Abstract
Experimental results for the density of states of hydrogenated amorphous silicon due to Jackson et al near the valence and conduction band edges were analyzed using Levenberg-Marquardt nonlinear fitting method. It is found that the density of states of the valence band and the conduction band can be fitted to a simple power law, with a power index 0.60 near the valence band edge, and 0.55 near the conduction band edge. These results indicate a modest but noticeable deviation from the square root law (power index=0.5) which is found in crystalline semiconductors. Analysis of Jackson et al density of states integral J(E) data over about (1.4 eV) of photon energy range, showed a significant fit to a simple power law with a power index of 2.11 close to that predicted from the density of states fitting results 2.15
Highlights
Amorphous silicon remains at the center of attention of amorphous solid state community for two main reasons
In amorphous semiconductor research there is still a controversy concerning the correct functional dependence of the density of states (DOS) distribution close to each of the valence band (VB) and conduction band (CB) mobility edges, its knowledge is crucial for optical properties and electronic device modeling [2]
Fig.2 shows Jackson et al [7] valence band density of states vs. state energy data in the energy range of (2-3.6 eV).The standard LevenbergMarquardt nonlinear least squares fitting method is used to fit the data near the band edge to a general simple power three parameter equation of the form: y= p1 (x-p2) p3 ...(4) where x is the independent variable,y is the dependent variable, p1,p2 and p3 are three fitting parameters, obviously p3 represents the fitting parameter of our concern here to obtain the VB DOS power index (s )
Summary
Amorphous silicon remains at the center of attention of amorphous solid state community for two main reasons. In amorphous semiconductor research there is still a controversy concerning the correct functional dependence of the density of states (DOS) distribution close to each of the valence band (VB) and conduction band (CB) mobility edges, its knowledge is crucial for optical properties and electronic device modeling [2].
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