Recently, there are many interests in hydrogen as alternative energy source and carrier. Hydrogen is emission-free fuel when reacted with oxygen to produce the heat of combustion of 141.9 kJ/g while 47.0 and 45.0 kJ/g are for gasoline and diesel. Electrochemical cells and combustion in internal engines are used to transport hydrogen-generated energy to power vehicles and electric devices. Great efforts have been devoted on the researches to produce hydrogen in efficient and economical ways such as photoelectrochemical water splitting, photocatalytic water splitting, radiolysis, and photobioligical water splitting.

Hydrogen is consumed in the petrochemical plant for hydrodealkylation, hydrodesulfurization, and hydrocracking, as a coolant in power stations due to its highest specific thermal conductivity of all gases, as an energy carrier in fuel-cell vehicles, in the propulsion of spacecraft, and in the semiconductor industry. Hydrogen gas is colorless, odorless, extremely reactive with oxygen, and has low ignition energy. When it leaks from pressurized container, its temperature rises up due to its negative Joule-Thomson coefficient, which can induce spontaneous flammable ignition. Therefore, hydrogen gas detection is very important issue in various hydrogen related industrial processes and equipments. Not only for early flammability alarm, a hydrogen sensor is also essential to monitor feed stream in the fuel-cell vehicle for efficient energy conversion.

GaN based material system is very suitable to construct hydrogen sensor.  Wide bandgap of GaN enable devices to operate at high temperature and harsh radiative environment, and mechanical and chemical robustness of GaN ensures reliability and durability of the device. Many types of GaN based hydrogen sensing devices including Schottky diode, metal oxide semiconductor (MOS) diode, GaN nanowire and AlGaN/GaN high electron mobility transistors (HEMTs) which employ platinum or palladium film as a catalytic active layer have been developed for fast and sensitive detection of hydrogen .

In this study, effect of crystal polarity and plane on hydrogen sensing characteristics of GaN based diodes was investigated. Also, AlGaN/GaN HEMT hydrogen sensors with dramatically increased active sites on platinum nanostructure and GaN diode sensors with etched large surface area will be introduced as an approach to improve the sensitivity of hydrogen sensors.