Effect of Cryogenic Dry Etching on Minority Charge Carrier Lifetime in Silicon

Abstract

Micro‐ and nanostructured silicon surface application is a promising way of photovoltaic development. An enhancement of optical absorption in solar cells can be achieved, for example, using vertically aligned silicon nanostructures with high aspect ratios. Cryogenic plasma etching is a suitable method for such structures' formation; however, there is still lack of data describing an effect of cryogenic inductively coupled plasma (ICP) etching on defect formation in silicon (Si). The defects may act as recombination centers, leading to solar cell characteristics degradation. Herein, the cryogenic dry etching effects on defect formation in float‐zone (FZ) n‐type silicon substrates and on the photovoltaic properties of solar cells made of plasma‐etched silicon substrate are presented. The decrease in low‐injection minority carrier lifetime in silicon from 0.85 to 0.55 ms is observed by photoluminescence decay after the ICP dry etching at −140 °C. This leads to an open‐circuit voltage drop for the (p)a‐Si:H/(n)c‐Si/(n)a‐Si:H heterojunction structure from 680 to 630 mV. A detailed study of the defect properties by deep‐level transient spectroscopy (DLTS), numerical simulation, and its behavior after wet etching and thermal annealing is presented.