The effect of bismuth on the optical properties of InGaAsBi/GaAs quantum well structures is investigated using the temperature-dependent photoluminescence from 12 K to 450 K.The incorporation of bismuth in the InGaAsBi quantum well is confirmed and found to result in a red shift of photoluminescence wavelength of 27.3 meV at 300 K.The photoluminescence intensity is significantly enhanced by about 50 times at 12 K with respect to that of the InGaAs quantum well due to the surfactant effect of bismuth.The temperature-dependent integrated photoluminescence intensities of the two samples reveal different behaviors related to various non-radiative recombination processes.The incorporation of bismuth also induces alloy non-uniformity in the quantum well,leading to an increased photoluminescence linewidth.
Linearly graded In_xGa_（1-x）As metamorphic buffers with different mismatch grading rates were grown on InP substrate by gas source molecular beam epitaxy.Room temperature photoluminescence spectra show that the sample with lower mismatch grading rate in the buffer has stronger photoluminescence signal,indicating the improved optical property.Atomic force microscope images show that the lower mismatch grading rate in the buffer leads to a slightly rougher surface.The relaxation procedure with two steps in the buffer layers has been observed by X-ray diffraction reciprocal space mapping.The measurements of X-ray diffraction also reveal that the lower mismatch grading rate in the buffer is beneficial for the lattice relaxation and release of residual strain.To further increase the relaxation degree,a lower mismatch grading rate and composition ＂overshoot＂ are suggested.
