【摘要】 通过光伏谱(PV)的测量发现,采用MOCVD方法生长的非故意掺杂GaN外延膜,电阻较大的样品在带隙内有明显的异常光吸收.吸收峰的能量位置表明这种异常吸收可能与激子有关.在这些高阻样品上制作的MSM型探测器,当入射光照射不同位置,其光谱响应显示了区域不一致性.20V偏压下反向偏置结处的光谱响应比正向偏置结处的光谱响应大一个数量级左右,峰值响应的位置也发生明显红移现象,红移的能量约为28meV,并且几乎不随环境温度变化.根据MSM结构的电场分布不均以及带边和激子响应对电场的依赖性不同,MSM型探测器的这种区域响应不一致性可以得到很好的解释.更多还原

【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.更多还原