DX CENTERS IN AL0.3GA0.7AS GAAS ANALYZED BY POINT-CONTACT MEASUREMENTS/

The influence of DX centers on the low-dimensional transport through p aint contacts in silicon delta-doped Al0.3Ga0.7As/GaAs heterostructure s is investigated. The charge state of the DX centers is changed by te mperature as well as optical and infrared irradiation. The experimenta l results reveal that the point contact resistance is strongly influen ced by carriers in a quantum well formed at the delta-doping layer. Th e carriers screen the split gate voltage of the point contact and the point contact resistance is reduced or even suppressed. During irradia tion with visible light a part of the electrons ionized from the DX ce nters remains in the quantum well at the silicon dopants and hinders f ormation of a point contact. After irradiation a strongly temperature dependent relaxation of these carriers was observed. Infrared radiatio n with wavelengths up to 11.5 mu m reduces the screening effect. Infra red and temperature dependent measurements suggest a logarithmic depen dence of the screening effect on the carrier density at the silicon do ping layer. (C) 1998 American Institute of Physics. [S0021-8979(98)038 16-X].