EPD of Reverse Micelle Pd and Pt Nanoparticles onto InP and GaN for High-Response Hydrogen Sensors

Abstract

We investigated properties of nanolayers electrophoretically deposited (EPD) onto semiconductor indium phosphide (InP) or gallium nitride (GaN) single crystals from colloid solutions of metal palladium (Pd), platinum (Pt) or bimetallic Pd/Pt nanoparticles (NPs) in isooctane. Colloids with metal NPs were prepared by reaction of metal compounds with the reducing agent hydrazine in water confined to reverse micelles of surfactant AOT.. Chopped DC electric voltage was applied for the time period to deposit metal NPs, only partly covering surface of the wafer. The deposits were image-observed by scanning electron microscopy (SEM)..Diodes with porous Schottky contacts were made by printing colloidal graphite on the NPs deposited surface and making ohmic contact on the blank side of the wafer. The diodes showed current-voltage characteristics of excellent rectification ratio and barrier height values close to Schottky-Mott limit, which was an evidence of negligible Fermi level pinning. Large increase of current was observed after switching on a flow of gas blend hydrogen in nitrogen (H2/N2). The diodes were measured with various H2/N2in the range from 1000 ppm to 1 ppm of H2. Current change ratios about 106and about 10 were achieved with 1000 ppm and 1 ppm H2/N2.