Limits to model amphoteric defect recombination via SRH statistics

Abstract

In semiconductor device modeling, it is common practice to approximate recombination via amphoteric defects by means of the Shockley-Read-Hall (SRH) theory. We show by means of a mathematically rigorous treatment that this approximation is only justified if: (i) the defect distribution of amphoteric defects is approximated by two equally-shaped energy distributions of acceptor-and donor-like defect states which are separated in energy by the effective correlation energy, (ii) the ratios of the capture cross-sections (CCS) of free carriers for charged and neutral defect states are strongly asymmetric, (iii) the correlation energy is positive, and (iv) the defect density has its maximum between the quasi-Fermi levels (QFLs) for the trapped carriers (TQFLs). In particular, we investigate this kind of SRH approximation for the case of injection-dependent recombination at the interface between crystalline silicon (c-Si) and amorphous silicon (a-Si:H), a system that has recently been used to passivate the surface of Si solar cells. It is shown that care must be taken when applying this SRH approximation at low excess carrier densities Dn, e.g., at pn-junctions between a-Si:H and c-Si or at low illumination levels, because the defect distributions may peak outside the TQFLs. We apply a selfconsistent model, which includes the band bending in c-Si caused by both light-induced, trapped charges in the a-Si:H layer and at the a-Si/c-Si interface. We show that these trapped charges significantly influence the recombination rate and should be taken into account, as opposed to common practice.

Extracting surface recombination parameters of germanium–dielectric interfaces by corona-lifetime experiments

“…[63][64][65][66][67][68][69] In the extensive literature on silicon surface passivation, the energy dependence of the D it is frequently assumed to consist of one or more Gaussian distributions centered around their characteristic trap energy E t 43,64,68,70 complemented with two exponentially decaying distributions arising from the conduction and valence band, so-called (Urbach) tail states. 43,68,[70][71][72][73] The sum of these distributions leads to the experimentally observed U-shape of the D it distribution. Constant values for σ p and σ n h i are assigned to the conduction band tail ( σ p CB and σ n h i CB ), the valence band tail ( σ p VB and σ n h i VB ), and each Gaussian distribution ( σ p G,i and σ n h i G,i ).…”

Influence of the Recombination Parameters at the Si/SiO2Interface on the Ideality of the Dark Current of High Efficiency Silicon Solar Cells

“…The interest in studying surface recombination through multi-charge Sah-Shockely recombination statistics [13] stems from the fact that the P b centers created by dangling bonds at the Si/SiO 2 interface are amphoteric recombination centers [6]. The latter can be neutral with capture cross sections s n 0 and s p 0 , positively charged and having a capture cross section s n + or negatively charged and having with a capture cross section s p -.…”

“…The present work presents a clear understanding of the recombination process at the Si/SiO 2 interface and the influence of the surface recombination parameters on the dark current of the PERL cell. This is achieved through analytical modeling of surface recombination based on SRH recombination statistics [5] and on amphoteric recombination modeling [6][7][8]. The accuracy of the modelling is enhanced by assuming that recombination centers form a continuum distributed over all energy levels in the energy bandgap.…”

Modeling Surface Recombination at the p-TypeSi/SiO2Interface via Dangling Bond Amphoteric Centers

“…It has been argued that the two-state charge Fermi-Dirac occupation function has some limitations in a-Si abundantly hosting amphoteric dangling bonds [8,11] and that multicharge Sah-Shockley correlated electron statistics [7] is more appropriate for this case. This may also apply to recombination at the Si/SiO 2 where defects are mainly due to dangling bond amphoteric centers.…”