The impact of Ge codoping on the enhancement of photovoltaic characteristics of B-doped Czochralski grown Si crystal

Abstract

The effect of Ge codoping on minority carrier lifetime in boron (B)-doped Czochralski-silicon (CZ-Si) crystals was investigated. The minority carrier lifetime increased from 110 to 176 µs as Ge concentration was increased from zero to 1 × 1020 cm−3 in B/Ge codoped CZ-Si crystals. Light-induced degradation (LID) experiments showed that B-doped CZ-Si degrades rapidly, while B/Ge codoped CZ-Si degrades more slowly. Moreover, the flow pattern defect (FPD) density of grown-in micro-defects (GMD) in as-grown B/Ge codoped CZ-Si decreased with increasing Ge concentration. From the infrared (IR) absorption studies, it was observed that the interstitial oxygen (Oi) concentration decreased as Ge concentration increased in the crystal. The suppressed LID effect in the B/Ge codoped CZ-Si appears to be related to the low concentration of B-O associated defects, possibly because Ge doping retards the Oi diffusion in addition to the low Oi concentration present (evidenced from IR studies). The mechanism by which the Ge concentration influences the reduction of FPDs and Oi concentration is discussed in terms of Ge-vacancy defect formation during post-growth cooling of the ingots.