Raman spectroscopy of localized vibrational modes from carbon and carbon-hydrogen pairs in heavily carbon-doped GaAs epitaxial layers

Heavily carbon-doped GaAs layers have been studied by Raman spectroscopy of localized vibrational modes. Films grown by three different epitaxial techniques - namely molecular-beam epitaxy, metalorganic vapor-phase epitaxy (MOVPE), and metalorganic molecular-beam epitaxy - have been examined. Samples grown by MOVPE show - besides scattering by the high12CsubAs local vibrational mode near 583 cm highminus1, which is observed for all three growth techniques - two additional lines at 452 and 2640 cmhighminus1 for carbon concentrations bigger than 5 x 10high19 cmhighminus3. These lines are assigned to the stretch mode of high12CsubAs-H pairs (2640cmhighminus1) and to a carbon mode of these pairs (452 cmhighminus1). The analysis of polarization selection rules indicates that the 452- cmhighminus1 mode is longitudinal (Asub1 symmetry). It shows a pronounced resonance enhancement in scattering strength for incident-photon energies in resonance with the GaAs Esub1 bandgap energy.