Understanding Growth-Faulted GaAsBi Samples by Reflectance Anisotropy Spectroscopy

Reflectance anisotropy spectroscopy (RAS) has been recently applied to molecular beam epitaxy (MBE) of GaAsBi alloys. The presence of the voluminous Bi atoms induces strain in the crystal lattice, modifying the substrate symmetry of the centrosymmetric GaAs(001) and then producing clear signatures in the anisotropy spectra of the GaAsBi layers. In particular, the amplitude of the characteristic structure measured below 2.5 eV is shown to be directly related to the Bi concentration, while the sign has a meaningful correlation to the strain conditions present in the sample. In this article, the application of RAS is extended to “faulted” GaAsBi samples, i.e., samples that after growth result not satisfactory for research because of problems or errors risen during the complex deposition process (wrong growth temperature, excess or deficiency of Bi flux, formation of dislocations, etc.). Herein, it is demonstrated that also in these cases RAS offers a useful characterization of the sample, possibly (if RAS runs during the deposition) singling out the occurrence of faults eventuality, and thus validating its potential applicability to an all-optical real-time monitoring of the deposition process.