Electrical properties of sputtered-indium tin oxide film contacts on n-type GaN

Abstract

A transparent indium tin oxide (ITO) Ohmic contact on n-type gallium nitride (GaN) (dopant concentration of 2×1017cm−3) having a specific contact resistance of 4.2×10−6Ωcm2 was obtained. In this study, ITO film deposition method was implemented by sputtering. We found that the barrier height, 0.68eV, between ITO and n-type GaN is the same for both evaporated- and sputtered-ITO films. However, the 0.68eV in barrier height renders the evaporated-ITO∕n-GaN Schottky contact. This behavior is different from that of our sputtered-ITO∕n-GaN, i.e., Ohmic contact. During sputtering, oxygen atoms on the GaN surface were significantly removed, thereby resulting in an improvement in contact resistance. Moreover, a large number of nitrogen (N) vacancies, caused by sputtering, were produced near the GaN surface. These N vacancies acted as donors for electrons, thus affecting a heavily doped n-type formed at the subsurface below the sputtered ITO∕n-GaN. Both oxygen removal and heavy doping near the GaN surface, caused by N vacancies, in turn led to a reduction in contact resistivity as a result of electrons tunneling across the depletion layer from the ITO to the n-type GaN. All explanations are given by Auger analysis and x-ray photoelectron spectroscopy.