Investigation of the photorefractive behavior of chrome-doped GaAs using two-beam coupling

Abstract

Recently, there has been considerable interest in the photorefractive properties of semiconductors1,2 because of the possible applications in optical data processing and phase conjugate optics. We have made measurements, at 1.06 µm, of the grating formation time and the two-beam coupling gain as a function of intensity, grating wavelength, and applied voltage. The GaAs sample has a chrome concentration of 1017 cm−3, dark resistivity of ~300 MΩ cm, and dimensions of 10 × 10 × 5.5 mm. The applied electric field and the polarization vector were along the [111] direction. The inverse of the grating formation time varies linearly with intensity in accordance with theoretical predictions. For an incident laser intensity of 35 mW/cm2, the grating formation time is 1.5 ms and increases to 1.8 ms on application of 6 kV. The gain increases with intensity and saturates. The saturated gain and the intensity required for saturation both increase with applied voltage. A maximum gain of 0.5 cm-1 at a grating spacing of 0.9 pm was measured with no voltage applied which leads to a trap concentration of 1015 cm−3. An applied voltage of 6 kV yielded a maximum gain of 0.9 cm−1 at a grating spacing of 1.2 µm. It was observed that reducing the intensity decreases the gain and, at the same time, shifts the maxima of the gain curves to higher values of grating spacing both with and without an applied voltage.