Correlation between resistivity and yellow luminescence intensity of GaN layers grown by MOCVD
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Correlation between resistivity and yellow luminescence intensity of GaN layers grown by MOCVD
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A. Hinoki1, Y. Hiroyama3 T. Tsuchiya3 T. Yamada3, M. Iwami3, K. Imada3, J. Kikawa3, T. Araki1,3, A. Suzuki2,3, and Y. Nanishi1,3 1
Dept. of Photonics, 2Res.Org.of Sci & Eng., Ritsumeikan University, 3 Advanced HF Device R&D Center, R&D Association for Future Electron Devices 1-1-1 Noji-Higashi, Kusatsu, Shiga, 525-8577, Japan E-mail: [email protected] (A. Hinoki) ABSTRACT For further improvements in AlGaN/GaN heterojunction field-effect transistor (HFET) performance, it is necessary to reduce the leakage current of the GaN buffer layer. We found a correlation between the leakage current and the intensity of the yellow luminescence of GaN layers taken by UV lamp excitation. The GaN layers were grown by metal organic chemical vapor deposition on SiC substrates. When the samples were excited by a UV (365 nm) lamp, visible yellow luminescence was observed. The leakage current of the GaN buffer layer was measured after deposition of ohmic metal contact. We confirmed clear correlation between the leakage current and the luminescence intensity based from result that the samples with the larger leakage current showed the stronger luminescence intensity. This correlation gives us useful information to understand the drain-source leakage current of AlGaN/GaN HFET. INTRODUCTION GaN and related alloys have attractive physical properties such as high saturation velocity, high breakdown electric field and good thermal conductivity. Owing to these inherent material properties, heterojunction field-effect transistor performance (HFET) have been extensively studied as promising electronic devices for high-speed, high-power and high-temperature operation [1]. For further improvements in device performance, however, there are still some issues to be solved. For example, reduction in leakage current through the Schottky barrier gate [2-3] and suppression of current collapse [4-5] are required to improve the power density. In addition, the reduction in drain-source leakage current [6] is also important in high-power operation. To reduce the drain-source leakage current, high-resistivity of the GaN epi-layer is necessary. Usually, the resistivity of a GaN epi-layer is measured by an I-V measurement after metal contacts are formed. In this work, we propose that a yellow luminescence image of a GaN epi-layer taken by UV lamp excitation gives us useful information to evaluate not only uniformity of epi-layer but also the leakage current and resistivity of the GaN epi-layer. We found clear correlation between the resistivity and the UV-excited luminescence intensity of the GaN epi-layers. The samples with
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the larger leakage current showed the stronger luminescence intensity. Possible origins for the luminescence of GaN with different leakage characteristics are also discussed.
EXPERIMENTAL DETAILS Unintentionally-doped 2 µm GaN epi-layers with different resistivities were grown by metal organic ch
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