EFFECT OF OXYGEN CONCENTRATION ON LIFETIME IN MAGNETIC CZOCHRALSKI SILICON

The effect of oxygen concentration on recombination lifetimes (tau-r) in as-grown as well as oxidized magnetic Czochralski (MCZ) silicon was investigated. Oxygen concentration was varied in the range of 5-10 ppm within the same ingot by changing the crucible rotational speed. Injection-sensitive photoconductive decay (PCD) technique was used to measure lifetime (tau-r) and to quantify Shockley-Read-Hall recombination, trap-assisted Auger recombination coefficient (B), and band-to-band Auger recombination coefficient (C). Recombination lifetime at an injection level of approximately 4 x 10(14) cm-3 (DELTA-N almost-equal-to 35 . N(D) in as-grown MCZ wafers was as high as 2.1 ms and was found to be independent of interstitial oxygen concentration up to 10 ppm. Contrary to the tau-r at relatively lower injection level, the lifetime at moderate injection level of approximately 5 x 10(15) cm-3 (N(I) > 400. N(d) was found to decrease with increasing oxygen concentration due to the increase trap-assisted Auger recombination coefficient (B). It is also shown for the first time that the trap-assisted Auger coefficient (B) increases monotonically with the oxygen concentration in MCZ silicon. The lifetimes in the oxidized wafers, measured at lower as well as moderate injection levels, showed a decrease with increasing oxygen concentration. The degradation in lifetime at lower injection level was attributed to the interaction between oxygen and diffused-in impurities during high-temperature processing. After oxidation, a substantial increase in the B coefficient was observed at all oxygen levels. However, band-to-band Auger recombination coefficient (C = 1.1 x 10(-30) cm6/s) was found to be independent of oxygen concentration, both before and after oxidation.