Current transport and deep levels in p-Si/n-Zn0.9Mg0.1O/n-ZnO heterojunction

Abstract

The paper describes the deep level transient spectroscopy (DLTS) measurements that were performed in order to investigate defects in p-Si/n-Zn0.9Mg0.1O/n-ZnO heterojunction (HJ). The HJ structure was grown by molecular beam epitaxy (MBE) technique on a p-type Si(111) substrate at 500 °C. The DLTS studies had been preceded by the current-voltage (I-V) and capacitance-voltage (C-V) measurements. The I-V measurements show the rectifying behavior of the HJ and indicate that the low forward bias (less than 0.6 V) mechanism of current transport is dominated by recombination-tunneling whereas at higher voltage space charge limited current (SCLC) governs the current transport. The I-V and C-V measurements yield donor concentration of ND = 5·1015 cm−3 in the Zn0.9Mg0.1O layer. This value is two orders of magnitude less than the acceptor concentration, NA = 2·1017 cm−3 in the Si substrate. Therefore it has been assumed that the depletion region extends mainly on the Zn0.9Mg0.1O side of the HJ and the DLTS signal has its origin in this layer and at the HJ interface. The DLTS measurements performed within the temperature range of 20–400 K revealed the presence of three electron traps, with activation energies of 0.06 eV, 0.38 eV, and 0.39 eV respectively. The latter two are ascribed to the defects in the Zn0.9Mg0.1O layer, while the trap with the activation energy of 0.06 eV is located either in the Zn0.9Mg0.1O layer or at the interface with Si.