Impurity bands and band tailing in moderately doped silicon

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Abstract
The density of states of the valence and conduction bands in silicon has been calculated at room temperature for dopant densities near the transition between the existence of a distinct impurity band and its coalescence with the continuum band to form a band tail. The dopant densities for the three cases considered are (1) 1.5×1018 cm−3 acceptors; (2) 6.2×1018 cm−3 acceptors; and (3) 1.2×1019 cm−3 donors compensated by 6.2×1018 cm−3 acceptors. The calculation is based on multiple-scattering theory with the self-energy calculated self-consistently to all orders of the interaction. The results show a small but significant amount of effective band-gap narrowing.