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

Yoshihiro Irokawa

doi:10.3390/s110100674

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.

Highlights

Hydrogen has attracted considerable attention as a clean energy source instead of petroleum
For GaN Schottky diode-type hydrogen sensors, it was reported that an oxidic intermediate layer between the catalytic Schottky contact and the GaN surface is the origin of the hydrogen sensitivity of
Several authors have reported the critical role of the dielectric layer between the Schottky metal and the GaN surface in hydrogen sensitivity of devices [16,17,18,19,20,21,22]

Summary

Introduction

Hydrogen has attracted considerable attention as a clean energy source instead of petroleum. Due to the large band-gap of GaN and SiC, and the associated chemical stability and mechanical robustness, these semiconductors can be used for many harsh applications, satisfying a considerable interest in developing hydrogen gas sensors capable of operation in harsh environmental conditions such as high-temperature and chemically corrosive ambients. These include gas sensing operations during chemical reactor processing, onboard fire alarms on aircraft and space vehicles, as well as detection of fuel leaks in automobiles and aircraft, to name but a few. I investigate the interaction mechanism of hydrogen with the nitride-based semiconductor diodes, focusing on the metal/semiconductor interfaces

Experimental

Results and Discussion

Conclusions and Future Work