Depending on the active region material, the band gap width of the semiconductor material of the blue light semiconductor laser varies, so the semiconductor laser can emit light of different colors. The active region material of the blue light semiconductor laser is GaN or InGaN. The structure of a typical GaN-based laser is shown in Figure 1. From bottom to top in the z direction, it is the n-electrode, GaN substrate, n-type A1GaN lower confinement layer, n-type hGaN lower waveguide layer, multi-quantum well (MQW) active region, unintentionally doped hGaN upper waveguide layer, p-type electron blocking layer (EBL), p-type A1GaN upper confinement layer, p-type GaN layer, and p-electrode
The material refractive index of the multi-quantum well active region (MQWs) is the highest, and the refractive index of the materials on both sides of the active region shows a decreasing trend. Through the distribution of the refractive index of the material in the z direction with high in the middle and low above and below, the light field in the z direction can be confined between the upper and lower waveguide layers. In the y direction, part of the p-type layer on both sides of the laser is removed by etching, and a thin layer of silicon dioxide (SiO2) is deposited, eventually forming a ridge structure. The refractive index of silicon dioxide and air is smaller than that of the p-type layer, so the refractive index in the y direction is high in the middle and low on both sides, and the light field is confined to the middle of the ridge. Due to the limiting effect of the y and z directions on the light field, the light field in the yz plane presents an elliptical distribution. In the x direction, the front and rear cavity surfaces can be formed by mechanical cleavage or etching, and the reflectivity of the front and rear cavity surfaces can be adjusted by evaporating the dielectric film. Usually, the reflectivity of the front cavity surface is smaller than that of the rear cavity surface to ensure that the laser is emitted from the front cavity surface.