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Abnormal photoabsorption in high resistance GaN epilayer

Liu Wen-Bao Zhao De-Gang Jiang De-Sheng Liu Zong-Shun Zhu Jian-Jun Zhang Shu-Ming Yang Hui

Abnormal photoabsorption in high resistance GaN epilayer

Liu Wen-Bao, Zhao De-Gang, Jiang De-Sheng, Liu Zong-Shun, Zhu Jian-Jun, Zhang Shu-Ming, Yang Hui
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  • Received Date:  17 January 2010
  • Accepted Date:  20 February 2010
  • Published Online:  15 November 2010

Abnormal photoabsorption in high resistance GaN epilayer

  • 1. State Key Laboratory on Integrated Optoelectronics,Institute of Semiconductors,Chinese Academy of Sciences,Beijing 100083,China

Abstract: Unintentionally doped GaN epilayers are grown by the metalorganic chemical vapor deposition (MOCVD). Photovoltaic (PV) spectroscopy shows that there appears an abnormal photoabsorption in some undoped GaN films with high resistance. The peak energy of the absorption spectrum is smaller than the intrinsic energy band gap of GaN. This phenomenon may be related to exciton absorption. Then metal-semiconductor-metal (MSM) Schottky photodetectors are fabricated on these high resistance epilayers. The photo spectrum responses are different when the light individually irradiates each of the two electrodes with the photodetector which are differently biased. When the excitation light irradiates around the reverse biased Schottky junction,the responsivity is almost one order of magnitude larger than that around the forward biased junction. Furthermore,when the excitation light irradiates the reverse biased Schottky junction,the peak energy of the spectrum has a prominent red-shift compared with the peak energy of the spectrum measured with the excitation light irradiating the forward biased Schottky junction. The shift value is about 28 meV, and it is found to be insensitive to temperature. According to the analyses of the distribution of the electric field within the MSM device and the different dependences of the response on the electric field intensity between the free carriers and excitons,a reliable explanation for the different response among various areas is proposed.

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