Bond-centered hydrogen in silicon studied byin situdeep-level transient spectroscopy

Abstract

In situ deep level transient spectroscopy (DLTS) has been applied to investigate n-type silicon implanted with protons at low temperatures. Two DLTS signals, labeled ${E3\mathrm{}}^{\prime }$ and ${E3\mathrm{}}^{″},$ originate from hydrogen-related donor centers. The electron emission rates of the donors are similar and the two signals are discernible only because they form and anneal differently. In n-type silicon, the ${E3\mathrm{}}^{\prime }$ and ${E3\mathrm{}}^{″}$ centers transform into negatively charged centers at ∼100 K and at ≲65 K, respectively. Both signals can be regenerated at 65 K: ${E3\mathrm{}}^{\prime }$ by forward-bias injection of holes and ${E3\mathrm{}}^{″}$ by illumination with band-gap light under reverse-bias conditions. During the ${E3\mathrm{}}^{\prime }$ regeneration long-range migration of hydrogen occurs, whereas ${E3\mathrm{}}^{″}$ regenerates without migration. In the space-charge layer of reverse biased diodes, ${E3\mathrm{}}^{\prime }$ converts into ${E3\mathrm{}}^{″}$ with an activation enthalpy of 0.44 eV in oxygen-rich material, whereas ${E3\mathrm{}}^{″}$ converts into ${E3\mathrm{}}^{\prime }$ with an activation enthalpy of 0.72 eV in oxygen-poor material. It is found that the density of hydrogen sites associated with ${E3\mathrm{}}^{″}$ approximately equals the oxygen concentration, whereas the density of ${E3\mathrm{}}^{\prime }$ sites is about ${10}^{23}{\mathrm{cm}}^{\mathrm{-}3}.$ These results provide further evidence for our previous assignment of ${E3\mathrm{}}^{\prime }$ to isolated hydrogen at a bond center site and leads to the assignment of ${E3\mathrm{}}^{″}$ to bond centered hydrogen perturbed by a nearby oxygen atom. We argue that dilated Si-Si bonds in the strain fields around impurities and defects are trapping sites for hydrogen.