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Characterization of optical quality of GaSe:Al crystals by exciton absorption peak parameters

Konstantin A. Kokh 1,2Yurii Andreev 3,4Tatyana Izaak 4Gregory Lanskii 3,4Anna Shaiduko 3,4Valery Svetlichnyi 4

1. Institute of Geology and Mineralogy SB RAS (IGM), Koptyuga ave., 3, Novosibirsk 630090, Russian Federation
2. Novosibirsk State University (NSU), Pirogov 2, Novosibirsk 630090, Russian Federation
3. Insitute of Climatic and Ecological Systems of SB RAS (IMCES), 10/3 ave Akademicheskii, Tomsk 634055, Russian Federation
4. Tomsk State University (TSU), Lenina, 36, Tomsk 634050, Russian Federation

Abstract
It is well known that doping of GaSe crystals with isovalent elements: Al [1], S [2, 3], In [4, 5], Te [6, 7] and Er [8] strengthens the structure and improves optical quality , which in turn increases efficiency of parametric frequency conversion into mid-IR and THz ranges. On the other hand, excess doping leads to destruction of the lattice structure [9]. So it is obvious that intermediate optimal doping should exist. Direct search of this concentration by conventional spectroscopic measurements is very complicated due to low optical losses of GaSe in the range of maximal trabsparency (absorption coefficient ≤0.1-0.2 cm-1). Available data on the optimal doping in GaSe that resulted in the best optical quality and maximal conversion efficiency are limited by the only paper on tellurium doping [10]. The proposed method of characterization included two stages: (1) recording of absorption spectra of GaSe crystals with a set of doping concentration out of maximal transparency range, i.e. THz absorption spectra, (2) selection of a sample with maximal phonon peak intensities and narrowest spectral bandwidths. Optimal doping of selected samples was then confirmed by efficiency of SHG and optical rectification experiments. But to apply this method one needs quite rare and expansive facility. In this study we propose the recording of exciton absorption spectra by widespread and cheap UV-visible absorption spectrophotometer. Selection of optimally doped crystal can be carried out by: (1) choosing a crystal with maximal intensity and narrowest spectral bandwidth of exciton absorption peak, (2) choosing of a crystal with maximal gradient of the absorption end, and (3) with minimal absorption at the bottom of the absorption end (Fig. 1). Physical basis for this proposal will be discussed.

Fig.1. Characteristics of short-wave absorption diagram for Al-doped GaSe crystals.

In Fig. 1 it is seen that maximal intensity of the exciton absorption peak, minimal spectral bandwidth and absorption coefficient at the bottom of the short-wave absorption end are owned y 0.02 wt.% Al-doped GaSe crystals. Close characteristics are possessed by 0.05 wt.% of Al doped crystal. Thus, optimal Al doping has to be about from 0.02 to 0.05 wt.%. This proposal is confirmed by THz generation efficiency by optical rectification method.

References

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Related papers

Presentation: Oral at 17th International Conference on Crystal Growth and Epitaxy - ICCGE-17, General Session 5, by Konstantin A. Kokh
See On-line Journal of 17th International Conference on Crystal Growth and Epitaxy - ICCGE-17

Submitted: 2013-04-14 10:50
Revised:   2013-07-17 11:14