Study of Schottky barriers prepared by deposition of colloidal graphite and Pt nanoparticles on InP and GaN

Schottky barriers were prepared by mechanical deposition of colloidal graphite on polished surfaces of InP or GaN single crystals. Before applying the graphite, the surface was sparsely covered with Pt nanoparticles deposited electrophoretically. Diodes, consisting of the Schottky barrier and an ohmic contact made on the plain surface, were studied by current voltage characteristics. The diodes showed high rectification ratio and electron transport governed by thermionic emission with a high Schottky barrier height indicating negligible Fermi level pinning. By testing with the flow of calibrated gas consisting of 10^-6 parts of hydrogen and rest nitrogen, the current voltage characteristics showed high sensitivity to hydrogen. The sensitivity represents more than three orders-of-magnitude improvements over the best results published previously by other authors. Besides extremely high sensitivity, the both types of diodes have short response and recovery times after hydrogen exposure, are temporally stable and low production price which properties make them prospective for practical applications as hydrogen sensors. The advantage of pricier GaN diodes is their potential use at high temperatures.