Objective In recent years, the quantum well mixing technology has been widely used in photonic integrated circuits, optoelectronic integrated circuits, and high-power semiconductor lasers with non-absorbing window structures. As for impurity-free vacancy induced quantum well mixing, due to the fact that there is no introduction of impurities, the process is simple, the cost is low, and the epitaxial wafer can maintain high lattice quality after quantum well mixing. The current literature reports are focused on the theoretical research, the exploration of experimental conditions, and the performance analysis of the related devices, but the reports on the influence of epitaxial structure on impurity-free vacancy induced quantum well mixing are still blank. In this article, the rapid thermal annealing experiment is carried out on the epitaxial wafers with different Al composition concentration waveguide layers and confinement layers, the influence of epitaxial structure on quantum well mixing is discussed, and the experimental results are theoretically analyzed and discussed. The research results provide a reference for the theoretical study of impurity-free vacancy induced quantum well mixing and the design of epitaxial structure of the device.
Methods Firstly, the InGaAs/GaAs single quantum well epitaxial wafer is grown using the metal-organic chemical vapor deposition equipment, the sample 1 is a high-aluminum structure, and the sample 2 is a low-aluminum structure, whose detailed epitaxial structures are shown in Figs. 1(a) and 1(b), respectively. Second, the 200 nm SiO2 dielectric film is grown on the surface of the samples 1 and 2 using the plasma enhanced chemical vapor deposition equipment. Then, the samples 1 and 2 are carried to a rapid thermal annealing treatment under different annealing temperature and time conditions. Finally, the PL spectral test is performed on the samples 1 and 2, and the experimental results are analyzed and discussed focusing on the influence of epitaxial structure on impurity-free vacancy-induced quantum well mixing.
Results and Discussions Firstly, the influence of annealing temperature on impurity-free vacancy induced quantum well mixing is analyzed. The wavelength blue shifts of these two samples are 20--50 nm in the range of 865--905 ℃. The wavelength blue shift gradually increases (Fig. 2) and the PL spectral intensity gradually decreases (Fig. 3) as the annealing temperature increases. The wavelength blue shifts of these two samples do not increase when the annealing temperature is greater than 895 ℃. Under the same experimental conditions, the wavelength blue shift of the sample 2 with a low aluminum structure is larger than that of the sample 1 with a high aluminum structure (Fig. 2), and the PL spectral intensity of the sample 2 decreases less (Fig. 3). Second, based on the influence of annealing temperature on impurity-free vacancy induced quantum well mixing, the influence of annealing time on impurity-free vacancy induced quantum well mixing is also studied. Under the condition of 875 ℃, with the increase of annealing time, the wavelength blue shift of the sample 2 gradually increases, and the PL spectral intensity gradually decreases.
Conclusions The influence of epitaxial structure on impurity-free vacancy induced quantum well mixing is discussed. The experimental results show that under the same experimental conditions, the sample 2 with a low-aluminum structure has a greater wavelength blue shift, and the PL spectral peak intensity decreases less. This shows that as for impurity-free vacancy induced quantum well mixng, Al and Ga in the epitaxial structure have different influences on the diffusion of point defects, and Ga is more conducive to the diffusion of point defects. According to the experimental results, we propose the following hypotheses: 1) when the InGaAs/GaAs quantum well epitaxial structure produces impurity-free vacancy-induced quantum well mixing, it is mainly induced by Ga vacancy diffusion, and the degree of quantum well mixing is proportional to the logarithmic function of Ga vacancy concentration; 2) when Ga vacancies generated in the cap layer of the epitaxial wafer diffuse downward and Si atoms diffuse into the epitaxial wafer and move in the epitaxial wafer, the Ga atoms in the lower layer are easier to occupy the upper Ga vacancies than Al atoms, and the Si atoms are easier to replace Ga Atoms, therefore, compared with Al atoms, Ga atoms are more likely to cause point defect Ga vacancies and Si atoms to diffuse downward.
