Electrical characteristics of a‐plane low‐Mg‐doped p‐GaN Schottky contacts

Abstract

Electrical characteristics of a variety of Schottky contacts formed with ten metal species on the a-plane of p-type lowMg-doped GaN grown on r-plane sapphire substrates were studied. We found that while current-voltage characteristics obtained under voltage scanning show no memory effect in samples formed on a-plane samples on c-plane showed a substantial memory effects. We consider that the absence of memory effect in the a-plane p-GaN samples is originating from a smaller density of interfacial defect than that in the cplane p-GaN samples. In internal photoemission spectra, we observed two linearly increasing portions suggesting two different Schottky barriers with different heights coexisting in a contact. A potential barrier corresponding to a linear increase locating at lower photon energy typically ranged between 1.6 and 2.5 eV; and that corresponding to another linear increase locating at higher energy ranged between 0.7 and 1.7. The barrier heights showed no relevance to metal work function. The a-plane GaN surface was found to reveal a lamellar structure with stripes along [0001] direction with a randomly oriented roughness. We thus speculate that contact barrier spatially varies according to the different crystal plane.

(Invited) Characterization of Metal/GaN Schottky Contacts - Review from the Early Days

“…High-temperature isothermal capacitance transient spectroscopy measurements revealed that the memory effect originated from acceptor-type defects of Ga vacancies (Ev + 1.1 eV) and that these defects were localized near the p-GaN surface (21). We also found less metal-workfunction dependence due to strong surface Fermi-level pinning (22), and large surface-orientation dependences between Ga-polarization c-plane, N-polarization c-plane, and a-plane p-GaN (23,24). Recently, as the power switching electron devices have become more complicated structures like Si power devices in order to realize an e-mode operation, metal/p-GaN interfaces have been studied again for the development of lateral junction FETs and vertical transistors (25)(26)(27).…”