Conduction mechanism in a metal-insulator-semiconductor structure with a low temperature GaAs insulating layer

We report results of electrical characterisation of MIS diode structures with Al metallisation, an insulating layer of low temperature grown (LT) GaAs on a n⁺ GaAs substrate. The I-V characteristics at varying temperatures between 120 K and 285 K and a.c. conductivity measurements between 1 kHz and 13 MHz at room temperature were examined. The I-V characteristics were analyzed through the dependence of the diode ideality factor on temperature. Values between 2.8 and 4 were obtained, typical of tunneling through the depletion potential barrier in the n⁺ GaAs at the interface. The high voltage part of the forward I-V characteristics indicates a low and weakly temperature dependent series resistance of the diode, associated with carrier transport through LT-GaAs, characterised by an activation energy of 32 meV. The a.c. dynamic resistance in the high voltage part of the I-V characteristics decreases as a function of frequency and between 2 MHz and 13 MHz approximately follows ω^s dependence with s = 0.65. These results are consistently interpreted as the result of the transport of injected carriers through the LT GaAs layer via a hopping mechanism involving defects.