RAMAN-SPECTROSCOPIC ASSESSMENT OF CARBON-HYDROGEN PAIRS IN CARBON-DOPED GAAS-LAYERS

Raman scattering by local vibrational modes of carbon-hydrogen pairs is reported for heavily carbon-doped epitaxial GaAs layers. Scattering by the longitudinal carbon mode of these pairs at 452 cm-1 shows a strong resonant enhancement for incident photon energies approaching the E1 band-gap energy of GaAs (congruent-to 3 eV). A possible mechanism for this resonance behavior is discussed in terms of the displacement of the carbon atom from its normal arsenic lattice site accompanied by a lengthening and weakening of the carbon-gallium bonds when carbon-hydrogen pairs form. The present findings demonstrate that resonant Raman scattering is an attractive tool for the detection of carbon-hydrogen pair formation in thin carbon-doped epitaxial GaAs layers grown from source materials containing hydrogen. The detection limit is estimated to be in the low 10(18) cm-3 range.