PHOTOENHANCEMENT AND PHOTOQUENCHING OF THE 0.68-EV EL2 PHOTOLUMINESCENCE EMISSION IN GAAS GROWN BY MOLECULAR-BEAM EPITAXY AT LOW-TEMPERATURES

We report the photoenhancement and photoquenching of the 0.68-eV EL2 p hotoluminescence emission in low-temperature GaAs grown at 200-350-deg rees-C. EL2 exists in both a quenchable and unquenchable configuration . For the layer grown at 200-degrees-C, EL2 is exclusively in the unqu enchable configuration. The concentration of EL2 in the unquenchable c onfiguration decreases with increasing growth temperature. The quencha ble and unquenchable configurations can be explained by a model of the isolated AS(Ga) under relaxed and strained conditions, respectively. The stress present in low-temperature layers is responsible for the un relaxed condition and consequently for the lack of quenchability. The photoenhancement is attributed to the hole photoionization of (As(Ga)) + and to the presence of a high concentration of the compensating V(Ga ).