Influence of surface oxides on hydrogen-sensitive Pd:GaN Schottky diodes

Abstract

The hydrogen response of Pd:GaN Schottky diodes, prepared by in situ and ex situ deposition of catalytic Pd Schottky contacts on Si-doped GaN layers is compared. Ex situ fabricated devices show a sensitivity towards molecular hydrogen, which is about 50 times higher than for in situ deposited diodes. From the analysis of these results, we conclude that adsorption sites for atomic hydrogen in Pd:GaN sensors are provided by an oxidic intermediate layer. In addition, in situ deposited Pd Schottky contacts reveal lower barrier heights and drastically higher reverse currents. We suggest that the passivation of the GaN surface before ex situ deposition of Pd also results in quenching of leakage paths caused by structural defects.

Detection of ppm‐order hydrogen gas by Pd/AlGaN/GaN high electron mobility transistor‐based sensors

“…This logarithmic relation between the detection current variation and the hydrogen concentration is suitable for the high-sensitive hydrogen sensors. A similar logarithmic relation between the variation of the Schottky barrier height and the hydrogen concentration has been reported by several authors [4,7,15]. These results indicate that the hydrogen gas changes the gate potential, and hence affects the electron density of the two-dimensional electron gas.…”

Electronics and sensors based on pyroelectric AlGaN/GaN heterostructures – Part B: Sensor applications

“…As reported in [36], surface treatments with HCl or HF, usually carried out before the deposition of metal contacts, do not remove the native surface oxide from such surfaces [31]. The electric characteristics of the in-situ deposited sample (not shown) indicate a significantly lower Schottky barrier height than that of ex-situ deposited samples, which we attribute to passivation of leakage paths by native oxidation in the latter case [35]. Surprisingly, as shown in Fig.…”

“…The bias voltage is 200 mV. The insitu deposited device shows almost no sensitivity, whereas the ex-situ deposited device shows a pronounced sensor signal, which corresponds to a decrease in barrier height of 560 mV [35].…”

“…Together with the observation that the dependence of the sensor signal on hydrogen partial pressure in oxygen free atmosphere follows a Temkin isothermal behaviour, it was concluded that signal generation is caused by interfacial adsorption of dissociated hydrogen. To identify the nature of hydrogen adsorption sites at the metal/GaN interface we have recently investigated the hydrogen sensitivity of Pd:GaN Schottky diodes with in-situ deposited Pd contacts (evaporated directly after the PIMBE growth without exposure to atmosphere) [35]. The characterization of the hydrogen sensitivity was carried out in vacuum under application of hydrogen steps at partial pressures of 1 mbar.…”

Effects of surface states on hydrogen sensing performance of Pt‐GaN Schottky diodes

“…Devices on GaN can be operated at elevated temperatures and are expected to realize high performance [4][5][6]. Previously, only a few literatures reported the effects of surface states of GaN on hydrogen sensing performance, and little is known about it [7]. Therefore, in this work, firstly, hydrogen sensing characteristics of Pt-GaN Schottky diodes fabricated on as-grown and annealed GaN surfaces are studied in order to investigate the correlation between the surface defects of GaN and hydrogen sensing performance.…”