Resonant Surface Raman Scattering in Direct-Gap Semiconductors

The Raman spectra of optical phonons in InAs, InSb, InP, and GaAs have been studied via reflection techniques, using 5145-, 4965-, 4880-, 4765-, and 4658-Å argon laser excitation. The scattering cross sections in InAs display strong enhancement for laser photon energies near the $E_1$ saddlepoint gap, and two-phonon processes are observed under these conditions. In InSb the laser frequencies are near the $E_1+{\Delta }_1$ gap, but no strong enhancement is observed. InP and GaAs were studied far from resonance with any known gap and demonstrate that such gap resonance is not essential for reflection studies of direct-gap semiconductors using visible-spectrum lasers.