Method for epitaxial growth of p-type bragg reflector, vertical cavity surface emitting laser and method for epitaxial growth thereof

Abstract

The application belongs to the technical field of semiconductor photoelectric device manufacturing, and particularly relates to an epitaxial growth method of a P-type Bragg reflection layer, a vertical cavity surface emitting laser and an epitaxial growth method thereof. The P-type Bragg reflection layer provided by the application is grown by a metal organic chemical vapor deposition-in-situ reflection monitoring method, comprises a plurality of layer unit structures arranged in layers, and each layer unit structure comprises, from bottom to top, a carbon-doped GaAs layer, a first carbon-doped AlGaAs layer, a delta-doped layer and a second carbon-doped AlGaAs layer. The delta-doped layer is located at an optical standing wave node, and the delta-doped layer is a third carbon-doped AlGaAs layer. The P-type Bragg reflection layer provided by the application can significantly reduce the resistance of a P-DBR device while maintaining high reflectivity, and the optimal balance of photoelectric performance can be achieved through accurate control of the doping position.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor optoelectronic device manufacturing technology, specifically relating to the epitaxial growth method of a P-type Bragg reflector layer, a vertical cavity surface-emitting laser and its epitaxial growth method. Background Technology

[0002] Vertical-cavity surface-emitting lasers (VCSELs) are important semiconductor laser devices widely used in optical communication, lidar, and 3D sensing. Their core structure consists of two distributed Bragg reflectors (DBRs), an N-type DBR (N-DBR) and a P-type DBR (P-DBR), respectively. The P-DBR requires p-type doping to achieve hole injection.

[0003] The performance of P-DBR directly affects the threshold current, output power, and conversion efficiency of VCSEL. An ideal P-DBR should have both high reflectivity (>99%) and low resistance. However, traditional methods struggle to achieve both: increasing the doping concentration can reduce resistance but increases free carrier absorption, reducing reflectivity; reducing doping increases reflectivity but increases resistance. Summary of the Invention

[0004] The purpose of this invention is to provide an epitaxial growth method for a P-type Bragg reflector layer, a vertical cavity surface-emitting laser and the epitaxial growth method thereof. The P-type Bragg reflector layer provided by this invention can significantly reduce the resistance of the P-DBR while maintaining high reflectivity, and achieve optimal balance of optoelectronic performance through precise control of doping positions.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] This invention provides an epitaxial growth method for a P-type Bragg reflector layer. The P-type Bragg reflector layer comprises a multilayer unit structure stacked together. Each unit structure comprises, from bottom to top, a carbon-doped GaAs layer, a first carbon-doped AlGaAs layer, a δ-doped layer, and a second carbon-doped AlGaAs layer. The δ-doped layer is located at an optical standing wave node. The δ-doped layer is a third carbon-doped AlGaAs layer, and the doping concentration of the third carbon-doped AlGaAs layer is greater than the doping concentrations of the carbon-doped GaAs layer, the first carbon-doped AlGaAs layer, and the second carbon-doped AlGaAs layer.

[0007] The P-type Bragg reflector layer is grown using a metal-organic chemical vapor deposition-in-situ reflection monitoring method, forming a single-layer unit structure. The growth process utilizes an in-situ reflection monitoring system to monitor reflectivity in real time, determining the optical standing wave node based on the reflectivity. The monitoring wavelength of the in-situ reflection monitoring system is 850–980 nm. The growth method for each single-layer unit structure includes the following steps: growing a carbon-doped GaAs layer using TMGa, AsH3, and CCl4 as source gases; then growing a first carbon-doped AlGaAs layer using TMGa, TMAl, AsH3, and CCl4 as source gases; growing a δ-doped layer upon reaching the optical standing wave node; and then growing a second carbon-doped AlGaAs layer. The CCl4 flow rate is 1–10 sccm during the growth of the first and second carbon-doped AlGaAs layers, and 45–55 sccm during the growth of the δ-doped layer. The growth time for the δ-doped layer is 0.1–1 s.

[0008] Preferably, the thickness of the δ-doped layer is 0.5~3nm.

[0009] Preferably, the doping concentration of the δ-doped layer is 1×10⁻⁶. 19 ~4×10 19 cm -3 .

[0010] Preferably, the growth temperature of the δ-doped layer is 650~750℃.

[0011] Preferably, the doping concentration of the carbon-doped GaAs layer, the first carbon-doped AlGaAs layer, and the second carbon-doped AlGaAs layer is 1×10⁻⁶. 18 ~5×10 18 cm -3 .

[0012] Preferably, the total thickness of the first carbon-doped AlGaAs layer, the δ-doped layer, and the second carbon-doped AlGaAs layer is 65~70 nm.

[0013] Preferably, the thickness of the carbon-doped GaAs layer is 55~60 nm.

[0014] Preferably, the number of layers in the unit structure is 10 to 20.

[0015] The present invention provides a vertical cavity surface-emitting laser, comprising a GaAs substrate, wherein an N-type Bragg reflector layer, an active region, an oxide confinement layer, a tunnel junction, a P-type Bragg reflector layer and a surface ohmic contact layer are sequentially stacked on the upper surface of the GaAs substrate, wherein the P-type Bragg reflector layer is obtained by the epitaxial growth method described in the above technical solution.

[0016] This invention provides an epitaxial growth method for a vertical-cavity surface-emitting laser as described above, comprising the following steps:

[0017] An N-type Bragg reflector layer, an active region, an oxide confinement layer, and a tunnel junction were sequentially grown on the surface of the GaAs substrate using a metal-organic chemical vapor deposition method.

[0018] A P-type Bragg reflector layer is obtained on the upper surface of the tunnel junction using the epitaxial growth method described above.

[0019] A surface ohmic contact layer is grown on the upper surface of the P-type Bragg reflector layer.

[0020] This invention provides an epitaxial growth method for a P-type Bragg reflector layer. This invention also provides a vertical-cavity surface-emitting laser. In this invention, the P-type Bragg reflector layer comprises a multilayer unit structure stacked together. Each unit structure, from bottom to top, includes a carbon-doped GaAs layer, a first carbon-doped AlGaAs layer, a δ-doped layer, and a second carbon-doped AlGaAs layer. The δ-doped layer is located at the optical standing wave node. The δ-doped layer is a third carbon-doped AlGaAs layer, and the doping concentration of the third carbon-doped AlGaAs layer is greater than the doping concentrations of the carbon-doped GaAs layer, the first carbon-doped AlGaAs layer, and the second carbon-doped AlGaAs layer. Each unit structure of the P-type Bragg reflector layer is grown using a metal-organic chemical vapor deposition-in-situ reflection monitoring method to obtain the P-type Bragg reflector layer. During the growth process, the reflectivity is monitored in real time using an in-situ reflection monitoring system, and the optical standing wave node is determined from the reflectivity. The monitoring wavelength of the in-situ reflection monitoring system is 850~980 nm. nm; The growth method for each unit cell structure includes the following steps: growing a carbon-doped GaAs layer using TMGa, AsH3, and CCl4 as source gases; then growing a first carbon-doped AlGaAs layer using TMGa, TMAl, AsH3, and CCl4 as source gases; growing a δ-doped layer when the optical standing wave node is reached; and then growing a second carbon-doped AlGaAs layer. The CCl4 flow rate is 1~10 sccm during the growth of the first and second carbon-doped AlGaAs layers, and the CCl4 flow rate is 45~55 sccm during the growth of the δ-doped layer. The growth time of the δ-doped layer is 0.1~1 s. This invention addresses the problems of high resistance and severe free carrier absorption in P-DBRs in VCSELs. This invention sets the aforementioned δ-doped layer at the optical standing wave node position. By introducing a high concentration of δ-doped layer at the optical standing wave node position, the P-type Bragg reflector layer significantly reduces resistance while maintaining high reflectivity. Meanwhile, the present invention employs a metal-organic chemical vapor deposition-in-situ reflection monitoring method to grow each unit structure of the P-type Bragg reflector layer, and uses an in-situ reflection monitoring system to monitor reflectivity in real time and accurately determine optical standing wave nodes, thereby achieving the feasibility and accuracy of the solution.

[0021] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0022] The P-type Bragg reflector layer provided by this invention has a significantly reduced resistance: This invention introduces high-concentration carbon doping at the optical standing wave node through δ-doping, where the electric field strength is minimal, the high doping has minimal impact on optical loss, and at the same time effectively improves conductivity, achieving a resistance reduction of more than 20%.

[0023] The P-type Bragg reflector layer provided by this invention maintains high reflectivity: This invention avoids introducing too many free carriers in the anti-node region with strong electric field by precise node doping, suppresses free carrier absorption, and maintains reflectivity above 99%.

[0024] This invention employs a metal-organic chemical vapor deposition-in-situ reflection monitoring method to grow each unit structure of the P-type Bragg reflector layer. During the epitaxial growth process, this invention uses an in-situ reflection monitoring system to monitor reflectivity in real time and uses reflectivity correlation to accurately determine the optical standing wave nodes, overcoming the inaccuracy of traditional thickness control and ensuring that the δ-doping positions of each layer are consistent. The epitaxial growth method provided by this invention has strong stability, high precision, and good repeatability. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the refractive index and standing wave of the VCSEL structure P-DBR prepared in Example 1 of the present invention;

[0026] Figure 2 This is a schematic diagram of the timing relationship between the CCl4 pulse and the in-situ monitored reflectivity in Embodiment 1 of the present invention. Detailed Implementation

[0027] This invention provides an epitaxial growth method for a P-type Bragg reflector layer. The P-type Bragg reflector layer comprises a multilayer unit structure stacked together. Each unit structure comprises, from bottom to top, a carbon-doped GaAs layer, a first carbon-doped AlGaAs layer, a δ-doped layer, and a second carbon-doped AlGaAs layer. The δ-doped layer is located at an optical standing wave node. The δ-doped layer is a third carbon-doped AlGaAs layer, and the doping concentration of the third carbon-doped AlGaAs layer is greater than the doping concentrations of the carbon-doped GaAs layer, the first carbon-doped AlGaAs layer, and the second carbon-doped AlGaAs layer.

[0028] The P-type Bragg reflector layer is grown using a metal-organic chemical vapor deposition-in-situ reflection monitoring method, forming a single-layer unit structure. The growth process utilizes an in-situ reflection monitoring system to monitor reflectivity in real time, determining the optical standing wave node based on the reflectivity. The monitoring wavelength of the in-situ reflection monitoring system is 850–980 nm. The growth method for each single-layer unit structure includes the following steps: growing a carbon-doped GaAs layer using TMGa, AsH3, and CCl4 as source gases; then growing a first carbon-doped AlGaAs layer using TMGa, TMAl, AsH3, and CCl4 as source gases; growing a δ-doped layer upon reaching the optical standing wave node; and then growing a second carbon-doped AlGaAs layer. The CCl4 flow rate is 1–10 sccm during the growth of the first and second carbon-doped AlGaAs layers, and 45–55 sccm during the growth of the δ-doped layer. The growth time for the δ-doped layer is 0.1–1 s.

[0029] The P-type Bragg reflector layer provided by this invention comprises a multi-layered unit structure. In this invention, the number of layers in the unit structure is preferably 10 to 20, and in some embodiments, it can be 15.

[0030] In this invention, the δ-doped layer is located at the optical standing wave node, and the first carbon-doped AlGaAs layer and the second carbon-doped AlGaAs layer belong to the conventional doping region and are located in the standing wave anti-node region.

[0031] In this invention, the unit structure includes a carbon-doped GaAs layer. The doping concentration of the carbon-doped GaAs layer is preferably 1 × 10⁻⁶. 18 ~5×10 18 cm -3 In the embodiment, it can be 2×10 18 cm -3 The thickness of the carbon-doped GaAs layer is preferably 55~60 nm, and in the embodiment it can be 58.35 nm.

[0032] In this invention, the unit structure includes a first carbon-doped AlGaAs layer disposed on the upper surface of the carbon-doped GaAs layer. The first carbon-doped AlGaAs layer may be a first carbon-doped Al... 0.1 Ga 0.9 As layer. The preferred doping concentration of the first carbon-doped AlGaAs layer is 1×10⁻⁶. 18 ~5×10 18 cm -3 In the embodiment, it can be 1×10 18 cm -3 .

[0033] In this invention, the unit structure includes a δ-doped layer disposed on the upper surface of the first carbon-doped AlGaAs layer. In this invention, the δ-doped layer is located at an optical standing wave node, and the δ-doped layer is a third carbon-doped AlGaAs layer. The doping concentration of the δ-doped layer is preferably ≥1×10⁻⁶. 19 cm -3 More preferably 1×10 19 ~4×10 19 cm -3 In the embodiment, it can be 4×10 19 cm -3 In this invention, the thickness of the δ-doped layer is preferably 0.5~3nm, and in the embodiments it can be 0.5nm, 1nm, 2nm or 3nm.

[0034] In this invention, the unit structure includes a second carbon-doped AlGaAs layer disposed on the upper surface of the δ-doped layer. The second carbon-doped AlGaAs layer can be a second carbon-doped Al... 0.1 Ga 0.9 As layer. The preferred doping concentration of the second carbon-doped AlGaAs layer is 1×10⁻⁶. 18 ~5×10 18 cm -3 In the embodiment, it can be 2×10 18 cm -3 .

[0035] In this invention, the total thickness of the first carbon-doped AlGaAs layer, the δ-doped layer, and the second carbon-doped AlGaAs layer is greater than the thickness of the carbon-doped GaAs layer. The total thickness of the first carbon-doped AlGaAs layer, the δ-doped layer, and the second carbon-doped AlGaAs layer is preferably 65-70 nm, and in this embodiment, it can be 69.06 nm.

[0036] This invention uses a metal-organic chemical vapor deposition-in-situ reflection monitoring method to grow each unit structure of the P-type Bragg reflector layer, thereby obtaining the P-type Bragg reflector layer. The growth process uses an in-situ reflection monitoring system to monitor the reflectivity in real time, and the optical standing wave node is determined from the reflectivity. The monitoring wavelength of the in-situ reflection monitoring system is 850~980 nm.

[0037] In this invention, unless otherwise specified, all raw materials / components used in the preparation are commercially available products well-known to those skilled in the art. The epitaxial growth method for the P-type Bragg reflector layer and the epitaxial growth method for the vertical-cavity surface-emitting laser (VCSEL) provided by this invention both employ metal-organic chemical vapor deposition (MOCVD) combined with in-situ reflection monitoring. The preferred monitoring wavelength is 850-980 nm, and in the embodiments, it can be 850 nm. In this invention, the epitaxial growth process of the P-type Bragg reflector layer and the VCSEL uses an in-situ reflection monitoring system to monitor reflectivity in real time. Preferably, the in-situ reflection monitoring system determines the reflection signal of the monitoring wavelength based on the wavelength of the VCSEL, and the monitoring wavelength of the in-situ reflection detection system is preferably the same as the wavelength of the VCSEL. Specifically: for an 850 nm VCSEL, the monitoring wavelength is 850 nm; for a 940 nm VCSEL, the monitoring wavelength is 940 nm; and for a 980 nm VCSEL, the monitoring wavelength is 980 nm. This invention improves the positioning accuracy of optical standing wave nodes and the accuracy of the thickness of each layer in a vertical cavity surface-emitting laser by detecting reflection signals of different wavelengths using different VCSELs. The epitaxial growth in this invention is performed using a metal-organic chemical vapor deposition (MOCVD) system; in this embodiment, an Aixtron MOCVD system is used, with the preferred pressure in the reaction chamber being 100 mbar and hydrogen gas as the carrier.

[0038] In this invention, the growth method of each unit cell structure includes the following steps: growing a carbon-doped GaAs layer using TMGa, AsH3 and CCl4 as source gases; then growing a first carbon-doped AlGaAs layer to the optical standing wave node using TMGa, TMAl, AsH3 and CCl4 as source gases, increasing the flow rate of CCl4 to grow a δ-doped layer, and then decreasing the flow rate of CCl4 to continue growing a second carbon-doped AlGaAs layer.

[0039] In this invention, the preferred conditions for growing the carbon-doped GaAs layer include: a flow rate of TMGa preferably of 30-70 sccm, which can be 50 sccm in the embodiment; a flow rate of AsH3 preferably of 150-250 sccm, which can be 200 sccm in the embodiment; and a flow rate of CCl4 preferably of 20-30 sccm, which can be 25 sccm in the embodiment. The preferred growth temperature of the carbon-doped GaAs layer is 650-750℃, which can be 680℃ in the embodiment. The thickness of the carbon-doped GaAs layer is λ / 4n, where λ is the design wavelength and n is the refractive index of the material (i.e., the carbon-doped GaAs).

[0040] In this invention, the preferred conditions for growing the first carbon-doped AlGaAs layer include: a flow rate of TMGa preferably of 30-70 sccm, which can be 50 sccm in the embodiment; a flow rate of TMAl preferably of 750-800 sccm, which can be 781 sccm in the embodiment; a flow rate of AsH3 preferably of 150-250 sccm, which can be 200 sccm in the embodiment; and a flow rate of CCl4 preferably of 1-10 sccm, which can be 5 sccm in the embodiment. The preferred growth temperature of the first carbon-doped AlGaAs layer is 650-750℃, which can be 680℃ in the embodiment.

[0041] This invention employs an in-situ reflection monitoring system to monitor reflectivity changes in real time. When the reflection signal indicates that the optical standing wave node (reflectivity extreme point) has been reached, the flow rate of CCl4 is preferably increased to 45-55 sccm, and in this embodiment, it can be 50 sccm, to perform the δ-doped layer. The preferred flow rates of the remaining gas sources are: TMGa, preferably 30-70 sccm, and in this embodiment, 50 sccm; TMAl, preferably 750-800 sccm, and in this embodiment, 781 sccm; and AsH3, preferably 150-250 sccm, and in this embodiment, 200 sccm. In this embodiment, except for the CCl4 flow rate, the flow rates of the remaining gas sources for growing the δ-doped layer are the same as those for growing the first carbon-doped AlGaAs layer. The growth time of the δ-doped layer is preferably 0.1-1 s. The growth temperature of the δ-doped layer is preferably 650-750℃, and in this embodiment, it can be 680℃.

[0042] In this invention, the preferred conditions for growing the second carbon-doped AlGaAs layer include: a flow rate of TMGa preferably of 30-70 sccm, which can be 50 sccm in the embodiment; a flow rate of TMAl preferably of 750-800 sccm, which can be 781 sccm in the embodiment; a flow rate of AsH3 preferably of 150-250 sccm, which can be 200 sccm in the embodiment; and a flow rate of CCl4 preferably of 1-10 sccm, which can be 5 sccm in the embodiment. The preferred growth temperature of the second carbon-doped AlGaAs layer is 650-750℃, which can be 680℃ in the embodiment.

[0043] The present invention provides a vertical cavity surface-emitting laser, comprising a GaAs substrate, wherein an N-type Bragg reflector layer, an active region, an oxide confinement layer, a tunnel junction, a P-type Bragg reflector layer and a surface ohmic contact layer are sequentially stacked on the upper surface of the GaAs substrate, wherein the P-type Bragg reflector layer is obtained by the epitaxial growth method described in the above technical solution.

[0044] The vertical cavity surface-emitting laser provided by the present invention includes a GaAs substrate. The GaAs substrate is preferably an n-type GaAs substrate with a (100) orientation.

[0045] The vertical cavity surface-emitting laser provided by the present invention includes an N-type Bragg reflector layer disposed on the upper surface of the GaAs substrate.

[0046] In this invention, the N-type Bragg reflector layer comprises a multilayer unit structure stacked together, each unit structure comprising, from bottom to top, a silicon-doped AlGaAs layer and a silicon-doped GaAs layer. In this invention, the doping element of the N-type Bragg reflector layer is Si, and the conductivity type is N-type.

[0047] The vertical-cavity surface-emitting laser provided by this invention includes an active region, an oxide confinement layer, and a tunneling junction sequentially disposed on the upper surface of the N-type Bragg reflector. The active region preferably includes multiple pairs of quantum wells.

[0048] The vertical-cavity surface-emitting laser provided by this invention includes a P-type Bragg reflector layer disposed on the upper surface of the tunnel junction. The dopant element of the P-type Bragg reflector layer is carbon, and the conductivity type is P-type.

[0049] The vertical cavity surface-emitting laser provided by the present invention includes a surface ohmic contact layer disposed on the upper surface of the P-type Bragg reflector layer.

[0050] This invention provides an epitaxial growth method for a vertical-cavity surface-emitting laser as described above, comprising the following steps:

[0051] An N-type Bragg reflector layer, an active region, an oxide confinement layer, and a tunnel junction were sequentially grown on the surface of the GaAs substrate using a metal-organic chemical vapor deposition method.

[0052] A P-type Bragg reflector layer is obtained on the upper surface of the tunnel junction using the epitaxial growth method of the P-type Bragg reflector layer described in the above technical solution.

[0053] A surface ohmic contact layer is grown on the upper surface of the P-type Bragg reflector layer.

[0054] This invention employs a metal-organic chemical vapor deposition (MOCVD) method to sequentially grow an N-type Bragg reflector layer, an active region, an oxide confinement layer, and a tunnel junction on the surface of a GaAs substrate. This invention does not impose special requirements on the growth methods of the N-type Bragg reflector layer, active region, oxide confinement layer, tunnel junction, and surface ohmic contact layer; parameters well-known to those skilled in the art can be used.

[0055] In this invention, the growing conditions for the N-type Bragg reflector layer are preferably as follows: the flow rate of TMGa is preferably 30-70 sccm, and in this embodiment it can be 50 sccm. The flow rate of TMAl is preferably 750-800 sccm, and in this embodiment it can be 781 sccm. The flow rate of AsH3 is preferably 150-250 sccm, and in this embodiment it can be 200 sccm. The flow rate of SiH4 is preferably 20-200 sccm, and in this embodiment it can be 100 sccm. The growth temperature of the silicon-doped AlGaAs layer is preferably 650-750℃, and in this embodiment it can be 680℃. The thickness of the silicon-doped AlGaAs layer is λ / 4n, where λ is the design wavelength and n is the refractive index of the silicon-doped AlGaAs layer material.

[0056] In this invention, the growing conditions for the N-type Bragg reflector layer are preferably as follows: the flow rate of TMGa is preferably 30-70 sccm, and in this embodiment it can be 50 sccm. The flow rate of AsH3 is preferably 150-250 sccm, and in this embodiment it can be 200 sccm. The flow rate of SiH4 is preferably 20-200 sccm, and in this embodiment it can be 100 sccm. The growth temperature of the silicon-doped GaAs layer is preferably 650-750℃, and in this embodiment it can be 680℃. The thickness of the silicon-doped GaAs layer is λ / 4n, where λ is the design wavelength and n is the refractive index of the silicon-doped GaAs layer material.

[0057] After obtaining the tunnel junction, the present invention obtains a P-type Bragg reflector layer on the upper surface of the tunnel junction by the epitaxial growth method of the P-type Bragg reflector layer described in the above technical solution.

[0058] To further illustrate the present invention, the technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0059] Example 1

[0060] This embodiment provides an epitaxial growth method for a vertical cavity surface-emitting laser, specifically including:

[0061] Using an N-type GaAs substrate as the substrate, the substrate was placed in an Aixtron MOCVD system. The reaction chamber pressure was 100 mbar, and the temperature was raised to 680 °C under AsH3 atmosphere protection. The in-situ reflection monitoring system was turned on, and the monitoring wavelength was set to 850 nm. H2 was used as the carrier gas, and the source gases included TMGa, TMAl, SiH4, CCl4, and AsH3.

[0062] First, using TMGa, TMAl, AsH3, and SiH4 as source gases, AlGaAs / GaAs N-DBRs are grown sequentially. Then, an active region, an oxide confinement layer, and a tunneling junction layer are grown on the surface of the N-DBR. Next, P-DBR growth begins, specifically including:

[0063] First, a carbon-doped GaAs high-refractive-index layer was grown. The gas source flow rates were set as follows: TMGa 50 sccm, AsH3 200 sccm, CCl4 25 sccm, with a thickness of 58.35 nm and a doping concentration of 2 × 10⁻⁶. 18 cm -3 .

[0064] Next, carbon-doped Al is grown. 0.9 Ga 0.1 The AlGaAs low-refractive-index layer has a total thickness of 69.06 nm, with the following flow rates: TMGa 50 sccm, TMAl 781 sccm, AsH 3200 sccm, and CCl4 5 sccm. Reflectivity changes are monitored in real time. When the reflection signal indicates the optical standing wave node (the extreme point of reflectivity, with an AlGaAs layer thickness of approximately 21 nm), the CCl4 flow rate is instantaneously increased to 50 sccm for 0.5 seconds (i.e., the CCl4 flow rate is pulsed and instantaneously changed), forming a layer approximately 2 nm thick with a doping concentration of 4 × 10⁻⁶. 19 cm -3 The δ-doped layer was formed. After 0.5 seconds, the CCl4 flow rate was restored to 5 sccm, and Al growth continued. 0.9 Ga 0.1 The As low-refractive-index layer reaches a total thickness of 69.06 nm. In this embodiment, a δ-doped layer is grown at the optical standing wave node (reflectivity extremum), and conventional carbon-doped Al is grown in the standing wave anti-node region. 0.9 Ga 0.1 As a low refractive index layer, carbon-doped Al in the standing wave antinode region 0.9 Ga 0.1 The doping concentration of the low-refractive-index layer is 2×10⁻⁶. 18 cm -3 .

[0065] Repeat the above process to grow 15 pairs of AlGaAs / GaAs unit structures to form a complete P-DBR structure.

[0066] A surface ohmic contact layer is grown on the surface of the P-DBR structure to obtain a VCSEL device.

[0067] Figure 1 This is a schematic diagram of the P-DBR refractive index and standing wave in the VCSEL device structure prepared in Example 1 of the present invention. Figure 1The horizontal axis represents the thickness, the vertical axis on the left represents the refractive index, and the vertical axis on the right represents the relative intensity of the standing wave.

[0068] Figure 1 The diagram shows the refractive index and standing wave of the VCSEL structure P-DBR of this invention. It can be seen that the standing wave node is generally located in the low refractive index epitaxial layer, but its position is not fixed.

[0069] Figure 2 The diagram illustrates the timing relationship between the CCl4 pulse and the in-situ monitored reflectivity in Example 1. When the in-situ monitored reflectivity signal detects a node, it triggers an increase in the CCl4 flow rate within time t1 to achieve δ-doping; the flow rate remains at the normal level for the rest of the time to ensure doping accuracy and repeatability.

[0070] Test results show that the hole concentration in the δ-doped region reaches 4 × 10⁻⁶. 19 cm -3 Regular area (AI) 0.9 Ga 0.1 The hole concentration in the low-refractive-index layer (As) is 2 × 10⁻⁶. 18 cm -3 .

[0071] The reflectivity of the 15 pairs of P-DBRs prepared in this embodiment reaches 99.1%. The resistance of the vertical-cavity surface-emitting laser prepared in this embodiment is 42.8 ohms. The method for testing the resistance of the vertical-cavity surface-emitting laser prepared in this embodiment is as follows: the epitaxial wafer of the vertical-cavity surface-emitting laser is fabricated into a chip with a Mesa diameter of 25 μm and an oxide aperture of 10 μm, and the resistance of the chip is tested at 6 mA.

[0072] Comparative Example 1

[0073] This comparative example provides a method for fabricating a vertical-cavity surface-emitting laser (traditional uniformly doped structure), specifically including:

[0074] Using an N-type GaAs substrate as the substrate, the substrate was placed in an Aixtron MOCVD system. The reaction chamber pressure was 100 mbar, and the temperature was raised to 680 °C under AsH3 atmosphere protection. The in-situ reflection monitoring system was turned on, and the monitoring wavelength was set to 850 nm. H2 was used as the carrier gas, and the source gases included TMGa, TMAl, SiH4, CCl4, and AsH3.

[0075] First, using TMGa, TMAl, AsH3, and SiH4 as source gases, AlGaAs / GaAs N-DBRs are grown sequentially. Then, an active region, an oxide confinement layer, and a tunneling junction layer are grown on the surface of the N-DBR. Next, P-DBR growth begins, specifically including:

[0076] First, a carbon-doped GaAs high-refractive-index layer was grown. The gas source flow rates were set as follows: TMGa 50 sccm, AsH3 200 sccm, CCl4 25 sccm, with a thickness of 58.35 nm and a doping concentration of 2 × 10⁻⁶. 18 cm -3 .

[0077] Next, carbon-doped Al is grown. 0.9 Ga 0.1 The As low-refractive-index layer has a total thickness of 69.06 nm, with the following flux settings: TMGa50 sccm, TMAl 781 sccm, AsH3200 sccm, and CCl45 sccm. Carbon-doped Al 0.9 Ga 0.1 The doping concentration of the low-refractive-index layer is 2×10⁻⁶. 18 cm -3 .

[0078] Repeat the above process to grow 15 pairs of AlGaAs / GaAs unit structures to form a complete P-DBR structure.

[0079] A surface ohmic contact layer is grown on the surface of the P-DBR structure to obtain a VCSEL device (a conventional uniformly doped structure).

[0080] The resistance of the conventional uniformly doped structure device prepared in this comparative example was tested according to the method in Example 1. The resistance of the conventional uniformly doped structure prepared in Comparative Example 1 was 54.8 hm. Therefore, the resistance of the VCSEL device prepared in Example 1 is 22% lower than that of the conventional uniformly doped structure prepared in Comparative Example 1.

[0081] As demonstrated by the above embodiments, this invention addresses the problems of high resistance and severe free carrier absorption in P-DBRs within VCSELs by proposing a δ-doped P-DBR epitaxial growth method based on in-situ reflection monitoring using metal-organic chemical vapor deposition (MOCVD). This method significantly reduces resistance while maintaining high reflectivity by introducing a high-concentration δ-doped layer at the optical standing wave node. The invention introduces high-concentration doping at the optical standing wave node, where the electric field strength is minimal, resulting in minimal impact on optical loss and effectively improving conductivity, achieving a resistance reduction of over 20%. The precise node doping of this invention avoids introducing excessive free carriers in the strong electric field region of the anti-node, suppressing free carrier absorption and maintaining reflectivity above 99%. Furthermore, the method provided by this invention offers high process precision and good repeatability: in-situ reflection monitoring is used to locate the node in real time, overcoming the inaccuracies of traditional thickness control and ensuring consistent δ-doping positions for each layer, resulting in strong process stability.

[0082] Although the above embodiments have provided a detailed description of the present invention, they are only some embodiments of the present invention, and not all embodiments. Other embodiments can be obtained based on these embodiments without creative effort, and these embodiments all fall within the protection scope of the present invention.

Claims

1. An epitaxial growth method for a P-type Bragg reflector layer, characterized in that, The P-type Bragg reflector layer comprises a multi-layered unit structure. Each unit structure, from bottom to top, includes a carbon-doped GaAs layer, a first carbon-doped AlGaAs layer, a δ-doped layer, and a second carbon-doped AlGaAs layer. The δ-doped layer is located at the optical standing wave node. The δ-doped layer is the third carbon-doped AlGaAs layer, and the doping concentration of the third carbon-doped AlGaAs layer is greater than the doping concentrations of the carbon-doped GaAs layer, the first carbon-doped AlGaAs layer, and the second carbon-doped AlGaAs layer. The doping concentration of the δ-doped layer is 1 × 10⁻⁶. 19 ~4×10 19 cm -3 The thickness of the δ-doped layer is 0.5~3 nm. The P-type Bragg reflector layer is grown using a metal-organic chemical vapor deposition-in-situ reflection monitoring method, forming a single-layer unit structure. The growth process utilizes an in-situ reflection monitoring system to monitor reflectivity in real time, determining the optical standing wave node based on the reflectivity. The monitoring wavelength of the in-situ reflection monitoring system is 850–980 nm. The growth method for each single-layer unit structure includes the following steps: growing a carbon-doped GaAs layer using TMGa, AsH3, and CCl4 as source gases; then growing a first carbon-doped AlGaAs layer using TMGa, TMAl, AsH3, and CCl4 as source gases; growing a δ-doped layer upon reaching the optical standing wave node; and then growing a second carbon-doped AlGaAs layer. The CCl4 flow rate is 1–10 sccm during the growth of the first and second carbon-doped AlGaAs layers, and 45–55 sccm during the growth of the δ-doped layer. The growth time for the δ-doped layer is 0.1–1 s.

2. The epitaxial growth method according to claim 1, characterized in that, The growth temperature of the δ-doped layer is 650~750℃.

3. The epitaxial growth method according to claim 1, characterized in that, The doping concentration of the carbon-doped GaAs layer, the first carbon-doped AlGaAs layer, and the second carbon-doped AlGaAs layer is 1×10⁻⁶. 18 ~5×10 18 cm -3 .

4. The epitaxial growth method according to claim 1, characterized in that, The total thickness of the first carbon-doped AlGaAs layer, the δ-doped layer, and the second carbon-doped AlGaAs layer is 65~70nm.

5. The epitaxial growth method according to claim 1, characterized in that, The thickness of the carbon-doped GaAs layer is 55~60 nm.

6. The epitaxial growth method according to claim 1, characterized in that, The number of layers in the unit structure is 10 to 20.

7. A vertical-cavity surface-emitting laser, characterized in that, The invention comprises a GaAs substrate, wherein an N-type Bragg reflector layer, an active region, an oxide confinement layer, a tunnel junction, a P-type Bragg reflector layer, and a surface ohmic contact layer are sequentially stacked on the upper surface of the GaAs substrate, wherein the P-type Bragg reflector layer is obtained by the epitaxial growth method according to any one of claims 1 to 6.

8. An epitaxial growth method for a vertical-cavity surface-emitting laser as described in claim 7, characterized in that, Includes the following steps: An N-type Bragg reflector layer, an active region, an oxide confinement layer, and a tunnel junction were sequentially grown on the surface of the GaAs substrate using a metal-organic chemical vapor deposition method. A P-type Bragg reflector layer is obtained on the upper surface of the tunnel junction using the epitaxial growth method described above. A surface ohmic contact layer is grown on the upper surface of the P-type Bragg reflector layer.

Images