Bandedge optical properties of MBE grown GaAsBi films measured by photoluminescence and photothermal deflection spectroscopy

The bandedge optical properties of GaAsBi films, as thick as 470 nm, with Bi content varying from 0.7% Bi to 2.8% Bi grown by molecular beam epitaxy on GaAs substrates are measured by photoluminescence (PL) and photothermal deflection spectroscopy (PDS). The PDS spectra were fit with a modified Fernelius model which takes into account multiple reflections within the GaAsBi layer and GaAs substrate. Three undoped samples and two samples that are degenerately doped with silicon are studied. The undoped samples show a clear Urbach absorption edge with a composition dependent bandgap that decreases by 56 meV/% Bi and a composition independent Urbach slope parameter of 25 meV due to absorption by Bi cluster states near the valence band. The doped samples show a long absorption tail possibly due to absorption by gap states and free carriers in addition to a Burstein-Moss bandgap shift. PL of the undoped samples shows a lower energy emission peak due to defects not observed in the usually available thin samples (50 nm or less) grown under similar conditions.