Infrared and Raman studies of carbon impurities in highly doped MBE AlAs-C.

Infrared absorption measurements of heavily carbon doped p-type AlAs have revealed a localized vibrational mode at 631.6 cmhigh-1 which appears as a Fano profile in uncompensated material. Raman scattering measurements show a corresponding line at about 637 cmhigh-1: possible reasons for the difference in frequency are discussed. The line is assigned to CsubAs acceptors and a comparison is made with a two parameter Keating cluster model. Additional weaker lines at 616.7, 632.8, 633.7 and 645.9 cmhigh-1 have been observed in absorption and possible interpretations, including CsubAs-CsubAs pairs, have been investigated. Passivation of a sample with hydrogen led to the observation of the H-CsubAs stretch mode at 2555.4 cmhigh-1, but satellites to this line have not been detected.