Academic journal article American Academic & Scholarly Research Journal

Structural and Electrical Sensitivity at Several Temperatures with Hydrogen Sensor of Ni/AlGaN Schottky Diode

Academic journal article American Academic & Scholarly Research Journal

Structural and Electrical Sensitivity at Several Temperatures with Hydrogen Sensor of Ni/AlGaN Schottky Diode

Article excerpt

Abstract. The characteristics of Ni Schottky diodes on AlGaN contact the Al mole fraction up to x = 0.11in pure nitrogen and 2% hydrogen in nitrogen ambient are studied. High temperature stability of Ni diode on AlGaN was achieved by long term annealing at 450°C at 1min. The diode I-V response from (50-450°C) has been characterized, revealing the diodes ability to detect 2% hydrogen in nitrogen ambient at 100°C up to 450°C and pure nitrogen from 150°C up to 450°C. For the samples without annealing under gas of 2% hydrogen in nitrogen ambient, the ideality factor decreases from 1.77 to 1.50, and series resistance decreases from 213 Ω to 126Ω, and the barrier height increases from 1.00 to 1.18 eV with increasing temperature. For the Schottky contacts annealed in nitrogen ambient at 450°C for 1min, the ideality factor decreases from 2.18 to 1.58, and series resistance decreases from 363Ω to 207Ω, and the barrier height increases from 0.77 to 1.04 eV with increasing temperature in a temperature range of 198-298 K. The ideality factor and series resistance of the Schottky contacts with annealing are higher than those without annealing, while the barrier height is lower than that without annealing at various temperatures.

Keywords: Ni Schottky diodes, AlGaN HEMT, Thermal annealing, gas sensors.

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1 INTRODUCTION

There is emerging interest in the use of GaN Schottky diodes as sensitive combustion gas sensors (Ambacher, et al., 2002, Casady, et al., 1998, Ekedahl, et al.,1998) and of AlGaN high electron mobility transistors (HEMTs) for chemical sensing (Kim, et al., 2003, Tarakji, et al., 2002, Mehandru, et al., 2005). The high carrier density formed at the AlGaN interface by spontaneous and piezoelectric polarization makes this structure particularly sensitive to changes in surface strain or potential. In addition, the ability to integrate these sensors with HEMT electronics for wireless communication systems is attractive for many applications. Neuberger et al. have suggested that the sensing mechanism for chemical adsorbates originated from compensation of the polarization induced bound surface charge by interaction with the polar molecules in the liquids (Casady, et al., 1998). There is a strong interest in wide band gap semiconductor gas sensors for applications including fuel leak detection in spacecraft. In addition these detectors would have dualuse in automobiles and aircraft, fire detectors, exhaust diagnosis and emissions from industrial processes (Svenningstorp, et al., 1999, Cheng, et al., 2008, Simin, et al., 2002). GaN electronics and sensors will reduce spacecraftlaunch weighs and increase satellite functional capabilities. Given the high cost per pound of launching payloads into earth orbit, the weight savings gained by using wide band gap devices could have large economic and competitive implications in the satellite industry. Existing commercial satellites require thermal radiators to dissipate heat generated by the spacecraftelectronics. These radiators could be eliminated with GaN, and allow greater functionality (more transponders in a commercial satellite) by utilizing the space and weight formerly occupied by the thermal management system. In addition, the radiation hardness of these materials would reduce the weight of shielding normally used to protect spacecraftelectronic components from radiation. GaN is capable of operating at much higher temperatures than more conventional semiconductors such as Si. Simple Schottky diode or field-effect transistor structures fabricated in GaN (and SiC) (Chen, et al., 1996) are sensitive to a number of gases, including hydrogen and hydrocarbons (Ayyildiz, et al., 2005). One additional attractive attribute of GaN and SiC is the fact that gas sensors based on this material could be integrated with high-temperature electronic devices on the same chip. There have already been reports of rad-hard (>300 M rad Co-60 gamma ray tolerance) Combustion gas detectors with extremely fast time response and capable of operating at high temperatures, eliminating bulky and expensive cooling systems. …

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