Carrier lifetime studies of deeply penetrating defects in self-ion implanted silicon

Abstract

Boron segregation to extended defects induced by self-ion implantation into siliconCarrier lifetime measurements have been used to characterize residual defects after low-energy implanting of silicon ions followed by high-temperature annealing ͑900 or 1000°C͒. The implant was found to result in two distinct regions of lifetime-reducing damage. First, a high recombination region, most likely due to stable dislocation loops, remained near the surface. In addition, deeply propagated defects, which were not present prior to annealing, were also detected. These deep defects, which are possibly silicon interstitials, diffuse so rapidly during annealing that their distribution becomes effectively uniform to a depth of 100 microns. Annealing at higher temperatures was found to reduce the severity of both the surface and the deeply propagated defects.

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

“…As can be seen, the dislocation loops and boron interstitial cluster defects are located at the nearsurface region. It can be expected that etching and repassivating the surface region would improve the lifetime by removing the defects, consistent with results from Macdonald et al [4].…”

“…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.…”

“…It has been shown that both ion implantation and annealing conditions affect the resultant carrier lifetimes. Higher ion dose resulted in a greater amount of residual damage and hence lower lifetime [4,6]. Also, more complete damage annealing at higher temperature results in a longer carrier lifetime.…”

“…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].…”

Studies of implanted boron emitters for solar cell applications

“…8 Lifetime degradation due to self‐implantation related defects have been observed by MacDonald et al . 9, 10 and explained in terms of dislocation formation. This paper deals with B shallow implants that do not form any extended defects after high‐temperature anneal.…”