Physical properties of GaAs on glass

Physical properties of GaAs layers grown by molecular beam epitaxy on glass substrates are investigated by Raman light scattering, Photothermal Deflection Spectroscopy (PDS), optical absorption and Scanning Electron Microscopy (SEM) measurements. The results indicate that the layers are polycrystalline and strain-free. Raman spectra exhibit GaAs-TO and LO modes at 260 and 283 cm^–1, respectively. The peaks are shifted by about 10 cm^–1 with respect to bulk GaAs which we attribute to local heating effects induced by laser excitation. The phonon lines are strong and have a bandwidth of about 5 to 8 cm^-1 indicating a good crystalline quality. However, neither photoluminescence nor the Hall effect could be observed that is suggestive of the presence of a large number of electronic defects. SEM micrographs taken from the surface and the interface exhibit a granular structure with the polycrystal sizes of well under 1 m. PDS results show about 10¹⁸ cm^–3 defects and some disorder at the band gap.