AlGaN Channel HEMT with Extremely High Breakdown Voltage
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AlGaN Channel HEMT with Extremely High Breakdown Voltage Takuma Nanjo1, Misaichi Takeuchi2, Akifumi Imai1, Yousuke Suzuki1, Muneyoshi Suita1, Katsuomi Shiozawa1, Yuji Abe1, Eiji Yagyu1, Kiichi Yoshiara1 and Yoshinobu Aoyagi2 1 Mitsubishi Electric Corporation, Advanced Technology R & D Center, 8-1-1, Tsukaguchihonmachi, Amagasaki, Hyogo 661-8661, JAPAN 2 Ritsumeikan Global Innovation Research Organization, Ritsumeikan University, 1-1-1 NojiHigashi, Kusatsu, Shiga 525-8577, JAPAN ABSTRACT A channel layer substitution of a wider bandgap AlGaN for a conventional GaN in high electron mobility transistors (HEMTs) is an effective method of enhancing the breakdown voltage. Wider bandgap AlGaN, however, should also increase the ohmic contact resistance. Si ion implantation doping technique was utilized to achieve sufficiently low resistive source/drain contacts. The fabricated AlGaN channel HEMTs with the field plate structure demonstrated good pinch-off operation with sufficiently high drain current density of 0.5 A/mm without noticeable current collapse. The obtained maximum breakdown voltages was 1700 V in the AlGaN channel HEMT with the gate-drain distance of 10 μm. These remarkable results indicate that AlGaN channel HEMTs could become future strong candidates for not only high-frequency devices such as low noise amplifiers but also high-power devices such as switching applications. INTRODUCTION GaN-based wide bandgap semiconductors have superior electrical properties such as a high electron saturation velocity and a high breakdown field. In particular AlGaN/GaN highelectron mobility transistors (HEMTs) with high-density two-dimensional electron gas have been widely studied for high-power and high-frequency applications.1-10 To increase a power density of HEMTs, it is a simple strategy to increase a breakdown voltage. Therefore applying a wider bandgap material for a channel layer, which generally enhances the breakdown field (Ec), is one of effective methods. Higher Al composition AlGaN is an available material to increase the breakdown voltage without decreasing a drain current density, because the Ec of AlN, which has about twice wide of the energy bandgap comparing to that of GaN, is about four times larger than that of GaN, and the electron saturation velocity of AlN is almost as same as that of GaN as shown in table I. Although the AlGaN channel HEMTs have high potential to increase the breakdown voltage, the wider bandgap leads to the difficulty to form a sufficiently low resistive ohmic contact. Therefore a breakthrough technology to reduce the contact resistance is required. In order to solve this problem, we employed Si ion implantation doping technique that we have developed for conventional GaN channel HEMTs.11 In this paper, we report that AlGaN channel HEMTs, where we utilized Si ion implantation doping technique to achieve sufficiently low resistive contacts, were operated with remarkably enhanced breakdown voltage and sufficiently high drain current density without noticeable current collapse.
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