Mechanism for hydrogen compensation of shallow-acceptor impurities in single-crystal silicon

Experimental results are presented which identify the following chemical reaction as being responsible for compensation of shallow-acceptor impurities when single-crystal silicon is exposed to monatomic hydrogen: A^-+h⁺+H⁰↔(AH)⁰, where A^- represents an ionized shallow acceptor, h⁺ is a (positively charged) free hole, and H⁰ is a neutral hydrogen atom. Infrared absorption spectroscopy on boron-doped silicon, combined with recent defect-model calculations, reveals that the hydrogen atom forms a Si-H bond at the site of a substitutional boron atom; the absorption band for the stretch mode appears at 1870 cm^-1. Measurements by secondary-ion mass spectrometry of impurity profiles in deuterated silicon reveal that shallow-acceptor passivation is suppressed by counter doping to produce n-type conductivity. These new results identify both the defect complex responsible for hydrogen compensation of shallow acceptors and the essential role of free holes, or equivalently neutral acceptors, in the chemical reaction.