Semiconductor lasers, which are known for their compact size, lightweight, high reliability, long lifespan, and low power consumption, have been widely applied in various fields such as laser communication, laser medical treatment, and laser display. The typical InGaAs/GaAs multi-quantum wells (MQWs) have been extensively used as the active region in semiconductor lasers operating in the near-infrared spectrum. However, the typical InGaAs/GaAs quantum wells exhibit issues at the 890 nm wavelength, including decreased gain and conduction band step, as well as lattice mismatch due to strain during epitaxial growth. In this regard, introducing P into the barrier layer to form InGaAs/GaAsP quantum wells can improve the strain and conduction-band offset of the quantum wells. The laser performance is significantly affected by defects generated during epitaxial growth, which primarily depend on the crystal quality of the epitaxial layer. Although studies that investigate the characteristics of semiconductor lasers based on InGaAs/GaAsP quantum wells and the optimization of the active region have been conducted, most of them used a relatively small number of quantum wells (less than six pairs). The interface quality of MQWs deteriorates as the number of quantum wells and barriers increases. However, to enhance the gain of the active region and achieve higher laser output power, the number of quantum wells used as the active region in semiconductor lasers must be increased.

A structure was designed and its emission wavelength was adjusted to 890 nm using the Crosslight software. The number of well layers was set to 10 to maintain a high material gain in the 890 nm wavelength band. Metal organic chemical vapor deposition (MOCVD) was performed, and a method of controlling growth-parameter combinations was employed to analyze the effects of different growth conditions on the interface quality and optical-gain characteristics of InGaAs/GaAsP MQWs. By performing photoluminescence (PL) detection, X-ray diffraction experiments, transmission electron microscopy, and secondary ion mass spectrometry, the epitaxial-growth quality of the samples was characterized and analyzed comprehensively.

The results indicate that as the growth temperature increases, the width of In segregation from the outer InGaAs well region into the barrier layer increases, thus resulting in a higher concentration of In atoms on the surface (Fig. 3). This increases the probability of In desorption, reduces the In content in the InGaAs well layer, and causes a blue shift in the PL peak (Fig. 2). Low-temperature growth tends to introduce more impurities, thus resulting in quantum wells with lower crystal quality. This increases the scattering of carriers and their capture by defects, thereby affecting the PL intensity of the MQWs (Fig. 2). Fitting the PL peaks of the samples and analyzing the X-ray diffraction spectra show that the sample grown at 680 ℃ exhibited the best epitaxial-growth quality. Excessively high Ⅴ/Ⅲ ratio can increase AsH₃-related complexes, thus causing the formation of interface defects and degrading the interface quality. The red shift of the PL peak is due to the shorter migration distance of In atoms under high AsH₃ concentrations (Fig. 5). The best interface quality is achieved at a Ⅴ/Ⅲ ratio of 34.2. The effect of the growth rate on the epitaxial-growth quality of the samples is primarily reflected in the transition of the growth modes. A high growth rate causes a partial transition from stable two-dimensional growth to three-dimensional growth, thus deteriorating the epitaxial quality of the samples. The optimal epitaxial-growth quality is achieved at a growth rate of 0.211 nm/s.

In this study, we designed and epitaxially grew 10 pairs of InGaAs/GaAsP MQWs with a gain wavelength of approximately 890 nm. The results show that three key parameters—growth temperature, Ⅴ/Ⅲ ratio, and growth rate—affected the epitaxial-growth quality of the samples, albeit via different mechanisms. The growth temperature and growth rate are more closely correlated with the epitaxial quality compared with the Ⅴ/Ⅲ ratio. Although In segregation on the surface is more severe at 680 ℃, it facilitated PH₃ decomposition, reduced impurity incorporation, and improved the interface quality. High growth rates can trigger a transition from two-dimensional to three-dimensional growth modes, thus degrading the epitaxial-growth quality. We separately achieved the best interface quality for the 10 pairs of InGaAs/GaAsP epitaxial structures at a growth temperature of 680 ℃, a Ⅴ/Ⅲ ratio of 34.2, and a growth rate of 0.211 nm/s. This finding is important for achieving semiconductor lasers with a large gain in the 890 nm band. In the future, we plan to incorporate a waveguide layer and cap layer to form a complete semiconductor-laser structure. Additionally, we plan to investigate the photoelectric conversion efficiency and gain of MQWs to achieve a high-power 890 nm semiconductor-laser pump source.