Effects of the high-refractive index SiN x passivation on AlGaN/GaN HFETs with a very low gate-leakage current
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Effects of the high-refractive index SiNx passivation on AlGaN/GaN HFETs with a very low gate-leakage current Hiroshi Kambayashi, Takahiro Wada, Nariaki Ikeda, and Seikoh Yoshida Yokohama R&D Laboratories, The Furukawa Electric Co., Ltd. 2-4-3 Okano, Nishi-ku, Yokohama, Kanagawa 220-0073, Japan ABSTRACT We have reported on the stress effects of the SiNx passivation film on AlGaN/GaN heterojunction field effect transistors (HFETs). The AlGaN/AlN/GaN heterostructure was grown using a metalorganic chemical vapor deposition (MOCVD). We first investigated the dependences between SiNx films and the refractive index of these. As a result, the stress type of the SiNx films was all Tensile. Moreover, the refractive index of SiNx increased, the stress was decreasing and almost invariable over refractive index 2.1. Furthermore, we fabricated some kinds of AlGaN/GaN HFETs and estimated the gate-leakage current and the current collapse of HFET. As a result, we confirmed the relationship between the stress of passivation film and gate-leakage current, and that the low stress SiNx film with a high-refractive index can suppress both a gate-leakage current and a current collapse. INTRODUCTION III-V nitride-based semiconductor devices have very excellent figure of merits for high-power, high-frequency, and high-temperature devices compared with conventional Si devices [1-4]. Especially, the specific on-state resistance (Ron) of the GaN based field effect transistors (FETs) is expected to be about one order of magnitude lower than that of Si based FETs. That is, GaN based electronic devices enable us to reduce the power loss of switching devices, such as inverters or converters, compared with these of using conventional Si devices, and consequently to reduce the cooling system. It is also expected that a higher switching speed, a high frequency operation, and a high efficiency operation can be realized by using GaN based FETs. For a practical use of an AlGaN/GaN heterojunction FETs (HFETs) as a low loss switching device, it is required to reduce the leakage current and to suppress the current collapse. In order to solve these problems, there are many reports [5-10]. However, the suppression of the leakage current and the current collapse was insufficient. In this paper, we investigated the stress effects of a passivation film on
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AlGaN/GaN HFETs in order to suppress the gate-leakage current and the current collapse of HFETs. EXPERIMENTAL We used a metalorganic chemical vapor deposition (MOCVD) apparatus for the GaN growth. As source gases, trimethylgallium (TMG), trimethylaluminum (TMA), and ammonia (NH3) were used for the growth. A heterostructure of an undoped Al0.25Ga0.75N (20 nm) / GaN (750 nm) / AlN based buffer (200 nm) was grown on the Si (111) substrate. Using this heterostructure, we fabricated HFETs with a gate width of 0.4 mm for unit-cell devices. The gate/source and drain/gate distance were 3000 nm and 0.01 mm, respectively. The gate length was 2000 nm. An isolation of the HFET was perform
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