"Negative" gap in the spectrum of localized states of (In2O3)0.9(SrO)0.1
Abstract
The reflection R( ħω), transmission t( ħω), absorption α( ħω), and refraction n( ħω) spectra of polycrystalline In2O3-SrO samples with low optical transparency, which contain In2O3 and In2SrO4 crystallites with In4SrO6 + δ interlayers, are examined. In the region of small ħω values, the reflection coefficient decreases as the resistance of samples saturated with oxygen increases. Spectral dependences n( ħω) and α( ħω) are calculated using the classical electrodynamics relations. The results are compared to the data based on the t( ħω) spectra. The calculated absorption spectra are interpreted within the model with an overlap of tails of the density of states in the valence band and in the conduction band. A "negative" gap E gn in the density of states with a width from-0.12 to-0.47 eV is formed in highly disordered samples in this model. It is demonstrated that the high density of defects and the band of deep acceptor states of strontium in the major matrix In2O3 phase are crucial to tailing of the absorption edge and its shift toward lower energies. The direct gap E gd = 1.3 eV corresponding to the In2SrO4 phase is determined. The energy band diagram and the contribution of tunneling, which reduces the threshold energy for interband optical transitions, are discussed.
- Publication:
-
Physics of the Solid State
- Pub Date:
- August 2017
- DOI:
- 10.1134/S1063783417080182
- Bibcode:
- 2017PhSS...59.1607O