Raman scattering in mixed crystal semiconductors
Abstract
The effects of substitutional disorder on the elastic light scattering by phonons in three semiconductor alloys GaSb(1-x)Ge2(x), GaAs(x)Sb(1-x), and Al(x)Ga(1-x)As were studied. The asymmetric broadening and shifting of the longitudinal optic (LO) phonon lines as a function of disorder were measured and the scattering from disorder-activated longitudinal acoustic (DALA) and transverse acoustic (DATA) modes were observed. The observation of zone-center (k = 0) selection rules for the dominant scattering, even in the most disordered alloys, demonstrates the importance of considering the k = 0 spectral projection of phonon-eigenstates in explaining the Raman lineshapes for LO phonons in mixed crystals. In a polarized resonance Raman study of three Al(x)Ga(1-x)As alloys, polarization selection rules were used to discriminate between the allowed deformation potential and forbidden intraband Froehlich scattering by LO phonons. The strong outgoing resonances were observed both first-order and second-order LO phonon scattering. Of particular interest is the discovery of an incident-wavelength-dependent shift between the deformation potential and an incident wavelength dependent shift between the deformation potential and intraband Froehlich scattering in the indirect samples. The forbibben allowed energy shift was attributed to a localization effect manifested through the correlation between local values of the energy gap and local phonon frequencies.
- Publication:
-
Ph.D. Thesis
- Pub Date:
- December 1987
- Bibcode:
- 1987PhDT........25M
- Keywords:
-
- Crystals;
- Disorders;
- Energy Gaps (Solid State);
- Phonons;
- Raman Spectra;
- Semiconductors (Materials);
- Aluminum Compounds;
- Deformation;
- Gallium Arsenides;
- Polarization (Charge Separation);
- Solid-State Physics