Hg_(0.72)Cd_(0.28)Te扫描隧道谱的模型解释

The scanning tunneling spectra of Hg_(0.72)Cd_(0.28)Te and the model interpretation

本工作利用截面扫描隧道显微镜(XSTM)研究了分子束外延生长的Hg_(0.72)Cd_(0.28)Te薄膜。扫描隧道谱(STS)测量表明,此碲镉汞材料的电流-电压(I/V)隧道谱呈现的零电流平台宽度(隧道谱表观带隙)比其实际材料带隙增大约130%,说明存在明显的针尖诱导能带弯曲(TIBB)效应。扫描隧道谱三维TIBB模型计算发现低成像偏压测量时获取的I/V隧道谱数据与理论计算结果有令人满意的一致性。然而较大成像偏压时所计算的I/V谱与实验谱线在较大正偏压区域存在一定偏离。这是目前的TIBB模型未考虑带带隧穿、缺陷辅助隧穿等碲镉汞本身的输运机制对隧道电流的影响造成的。

The cross-sectional scanning tunneling microscopy(XSTM)technique was used to study the cleaved surface of Hg_(0.72)Cd_(0.28)Te grown by molecular beam epitaxy.Scanning tunnel spectroscopy(STS)’s measurements show that the width of zero current plateau(the apparent tunneling gap)of current-voltage(I/V)spectra is about 130%larger than the practical band gap of the material,implying the existence of obvious tip-induced band bending(TIBB)effect with the measurement.Based on the 3D TIBB model,the STS data can however be interpreted and the calculated I/V spectra are in good agreement with the measurement.Nevertheless,certain deviation appears for those I/V data which were acquired with a large imaging bias.This is because the current TIBB model does not take into account the transport mechanism of the material itself,for which the band-to-band tunneling,trap assisted tunneling etc.could be non-negligible factors for the tunneling.