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Oyama, Japan

Nakano Y.,Chubu University | Irokawa Y.,Japan National Institute of Materials Science | Sumida Y.,POWDEC | Yagi S.,POWDEC | Kawai H.,POWDEC
Electrochemical and Solid-State Letters | Year: 2012

We have investigated band-gap states in AlGaN/GaN hetero-structures with different growth conditions of GaN buffer layers in view of C impurity incorporation. The C incorporation was enhanced with decreasing the growth temperature of the GaN buffer layer between 1120 and 1170°C. Acting in concert, three specific deep levels located at ∼2.07, ∼2.70, and ∼3.23 eV below the conduction band were found to become dense significantly at the low growth temperature. Therefore, these levels are probably attributable to Ga vacancies and/or shallow C acceptors produced by the C impurity incorporation, and are likely in conjunction with each other. © 2011 The Electrochemical Society. Source


Nakano Y.,Chubu University | Irokawa Y.,Japan National Institute of Materials Science | Sumida Y.,POWDEC | Yagi S.,POWDEC | Kawai H.,POWDEC
Journal of Applied Physics | Year: 2012

We report on a correlation between deep-level defects and turn-on recovery characteristics in AlGaN/GaN hetero-structures, employing Schottky barrier diodes. Photo-capacitance spectroscopy measurements reveal three specific deep levels located at ∼2.07, ∼2.80, and ∼3.23 eV below the conduction band, presumably attributable to Ga vacancies and/or impurity C present in the GaN buffer layer. Additionally, from photo-assisted turn-on current recovery measurements, by using 390 and 370 nm long-pass filters, the recovery time becomes significantly faster due to inactivation of their corresponding deep-level traps. Therefore, the ∼2.80 and ∼3.23 eV levels are probably responsible for the carrier-trapping phenomena in the bulk region. © 2012 American Institute of Physics. Source


Nakano Y.,Chubu University | Irokawa Y.,Japan National Institute of Materials Science | Sumida Y.,POWDEC | Yagi S.,POWDEC | Kawai H.,POWDEC
Physica Status Solidi - Rapid Research Letters | Year: 2010

We have investigated electronic deep levels in two AlGaN/GaN hetero-structures with different current collapses grown at 1150 and 1100 °C by a photo-capacitance spectroscopy technique, using Schottky barrier diodes. Three specific deep levels located at ~2.07, ~2.80, and ~3.23 eV below the conduction band were found to be significantly enhanced for severe current collapse, being in reasonable agreement with photoluminescence and capacitance-voltage characteristics. These levels probably originate in Ga vacancies and residual C impurities and are probably responsible for the current collapse phenomena of the AlGaN/GaN hetero-structures. This Letter reports on the correlation between deep-level defects and current collapse in AlGaN/GaN hetero-structures by using photoluminescence, capacitance-voltage, and photo-capacitance spectroscopy techniques. The experimental results obtained in this study and their further detailed investigations are expected to provide important information on the electronic properties needed to improve the switching performance of AlGaN/GaN-based HEMTs. Copyright © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source


Nakano Y.,Chubu University | Irokawa Y.,Japan National Institute of Materials Science | Sumida Y.,POWDEC | Yagi S.,POWDEC | Kawai H.,POWDEC
Materials Research Society Symposium Proceedings | Year: 2011

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. © 2011 Materials Research Society. Source


Nakano Y.,Chubu University | Irokawa Y.,Japan National Institute of Materials Science | Sumiya M.,Japan National Institute of Materials Science | Sumida Y.,POWDEC | And 2 more authors.
Materials Research Society Symposium Proceedings | Year: 2014

We have investigated on a relation between C-related deep-level defects and turn-on recovery characteristics in bulk regions of AlGaN/GaN hetero-structures containing various C concentrations, employing their Schottky barrier diodes. With decreasing the growth temperature of the GaN buffer layer, three specific deep-level defects located at ∼2.07, ∼2.75, and ∼3.23 eV below the conduction band were significantly enhanced probably due to the C impurity incorporation into the GaN buffer layer. Among them, the ∼2.75 and ∼3.23 eV levels are considered to be strongly responsible for the two-dimensional electron gas (2DEG) carrier trapping in the bulk regions of the hetero-structures, from their turn-on current recovery characteristics under various optical illuminations. Copyright © Materials Research Society 2014. Source

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