Recombination centers resulting from reactions of hydrogen and oxygen in n-type Czochralski silicon

Abstract

Hydrogen is often present in silicon solar cell fabrication introduced, for example, from silicon nitride anti-reflection layers. In general this has an important beneficial effect in reducing surface recombination. In this paper we show that in n-type Czochralski material the hydrogen reacts with interstitial oxygen related defects to form powerful recombination centers which reduce the minority carrier lifetime in the silicon region into which the hydrogen has diffused. We have studied electronic grade silicon and solar silicon grown by continuous Czochralski techniques. Hydrogen has been introduced into the silicon by wet etching, remote hydrogen plasma and from silicon nitride films. DLTS, MCTS and Laplace DLTS have been used to characterize and quantify parameters of the recombination centers and microwave photoconductivity decay to measure the minority carrier lifetime. The dominant recombination center has an acceptor level at 0.36 eV from the valence band. This center anneals out in the range 150 to 200°C but reforms on cooling.