Impurity resonance states in semiconductors
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Impurity Resonance States in Semiconductors V. Ya. Aleshkina, L. V. Gavrilenkoa, M. A. Odnoblyudovb, and I. N. Yassievichb^ aInstitute
for Physics of Microstructures, Russian Academy of Sciences, Nizhni Novgorod, 603950 Russia Physicotechnical Institute, Russian Academy of Sciences, St. Petersburg, 194021 Russia ^e-mail: [email protected]
bIoffe
Submitted February 6, 2008; accepted for publication February 11, 2008
Abstract—The present-day situation in studies of localized and resonance impurity states in quantum-dimensional structures and stressed semiconductors is discussed. Resonance optical transitions caused by interaction with optical phonons are also considered. Various methods for calculating the characteristics of both donor and acceptor resonance and localized states are analyzed; a large body of experimental data is reported and discussed. PACS numbers: 71.23.An, 71.70.Fk DOI: 10.1134/S1063782608080034
1. INTRODUCTION Impurities in semiconductors can give rise not only to localized states whose energy is within the band gap but also to resonance (or quasi-stationary) states that are located in allowed bands. Resonance states differ from conventional states of the continuous spectrum primary in larger amplitudes of the wave function near an impurity center. Resonance states of impurities in semiconductors have been studied for a fairly long time; quite a large number of various types of these states are known. For example, in the presence of a quantizing magnetic field, shallow-impurity states formed of wave functions of the Landau subbands with high cyclotron energies are found in the continuous spectrum of lower subbands and are resonance states [1]. Other well-known examples of resonance states are represented by impurity states in zero- or narrow-gap semiconductors [2] and states of deep impurities in IV– VI semiconductors [3]. Typically, the presence of several subbands closely spaced in energy (these subbands can be Landau subbands, states in the conduction and valence bands in narrow-gap semiconductors, or states in the dimensional-quantization subbands in quantum wells (QWs)) is necessary for origination of resonance impurity states. Resonance states of shallow acceptors in the valence band of silicon are well known; these states are caused by the presence of a spin-related splitoff band [4]. Finally, in the case of germanium, uniaxial deformation splits the bands of light and heavy holes and also gives rise to resonance states of acceptors [5]. Specific resonance states of an impurity emerge as a result of interaction of electrons with optical phonons; we will refer to these states as Fano resonances. It is rather difficult to change the properties of impurity states (including resonance states) in bulk semiconductors. Most often, these changes are achieved using a magnetic field or deformation. It is much simpler to
control the properties of both localized and resonance states in heterostructures with QWs; the reason for this is that, in this case, properties of impurity sta
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