| Abstract [eng] |
The GaAsBi bismides presently are widely studied semiconductor alloys, due to their perspective potential applications in engineering of telecommunication-wavelength-range lasers, multi-junction solar cells, and other IR optoelectronic devices. Recently, atomic structure investigations of bismides revealed the spontaneous CuPtB-type atomic ordering. The goal of the present work is to determine the influence of the atomic ordering on bismide optical properties using the spectroscopic ellipsometry techniques. The MBE-grown epitaxial GaAs1-xBix bismide samples with x ~ 0.03–0.08 relative Bi concentrations were investigated. The CuPtB-type atomic ordering induces optical polarization anisotropy of the epitaxial samples even at normal (to the sample surface) light propagation. The anisotropy was revealed by ellipsometric measurements of transmission, linear birefringence, and dichroism spectra, as well as confirmed by polarized photoluminescence measurements. The main physical reason of the anisotropy is the atomic-ordering induced valence band splitting c. The splitting in bismides was estimated to be of about 50 meV at the x  0.05 Bi concentrations. The bismide splitting essentially, by two orders of magnitude, exceeds that expected in the conventional III-V semiconductor alloys – namely, Ga1-xInxP or GaAs1-xSbx, – at the corresponding atomic compositions, x ~ 0.05. The Mueller-matrix based ellipsometric measurement scheme is suggested, which allows for an effective direct test of a manifestation of CuPt-type atomic ordering in thin epitaxial layers. The testing, carried out on numerous bismide samples, shows that all bismide epitaxial layers, which have structurally qualitative crystalline lattice, manifest the CuPt ordering. This is a distinctive feature of bismides as compared to the conventional III-V semiconductor alloys, in which the ordering can be induced only by specific epitaxial-growth conditions. |
