Electrical and structural investigation of Pt/n-type GaN Schottky contacts: The possible origin of inhomogeneous barrier

Abstract

An ideal metal/GaN interface is not usually possible and the surface states are often present at such interface and therefore affect the Schottky barrier diode (SBD) performance. In this work the interface states in Pt/n-type GaN SBD were extracted using temperature dependent forward current–voltage (I-V-T) characteristics over a large temperature range (80–400 K). The energy profile distribution of the density of interface states N_SS (E) and its dependence on the temperature were determined from the bias and temperature dependence of the measured effective barrier height ${Ф}_{0bn}(V,T)$ and ideality factor n (V, T). It is shown that the interface states density at room temperature decreases with increasing energy with respect to the conduction band. It is shown that the effective Schottky barrier height (SBH) and ideality factor are correlated to the density of interface states. This result suggests that interface states density contributes to barrier inhomogeneities in Pt/n-type GaN SBD. Fourier transform deep level transient spectroscopy (FT-DLTS) has been employed to extract qualitative information about the native defects present in as-grown n-type GaN. From FT-DLTS, two prominent native defects D₂ and D₃ were observed in GaN. The defect D₂ located at E_C- 0.56 eV could be associated with impurity at Ga site. The defect D₃ located at E_C- 0.26 eV has been assigned to nitrogen-related energy level. These native defects are interpreted as responsible of the existence of interface states and then to the barrier inhomogeneities at Pt/n-type GaN contacts. Furthermore, other possible origins of the interface states at Pt/n-type GaN interface are discussed in terms of the threading dislocations inside the GaN templates that reach the surface and other possible irregularities at this interface.