Photomodulated transmittance of GaBiAs layers grown on (0 0 1) and (3 1 1)B GaAs substrates

In this work, photomodulated transmittance (PT) has been applied to investigate the energy gap of GaBiAs layers grown on (001) and (311)B GaAs substrates. In PT spectra, a clear resonance has been observed below the GaAs edge. This resonance has been attributed to the energy gap-related absorption in GaBiAs. The energy and broadening of PT resonances have been determined using a standard approach in electromodulation spectroscopy. It has been found that the crystallographic orientation of GaAs substrate influences on the incorporation of Bi atoms into GaAs and quality of GaBiAs layers. The Bi-related energy gap reduction has been determined to be ~90meV per percent of Bi. In addition to PT spectra, common transmittance spectra have been measured and the energy gap of GaBiAs has been determined from the square of the absorption coefficient α2 around the band-gap edge. It has been found that the tail of density of states is significant for GaBiAs and influences the accuracy of energy gap determination from the α2 plot. In the case of PT spectra, the energy gap is determined unambiguously since this technique is directly sensitive to singularities in the density of states.

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