Absorption spectra of GaN: film characterization by Urbach spectral tail and the effect of electric field

The absorption tail of undoped and Si-doped GaN films was investigated at d ifferent temperatures and under applied electric field. It was found that t he spectral dependence of logarithm of absorption coefficient is combined o f two linear functions: In[alpha (hv)] = C-1 + (hv - E-g)/U-1 for hv < 3.42 eV and In[alpha (hv)] = C-2 + (hv - E-g)/ U-2 for 3.44 < hv < 3.5 eV with Urbach energies U-1 =400-470 meV and U-2 =10-20 meV. The influence of an el ectric field effect on the absorption spectra follows the Dow and Redfield theory. It was shown that the intrinsic electric field about 10(5) V/cm exi sts in our samples. The implemented analysis of the absorption spectra give s the qualitative method of film characterization. Crown copyright. (C) 200 1 Published by Elsevier Science B.V. All rights reserved.