A method for preparing a ridge waveguide analog laser with low threshold current

Abstract

The present invention discloses a method for preparing a ridge waveguide analog laser with a low threshold current. The method comprises the following steps: cleaning the substrate with an organic solvent to remove surface contaminants and oxides; introducing nitrogen gas into a dry and clean reactor; placing the substrate on a carrier plate in the reactor, and heating the reactor to the growth temperature; introducing source gases into the reactor using a flow controller to control the flow rates of various source gases; and automatically controlling the film thickness via the reactor. After growth is complete, the reactor temperature is gradually lowered. After cooling, all substrates and observation films are removed. High-resolution X-ray diffraction and photoluminescence measurements are performed to confirm that the tensile strain of the quantum wells grown in the crystals is consistent with the design, thereby ensuring the crystal quality and device performance of the epitaxial wafer. The present invention can reduce the threshold current of the laser by 50% under the same conditions. The unique quantum well design achieves high gain and narrow linewidth, making it valuable for widespread application.

Description

Technical Field

[0001] The present invention relates to the technical field of semiconductor preparation, and in particular to a method for preparing a ridge waveguide analog laser with low threshold current. Background Art

[0002] Optoelectronic devices featuring buried heterostructures (BH) and similar structures typically utilize etched or appropriately doped barrier layers to physically restrict the direction of current flow within the device. These structures have demonstrated performance advantages over traditional ridge waveguide lasers. However, BH laser diodes are expensive and complex to manufacture. Therefore, improving the performance of ridge waveguide laser diodes while leveraging their ease of fabrication is desirable. One of the most important parameters of a laser diode is the threshold current. A lower threshold current improves relative RIN, dynamic performance, and linearity.

[0003] Conventional high-speed digital and analog communication lasers typically rely on compressively strained multi-quantum well (MQW) active regions based on AlGaInAs or InGaAsP material systems grown on InP substrates. Devices based on these designs have been widely deployed. In contrast, MQW lasers employing tensile strain are less common. However, tensile strained MQW designs offer several attractive features due to their unique electronic band structure. Summary of the Invention

[0004] The object of the present invention is to provide a method for preparing a ridge waveguide analog laser with low threshold current.

[0005] To achieve the above object, the present invention is implemented according to the following technical solutions:

[0006] The active layer of the ridge waveguide simulated laser with low threshold current of the present invention adopts multiple wide quantum wells with the same or different tensile stresses. The structure of the active layer is formed by alternating multiple tensile strained wide quantum wells and quantum barriers. The specific stacked structure is: barrier hole injection layer, wide quantum well 1, barrier layer 1, wide quantum well 2, barrier layer 2...wide quantum well N, barrier layer N. The method for preparing the epitaxial structure of the ridge waveguide simulated laser with low threshold current includes the following steps:

[0007] S1: Cleaning the substrate with an organic solvent to remove surface contaminants and oxides;

[0008] S2: nitrogen is passed into a dry and clean reactor;

[0009] S3: placing the substrate on a carrier in the reactor and heating the reactor to the growth temperature;

[0010] S4: using a flow controller to introduce source gases into the reactor and control the flow rates of various source gases;

[0011] S5: Automatically control the thickness of the film layer through the reactor;

[0012] S6: After growth is complete, the reactor temperature is gradually lowered. After cooling, all substrates and observation slides are removed. High-resolution X-ray diffraction and photoluminescence measurements are performed to verify that the tensile strain stress of the actual epitaxial quantum wells is consistent with the design and to confirm the crystal quality and crystallinity of the quantum wells, thereby optimizing the laser threshold current. After optimization, the threshold current that meets the tensile strain design requirements using wide quantum wells is less than 4mA, an improvement of more than 50% compared to the traditional design.

[0013] The beneficial effects of the present invention are:

[0014] The present invention is a method for preparing a ridge waveguide analog laser with a low threshold current. Compared with the existing technology, the present invention can reduce the threshold current of the laser by 50% under the same conditions by introducing an active region design of a tensile strain wide quantum well structure. At the same time, this design scheme can also achieve and optimize the high gain and narrow linewidth characteristics of the laser, and has practical application value. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 2. It is a schematic diagram comparing the designs of compressive strain and tensile strain multiple quantum wells of the present invention;

[0016] Figure 2 It is a schematic structural diagram of an application example of the present invention;

[0017] Figure 3 This is the optical power-current curve under the compressive strain and tensile strain quantum well designs of the present invention;

[0018] Figure 4 It is the lateral hole carrier density curve of the two strain designs at 100mA working current;

[0019] Figure 5 This is a comparison curve of the bevel efficiency of the two strain designs of the present invention;

[0020] Figure 6 This is a comparison curve of the non-radiative recombination rates of the two strain designs of the present invention. DETAILED DESCRIPTION

[0021] The present invention will be further described below with reference to the accompanying drawings and specific embodiments. The exemplary embodiments and descriptions of the present invention are used to explain the present invention but are not intended to limit the present invention.

[0022] The quantum wells of conventional laser products are of compressive strain type, and the mobility of their carriers will affect the diffusion of the lateral current in the ridge waveguide. At the band edge, the holes under the compressive strain type multi-quantum well have light mass on the well plane, so the mobility increases. On the contrary, the holes affected by the tensile strain type multi-quantum well are dominated by heavy holes with larger effective mass on the well plane. Equations (1) and (2) show how the hole mass affects the mobility and how it affects the resistivity. In equations (1) and (2), σ represents conductivity, q or e represents electron charge, n represents carrier density, µ represents carrier mobility, τ represents the average time between carrier collisions, represents the effective hole mass.

[0023] (1)

[0024] (2)

[0025] Therefore, the use of tensile strain quantum wells can theoretically reduce the threshold current within a certain range.

[0026] Another characteristic of tensile strained multi-quantum wells is related to their electronic structure, which requires wider wells in the vertical direction to confine light-mass holes. The benefit of this is that the effective refractive index of the multi-quantum well active region is increased. Accordingly, the tensile strain design of the wide quantum well can increase the relative optical mode gain of the laser, thereby reducing the threshold current of the device. Although the effect of reducing current diffusion is small, when combined with a wider quantum well design, the threshold current of an optimized tensile strained multi-quantum well can be reduced by more than 50% compared to the threshold current of a compressive strained multi-quantum well structure under the same optimization conditions. For a comparison of designs using compressive and tensile strained multi-quantum wells, see Figure 1 .exist Figure 1 (a): Compressive strain multi-quantum well. There are 10 quantum wells (gray) and 10 spacer layers (black), each 6nm thick. (b): Tensile strain multi-quantum well. There are 6 quantum wells (gray) and 6 spacer layers (black). Each quantum well is 14nm thick, and the spacer layer is 6nm thick. A typical application example structure based on tensile strain multi-quantum well design is shown in Figure 2. Figure 2 . Figure 2 In the figure, 1-metal conductive layer; 2-P-type semiconductor covering layer; 3-P-type semiconductor upper cladding layer; 4-grating layer; 5-P-type semiconductor isolation layer; 6-quantum well layer with appropriate tensile strain; 7-N-type semiconductor lower cladding layer; 8-base substrate (taking N-type as an example).

[0027] The laser epitaxial structure of the present invention can be grown in a low-pressure metal-organic vapor phase epitaxy (MOVPE) reactor. Before growth, 100 sccm of nitrogen gas must be introduced into the reactor to ensure dryness and cleanliness. The substrate must also be cleaned with organic solvents (acetone, isopropyl alcohol, and methanol) to remove surface contaminants and oxides. After preparation, the substrate is placed on a carrier in the reactor, and the reactor is heated to a growth temperature of 720°C. Source gases (trimethylindium, triethylgallium, trimethylaluminum, arsine, and phosphine) are introduced into the reactor using flow controllers to control the flow rates of the various source gases. In, Ga, and Al are Group III source gases, and As is a Group V source gas. The ratio of Group III to Group V source gases is 100:1. Film thickness control is automatically performed by the reactor. After growth is completed, the reactor temperature is gradually lowered at a rate of approximately 135°C / hour. After cooling, all substrates and observation pieces were removed, and the amount of tensile strain was adjusted and the crystal quality and crystallinity of the quantum wells were confirmed through high-resolution X-ray diffraction measurement and photoluminescence measurement.

[0028] The calculated threshold current of the traditional compressive strain multi-quantum well is about 6.2mA, while the calculated threshold current of the tensile strain multi-quantum well is less than 4mA. The calculation comparison results are detailed in Figure 3 Assuming the two designs have the same single-mode ridge waveguide structure and active region thickness, the longitudinal light field confinement factors of the compressive and tensile strain quantum well designs are approximately 11.5% and 17.5%, respectively. The wide quantum well design with tensile strain improves the light field confinement factor by more than 50%, thereby improving the gain characteristics of the device. Figure 4 The calculated lateral hole carrier density is shown, and it can be seen that the peak and carrier density are both located outside the 2μm wide ridge waveguide. Figure 5 The slope efficiency vs. current is shown, showing the improved linearity of the tensile strained MQW design. Figure 6 The results show that the non-radiative recombination rate in tensile-strained quantum wells is significantly reduced compared to compressive-strained designs, which means that tensile-strained quantum wells can ensure that the slope efficiency remains constant as the current increases.

[0029] The technical solution of the present invention is not limited to the above-mentioned specific embodiments. Any technical variations made according to the technical solution of the present invention fall within the protection scope of the present invention.

Claims

1. A method for preparing a ridge waveguide analog laser with a low threshold current, characterized in that: The active layer of the ridge waveguide simulated laser with low threshold current uses multiple wide quantum wells with the same or different tensile stresses. The structure of the active layer is formed by alternating multiple tensile strained wide quantum wells and quantum barriers. Its specific stacked structure is: barrier hole injection layer, wide quantum well 1, barrier layer 1, wide quantum well 2, barrier layer 2...wide quantum well N, barrier layer N. The thickness of each wide quantum well is 14 nm. The preparation method of the epitaxial structure of the ridge waveguide simulated laser with low threshold current includes the following steps: S1: Cleaning the substrate with an organic solvent to remove surface contaminants and oxides; S2: passing nitrogen into a dry and clean reactor, which is a low-pressure metal organic vapor phase epitaxy reactor; S3: placing the substrate on a carrier in the reactor and heating the reactor to a growth temperature of 720°C; S4: using a flow controller to introduce source gases into the reactor to control the flow rates of various source gases, wherein In, Ga, and Al are group III source gases, As is group V source gas, and the ratio of group V source gas to group III source gas is 100:1; S5: Automatically control the thickness of the film layer through the reactor; S6: After the growth is completed, the reactor temperature is gradually lowered. After cooling, all substrates and observation slices are removed. High-resolution X-ray diffraction measurement and photoluminescence measurement are used to verify that the actual epitaxial quantum well tensile strain stress is consistent with the design, and the crystal quality and crystallinity of the quantum well are confirmed, thereby optimizing the laser threshold current.

2. The method for preparing a ridge waveguide analog laser with a low threshold current according to claim 1, wherein: An N-type semiconductor lower cladding layer (7), a quantum well layer (6) with appropriate tensile strain, a P-type semiconductor isolation layer (5), a grating layer (4), a P-type semiconductor upper cladding layer (3), a P-type semiconductor covering layer (2), and a metal conductive layer (1) are sequentially grown on the substrate.

3. The method for preparing a ridge waveguide analog laser with a low threshold current according to claim 1, wherein: The nitrogen gas flow rate in step S2 is 80 sccm-120 sccm.

4. The method for preparing a ridge waveguide simulated laser with a low threshold current according to claim 1, wherein: The organic solvent is one of acetone, isopropanol or methanol.

5. The method for preparing a ridge waveguide simulated laser with a low threshold current according to claim 1, wherein: The source gas includes one or more of trimethylindium, triethylgallium, trimethylaluminum, arsine, and phosphine.

6. The method for preparing a ridge waveguide simulated laser with a low threshold current according to claim 5, characterized in that: The cooling rate of the reactor temperature in step S6 is about 135°C / hour.

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