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 (D-it) 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 (tau(n)) was measured by the Quasi-Steady State Photoconductance technique (QSSPC), and the Electrochemical Impedance Spectroscopy was used to evaluate D-it. 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 (tau(app) thorn obtained with 23 wt.% KOH etching as compared to those obtained with 30 wt.% NaOH; viz. 825 cm.s(-1) against 1500 cm.s(-1) and 32 mu s against 23 mu s, respectively. These findings were corroborated by D-it measurements which gave 1.55 x 10(11) ev(-1)cm(-2) for KOH treatment and 5.67 x 10(12) ev(-1)cm(-2) for NaOH treatment.