INFLUENCE OF THE ALKALI SURFACE TREATMENTS ON THE INTERFACE-STATES DENSITY AND MINORITY CARRIER LIFETIME IN Cz–SILICON WAFER

摘要

The chemical etching of the surface of silicon wafers is a critical step in the manufacturing process of all semiconductor devices. In this contribution, we investigate the effect of alkaline etching on minority carrier lifetime and interface-states density (Dit) of silicon wafers intended to be used as solar cell substrates. After alkali treatment, the surface morphology was analyzed using scanning electron microscopy (SEM) and UV-visible-NIR optical spectroscopy. Besides and as electrical characterizations, the minority charge carrier lifetime (τn) was measured by the Quasi-Steady State Photoconductance technique (QSSPC), and the Electrochemical Impedance Spectroscopy was used to evaluate Dit. These results were correlated with the surface recombination velocity (SRV) calculated by fitting the experimental data to the theory. The results of characterization showed a lower SRV and a higher apparent lifetime (τapp) obtained with 23wt.% KOH etching as compared to those obtained with 30wt.% NaOH; viz. 825cm?s?1 against 1500cm.s?1 and 32μs against 23μs, respectively. These findings were corroborated by Dit measurements which gave 1.55×1011ev?1cm?2 for KOH treatment and 5.67×1012ev?1cm?2 for NaOH treatment.