Copper Oxide Edge-Termination for GaN Schottky Barrier Diodes with Low Turn-on Voltage
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Copper Oxide Edge-Termination for GaN Schottky Barrier Diodes with Low Turn-on Voltage Yuichi Minoura, Naoya Okamoto, Masahito Kanamura, Tadahiro Imada, Toshihiro Ohki, Kenji Imanishi, Keiji Watanabe, Kazukiyo Joshin, and Toshihide Kikkawa Fujitsu Laboratories Ltd., 10-1 Morinosato-Wakamiya, Atsugi, Kanagawa, 243-0197, Japan ABSTRACT In this study, we propose copper oxide (CuOx) edge-termination for GaN-based Schottky barrier diodes (SBDs) with low turn-on voltage. CuOx fabricated by thermal oxidization of sputtered Cu film at 275°C consisted mainly of Cu2O which is known as a p-type semiconductor. We applied CuOx edge-termination to GaN SBDs with tantalum (Ta) Schottky electrode which has low work function of 4.25 eV. The experimental results of current-voltage characteristics insisted that CuOx edge-termination structure was effective to increase breakdown voltage of GaN SBDs with keeping low turn-on voltage of 0.29 V at 10 A/cm2. INTRODUCTION Owing to its superior properties, such as wide band gap, high electron velocity and high breakdown field, GaN has been extensively investigated for high power and high frequency devices [1]. GaN SBDs are very attractive as low-loss switching devices because of the lower on-resistance and higher breakdown field compared to Si or SiC [2]. Therefore, GaN SBDs can be used in the power supply units. In usual, high breakdown voltage of over 600 V was mainly reported for 200-V class AC-DC converters [3,4]. For DC-DC converters, i.e., enabling conversion from 48 V to 3V, however, breakdown voltage of over 600 V is not needed. Extremely low on-resistance with breakdown voltage of 50-100 V is required. In this paper, we focused on the development of GaN SBDs for the DC-DC converters which operates at less than 50V. To realize low on-resistance, the reduction in the turn-on voltage by using low work function metals as a Schottky electrode is a key point. However, the use of low work function metals leads to the considerable reduction in the breakdown voltage and the increase of the reverse leakage current compared to higher work function metals. In order to increase the breakdown voltage of GaN SBDs with low turn-on voltage, it is necessary to improve the edge structure of a Schottky electrode, such as field plate structure [3] and ion-implanted edgetermination structure [4]. However, it is very difficult to apply p-type ion-implanted edgetermination used in Si or SiC SBDs to GaN SBDs because of its extremely low activation. Here, we propose the novel edge-termination structure by using copper oxide (CuOx). Cuprous oxide (Cu2O) which is a kind of CuOx is promising material as a p-type semiconductor with band gap energy of 2.17 eV [5]. Since Cu2O can be prepared by low cost method, it has been researched as a material for solar cells [6]. In resent years, field effect transistor (FET) with Cu2O on Cu wire was reported [7]. Several techniques have been proposed
to form Cu2O, such as reactive sputtering [8], chemical vapor deposition (CVD) [9] and thermal oxidation [10]. In this study,
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