Abstract
An integral model is proposed for recombination at the silicon/silicon dioxide (Si/SiO2) interface of thermally oxidized p-type silicon viaPbamphoteric centers associated with surface dangling bonds. The proposed model is a surface adaptation of a model developed for bulk recombination in amorphous silicon based on Sah-Shockley statistics which is more appropriate for amphoteric center recombination than classical Shockley-Read-Hall statistics. It is found that the surface recombination via amphoteric centers having capture cross-sections larger for charged centers than for neutral centers is distinguished from Shockley-Read-Hall recombination by exhibiting two peaks rather than one peak when plotted versus surface potential. Expressions are derived for the surface potentials at which the peaks occur. Such a finding provides a firm and plausible interpretation for the double peak surface recombination current measured in gated diodes or gated transistors. Successful fitting is possible between the results of the model and reported experimental curves showing two peaks for surface recombination velocity versus surface potential. On the other hand, if charged and neutral center capture cross-sections are equal or close to equal, surface recombination via amphoteric centers follows the same trend as Shockley-Read-Hall recombination and both models lead to comparable surface recombination velocities.
Highlights
Recombination at the Si/SiO2 interface has been classically modeled using the two-charge-state Shockley-ReadHall (SRH) statistics [1] based on Fermi-Dirac occupation probability
It is found that the surface recombination via amphoteric centers having capture cross-sections larger for charged centers than for neutral centers is distinguished from Shockley-ReadHall recombination by exhibiting two peaks rather than one peak when plotted versus surface potential
The model is an adaptation to the surface of the model developed for the bulk recombination in amorphous silicon based on Sah-Shockley multicharge statistics for energy correlated amphoteric dangling bond defects
Summary
Recombination at the Si/SiO2 interface has been classically modeled using the two-charge-state Shockley-ReadHall (SRH) statistics [1] based on Fermi-Dirac occupation probability. Recombination via amphoteric centers is better described by Sah-Shockley recombination statistics [7] which has been used to model bulk recombination due to dangling bond defects in amorphous silicon (a-Si) [8] taking into account the multicharge nature of the centers and the energy correlation between them. Models for recombination via amphoteric dangling bond defects at the a-Si/c-Si interface of heterojunction silicon solar cells using Sah-Shockley statistics have been developed [9, 10], and their application to recombination at the Si/SiO2 interface has been proposed [10]. The surface recombination velocity is calculated using the proposed model and using SRH classical recombination adapted to the surface In both models, recombination centers are assumed to form a continuum distributed throughout the energy gap and carrier dependence on surface potential at the thermally oxidized Si/SiO2 interface is taken into account. By fitting previously reported experimental data with the results of the proposed amphoteric center model, an attempt is made to give a convincing explanation for the double peak surface recombination velocity extracted from recombination current in gated diodes and gated transistors
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