Onset of implant-related recombination in self-ion implanted and annealed crystalline silicon

Abstract

The impact of residual recombination centers after low-energy self-implantation of crystalline silicon wafers and annealing at 900 °C has been determined by bulk carrier lifetime measurements as a function of implant dose. Doses below 10(exp 13) cm-2 resulted in no measurable increase in recombination, while higher doses caused a linear increase in the recombination center density. This threshold value corresponds to the known critical dose required for the formation of relatively stable dislocation loops during high temperature annealing. Deep level transient spectroscopy revealed a decrease in the vacancy-related defect concentration in the high-dose samples, which we interpret as reflecting an increase in the silicon interstitial concentration. This suggests that silicon interstitials, arising from the slowly dissolving dislocation loops, may be responsible for the increased recombination deep within the samples

Recombination activity of manganese in p- and n-type crystalline silicon

“…This is above the targeted volume concentrations, meaning that precipitation should indeed be avoided. Note also that any lifetime-reducing crystal damage caused by the low doses and energy used here have previously been shown to be effectively removed during such annealing [13]. This allows us to attribute any reduction in carrier lifetime after annealing to the presence of the implanted atoms themselves (in this case either Mn or O).…”

Insights to emitter saturation current densities of boron implanted samples based on defects simulations

“…This could be due to a more complete annealing of the deeply-penetrating defects, as a result of a higher probability that any diffusing defects reach the wafer surface or interface with higher thermal budget. These deeply-penetrating defects are known to be distributed uniformly down to a depth of at least 100 ȝm [4][5]. However, these defects are not evident in the simulations.…”

“…Even with the complete dissolution of dislocation loops, very stable boron interstitial clusters can still persist to be detrimental to J oe . Although lifetime and J oe depends on defect-free, well-passivated substrate, in the presence of defects, lifetime degradation at high boron ion implant doses has been shown to be identical for both thermal oxide and AlOx, which is known to be a better passivating dielectric [5].…”

“…Lifetime degradation due to ion implantation induced defects has been explained in terms of near-surface stable dislocation loops, as well as deeply-penetrating defects that result in uniformly-degraded lifetimes up to a depth of 100 ȝm [5]. It has been shown that both ion implantation and annealing conditions affect the resultant carrier lifetimes.…”

“…Regardless of the concern over defects, the use of ion implantation [1][2][3][4][5][6] and annealing [7] applied to solar cells has been studied for many years. Lifetime degradation due to ion implantation induced defects has been explained in terms of near-surface stable dislocation loops, as well as deeply-penetrating defects that result in uniformly-degraded lifetimes up to a depth of 100 ȝm [5].…”