Evolution of defect structures in silicon after low temperature implantation of hydrogen

Proton implantation into n-type silicon at initiates the formation of two deep donor centers containing hydrogen. These centers, denoted E3′ and E3′′, can be observed when deep-level transient spectroscopy is applied in-situ to as-implanted diodes. The emission rates of E3′ and E3′′ are very similar, and the centers are discernible only because they form and anneal differently. In their neutral charge states (i.e. zero-bias annealing) E3′ anneals in ≈10 min at 100 K and E3′′ anneals in ≈50 ms at 75 K. The zero-bias anneals lead to a negatively charged center from which both E3′ and E3′′ can be recovered at low temperature: E3′ by forward-bias injection of holes, and E3′′ by reverse-bias illumination with band-gap light. The E3′ recovery is associated with fast migration of hydrogen, while E3′′ recovers instantly without migration. The analogous anneals in the positive charge states (i.e. reverse-bias annealing) differ for oxygen-rich and oxygen-poor material. In Cz silicon E3′ converts at ≈220 K to E3′′ which then subsequently anneals at ≈260 K. In Fz silicon the order of anneals is reversed. Here E3′′ converts to E3′ at ≈230 K. Both centers disappear in the temperature range 240–260 K. We analyze the annealing scenario within a quantitative diffusion model that complies with the present theoretical understanding of isolated hydrogen in silicon. We conclude that the density of hydrogen sites associated with E3′′ approximately equals the oxygen concentration while the density of E3′ sites corresponds to the atomic density of silicon. We identify the E3′ center as isolated bond-center hydrogen and E3′′ as bond-center hydrogen which is perturbed (and stabilized in the positive charge state) by nearby interstitial oxygen. We argue that dilated Si–Si bonds, present in the strain field around impurities and defects, rather generally may act as trapping sites for otherwise isolated hydrogen resulting in the formation of a family of bond-center type centers that are very much alike.