光照和偏压对微晶硅薄膜室温电导的影响

Influence of light exposure and applied bias on the conductivity of microcrystalline silicon films at room temperature

报道了SiCl4/H2等离子体化学气相沉积方法制备的未掺杂微晶硅薄膜,在短时间光照或加上直流偏压后其室温暗电导随时间缓慢变化的行为.Raman散射谱结果表明,薄膜的晶态体积比大于70%.暗电阻的实验结果显示:材料具有弱的持久光电导效应;薄膜的暗电导在外加直流电场的作用下缓慢上升,电场反向后出现暗电导的恢复过程,而且暗电导变化速度与偏压大小和温度有关.根据异质结势垒模型,指出外加条件下载流子的空间分离和重新分布以及材料非均匀性造成的势垒是引起电导缓慢变化的主要原因.

Microcrystalline silicon films were deposited using the plasma enhanced chemical vapor phase deposition system and SiCl4/H2 gas source. We investigate the evolution of the dark conductivity of the fabricated films after a brief exposure to light or under DC bias. Raman spectra measurements indicate that the volume fractions of crystalline phase for all samples are over 70%. The measurement of dark resistance reveals the existence of weak persistent photoconductivity in our samples. Under DC electric field, it is found that the dark conductivity increases slowly with time and a restoration process occurs once the field is reversed. This behavior depends on the DC bias level and the measurement temperature and can be explained by a heterojunction barrier model. It is suggested that the spatial separation and redistribution of charge carriers under applied conditions and the potential barrier associated with inhomogeneity are responsible for the observed phenomena.