Visualization of electrical domains in semi-insulating GaAs:Cr and potential use for variable grating mode operation

The results of an experimental optical technique for imaging the electrical domain repartition in semi-insulating GaAs:Cr are reported. The technique is based on the use of the crystal as the active component of a transverse electro-optic two-dimensional light modulator. Under dc applied voltage, the electrical domains are traveling from the cathode to the anode at a velocity that increases with the applied voltage and with the incident illumination (v≂10–100 mm/s). Results for ac applied voltages are also presented. In particular, the observation of stationary and periodically distributed high-field domains in GaAs:Cr is reported for sawtooth applied voltages (1 kV, 50–250 Hz). These high-field domains induce a phase structure whose period is shown to be electrically controllable. This is the first reported demonstration of the possibility of a variable grating mode operation in semiconductors.