Modification of localized and resonant states at asymmetric short-range defects under hydrostatic compression
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Modification of Localized and Resonant States at Asymmetric Short-Range Defects under Hydrostatic Compression F. T. Vas’ko* and M. V. Strikha** Institute of Semiconductor Physics, National Academy of Sciences of Ukraine, Kyiv, 03650 Ukraine *e-mail: [email protected] **e-mail: [email protected] Received July 9, 2007
Abstract—Modification of localized and resonant states at asymmetric short-range defects in III–V semiconductors under hydrostatic compression was studied within the kp method. The impurity contribution to the density of states was calculated using the multiband generalization of the Slater–Koster approximation for defects asymmetric along [001], [110], or [111] axes. The transition between resonant and localized states was studied, the mechanism of the appearance and disappearance of a pair of levels under compression was described. The possibility of comparing the calculation results and experimental data was discussed. PACS numbers: 71.55.-i, 71.55.Eq, 71.70.Fk DOI: 10.1134/S1063776108030151
1. INTRODUCTION Hydrostatic compression modifies electronic states at short-range defects and is a convenient method for studying their structure [1, 2]. We note that, in contrast to other external perturbations (such as uniaxial deformation, electric or magnetic field), hydrostatic compression does not change the problem symmetry. Therefore, the results of such studies are easily interpreted taking into account known parametric dependences of III–V semiconductor parameters on compression. Modifications of electronic states at short-range defects, caused by deformation were theoretically treated within several computational methods, including the tight binding approximation [3], the use of pseudopotentials (both empirical [4] and expanded in plane waves [5]), or calculations of the density functional (see references in [6]). In this paper, we use the simplest multiband kp method in which deformation is considered as an additional change in the Hamiltonian of an initial material [7]. The contribution of the center is usually taken into account as a short-range (δ-shaped) scalar energy added to the Hamiltonian [8]. Such an approach is widely used to describe various electronic processes involving the states at short-range defects whose energy is close to the conduction band bottom [9]. This approach was generalized to the case of deep states interacting with several bands in [10]; the case of centers in deformed narrow-bandgap semiconductors was considered in [11]. Recently [12], the matrix structure of the short-range potential in the Hamiltonian, which
results in mixing of various band states due to lowering of the center symmetry, was considered. Due to such mixing, bound state modifications are formed and the resonant state becomes possible. Although the problem of the matrix nature of the impurity contribution to the kp equation arose even in the first studies of short-range impurities (see [1]), cases where such a contribution was significant were observed have not yet been obs
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