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ll921

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Fig. 2 was the absorption spectrum of the as-grown xxx crystal. It can be found that the as-grown xxx crystal has a low absorption coefficient (α) in the wavelength range from 1000 to 366 nm, α~3 cm-1 representing the transparent region. In the UV region (<366 nm), the α increases steeply to 15 cm-1.
The absorption coefficient α is known to be related to the incident photon energy hv by the expression[28]:
αhν =A(hν - Eg)1/n (1)
where A is a constant. The exponent n can take values of 2, 1/2, 2/3, and 1/3 for the allowed direct, the allowed indirect, the forbidden direct and the forbidden indirect transitions, respectively. The previous reports on the polycrystalline samples gave that the xxx band gap by estimating the absorption edge and measuring the conductivity, respectively [12, 23-25]. However, none of the above authors pointed out the interband transition types, and also no study by the theoretical calculation. For the as-grown xxx crystal, the best fitting is obtained with n = 1/2, implying that xxx is an indirect band gap material. The indirect transition is a transition with the aid of phonons. In this condition, electrons transferred from the top of the valence band to the bottom of the conduction band will have different momenta, owing to the change in their wavevector. To conserve the energy, indirect transition may occur with suitable phonons participating. In this case, the absorption coefficient can be expressed as the following formula。

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master2006

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ll921: 金币+20, 翻译EPI+1, ★★★★★最佳答案 2012-09-23 09:46:46

Figure.Growth XXX absorption spectra. It can be found that growth XXX crystals from 1000 to 366 nm wavelength range has a low absorption coefficient (α), α to 3 cm -1 representative of the transparent region. Α increases sharply in the UV region (<366 nm), 15 cm-1.
The absorption coefficient α is a known case, the incident photon energy hv by the expression [28]:
αhν = A (hν of - EG) of 1 / n (1)
Wherein A is a constant. Exponent n value of 2,1 / 2,2 / 3 and 1/3 to allow direct, allows indirect ban on direct and indirect conversion prohibit, respectively. Previous reports in polycrystalline samples to the bandgap XXX estimated absorption edge and measuring conductivity, respectively [12, 23 and 25]. However, the authors pointed out that the type of interband transitions, and theoretical calculations of. XXX crystal growth, with n = 1/2 to give the best fit, and this means that XXX is an indirect bandgap material. Indirect transition is a transition with the help of phonons. Under this condition, from the top of the valence band to the bottom of the conduction band of the electron transfer will have a different momentum, due to the change in the wave vector. To save energy, the indirect changes may appear appropriate phonon participation. In this case, the absorption coefficient can be expressed as the following equation.

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