Hydrogen Sensors Made on InP or GaN with Electrophoretically Deposited Pd or Pt Nanoparticles

High quality Schottky diodes were prepared by printing colloidal graphite on the polished wafers of n-type InP or n-type GaN. The wafers were earlier sparsely covered with palladium or platinum nanoparticles by electrophoresis from prepared colloid solutions in isooctane. Deposited contacts and nanoparticles were observed by scanning electron mictroscopy. Current voltage characteristics of the Schottky diodes showed high rectification ratios and the barrier heights close to the value of vacuum-level-alignment of the Schottky-Mott limit. The sensitivity to hydrogen of the diodes was measured in the flow of hydrogen/nitrogen mixtures of various hydrogen concentrations in the range from 1 ppm to 1000 ppm. The estimated detection limits of the diodes were in the sub-ppm range. The diodes represent orders-of-magnitude improvement over the best hydrogen sensors reported previously.