Mapping of n-GaN Schottky contacts formed on facet-growth substrates using near-ultraviolet scanning internal photoemission microscopy

Abstract

Scanning internal photoemission microscopy (SIPM) is applied to characterize Ni Schottky contacts formed on the thick low-carrier-density drift layer grown on facet-growth freestanding GaN substrate. Four variations of the Schottky contact dots are prepared: dots formed in the c-plane growth region, in the facet growth region, in the region including the boundary between the c-plane and facet regions, and in the region including a large-dislocation-density area at the center of the facet growth region. For all the samples, the SIPM photoyield (Y) maps obtained using visible lasers show that the Y and Schottky barrier height were sufficiently uniform over the contacts, resulting in uniform metal–semiconductor interfaces. The growth mode boundary and the large-dislocation area as a vague pattern consisted of large- and small-Y regions in about 100-μm large are clearly observed in the Y map using a near-ultraviolet laser. Device breakdown under high voltage occurs in the large-dislocation-density region with large Y. The results indicate that this method can predict device failure in conjunction with crystal defects and electrical characteristics of Schottky contacts.