应力对(GaP)_1/(InP)_1(111)超晶格体内和表面电子结构的影响

EFFECT OF STRAIN ON THE BULK AND THE SURFACE ELECTRONIC STRUCTURES OF (GaP)_1/(InP)1(lll) SUPERLATTICE

考虑到应力对超薄层(GaP)_1/(InP)_1(111)结构中Ga-P和In-P键长的作用为均匀分布的情况,本文提出在紧束缚近似下,将应力的影响直接反映到Harrison的交迭积分项中,并利用Recursion方法全面计算了由Keating模型确定的稳定(GaP)_1/(InP)_1(111)超晶格体内和表面的电子结构,结果表明,这种材料的带隙为1.88eV,它比体材料GaP(2.91eV)和InP(1.48eV)的平均值小0.31eV.通过对辅助模型的研究,可以发现随键长应力的增大,系统带隙加宽,费密能级移动,同时计算得到的各晶位上原子的电子占有数结果清楚地反映了InP的离化程度比GaP高,最后证明这类应力超晶格(111)表面有类似的SP_z+P_x—P_y退杂化轨道存在,但是各分波轨道对它的贡献与(GaAs)_1/(AIAs)_1(001)超晶格中(001)表面的相应情况是不同的。

Under the tight-binding formalism, this paper suggests that effect of strain can be considered in terms of Harrison's interatomic matrix elements, taking acount of the homogeneous bond stretching and bond bending in ultrathin layer (GaP)1/(InP)1(lll) systems. Using recursion method, we have calculated the bulk and the surface electronic structures of the stable (GaP)1/(InP)1(lll) superlattice determined by the Keating model. Our result shows that its band gap is 1.88 eV, which is smaller by 0.31 eV than the average of the calculated gaps of bulk GaP(2.91 eV) and lnP(1.48 eV). As compared with the calculated auxiliary systems, we find that the band gaps of the superlattices become larger and the Fermi levels become lower with the increasing of the strain of the bond length. Furthermore, the obtained number of the occupied electrons on different sites clearly shows that InP is more ionic than GaP. Finally, we show the existence of an approxiamte SP_z+P_x-P_y dehybrid on (111) surface of this strained-layer superlattice and point out that the contribution of S or P partial orbital of a (111) surface atom to this dehybrid is different from the case of a (001) surface atom of GaAs/AlAs (001) superlattice.