Sputter-deposited metal contacts for n-type GaN

Abstract

Sputter-deposited Au, Pt, Cr, Ni and Cu contacts for n-type GaN films were studied using current-voltage (I -V ) and capacitance-voltage (C-V ) measurements. These films were grown by molecular beam epitaxy (MBE), heteroepitaxially on the basal plane of sapphire. The contacts were non-ideally rectifying in nature. Assuming that the non-ideality was due to effects of series resistance and recombination current, a computer curve fitting procedure was employed that enabled the separation of these effects from the thermionic emission current, thereby permitting the calculation of the barrier height. An analysis of the results indicates that the barrier heights for metal contacts on GaN are determined by the difference between the metal and the semiconductor electronegativities and substantially influenced by metal induced gap states (MIGS)/sputtering damage induced surface states (SDISS). The concentration of metal induced gap states/sputtering induced damage states was determined to be approximately 2.7 × 10 13 states cm −2 eV −1 .

Generalized model of the metal/n-GaN Schottky interface and improved performance by electrochemical Pt deposition

“…To the author's knowledge, Hall et al 13 were the first to point out that the real series resistance of a metal/GaN Schottky should be several orders of magnitude smaller than the values usually assumed for a satisfactory fitting of experimental I-V curves. However, no explanation could be found for such a large difference.…”

“…[12][13][14] However, in an attempt to fit experimental data, an exaggerated value of the series resistance has to be assumed. A significant leakage current can reasonably be attributed to an existence of various material defects, surface states, and/or regions with a reduced barrier.…”