Preparation method of ridge waveguide simulation laser with low threshold current

Abstract

The invention discloses a preparation method of a ridge waveguide simulation laser with low threshold current. The preparation method comprises the following steps: cleaning a substrate by adopting an organic solvent to remove pollutants and oxides on the surface; introducing nitrogen into the dry and clean reactor; placing the substrate on a tray in a reactor, and heating the reactor to a growth temperature; introducing source gases into the reactor by using a flow controller, and controlling the flow of various source gases; the thickness of the film layer is automatically controlled through the reactor; and after the growth is completed, gradually reducing the temperature of the reactor, taking out all substrates and observation sheets after the cooling is completed, and confirming that the tensile strain of the quantum well for crystal growth accords with the design through high-resolution X-ray diffraction measurement and photoluminescence measurement so as to ensure the crystal quality and device performance of the epitaxial wafer. According to the invention, the threshold current of the laser can be reduced by 50% under the same condition; a special quantum well design is adopted, the technical effects of high gain and narrow linewidth are achieved, and the application and popularization value is achieved.

Description

Technical Field

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

[0002] Optoelectronic devices with buried heterostructures (BH) and other similar structures usually use etched or appropriately doped barrier layers to physically restrict the direction of current flow inside the device. These structures have been shown to have performance advantages over traditional ridge waveguide lasers. However, the manufacturing cost of BH laser diodes is high and complex. Therefore, it is desirable to improve the performance of ridge waveguide laser diodes and take advantage of their superior properties of easy manufacturing. One of the most important parameters of laser diodes is the threshold current. A lower threshold current can improve relative RIN, dynamic performance, and linearity.

[0003] Conventional high-speed digital and analog communication lasers typically rely on compressively strained multi-quantum well active region designs based on AlGaInAs or InGaAsP material systems grown on InP substrates. Devices based on these designs have been widely used. In contrast, multi-quantum well lasers using tensile strain designs are less common. The tensile strain multi-quantum well design has some attractive features due to its 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 a low threshold current.

[0005] To achieve the above object, the present invention is implemented according to the following technical solutions: 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 wide quantum wells and quantum barriers with tensile strains. 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 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: nitrogen is passed into a dry and clean reactor; S3: placing the substrate on a carrier in the reactor and heating the reactor to a growth temperature; S4: introducing source gases into the reactor using a flow controller to control the flow rates of various source gases; 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 films are taken out. Through high-resolution X-ray diffraction measurement and photoluminescence measurement, it is verified that the actual epitaxial quantum well tensile strain stress is consistent with the design, and the crystal quality crystallinity of the quantum well is confirmed, so as to optimize the laser threshold current. After optimization, the threshold current that meets the tensile strain design using a wide quantum well is less than 4mA, which is more than 50% better than the traditional design.

[0006] The beneficial effects of the present invention are: The present invention is a method for preparing a ridge waveguide analog laser with a low threshold current. Compared with the prior art, 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, the present design scheme can also realize and optimize the high gain and narrow linewidth characteristics of the laser, and has practical application value. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Figure 1 1. It is a schematic diagram comparing the designs of compressive strain and tensile strain type multiple quantum wells of the present invention; Figure 2 It is a schematic diagram of the structure of an application example of the present invention; Figure 3 It is the optical power-current curve under the compressive strain and tensile strain quantum well design of the present invention; Figure 4 It is the lateral hole carrier density curve of two strain designs under 100mA working current; Figure 5 It is the comparison curve of the bevel efficiency of the two strain designs of the present invention; Figure 6 It is a comparison curve of the non-radiative recombination rates of the two strain designs of the present invention. DETAILED DESCRIPTION

[0008] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments. The illustrative embodiments and descriptions of the present invention are used to explain the present invention but are not intended to limit the present invention.

[0009] The quantum wells of conventional laser products are of compressive strain type, and the mobility of their carriers will affect the diffusion amount of the lateral current in the ridge waveguide. At the band edge, the holes under the compressive strain type multiple quantum wells have light mass on the well plane, so the mobility increases. On the contrary, the holes affected by the tensile strain type multiple quantum wells 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.

[0010] (1) (2) Therefore, the use of tensile strain quantum wells can theoretically reduce the threshold current within a certain range.

[0011] Another feature of tensile strained multiple 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 active region of the multiple quantum wells is increased. Accordingly, the tensile strain design of wide quantum wells 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 multiple quantum well can be reduced by more than 50% compared to the threshold current of a compressive strained multiple quantum well structure under the same optimization conditions. For a comparison of designs using compressive and tensile strained multiple quantum wells, see Figure 1 .exist Figure 1 In the figure, (a): Compressive strain multi-quantum well. There are 10 quantum wells (gray) and 10 isolation layers (black), each with a thickness of 6nm. (b): Tensile strain multi-quantum well. There are 6 quantum wells (gray) and 6 isolation layers (black). The thickness of each quantum well is 14nm, and the thickness of the isolation layer is 6nm. A typical application example structure based on tensile strain multi-quantum well design is shown in 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).

[0012] 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 needs to be passed into the reactor to ensure that it is dry and clean. Before growth, the substrate also needs to be cleaned with an organic solvent (acetone, isopropanol and methanol) to remove surface pollutants and oxides. After the preparation work is completed, the substrate is placed on a carrier in the reactor, and the reactor is heated to a growth temperature of 720°C. A flow controller is used to introduce source gases (trimethylindium, triethylgallium, trimethylaluminum, arsenic and phosphine) into the reactor to control the flow of various source gases. In, Ga, and Al in the source gas are group III source gases, As is a group V source gas, and the ratio of group III source gas to group V source gas is 100:1. The thickness control of the film layer is automatically performed by the reactor. After the growth is completed, the reactor temperature is gradually reduced, and the cooling rate is about 135°C / hour. After cooling, all substrates and observation pieces were taken out, and the amount of tensile strain was adjusted and the crystal quality and crystallinity of the quantum wells were confirmed by high-resolution X-ray diffraction measurement and photoluminescence measurement.

[0013] The calculated threshold current of the conventional 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 that the two designs have the same single-mode ridge waveguide structure and active region thickness, the longitudinal light field confinement factors of the compressive strain 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 both the peak and the carrier density are located outside the 2um 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 authors show that the nonradiative recombination rate in tensile-strained quantum wells is greatly 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.

[0014] The technical solution of the present invention is not limited to the above-mentioned specific embodiments. All 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 adopts multiple wide quantum wells with the same or different tensile stresses. The structure of the active layer is formed by alternating multiple wide quantum wells and quantum barriers with tensile strains. 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 preparation method of the ridge waveguide simulated laser epitaxial structure with low threshold current includes the following steps: S1: Cleaning the substrate with an organic solvent to remove surface contaminants and oxides; S2: nitrogen is passed into a dry and clean reactor; S3: placing the substrate on a carrier in the reactor and heating the reactor to a growth temperature; S4: introducing source gases into the reactor using a flow controller to control the flow rates of various source gases; 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 films are taken out. Through high-resolution X-ray diffraction measurement and photoluminescence measurement, it is verified that the actual epitaxial quantum well tensile strain stress is consistent with the design, and the crystal quality crystallinity of the quantum well is 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, characterized in that: 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 capping 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, characterized in that: The reactor is a low-pressure metal organic vapor phase epitaxy reactor.

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

5. The method for preparing a ridge waveguide analog laser with a low threshold current according to claim 1, characterized in that: The organic solvent is one of acetone, isopropanol or methanol.

6. The method for preparing a ridge waveguide analog laser with a low threshold current according to claim 1, characterized in that: The reactor was heated to a growth temperature of 720°C.

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

8. The method for preparing a ridge waveguide analog laser with a low threshold current according to claim 7, characterized in that: Among the source gases, 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.

9. The method for preparing a ridge waveguide analog laser with a low threshold current according to claim 7, characterized in that: The cooling rate of the reactor temperature in step S6 is about 135°C / hour.

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