Hydrogen Sensors Using Nitride-Based Semiconductor Diodes: The Role of Metal/Semiconductor Interfaces

Abstract

In this paper, I review my recent results in investigating hydrogen sensors using nitride-based semiconductor diodes, focusing on the interaction mechanism of hydrogen with the devices. Firstly, effects of interfacial modification in the devices on hydrogen detection sensitivity are discussed. Surface defects of GaN under Schottky electrodes do not play a critical role in hydrogen sensing characteristics. However, dielectric layers inserted in metal/semiconductor interfaces are found to cause dramatic changes in hydrogen sensing performance, implying that chemical selectivity to hydrogen could be realized. The capacitance-voltage (C–V) characteristics reveal that the work function change in the Schottky metal is not responsible mechanism for hydrogen sensitivity. The interface between the metal and the semiconductor plays a critical role in the interaction of hydrogen with semiconductor devises. Secondly, low-frequency C–V characterization is employed to investigate the interaction mechanism of hydrogen with diodes. As a result, it is suggested that the formation of a metal/semiconductor interfacial polarization could be attributed to hydrogen-related dipoles. In addition, using low-frequency C–V characterization leads to clear detection of 100 ppm hydrogen even at room temperature where it is hard to detect hydrogen by using conventional current-voltage (I–V) characterization, suggesting that low-frequency C–V method would be effective in detecting very low hydrogen concentrations.

Electrodes for Semiconductor Gas Sensors

“…The Ohmic electric contact made between the device and the electrode material is acceptable; however, the semiconductor gas sensor sometimes requires a rectifying contact between the sensing material and electrode. A rectifying contact would create a dipole in the interfacial zone of a metal and semiconductor triggered by gas adsorption, reducing a potential barrier from time to time or leading to complex phenomena such as field emission or tunneling effect due to thermionic field emission [ 36 , 37 , 38 , 39 , 40 , 41 , 42 ]. In special cases where the semiconductor gas sensor is applied to cars or in the aerospace industry, the electrode material should be able to operate above 600 °C [ 5 , 43 ].…”

Comparative structural and electronic studies of hydrogen interaction with isolated versus ordered silicon nanoribbons grown on Ag(110)

“…Hydrogen modifies the electrical properties of semiconductor materials and the behaviour of electronic devices [2]. The technological implications of such effects are now widely recognized [3].…”

Carrier transport mechanism of Se/n-type Si Schottky diodes

“…5 exhibits the plots of Fowler-Nordheim tunneling (I R /E 2 versus 1/E), PooleFrenkel emission (I R /E versus E 1/2 ) and Schottky emission (I R /T 2 versus E 1/2 ). The current through the diode when dominated by Fowler-Nordheim tunneling is given by [23][24][25] …”