Influence of the type of interlayer on current transport mechanisms and defects in n-ZnO/ZnCdO/p-Si and n-ZnCdO/ZnO/p-Si heterojunctions grown by molecular beam epitaxy

Abstract

A pair of heterojunctions with different type of interlayer: n-ZnO/ZnCdO and n-ZnCdO/ZnO were grown by molecular beam epitaxy on p-Si substrate and investigated in the present work. At first, their electrical properties and parameters were discussed following current-voltage (I-V) characteristics measured over a wide range of temperatures from 40 K to 300 K. The analysis of I-V plots in log-log scale pointed out the presence of different carrier transport mechanisms: tunneling, multi-tunneling capture-emission and space-charge limited currents. Next, the capacitance-voltage characteristics were studied to determine the dopant concentration of the investigated junctions, along with the net doping profiles and their temperature dependence in the range of 40 K to 300 K. Finally, a deep level transient spectroscopy method was applied to characterise defects in the studied junctions. Donor-like traps were identified and their parameters, such as activation energy and capture cross section, were calculated. Furthermore, the influence of cadmium ions in ZnCdO interlayer of n-ZnO/ZnCdO/p-Si diode on the energy position of trap levels was noticed. Moreover, it was demonstrated that the interlayer type affects junction parameters, especially its built-in potential, as well as it modifies the current transport mechanisms in the intermediate range of voltage.