Bismuth concentration inhomogeneity in GaAsBi bulk and quantum well structures

The optical and structural properties of GaAsBi bulk and quantum well (QW) samples grown under various conditions were studied by photoluminescence (PL), high resolution x-ray diffraction (HR-XRD) and transmission electron microscopy (TEM). At 10 K, the 90 nm bulk sample shows two PL peaks at 1.18 and 1.3 eV. The temperature and power dependent PL data suggest that both PL peaks originate from the GaAsBi layer which consists of two regions with different Bi concentrations. The TEM images verify that the Bi concentration decreases monotonically across the layer, showing a high Bi concentration (∼0.053) close to the bottom interface which then reduces to ∼0.02 for thicknesses >25 nm. Besides, the high Bi content region cannot be detected by HR-XRD due to a broad and weak diffraction intensity. For multiple QW samples, a similar Bi profile was also observed in which the first well has a significantly higher Bi content compared to the other wells. The energy separation between the PL peaks is 0.12 eV and is consistent with the energy difference observed for the bulk sample. However, two PL peaks were not observed in the other GaAsBi bulk sample which was grown under different conditions, showing the importance of growth optimizations.