Stable hydrogen sensors from AlGaN∕GaN heterostructure diodes with TiB2-based Ohmic contacts

The use of TiB2-based Ohmic contacts on Pt-gate AlGaN∕GaN heterostructure diode hydrogen sensors is shown to provide very stable operation for detection of 1% H2 in air under field conditions where temperature is allowed to vary. In contrast, the use of more conventional Ti∕Al∕Pt∕Au Ohmic contacts led to higher background variations in current that affect the ultimate detection threshold of the sensors. Combined with a differential pair geometry that compares current from an active diode with Pt-gate contact and a passive diode with Ti∕Au gate, the more stable TiB2-based Ohmic contacts reduce false alarms due to ambient temperature changes. The diodes exhibit a change in forward current of more than 1mA at 1.5V when 1% H2 is introduced into an air ambient.