Resonance enhanced Raman studies of as-grown and laser-processed HgCdTe

Raman spectroscopy in Hg(1-x)Cd(x)Te (MCT) is a powerful, nondestructive surface probe of alloy composition and crystallinity. The frequencies and the relative amplitudes of the HGTe-like and CdTe-like phonon modes change with Cd fraction; the E1 and E1 + Delta 1 critical points shift with x value and strongly influence the Raman spectra obtained with the green and blue lines of the argon laser. The resonance enhancement of the two LO and two TO modes and a cluster mode in as-grown samples of MCT are studied for x values between 0.20 and 0.31. Also studied are the changes that occur in the Raman spectra after exposure of the MCT surfaces to single pulses from a dye laser with pulse energies above the melt threshold. The Raman spectra show clear evidence of compositional changes near the surface when processing occurs in air. However, when the irradiation occurs in an ambient of about atm of argon, the major effect is a reduction of the peak associated with a cluster mode. The results are consistent with a strong suppression of clustering after pulsed laser annealing.