Mapping of n-GaN Schottky contacts formed on facet-growth substrates using near-ultraviolet scanning internal photoemission microscopy
Scanning internal photoemission microscopy (SIPM) is applied to characterize Ni Schottky contacts formed on a thick low-carrier-density drift layer grown on facet-growth freestanding GaN substrate. Four variations of the Schottky contact dots are prepared, those 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 a 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 showed 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 consisting of large- and small-Y regions of about 100 μm, are clearly observed in the Y map using a near-ultraviolet laser. Device breakdown under high voltage occurred 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 the electrical characteristics of Schottky contacts.