Anomalous shape of a triplet vibrational mode line: Random electric-field broadening

A theory is presented for the homogeneous broadening of triplet localized v ibrational mode (LVM) absorption lines arising from point defects with Td s ymmetry. The source of the broadening is electric fields at a defect due to other randomly distributed immobile charged defects. The line shape is cal culated by making an application of a long-established result for the stati stical distribution of field strength at the defect, due originally to Holt smark. This provides a satisfactory explanation for recently reported unusu al profiles for LVM absorption lines in semi-insulating InP heavily doped w ith carbon. [S0163-1829(99)14739-8].