Disorder-induced phonon modes, built-in electric fields and structural properties of CdTe/GaAs heterostructures grown by MBE

We present the results of an optical characterization of CdTe/GaAs(100) het erostructures grown by molecular beam epitaxy prepared following different protocols for substrate preparation: (i) As-decapping and, (ii) cycles of a nnealing and Ar+ sputtering. Their structural, vibrational and electronic p roperties have been studied by experiments of Raman: and photoreflectance s pectroscopies. The line shape of the low temperature Raman spectra presente d the transverse and longitudinal optic modes as well as a broad feature ar ound 162 cm(-1). This feature has been interpreted in terms of disorder-ind uced phonons corresponding to maxima in the one phonon density of states of CdTe. We did not find any evidence of phonons from an interfacial GaTe lay er or Te oxide compounds. The value of the CdTe band gap energy was obtaine d from fittings of the PR spectra around the E-0 critical point and also fr om the corresponding: analysis of the Franz-Keldysh oscillations present in the spectra. This procedure allowed us to determine the magnitude of the e lectric held at both the CdTe/GaAs interface and CdTe surface.