Objective In recent years, III-V semiconductor materials have been widely used in optoelectronic devices, such as lasers, detectors, and LEDs, and have attracted widespread attention of researchers. Among these materials, the band gap of the InGaAsSb/AlGaAsSb quantum well structure is between that of GaSb and InAs. Therefore, the InGaAsSb/AlGaAsSb quantum well structure is the preferred material for the preparation of antimonide semiconductor lasers with a wavelength range of 1.8--3 μm. In molecular beam epitaxial (MBE) growth of antimony alloy semiconductor materials, defects and molecular clusters are introduced. These defects reduce the light-emitting characteristics of the materials, affecting the threshold current, output power, and spectral line width of the laser. In order to further improve the optical properties of InGaAsSb/AlGaAsSb quantum well materials, a rapid thermal annealing method is used to treat the quantum well structure. The effects of rapid thermal annealing on the performance of quantum wells are studied here using photoluminescence spectroscopy.

Methods An InGaAsSb/AlGaAsSb quantum well structure is grown using a DCA-P600 MBE system. A GaSb buffer layer with a thickness of 500 nm is first grown on an n-type GaAs substrate. Then, three periods of In_0.1Ga_0.9As_0.08Sb_0.92/Al_0.3Ga_0.7As_0.13Sb_0.87 are grown on the buffer layer. The thickness of the In_0.1Ga_0.9As_0.08Sb_0.92 well layer is 20 nm and the thickness of the Al_0.3Ga_0.7As_0.13Sb_0.87 barrier layer is 30 nm. The as-grown sample is cleaved into four pieces of equal size. One of the samples is designated as the as-grown sample and does not undergo rapid thermal annealing. The other three samples are subjected to rapid thermal annealing for 30 s in a nitrogen atmosphere at either 500 ℃, 550 ℃, or 600 ℃. A laser with a wavelength of 655 nm and spot area of 0.4 cm ² is used to measure the photoluminescence spectrum of the samples. A HORIBA iHR550 spectrometer, with an InGaAs detector kept at -30 ℃, is used to detect photoluminescence signals. The line density of the selected spectrometer grating is 600 line/mm and the wavelength of filter is selected 1000 nm. All tests are carried out in a closed-circulation liquid helium cryostat with a CaF₂ window. The laser power density is changed from 1 mW/cm ² to 300 mW/cm ² during the power-dependent photoluminescence measurement and the temperature is changed from 10 K to 300 K during the temperature-dependent photoluminescence measurement.

Results and Discussions The photoluminescence results show that rapid thermal annealing causes atoms to interdiffuse throughout the quantum well layer and the barrier layer interface in the quantum well structure. This can improve the crystal quality of the quantum well material and reduce structural strain, thereby improving the optical properties of the quantum well material. At room temperature, the photoluminescence spectrum shows a gradual blue-shift with increasing annealing temperature. When the annealing temperature is 500 ℃, 550 ℃, and 600 ℃, the photoluminescence shift is 7 meV, 8 meV, and 9 meV, respectively (Fig. 2). From the temperature-dependent and power-dependent photoluminescence spectra, it can be seen that the emission peak at 0.687 eV is the result of local carrier recombination and the emission peak at 0.701 eV is the result of free exciton recombination (Fig. 4). The experimental results show that increasing the annealing temperature can reduce the proportion of local carrier recombination. When the temperature is 600°C, the intensity ratio of local carriers to free excitons is reduced to 22.6% of that of the sample annealed at 500 ℃ (Fig. 5). The experimental results show that the photoluminescence performance of the quantum well material can be effectively improved with the appropriate rapid thermal annealing temperature.

Conclusions An InGaAsSb/AlGaAsSb quantum well structure was grown on a GaAs substrate using a MBE system and the effects of rapid thermal annealing on luminescence properties of the quantum well material are systematically discussed. The experimental results show that rapid thermal annealing causes interdiffusion of elements on the heterogeneous interface between the quantum barrier layer and the well layer. This interdiffusion increases the energy of the ground state transition of the quantum well material and thus causes a blue-shift of the room temperature photoluminescence peak of the quantum well material. The emission of the quantum well samples is determined by excitation power-dependent photoluminescence spectrum and temperature-dependent photoluminescence spectrum. There is recombination of localized state carriers and recombination of free excitons at the low energy and high energy end of the photoluminescence peak, respectively. The localized carrier emission of the material is reduced with the increase of rapid thermal annealing temperature. These results show that rapid thermal annealing is beneficial for uniform distribution of atomic clusters produced by diffusion and that it can also promote healing of resulting holes. The rapid thermal annealing process can optimize emission in the quantum well structure when the appropriate annealing temperature is selected, thereby effectively improving the performance of laser materials and laser devices.