Temperature dependence of biaxial strain and its influence on phonon and band gap of GaN thin film |
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Authors: | Xu Hong-Yan Jian Ao-Qun Xue Chen-Yang Chen Yang Zhang Bin-Zhen Zhang Wen-Dong Zhang Zhi-Guo and Feng Zhen |
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Institution: | Key Laboratory of Instrumentation Science &
Dynamic Measurement (North University of China), Ministry of
Education;National Key Laboratory for Electronic
Measurement Technology North University of China, Taiyuan
030051,
China; The 13th research institute of CETC, Shijiazhuang
050051, China |
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Abstract: | Hexagonal GaN epilayer grown on sapphire substrate by metal organic
chemical vapour deposition (MOCVD) is studied using Raman scattering
and photoluminescence in a temperature range from 100\,K to 873\,K.
The model of strain (stress) induced by the different lattice
parameters and thermal coefficients of epilayer and substrate as a
function of temperature is set up. The frequency and the linewidth of
$E_2^{\rm high}$ mode in a GaN layer are modelled by a theory with
considering the thermal expansion of the lattice, a symmetric decay
of the optical phonons, and the strain (stress) in the layer. The
temperature-dependent energy shift of free exciton A is determined by
using Varshni empirical relation, and the effect of strain (stress)
is also investigated. We find that the strain in the film leads to a
decreasing shift of the phonon frequency and an about
10meV-increasing shift of the energy in a temperature range from
100\,K to 823\,K. |
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Keywords: | biaxial strain phonon band
gap GaN |
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