Influence of Cu contamination on dislocation related luminescence

Abstract

This work is devoted to investigation of Cu contamination on dislocation related luminescence (DRL) in Si. Cu is known to be a very fast diffuser with high solubility. Fz Si samples were plastically deformed at 950 °C up to dislocation density of about 10 7 cm -2. Cu diffusion was performed by diffusion at 950 °C from a quartz ampoule contaminated with Cu. The presence and concentration of luminescent copper (Cu PL) centers was evaluated from the excitation dependence of the copper bound exciton no-phonon line (BE NP) line at 1.014eV, which was activated after annealing at 1100 °C and rapid quenching in the water. 10 minutes isochronous annealing of the samples in the temperature range 300-600 °C revealed quite a different behavior of D4 and D1/D2 lines. It was assumed that a strong decrease of D1/D2 line intensity in annealing interval 400-500 °C could be attributed to passivation of D1/D2 luminescence centers by Cu atoms. [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. The latter statement is supported by observation of dependence of dislocation recombination activity on the level of Cu contamination. For low level (∼1 ppb) the EBIC contrast increased markedly at low temperatures, while for a Cu concentration of about 15 ppb the contrast was observed in the whole temperature range (80-300 K) [5]. In material with high Cu contamination (ppm range) the authors observed Cu precipitates along dislocations and dramatic increase of the contrast in the whole temperature range. The formation of copper precipitates in silicon greatly decreases carrier diffusion length [6]. The process of precipitation goes much faster in the presence of extended defects and at high Cu concentration even precipitate colonies have been observed [7]. The colonies are very effective recombination regions; an EBIC contrast as high as 93% has been reported for such colonies [8]. While the dramatic decrease of minority carrier life time at high Cu contamination is caused by formation of precipitate related defect band, less definitely we can presume an influence of Cu at low contamination level. At least four reproducible Cu related levels have been found in Si [9]. Their activity de-

Time-resolved measurements of dislocation-related photoluminescence bands in silicon

“…Samples A2d13 and b2-1 should be free of metal impurities due to gettering in a chlorine atmosphere. Special PL measurements confirmed the reduction of copper impurities below the detection level after Cl gettering, while it was measured in as received samples [11]. Other impurities were not checked.…”

Time‐resolved measurements of dislocation‐related photoluminescence bands in silicon

“…The effectiveness of this procedure has been proved by recording Cu-related luminescence in quenched samples. Typically Cu-related luminescence decreased below detection level after Cl gettering, while it was clearly observed in as-received samples [8]. Sample a2d16 is as-deformed and has a more ordered dislocation structure due to the larger separation between outer supports during 3-point deformation, and a smaller stress gradient.…”