INFLUENCE OF HYDROSTATIC-PRESSURE ON DX-CENTER LEVELS IN GAAS1-XPX-S

The paper deals with the investigation of the DX centres in GaAs1-xPx:S under a hydrostatic pressure of up to 1.1 GPa by capacitance methods (C V and deep-level transient spectroscopy measurement) and impedance analysis. In samples with x = 0.3 and 0.4 we have found two levels exhibiting properties of the DX centre. The first of these can be observed for x > 0.35, where it crosses the conduction-band edge and enters the gap. For 0.4 < x < 0.5 it follows the X minimum of the conduction band; however, for x almost-equal-to 0.3 it behaves as if it were associated with both X and L minima. The level determines the transport properties of the material, and especially the increase in resistivity at low temperatures for x > 0.35. The second level is located approximately 40 meV below the first level. Both levels have a small thermally activated capture cross-section for electrons, which leads to a metastable behaviour at temperatures below about 100 K. We have investigated systematically the capture process and the influence on it of hydrostatic pressure. The capture kinetics may be explained by a model of alloy broadening. The pressure coefficients obtained for both levels support the model of large lattice relaxation accompanying the capture or the emission.