InGaAs(110)解理面的扫描隧道谱的理论诠释

Theoretical explanation of scanning tunneling spectrum of cleaved(110)surface of InGaAs

本工作应用截面扫描隧道显微镜(XSTM)研究了In_(0.53)Ga_(0.47)As/InP异质结构的(110)解理面.扫描隧道谱(STS)测量结果显示,InGaAs的电流-电压(I-V)隧道谱呈现与衬底InP(110)面完全不同特点.InP的I-V谱呈现的零电流平台宽度(隧道谱表观带隙)接近材料带隙,可基于平带模型解释.In_(0.53)Ga_(0.47)As的表观带隙却比其带隙(室温0.74 eV)高出约50%.这反映了针尖与InGaAs发生隧穿时的不同物理图像,需应用针尖诱导能带弯曲(TIBB)模型来解释.基于三维TIBB模型的计算,我们发现表面态密度是对隧道谱线特征具有敏感影响的参数.适当选取参数不仅能定量解释InGaAs的I-V谱的零电流平台宽度,而且能较准确预言零电流平台的起、止能量位置,并能计算给出与实验高度重合的I-V理论谱线.

The cross-sectional(110)surface of In_(0.53)Ga_(0.47)As/InP hetero-structure grown by molecular beam epitaxy on an InP(001)substrate is characterized by the cross-sectional scanning tunneling microscopy(XSTM).The cleaved(110)surface across the interface between the In_(0.53)Ga_(0.47)As layer and InP layer is atomically flat but displays slight different image contrast between the two neighbor regions.The scanning tunneling spectroscopy(STS)is used to measure the current/voltage(I-V)spectra.The I-V data of the InGaAs surface and InP(110)surface show the different characteristics.The voltage range of zero-current plateau(apparent band gap)in the I-V spectrum of InP displays the values close to its energy band gaps whereas the plateau ranges in the spectra of In_(0.53)Ga_(0.47)As are by contrast generally 50%larger than the energy band gap of In_(0.53)Ga_(0.47)As.The above phenomenon implies the different physical pictures on the tunneling of two surfaces.In the case of InP,the flat band model is feasible since the band edge states existing in the InP(110)surface can prevent the surface from being affected by the tip–induced band bending(TIBB)effect.In contrast,the TIBB effect must be taken into account to explain the I-V spectra of the In_(0.53)Ga_(0.47)As(110)surface.A statistical analysis of the I-V data of In_(0.53)Ga_(0.47)As reveals that the width of current plateau in the I-V spectrum is generally between 1.05 eV and 1.20 eV and the current onset points(turn-points)with the plateau for the different spectra are slightly different from each other.We are able to explain quantitatively the above features based on the three-dimensional TIBB model given by Feenstra(2003 J.Vac.Sci.Technol.B 212080).Our calculation reveals that the parameter of density of surface states(DOSS)is a sensitive parameter responsible for the I-V features mentioned above.According to an appropriate assignment of the value of DOSS,which is generally taken in the scope of(0.8–3.0)×10^(12)(cm^(2)·eV)^(–1),we well predict both the width and the onset points of the current-plateau.Moreover,the model also reproduces the line-shapes of the I-V spectra measured on In_(0.53)Ga_(0.47)As.