半导体缺陷能级的应力效应

本文讨论用瞬态方法测量立方半导体缺陷能级应力移动和判别缺陷势对称性的有关问题。对于简并能级E_s引入应力下分裂平均值E_s,它具有原哈密顿群对称操作不变性,因此可以用群论方法得出应力系数间关系并用以判断缺陷势对称性。比如当缺陷势具有T群以上对称时,缺陷能级平均值E_T相对导带底或价带顶单轴应力系数(?(E_c-E_T))/(?F)或(?(E_T-E_v))/(?F)与应力F方向无关且等于流体静压系数的1/3。也讨论了C_3v对称缺陷势的情况。缺陷能级对导带的平均电子发射率e_n和俘获率c_n满足简洁关系 e_n=g_Tg_c^-1c_nN′_ce^{(-(E_c-E_T)/kT)}。指出通过测量e_n的应力关系判断缺陷势对称性的各种方案比较。分析了用瞬态法测量e_n有关问题。当E_T分裂但诸能级间允许跃迁时,瞬态讯号呈单指数衰减,时间常数为e_n^-1。当E_T分裂但诸能级间禁止跃迁时,瞬态讯号呈多指数衰减。用初始斜率可求得e_n。关键词：

STRESS DEPENDENCE OF DEFECT LEVELS IN SEMICONDUCTORS

New criterion for symmetric properties of defect potential in semiconductors is presented. For a degenerate energy level E_s, we introduce the average E_s of energy splitling under stress. E_s is invariant under symmetry operation of Hamiltonian. Therefore, it is straight foward to reduce the stress coefficient tensor of E_s by group theoretical method. For instance, for cubic semiconductors, if the defect level E_T is withdefect potential of T group symmetry, the uniaxial stress coefficient of (?(E_c-E_T))/(?F) or (?(E_T-E_v))/(?F) is isotropic and equal to one third of corresponding hydrostatic pressurecoefficient. The case of defect potential with C_3v symmetry is also discussed.The electron (or hole) emission and capture processes of defect levels under energy splitting are analysed. The weighted average of emission rate e_n and capture rate c_n satisfy the following relation: e_n=g_Tg_c^-1c_nN′_ce^{(-(B_c-B_T)/kT)} By measuring the stress dependence of e_n., various schemes for determining the symmetry property of defect potential are discussed. The transient processes under defect level splitting are also discussed. When transitions are al lowed between the splitting states, the transient is exporential with single decay time constant e_n^-1. When transitions between different states are forbidden, the transient is decay with multi-exponential time constants. e_n is determined by the initial transient slope.
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