Abstract
Depositions on surfaces of semiconductor wafers of InP and GaN were performed from isooctane colloid solutions of palladium (Pd) nanoparticles (NPs) in AOT reverse micelles. Pd NPs in evaporated colloid and in layers deposited electrophoretically were monitored by SEM. Diodes were prepared by making Schottky contacts with colloidal graphite on semiconductor surfaces previously deposited with Pd NPs and ohmic contacts on blank surfaces. Forward and reverse current-voltage characteristics of the diodes showed high rectification ratio and high Schottky barrier heights, giving evidence of very small Fermi level pinning. A large increase of current was observed after exposing diodes to flow of gas blend hydrogen in nitrogen. Current change ratio about 700,000 with 0.1% hydrogen blend was achieved, which is more than two orders-of-magnitude improvement over the best result reported previously. Hydrogen detection limit of the diodes was estimated at 1 ppm H2/N2. The diodes, besides this extremely high sensitivity, have been temporally stable and of inexpensive production. Relatively more expensive GaN diodes have potential for functionality at high temperatures.
Highlights
Hydrogen gas (H2) monitoring sensors are in demand mainly for detection of H2 leakage in many industry productions such as, H2 filling stations, cryogenic cooling, research labs, etc
Rounded black spots represent Pd NPs; most of them are circular of about 10 nm in diameter and the others are their aggregations of various sizes
A tendency to create aggregates was stronger in the case of Electrophoretic depositions (EPD) on InP than on GaN, as it can be seen by comparing Figure 2 with Figure 1
Summary
Hydrogen gas (H2) monitoring sensors are in demand mainly for detection of H2 leakage in many industry productions such as, H2 filling stations, cryogenic cooling, research labs, etc. Sensitive and selective (i.e., exclusive to one gas) H2 sensors are needed in forming gas leak detectors for testing leaks in various equipment like vacuum apparatuses, refrigerators, heat exchangers or fuel systems in cars, etc. Such detectors contain highly sensitive H2 sensors and forming gas (noncombustive mixture of H2 in nitrogen) in place of expensive helium (the price of helium has recently risen sharply due to increased demand and limited resources) [1]. High sensitivity with about six orders-of-magnitude response to 5,000 ppm H2 in N2 has been achieved with porous Pd/ GaN Schottky sensors [4]. Similar behavior can be expected at other Schottky barrier sensors as well
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