Copper passivation of dislocations in silicon

Abstract

The J-V characteristics of metal-insulator-semiconductor solar cells fabricated on Si samples which are damaged (lapped) with I-pm grit size of A1 2 0 3 are substantially degraded. The introduction of copper at 250-400 "C passivates the dislocations. The copper is diffused in from the surface. Anodic oxidation followed by etching in aqua regia and 48% HF was used to remove excess copper remaining on the damaged surface and to etch away controlled amounts of the silicon wafers. The experimental results are compared to the model of Divigalpitiya and Morrison [1. App1. Phys. 60, 406 (1986)]. It is concluded using the model that copper passivation reduces the product of the density of hole traps and the capture cross section of hole traps and may also increase the specific conductance of the dislocations. Results for samples lapped with finer-grit alumina (0.3 /lm) seem qualitatively different from those with i-pm alumina. The variation in dislocation density as a function of depth into the surface is used to explain the difference qualitativ(~iy. The dislocation density decreases rapidly with distance from the damaged surface.

Impurity Precipitation, Dissolution, Gettering and Passivation in PV Silicon: Final Technical Report, 30 January 1998--29 August 2001

“…Thus, it is clear that the presence of low concentrations of copper compensates the detrimental effect of other defects and impurities and increases the minority carrier diffusion length in the samples. This confirms observations previously reported in literature [74,79,81]. Since interstitial copper is somewhat similar to hydrogen (i.e., it is also a fast diffuser in silicon and is positively charged), we think that its compensating effect is also similar to that of hydrogen, i.e., interaction of interstitial copper with recombination-active defects in silicon results in the formation of less recombination active complexes.…”

Influence of copper contamination on the illuminated forward and dark reverse current‐voltage characteristics of multicrystalline p‐type silicon solar cells

“…Such unexpected results which should be confirmed by other and complementary measurements are not fully understood. Mechanisms such as the direct electrical passivation of dislocations by Cu atoms as reported in [6], or the presence of liquid Cu silicides during the cooling of the ingot which would develop internal gettering effects as reported in [7], could contribute to these weak effects. can be reverse biased and act as a receptor thereby severely limiting the module output power.…”

Influence of Cu contamination on dislocation related luminescence

“…At low temperature annealing Cu atoms diffuse to dislocations and interact with dislocation related defects. The sharp decrease of D1/D2 lines at 400 °C and 500 °C means that corresponding centers are passivated due to this interaction [3]. On the contrary, the intensity of BE TO line increases in this temperature interval (Fig.…”

“…The passivation of dislocations by Cu contamination has been reported in Ref. [3] and quite the contrary an increase of recombination activity has been observed after contamination of dislocations with Ni [4]. This contradiction probably arises from a very complicated set of energetic levels introduced by dislocations into the forbidden gap and dependence of interaction of impurities with dislocations on the contamination level.…”