity control, strain management optimization, and efficient carrier transport, thereby significantly improving direct modulation bandwidth while maintaining high output power, it has become the core key to promoting the breakthrough development of quantum dot lasers in the field of high-speed communication. Summary of the Invention

[0008] The purpose of this invention is to improve the carrier injection efficiency and increase the output power and direct modulation rate of quantum dot lasers by optimizing the epitaxial growth method of the InAs quantum dot active region, thereby increasing the number of quantum dot layers while controlling the thickness of the GaAs spacer layer and the total thickness of the quantum dot active region.

[0009] To achieve the above objectives, the present invention provides a method for fabricating a high-power, high-speed, directly modulated quantum dot laser, the method comprising the following steps:

[0010] S1. The N-type GaAs substrate is fed into the MBE cavity, and the oxide layer on the surface of the N-type GaAs substrate is removed by the high temperature inside the MBE cavity.

[0011] S2. Grow an N-type GaAs contact layer on an N-type GaAs substrate with the surface oxide layer removed;

[0012] S3. Grow an N-type AlGaAs confinement layer on the N-type GaAs contact layer;

[0013] S4. Epitaxially grow the first undoped GaAs waveguide layer on the N-type AlGaAs confinement layer;

[0014] S5. Epitaxially grow a multilayer quantum dot active region on the first undoped GaAs waveguide layer;

[0015] S6. Epitaxially grow a second undoped GaAs waveguide layer on the active region of multilayer quantum dots;

[0016] S7. Grow a P-type AlGaAs confinement layer on the second undoped GaAs waveguide layer;

[0017] S8. A P-type GaAs contact layer is grown on the P-type AlGaAs confinement layer to obtain a high-power, high-speed, directly modulated quantum dot laser.

[0018] Preferably, step S1 is implemented by: sending the N-type GaAs substrate into an MBE cavity at a temperature between 500-700°C for high-temperature deoxidation treatment to remove the oxide layer on the surface of the N-type GaAs substrate.

[0019] Preferably, step S2 is specifically implemented as follows: controlling the temperature inside the MBE cavity between 500-700℃, epitaxially growing an N-type GaAs contact layer with a thickness of 300nm on an N-type GaAs substrate with the surface oxide layer removed, the GaAs growth rate being 0.1–1ML / s, the impurity being Si, and the doping concentration being 1×10⁻⁶. 18 –2×10 19 cm -3 between.

[0020] Preferably, step S3 is specifically implemented as follows: controlling the temperature inside the MBE cavity between 550-700℃, and growing an N-type Al layer with a thickness of 1-1.5µm on the N-type GaAs contact layer. x Ga 1-x As the confinement layer, Al x Ga 1-x The growth rate of As is 0.1–1 mL / s, the value of x ranges from 0.2 to 0.5, the impurity is Si, and the doping concentration is 5 × 10⁻⁶. 17 –1×10 19 cm -3 between.

[0021] Preferably, step S4 is specifically implemented by controlling the temperature inside the MBE cavity between 500-700℃, in N-type Al x Ga 1-x An undoped GaAs waveguide layer with a thickness of 30-50 nm is epitaxially grown on the As confinement layer at a growth rate of 0.1-1 mL / s.

[0022] Preferably, the multilayer quantum dot active region in step S5 includes several active regions and several graded active regions. The specific implementation of S5 is as follows:

[0023] S51, preset the total number of growth layers n in the quantum dot active region, the number of growth layers m in the active region, and the number of growth layers nm in the gradient active region;

[0024] S52. On the first undoped GaAs waveguide layer, m active regions are epitaxially grown using a fixed quantum dot growth method, with each active region having a thickness of 22-28 nm.

[0025] S53. Starting from the (m+1)th layer, the quantum dot growth temperature, As / In ratio, and P-type GaAs are adjusted using gradient control. z P 1-z The growth method of z in the capping layer involves epitaxially growing a gradient active region layer by layer on the m-layer active region until the total number of grown layers of the gradient active region reaches nm layers, thereby obtaining a multilayer quantum dot active region with a total thickness ≤350nm.

[0026] Preferably, the first active region in the m-layer active region in step S52 is specifically implemented as follows:

[0027] S521. Control the temperature inside the MBE cavity between 400-500℃, and epitaxially grow an undoped In layer with a thickness of 1-2nm on the first undoped GaAs waveguide layer. y Ga 1-y As the impregnation layer, the growth rate is 0.1-1 mL / s, and the value of y ranges from 0.1 to 0.16.

[0028] S522. Control the temperature inside the MBE cavity between 400-500℃, and control the As:In ratio to be 10-30, in the absence of In doping. y Ga 1-y N-type doped quantum dots are epitaxially grown in the As wetted layer, with Si as the impurity.

[0029] S523. Control the temperature inside the MBE cavity between 400-500℃, and epitaxially grow an undoped In layer with a thickness of 1-3nm on the N-type doped quantum dots. y Ga 1-y As capping layer, growth rate is 0.1-1 mL / s, and y ranges from 0.15 to 0.2;

[0030] S524, in undoped In y Ga 1-y The first undoped GaAs capping layer is epitaxially grown on the As capping layer;

[0031] S525. Control the temperature inside the MBE cavity between 550-700℃, and epitaxially grow a 5-10nm thick P-type GaAs layer on the first undoped GaAs capping layer. z P 1-z The cap layer has a growth rate of 0.1-1 mL / s, a z value ranging from 0.05 to 0.1, is p-type doped with Be as the dopant element, and has a doping concentration of 8-15 holes / quantum dots.

[0032] S526. Control the temperature inside the MBE cavity between 550-700℃ in P-type GaAs. z P 1-z A second undoped GaAs capping layer with a thickness of 1-5 nm is epitaxially grown on the capping layer at a growth rate of 0.1-1 mL / s, thereby obtaining a first active region layer with a thickness of 22-28 nm.

[0033] Preferably, step S7 is specifically implemented as follows: controlling the temperature inside the MBE cavity between 550-700℃, and epitaxially growing a P-type Al layer with a thickness of 500-1500nm on the second undoped GaAs waveguide layer. x Ga1-x As confinement layer, growth rate 0.1-1 mL / s, x 0.2-0.5, doping concentration 5 × 10⁻⁶ 17 –1×10 19 cm -3 The impurity is Be.

[0034] Preferably, step S8 is specifically implemented by controlling the temperature inside the MBE cavity between 450-550℃, in the P-type Al x Ga 1-x A p-type GaAs contact layer with a thickness of 300-500 nm is epitaxially grown on the As confinement layer at a growth rate of 0.1-1 mL / s and a doping concentration of 1 × 10⁻⁶. 18 –5×10 19 cm -3 The impurity is Be.

[0035] In another aspect, the present invention provides a high-power, high-speed, directly modulated quantum dot laser, which is fabricated using the fabrication method for high-power, high-speed, directly modulated quantum dot lasers described above.

[0036] In this invention, an N-type GaAs substrate is fed into an MBE cavity, and the oxide layer on its surface is removed using the high temperature within the MBE cavity. On the oxide-free N-type GaAs substrate, an N-type GaAs contact layer, an N-type AlGaAs confinement layer, a first undoped GaAs waveguide layer, a multilayer quantum dot active region, a second undoped GaAs waveguide layer, a P-type AlGaAs confinement layer, and a P-type GaAs contact layer are sequentially grown, thereby obtaining a high-power, high-speed, directly modulated quantum dot laser. This method, by controlling the growth conditions of the quantum dots and the thickness of the spacer layer, significantly increases the number of quantum dot layers while controlling the thickness of the active region, thereby increasing the differential gain and carrier injection efficiency of the quantum dots and greatly improving the output power and direct modulation rate of the quantum dot laser. Attached Figure Description

[0037] Figure 1 This is a flowchart of a method for fabricating a high-power, high-speed, directly modulated quantum dot laser according to the present invention;

[0038] Figure 2 This is a schematic diagram of the structure of a high-power, high-speed, directly modulated quantum dot laser according to the present invention;

[0039] Figure 3 This is a schematic diagram of the structure of each active region in this invention;

[0040] Figure 4 This is a comparison diagram of the effects of no doping and N-type doping on the luminescence properties of quantum dots in one embodiment of the present invention. Detailed Implementation

[0041] To enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings.

[0042] Figure 1 The flowchart of a method for fabricating a high-power, high-speed, directly modulated quantum dot laser proposed in this invention is shown. Figure 2 A schematic diagram of the structure of the high-power, high-speed, directly modulated quantum dot laser proposed in this invention is shown.

[0043] In one embodiment, a method for fabricating a high-power, high-speed, directly modulated quantum dot laser specifically includes the following steps:

[0044] S1. The N-type GaAs substrate is fed into the MBE cavity, and the oxide layer on the surface of the N-type GaAs substrate is removed by the high temperature inside the MBE cavity.

[0045] S2. Grow an N-type GaAs contact layer on an N-type GaAs substrate with the surface oxide layer removed;

[0046] S3. Grow an N-type AlGaAs confinement layer on the N-type GaAs contact layer;

[0047] S4. Epitaxially grow the first undoped GaAs waveguide layer on the N-type AlGaAs confinement layer;

[0048] S5. Epitaxially grow a multilayer quantum dot active region on the first undoped GaAs waveguide layer;

[0049] S6. Epitaxially grow a second undoped GaAs waveguide layer on the active region of multilayer quantum dots;

[0050] S7. Grow a P-type AlGaAs confinement layer on the second undoped GaAs waveguide layer;

[0051] S8. A P-type GaAs contact layer is grown on the P-type AlGaAs confinement layer to obtain a high-power, high-speed, directly modulated quantum dot laser.

[0052] Specifically, the substrate can be an N-type substrate or a semi-insulating substrate, such as N-type GaAs (gallium arsenide), semi-insulating (SI) type, and Si (silicon) substrates. Taking an N-type GaAs substrate as an example, the N-type GaAs substrate is placed into an MBE cavity, and the oxide layer on the surface of the N-type GaAs substrate is removed using the high temperature inside the MBE cavity. On the N-type GaAs substrate with the surface oxide layer removed, an N-type GaAs contact layer, an N-type AlGaAs confinement layer, a first undoped GaAs waveguide layer, a multilayer quantum dot active region, a second undoped GaAs waveguide layer, a P-type AlGaAs confinement layer, and a P-type gallium arsenide contact layer are grown sequentially.

[0053] In one embodiment, step S1 is specifically implemented by: sending the N-type GaAs substrate into an MBE cavity at a temperature between 500-700°C for high-temperature deoxidation treatment to remove the oxide layer on the surface of the N-type GaAs substrate.

[0054] Specifically, an N-type GaAs substrate is fed into an MBE cavity, and the oxide layer on the surface of the N-type GaAs substrate is removed by using the high temperature (500-700℃) inside the MBE cavity.

[0055] In one embodiment, step S2 is specifically implemented as follows: controlling the temperature inside the MBE cavity between 500-700℃, epitaxially growing an N-type GaAs contact layer with a thickness of 300nm on an N-type GaAs substrate with the surface oxide layer removed, the GaAs growth rate being 0.1–1ML / s (i.e., single atomic layer / second), the impurity being Si, and the doping concentration being 1×10⁻⁶. 18 –2×10 19 cm -3 between.

[0056] Specifically, a 300 nm thick GaAs contact layer is epitaxially grown on an N-type GaAs substrate with the surface oxide layer removed at a growth rate of 0.1-1 mL / s and a doping concentration of 1 × 10⁻⁶. 18 –2×10 19 cm -3 The doping method is N-type doping (N-type doping is Si doping), and the growth temperature is between 500-700℃.

[0057] In one embodiment, step S3 is specifically implemented as follows: controlling the temperature inside the MBE cavity between 550-700℃, and growing an N-type Al layer with a thickness of 500nm-1.5µm on the N-type GaAs contact layer. x Ga 1-x As the confinement layer, Al x Ga 1-x The growth rate of As is 0.1–1 mL / s, the value of x ranges from 0.2 to 0.5, the impurity is Si, and the doping concentration is 5 × 10⁻⁶. 17 –1×10 19 cm -3 between.

[0058] Specifically, an N-type Al layer with a thickness of 500 nm to 1.5 µm is epitaxially grown on the N-type GaAs contact layer. x Ga 1-x As confinement layer, growth rate is 0.1-1 mL / s, x value is between 0.2-0.5, doping concentration is 5 × 10⁻⁶. 17 –1×10 19 cm -3The growth temperature is between 550-700℃.

[0059] In one embodiment, step S4 is specifically implemented as follows: controlling the temperature inside the MBE cavity between 500-700℃, in N-type Al x Ga 1-x An undoped GaAs waveguide layer with a thickness of 30-50 nm is epitaxially grown on the As confinement layer at a growth rate of 0.1-1 mL / s.

[0060] Specifically, in N-type Al x Ga 1-x An undoped GaAs waveguide layer with a thickness of 30-50 nm is epitaxially grown on the As confinement layer at a growth rate of 0.1-1 mL / s and a growth temperature of 500-700 °C.

[0061] In one embodiment, the multilayer quantum dot active region in step S5 includes several active regions and several gradient active regions. The specific implementation of S5 is as follows:

[0062] S51. Preset the total number of growth layers n in the active region of quantum dots, the number of growth layers m in the active region, and the number of growth layers nm in the gradient active region.

[0063] S52. On the first undoped GaAs waveguide layer, m (m < n) active regions are epitaxially grown using a fixed quantum dot growth method, with each active region having a thickness of 22-28 nm.

[0064] Further, see Figure 3 The specific implementation method of the first active region in the m-layer active region in step S52 is as follows:

[0065] S521. Control the temperature inside the MBE cavity between 400-500℃, and epitaxially grow an undoped In layer with a thickness of 1-2nm on the first undoped GaAs waveguide layer. y Ga 1-y As the impregnation layer, the growth rate is 0.1-1 mL / s, and the value of y ranges from 0.1 to 0.16.

[0066] S522. Control the temperature inside the MBE cavity between 400-500℃, and control the As:In ratio to be 10-30, in the absence of In doping. y Ga 1-y N-type doped quantum dots are epitaxially grown in an As impregnation layer, with Si as the dopant.

[0067] Specifically, the temperature inside the MBE cavity is controlled between 400-500℃, and the As:In ratio is controlled at 10-30. First, in undoped In... y Ga 1-yQuantum dots are epitaxially grown in an As-impregnated layer for 11-15 seconds. Then, in an As-rich environment, the In baffle is opened and held for 0.3-0.5 seconds before being closed. The Si baffle is then opened and held for 0.5-1 seconds before being closed. The quantum dots are then N-type doped with a doping concentration of 0.4-1.2 electrons / quantum dot. The total growth time of the quantum dots is controlled at 18-20 seconds, thus obtaining N-type doped quantum dots.

[0068] S523. Control the temperature inside the MBE cavity between 400-500℃, and epitaxially grow an undoped In layer with a thickness of 1-3nm on the N-type doped quantum dots. y Ga 1-y As capping layer, growth rate is 0.1-1 mL / s, and y ranges from 0.15 to 0.2.

[0069] S524, in undoped In y Ga 1-y The first undoped GaAs capping layer is epitaxially grown on the As capping layer.

[0070] Specifically, the temperature inside the MBE cavity is controlled between 400-500℃, in the presence of undoped In. y Ga 1-y A low-temperature undoped GaAs capping layer with a thickness of 5-10 nm is epitaxially grown on the As capping layer; the pressure of As is controlled at 1×10⁻⁶. -5 –2×10 -5 Between mbar, the temperature inside the MBE cavity is raised to between 550-700℃, and a high-temperature undoped GaAs capping layer with a thickness of 5-10nm is epitaxially grown on the low-temperature undoped GaAs capping layer. The low-temperature undoped GaAs capping layer and the high-temperature undoped GaAs capping layer together constitute the first undoped GaAs capping layer.

[0071] S525. Control the temperature inside the MBE cavity between 550-700℃, and epitaxially grow a 5-10nm thick P-type GaAs layer on the first undoped GaAs capping layer. z P 1-z The capping layer has a growth rate of 0.1-1 mL / s, a z value range of 0.05-0.1, a p-type doping mode, a be-type doping element, and a doping amount of 8-15 holes / quantum dots.

[0072] S526. Control the temperature inside the MBE cavity between 550-700℃ in P-type GaAs. z P 1-z A second undoped GaAs capping layer with a thickness of 1-5 nm is epitaxially grown on the capping layer at a growth rate of 0.1-1 mL / s, thereby obtaining a first active region layer with a thickness of 22-28 nm.

[0073] The growth process, from S521 to S526, is repeated m times to obtain m active regions. For example, when m=6, the above process is repeated 6 times to obtain 6 active regions.

[0074] S53. Starting from the (m+1)th layer, the quantum dot growth temperature, As / In ratio, and P-type GaAs are adjusted using gradient control. z P 1-z The growth method of z in the capping layer is to epitaxially grow the gradient active region layer by layer on the m active region layer until the total number of growth layers of the gradient active region reaches nm layers, thereby obtaining a multilayer quantum dot active region with a total thickness of less than or equal to 350 nm.

[0075] Specifically, after obtaining 6 active regions through 6 cycles of growth, it was found that continuing to grow the 7th quantum dot layer resulted in vertical coupling of the quantum dots. This vertical coupling manifested as a decrease in quantum dot density, a sharp increase in quantum dot size and emission wavelength, and a significant decline in quantum dot uniformity, leading to a rapid broadening of the half-width at half-maximum (WHM). Therefore, from the 7th layer to the nth layer, while keeping other growth conditions constant, the quantum dot growth temperature, As / In ratio, and P-type GaAs were gradually adjusted. z P 1-z The proportion of z in the capping layer is as follows: for each additional quantum dot active region layer, the growth temperature decreases by 2-5℃, the As / In ratio increases by 2-6, and the growth is P-type GaAs. z P 1-z The proportion of z in the capping layer is 0.1 + (nm) × 0.05;

[0076] For example, if the As / In ratio is controlled at 30 during the production of the first six active layers, and starting from the growth of the 7th gradient active layer, the As / In ratio of each gradient active layer increases by 5, then the As / In ratio of the nth gradient active layer is (n-6)×5+30; if the growth temperature of the first six active layers is 460℃, then the temperature from the 7th gradient active layer to the nth gradient active layer is 460℃-(n-6)×2℃; starting from the 7th gradient active layer, the As / In ratio of P-type GaAs is gradually increased. z P 1-z The proportion of z in each layer is specifically increased by 0.1 for each layer, that is, from the 7th layer to the nth layer of the graded active region, the proportion of p-type GaAs in each graded active region is... z P 1-z The proportion of z in the layer is 0.1 + (n-6) × 0.05. By increasing the proportion of phosphorus, stress transmission is controlled, which greatly suppresses the transmission of stress to the upper layer of the gradual active region.

[0077] The main purpose of the above approach is to force quantum dots to undergo random nucleation growth rather than increase the existing quantum dot size by suppressing the drift distance of As during quantum dot nucleation, thereby suppressing the growth of undoped In in the spacer layer (i.e., the undoped In in each active region). y Ga 1-y As capping layer, first undoped GaAs capping layer, p-type GaAs z P 1-z The stress transmission problem caused by the capping layer (second undoped GaAs capping layer) is prevented from forming columnar quantum dot stacks.

[0078] Based on the above growth conditions, the total number of active layers in the multilayer quantum dot is controlled between 10 and 15 layers to maintain the total active region thickness between 300 and 350 nm.

[0079] See Figure 4 , Figure 4 This is a comparison diagram showing the effect of no doping and N-type doping on the luminescence properties of quantum dots in one embodiment of the present invention. Figure 4 It can be seen that the above method optimizes the quantum dot density, uniformity, photoluminescence intensity of a single layer of quantum dots, and the total number of quantum dot layers. It can improve the differential gain of quantum dots, thereby increasing the linewidth broadening factor of quantum dots, increasing the output power and direct modulation rate of quantum dot lasers.

[0080] In one embodiment, step S7 is specifically implemented as follows: controlling the temperature inside the MBE cavity between 550-700℃, and epitaxially growing a P-type Al layer with a thickness of 500-1500nm on the second undoped GaAs waveguide layer. x Ga 1-x As confinement layer, growth rate 0.1-1 mL / s, x 0.2-0.5, doping concentration 5 × 10⁻⁶ 17 –1×10 19 cm -3 The impurity is Be.

[0081] Specifically, while keeping the temperature constant, a second undoped GaAs waveguide layer is epitaxially grown on the active region of the multilayer quantum dot at a growth rate of 0.1-1 mL / s. Then, a p-type Al layer with a thickness of 500-1500 nm is epitaxially grown on the second undoped GaAs waveguide layer. x Ga 1-x As the confinement layer, Al x Ga 1-x The growth rate of As is 0.1-1 mL / s, x is 0.2-0.5, and the doping concentration is 5 × 10⁻⁶. 17 –1×10 19 cm -3 The growth temperature is 550-700℃, and the doping method is beryllium (Be) doping.

[0082] In one embodiment, step S8 is specifically implemented by controlling the temperature inside the MBE cavity between 450-550℃, in the P-type Al x Ga 1-x A p-type GaAs contact layer with a thickness of 300-500 nm is epitaxially grown on the As confinement layer at a growth rate of 0.1-1 mL / s and a doping concentration of 1 × 10⁻⁶. 18 –5×10 19 cm -3 The impurity is Be.

[0083] Specifically, in P-type Al x Ga 1-x A 300-500 nm thick p-type GaAs contact layer is epitaxially grown outside the As confinement layer at a growth rate of 0.1-1 mL / s, with a p-type doping concentration of 1 × 10⁻⁶. 18 -5×10 19 cm -3 The growth temperature is 450-550℃.

[0084] The above-mentioned method for fabricating high-power, high-speed, directly modulated quantum dot lasers, by precisely controlling the growth conditions of quantum dots and the thickness of the spacer layer, can greatly increase the number of quantum dot layers while controlling the thickness of the active region of the quantum dots, thereby increasing the differential gain and carrier injection efficiency of the quantum dots and greatly improving the direct modulation rate of the quantum dot laser.

[0085] In one embodiment, a high-power, high-speed, directly modulated quantum dot laser is fabricated using the fabrication method for high-power, high-speed, directly modulated quantum dot lasers described above.

[0086] Furthermore, in this invention, the epitaxial fabrication tool can be replaced by metal-organic chemical vapor deposition (MOCVD). However, quantum dot crystals prepared using MOCVD have poor quality. Additionally, the N-type gallium arsenide substrate in this solution can be replaced by a semi-insulating GaAs substrate or a Si substrate. If epitaxy is performed on a Si substrate, a GaAs / AlGaAs superlattice filter layer needs to be added.

[0087] In this invention, an N-type GaAs (gallium arsenide) substrate is fed into an MBE cavity. The high temperature within the MBE cavity removes the oxide layer from the surface of the N-type GaAs substrate. On the oxide-free N-type GaAs substrate, an N-type GaAs contact layer, an N-type AlGaAs confinement layer, a first undoped GaAs waveguide layer, a multilayer quantum dot active region, a second undoped GaAs waveguide layer, a P-type AlGaAs confinement layer, and a P-type GaAs contact layer are sequentially grown, thereby obtaining a high-power, high-speed, directly modulated quantum dot laser. This method, by controlling the growth conditions of the quantum dots and the thickness of the spacer layer, significantly increases the number of quantum dot layers while controlling the thickness of the active region, thereby increasing the differential gain and carrier injection efficiency of the quantum dots and greatly improving the output power and direct modulation rate of the quantum dot laser.

[0088] The foregoing has provided a detailed description of a high-power, high-speed, directly modulated quantum dot laser and its fabrication method. Specific examples have been used to illustrate the principles and implementation methods of the invention; these examples are merely illustrative of the core ideas of the invention. It should be noted that those skilled in the art can make various improvements and modifications to the invention without departing from its principles, and these improvements and modifications also fall within the scope of protection of the claims.

Claims

1. A method for fabricating a high-power, high-speed, directly modulated quantum dot laser, characterized in that, The method includes the following steps: S1. The N-type GaAs substrate is fed into the MBE cavity, and the oxide layer on the surface of the N-type GaAs substrate is removed by the high temperature inside the MBE cavity. S2. Grow an N-type GaAs contact layer on an N-type GaAs substrate with the surface oxide layer removed; S3. Grow an N-type AlGaAs confinement layer on the N-type GaAs contact layer; S4. Epitaxially grow the first undoped GaAs waveguide layer on the N-type AlGaAs confinement layer; S5. Epitaxially grow a multilayer quantum dot active region on the first undoped GaAs waveguide layer; S6. Epitaxially grow a second undoped GaAs waveguide layer on the active region of multilayer quantum dots; S7. Grow a P-type AlGaAs confinement layer on the second undoped GaAs waveguide layer; S8. A P-type GaAs contact layer is grown on the P-type AlGaAs confinement layer to obtain a high-power, high-speed, directly modulated quantum dot laser. The multi-layer quantum dot active region in step S5 includes several active regions and several gradient active regions. The specific implementation of S5 is as follows: S51, preset the total number of growth layers n in the quantum dot active region, the number of growth layers m in the active region, and the number of growth layers nm in the gradient active region; S52. On the first undoped GaAs waveguide layer, m active regions are epitaxially grown using a fixed quantum dot growth method, with each active region having a thickness of 22-28 nm. S53. Starting from the (m+1)th layer, the quantum dot growth temperature, As / In ratio, and P-type GaAs are adjusted using gradient control. z P 1-z The growth method of z in the capping layer involves epitaxially growing a gradient active region layer by layer on the m-layer active region until the total number of grown layers of the gradient active region reaches nm layers, thereby obtaining a multilayer quantum dot active region with a total thickness ≤350nm.

2. The fabrication method for high-power, high-speed, directly modulated quantum dot lasers as described in claim 1, characterized in that, The specific implementation of step S1 is as follows: the N-type GaAs substrate is sent into the MBE cavity at a temperature between 500-700℃ for high-temperature deoxidation treatment to remove the oxide layer on the surface of the N-type GaAs substrate.

3. The method for fabricating a high-power, high-speed, directly modulated quantum dot laser as described in claim 2, characterized in that, The specific implementation of step S2 is as follows: The temperature inside the MBE cavity is controlled between 500-700℃. An N-type GaAs contact layer with a thickness of 300nm is epitaxially grown on an N-type GaAs substrate with the surface oxide layer removed. The GaAs growth rate is 0.1–1 ML / s, and the impurity is Si with a doping concentration of 1×10⁻⁶. 18 –2×10 19 cm -3 between.

4. The method for fabricating a high-power, high-speed, directly modulated quantum dot laser as described in claim 3, characterized in that, The specific implementation of step S3 is as follows: controlling the temperature inside the MBE cavity between 550-700℃, and growing an N-type Al layer with a thickness of 1-1.5µm on the N-type GaAs contact layer. x Ga 1-x As the confinement layer, Al x Ga 1-x The growth rate of As is 0.1–1 mL / s, the value of x ranges from 0.2 to 0.5, the impurity is Si, and the doping concentration is 5 × 10⁻⁶. 17 –1×10 19 cm -3 between.

5. The method for fabricating a high-power, high-speed, directly modulated quantum dot laser as described in claim 4, characterized in that, The specific implementation of step S4 is as follows: controlling the temperature inside the MBE cavity between 500-700℃, in N-type Al... x Ga 1-x An undoped GaAs waveguide layer with a thickness of 30-50 nm is epitaxially grown on the As confinement layer at a growth rate of 0.1-1 mL / s.

6. The method for fabricating a high-power, high-speed, directly modulated quantum dot laser as described in claim 5, characterized in that, The specific implementation method of the first active region in the m-layer active region in step S52 is as follows: S521. Control the temperature inside the MBE cavity between 400-500℃, and epitaxially grow an undoped In layer with a thickness of 1-2nm on the first undoped GaAs waveguide layer. y Ga 1-y As the impregnation layer, the growth rate is 0.1-1 mL / s, and the value of y ranges from 0.1 to 0.

16. S522. Control the temperature inside the MBE cavity between 400-500℃, and control the As:In ratio to be 10-30, in the absence of In doping. y Ga 1- y N-type doped quantum dots are epitaxially grown in the As wetted layer, with Si as the impurity. S523. Control the temperature inside the MBE cavity between 400-500℃, and epitaxially grow an undoped In layer with a thickness of 1-3nm on the N-type doped quantum dots. y Ga 1-y As capping layer, growth rate is 0.1-1 mL / s, and y ranges from 0.15 to 0.2; S524, in undoped In y Ga 1-y The first undoped GaAs capping layer is epitaxially grown on the As capping layer; S525. Control the temperature inside the MBE cavity between 550-700℃, and epitaxially grow a 5-10nm thick P-type GaAs layer on the first undoped GaAs capping layer. z P 1-z The cap layer has a growth rate of 0.1-1 mL / s, a z value ranging from 0.05 to 0.1, is p-type doped with Be as the dopant element, and has a doping concentration of 8-15 holes / quantum dots. S526. Control the temperature inside the MBE cavity between 550-700℃ in P-type GaAs. z P 1-z A second undoped GaAs capping layer with a thickness of 1-5 nm is epitaxially grown on the capping layer at a growth rate of 0.1-1 mL / s, thereby obtaining a first active region layer with a thickness of 22-28 nm.

7. The method for fabricating a high-power, high-speed, directly modulated quantum dot laser as described in claim 6, characterized in that, The specific implementation of step S7 is as follows: controlling the temperature inside the MBE cavity between 550-700℃, and epitaxially growing a P-type Al layer with a thickness of 500-1500nm on the second undoped GaAs waveguide layer. x Ga 1-x As confinement layer, growth rate 0.1-1 mL / s, x 0.2-0.5, doping concentration 5 × 10⁻⁶ 17 –1×10 19 cm -3 The impurity is Be.

8. The method for fabricating a high-power, high-speed, directly modulated quantum dot laser as described in claim 7, characterized in that, The specific implementation of step S8 is as follows: controlling the temperature inside the MBE cavity between 450-550℃, in the P-type Al... x Ga 1-x A p-type GaAs contact layer with a thickness of 300-500 nm is epitaxially grown on the As confinement layer at a growth rate of 0.1-1 mL / s and a doping concentration of 1 × 10⁻⁶. 18 –5×10 19 cm -3 The impurity is Be.

9. A high-power, high-speed, directly modulated quantum dot laser, characterized in that, The quantum dot laser is fabricated using the fabrication method for high-power, high-speed, directly modulated quantum dot lasers as described in any one of claims 1 to 8.

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