ZnO thin film and porous silicon co-gettering of impurities in multicrystalline silicon through a VTP process

Abstract

In this study, a novel zinc oxide and porous silicon co-gettering experiment has been applied as a beneficial approach to improve the electrical properties of low quality multicrystalline silicon substrates (mc-Si). We investigated the combined effect of ZnO and porous silicon (ZnO/PS) to enhance the gettering process efficiency. A systematic comparison has been carried out between two different routes of annealing after coating the front surface with zinc oxide thin film. The first one consists of a one step annealing (classic annealing) and the second consists in subjecting the samples to a variable annealing temperature process (VTP) using two steps, starting by the precipitate temperature at Tp = 1000 °C followed consecutively by a gettering temperature at Tg = 850 °C for different durations. Obtained results show that the Zn-gettering processes via the classic annealing process allow a significant improvement of the substrate quality. Nonetheless, highest values of the effective minority carrier lifetime exceeding 508 µs were obtained after using VTP annealing. Zn-gettering was investigated and found to have a crucial effect on the recombination activities mainly into the grain boundaries. Obtained results showed a significant enhancement of the gettered multicrystalline silicon electrical properties, resulting after the high increase of the effective minority carrier lifetime from 5 to 508 µs and the increase of the Hall mobility from 72 to 193 cm2 V− 1 s− 1. These enhancements have been further confirmed with the internal quantum efficiency (IQE) measurements. Thus, it is inferred that the applied co-gettering experiment has a synergetic effect to improve the electrical properties of the mc-Si substrates. The morphological structure of silicon was signed out by the Field emission scanning electron microscopy (FESEM).