Ohmic contacts and Schottky barriers to n-GaN

Gallium nitride is a highly promising wide bandgap semiconductor with applications in high power electronic devices and optoelectronic devices. For these devices to be realized, metallization, both ohmic and rectifying must be available. In this manuscript, we discuss the properties of ohmic contacts and Schottky barriers on n-type GaN. The most recent ohmic metallization scheme involves Ti/Al based composites, namely Ti/Al/Ni/Au (150 Angstrom/2200 Angstrom/400 Angstrom/500 Angstrom.) preceded by a reactive ion etching (RIE) process which most likely renders the surface highly n-type. With annealing at 900 degrees C for 30 s, contacts with specific resistivity values less than rho(s) = 1 x 10(-7) Omega cm(2) for a doping level of 4 x 10(17) cm(-3) were obtained. Schottky barriers with Ti, Cr, Pd, Au, Ni, and Pt have been reported; however, we will concentrate here on Pt based structures as they yield a large barrier height of 1.1 eV. Both capacitance-voltage and current-voltage analyses have been carried out as a function of temperature to gain insight into the current conduction processes involved. Attention must now be turned to the modifications needed to render these contacts reliable.