Correlation between Deep-Level Defects and Current Collapses in AlGaN/GaN Hetero-Structures Probed by Steady-State Photo
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Correlation between Deep-Level Defects and Current Collapses in AlGaN/GaN Hetero-Structures Probed by Steady-State Photo-Capacitance Spectroscopy Yoshitaka Nakano1, Yoshihiro Irokawa2, Yasunobu Sumida3, Shuichi Yagi3, and Hiroji Kawai3 1 Chubu University, Kasugai, Aichi 487-8501, Japan 2 National Institute of Materials Science, Tsukuba, Ibaraki 305-0044, Japan 3 POWDEC, Oyama, Tochigi 323-0028, Japan ABSTRACT We have investigated a correlation between electronic deep levels and current collapses in AlGaN/GaN hetero-structures by capacitance-voltage and photo-capacitance spectroscopy techniques, using Schottky barrier diodes. Three specific deep levels located at ~2.07, ~2.80, ~3.23eV below the conduction band were found to be significantly enhanced for the severe current collapse. These levels probably originate in Ga vacancies and residual C impurities and are probably responsible for the current collapses of the AlGaN/GaN hetero-structures. INTRODUCTION Electronic devices based on AlGaN/GaN hetero-structures are of great current interest because of their capability of operating at high temperature, high power, and high frequency. In particular, the AlGaN/GaN hetero-structure has a thin, high-mobility channel due to a twodimensional electron gas (2DEG) produced at the hetero-interface. Excellent device characteristics have been reported for these high electron mobility transistors (HEMTs) [1]. However, these devices are generally known to encounter undesirable current collapse issues, where actual device performances at high frequencies can be limited by the presence of deeplevel defects in the AlGaN/GaN hetero-structures [1]. i.e., electrical charge, trapped by the deep levels, modifies the 2DEG concentration in the channel and limits the switching characteristics of the devices. Although surface treatments on AlGaN top layer have already been reported to be effective in decreasing the current collapses by inactivating the surface states in AlGaN, the current collapses have yet to be completely eliminated [2]. In order to educe the promising potential of AlGaN/GaN HEMTs, it is needed to perform basic investigation of deep-level defects in AlGaN/GaN hetero-structures from a viewpoint of the current collapses. To date, a number of research approaches have been employed to detect and identify these defects in the AlGaN/GaN hetero-structures by using various electrical characterization techniques such as photo-ionization spectroscopy, deep-level transient spectroscopy (DLTS), and deep-level optical spectroscopy (DLOS) [3-6]. However, a detailed correlation between the deep-level defects and the current collapses still remains uncertain. In this study, we have characterized electronic deep levels in AlGaN/GaN hetero-structures with different current collapses, employing capacitancevoltage (C-V) and steady-state photo-capacitance spectroscopy (SSPC) techniques. EXPERIMENTAL
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Two AlGaN/GaN hetero-structures used in this study were grown on c-plane sapphire substrates at 1150 and 1100 °C, using metal-organic chemica
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