OH BONDS IN GALLIUM-ARSENIDE GROWN BY THE LIQUID-ENCAPSULATED CZOCHRALSKI CRYSTAL-GROWTH METHOD

H-related vibrational lines observed at 6 K between 2940 and 3500 cm-1 in O-containing semi-insulating GaAs samples are attributed to OH and NH modes. The detection of an O-18 mode enables us to assign the stro ngest line of the spectrum to an OH mode in a semiconductor. In sample s where holes can be emitted during photoneutralization of EL2 defects , the intensity of many of these lines is photosensitive and additiona l vibrational lines appear after near-infrared illumination. This phot osensitivity is not due to a metastability effect, but rather to diffe rent charge states of the centers where these OH and NH bonds are incl uded and it is interpreted as the capture of a hole by the center. Str ess-induced splitting of some lines could be studied in one sample; an d for one line, the splitting was interpreted by assuming two simultan eously possible orientations of an OH bond and a low-temperature reori entation of this bond under stress. Tentative models are given for the centers associated with two of these lines.