Grain Boundary Interface Research Articles

Spectral response of photoconductivity in polycrystalline semiconductors

Photoconductivity in polycrystalline semiconductors can arise from the modulation, by the optical illumination, of the diffusion potentials at the grain boundaries, which in turn control the majority carrier current in these materials. The photogenerated carriers are captured by interface states at the grain boundaries through Shockley-Read-Hall processes, and under constant illumination this affects the steady-state charge at these boundaries so as to reduce the diffusion potentials from their dark values. The dependence of the diffusion potentials and of the photoconductivity upon position is calculated from the dependence of the optical absorption on wavelength. Finally, the average photoconductivity (expected from measurement) of polycrystalline semiconductor thin films is determined as a function of the intensity of the optical illumination, the grain size, the film thickness and the grain-boundary interface parameters.

Minority-carrier injection(dark) metal-polycrystalline silicon contacts

The dependence of minority-carrier injection current Jp on applied forward-bias voltage of metalpolysilicon contacts has been calculated within a general treatment of the recombination at grain boundaries. A uniform distribution of interface states in energy at the grain boundaries is assumed throughout. It is found approximately that Jp ̃ exp (q V/KT) for (grain-boundary) recombination limited by the supply of minority carriers, Jp ̃ exp (q V/KT) or exp (q V/2KT) for high and low grain-boundary interface state densities for recombination limited by the supply of majority carriers, and Jp ̃ exp (3q V/4KT) for intrinsic recombination (limited equally by holes and electrons). Electrostatic effects of grain-boundary interface states, resulting in a bias dependence of grain-boundary barrier height øg, are significant for interface state densities Nis > 1010–1011cm−2V−1. depending upon the doping within the grains. The effective diffusion length for the injected minority carriers also shows an appreciable bias dependence, especially for intrinsic recombination, and for majority-carrier limited recombination at high øg and low Nis.Minority-carrier injection dominates the dark current (as it does in a p-n junction) for Schottky-barrier height øb > 0.8 V, for typical grain size d≃10−3cm, interface state densities Nis≃1013cm−2V−1, and relatively low doping Nd≃1014cm−3.