DX centers in Al0.3Ga0.7As/GaAs analyzed by point contact measurements

The influence of DX centers on the low-dimensional transport through paint contacts in silicon delta-doped Al0.3Ga0.7As/GaAs heterostructures is investigated. The charge state of the DX centers is changed by temperature as well as optical and infrared irradiation. The experimental results reveal that the point contact resistance is strongly influenced by carriers in a quantum well formed at the delta-doping layer. The carriers screen the split gate voltage of the point contact and the point contact resistance is reduced or even suppressed. During irradiation with visible light a part of the electrons ionized from the DX centers remains in the quantum well at the silicon dopants and hinders formation of a point contact. After irradiation a strongly temperature dependent relaxation of these carriers was observed. Infrared radiation with wavelengths up to 11.5 mu m reduces the screening effect. Infrared and temperature dependent measurements suggest a logarithmic dependence of the screening effect on the carrier density at the silicon doping layer. (C) 1998 American Institute of Physics. [S0021-8979(98)03816-X].