Abstract
In this paper we try to give a reasonable account for the origin of the experimental optical energy gap Eo of a-Si:H deduced from the plot due to Cody ( vs. E). Using a realistic model density of states diagram for a-Si:H and the constant dipole matrix element assumption, and a reasonable definition of the real optical energy gap EG, a new theoretical equation for ε2(E) was derived. The plot of the square root of this function as a function of the photon energy E for appropriate fitting parameters gives a straight line fit in the energy region of significance extrapolating to the energy axis at a value similar to the experimental optical gap but about 0.1 eV lower than the theoretical optical gap EG proposed in our paper. We conclude that the experimental optical gap Eo does not necessarily coincide with any optical transition threshold in the density of states diagram of a-Si:H.
Highlights
IntroductionIn two previous papers [1,2], we concluded from the re-analysis of the experimental results of Jackson et al [3]
Cody [4] is the suitable theoretical model for the interpretation of the optical data at the high absorption region of the optical absorption edge of this important material. This model assumes a parabolic density of states (DOS)
Which is ~1.68 eV does not match with the value of the mobility gap of Jackson et al [3] samples i.e. ~1.93 eV
Summary
In two previous papers [1,2], we concluded from the re-analysis of the experimental results of Jackson et al [3]. Cody [4] is the suitable theoretical model for the interpretation of the optical data at the high absorption region of the optical absorption edge of this important material. The problem of the interpretation of the optical energy gap Eopt is still a matter of controversy in literature [4,6]. Which is ~1.68 eV does not match with the value of the mobility gap of Jackson et al [3] samples i.e. 1 2 vs E) ~1.89 eV is significantly closer to the value of the mobility gap for Jackson et al samples. Clue towards the understanding of the problem of the interpretation of the optical energy gap problem in amorphous semiconductors
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