Absorption, luminescence excitation, and infrared transmittance spectra of ZnS(O)-ZnSe(O) crystals in the context of the
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TRONIC AND OPTICAL PROPERTIES OF SEMICONDUCTORS
Absorption, Luminescence Excitation, and Infrared Transmittance Spectra of ZnS(O)–ZnSe(O) Crystals in the Context of the Band Anticrossing Theory N. K. Morozova^, D. A. Mideros, and N. D. Danilevich Moscow Power Engineering Institute (Technical University), Moscow, 111250 Russia ^e-mail: [email protected] Submitted April 28, 2008; accepted for publication April 28, 2008
Abstract—The paper reports the results of optical studies of the absorption, luminescence excitation, and infrared transmittance spectra for the set of ZnS(O)–ZnSe(O) alloys with highly inconsistent properties of anions. It is shown that the band anticrossing theory applied to the alloys provides a general interpretation of their specific optical properties not properly understood previously. A band model of transitions with absorption in a complex multiband formed due to oxygen is presented. The specific features of the absorption and luminescence excitation spectra are interpreted to gain an insight into the distribution and states of oxygen in the crystals. The effect of oxygen on the transmittance band of the ZnS–ZnSe alloys in the near-infrared spectral region is considered. A new approach to the interpretation of the infrared absorption bands associated with oxygen is developed. The calculation algorithms that provide a means for determining the spectral position of the bands in relation to the dissolved oxygen content are suggested. PACS numbers: 71.23.An, 71.55.Gs, 78.40.Fy, 78.55.Et, 78.66.Hf DOI: 10.1134/S1063782609020080
1. INTRODUCTION Introduction of an isoelectron impurity (IEI) dramatically distorting the local crystal lattice provides a means for producing a new class of multiple-gap materials on the basis of III–V and II–VI semiconductors [1–6]. Such materials are highly mismatched alloys (HMAs), i.e., alloys with highly inconsistent properties in the components [1–3]. Even a ~1% content of a substitutional impurity induces a new resulting band involving two direct subband gaps. This remarkable modification in the band structure has already been described by the band anticrossing theory [1–4]. The energy gap between the E+ and E– subbands in the conduction band depends on the impurity content, but this gap is much narrower than the energy separation of these subbands from higher bands. Optical transitions with absorption can occur from the valence band states (EV) to the E+ and E– subband levels [3, 4] as well as between the E+ and E– subbands [1]. The absorption coefficient in the region of interband transitions is comparable with the fundamental absorption coefficient for an undoped crystal. At the present time, a large body of experimental data is available to support this statement (see, e.g., [1–4, 7–13]). Interpretation of the role of oxygen in the HMA-type ZnS(O)–ZnSe(O) system is now based on a number of alternative concepts. Analysis of the data obtained by us shows that the relatively new band anticrossing (BAC) model provides general understanding
for the specific feature
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