Bond-centered hydrogen in silicon studied by<i>in situ</i>deep-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 ${E3}^{\ensuremath{'}}$ and ${E3}^{\ensuremath{''}},$ 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 ${E3}^{\ensuremath{'}}$ and ${E3}^{\ensuremath{''}}$ centers transform into negatively charged centers at \ensuremath{\sim}100 K and at \ensuremath{\lesssim}65 K, respectively. Both signals can be regenerated at 65 K: ${E3}^{\ensuremath{'}}$ by forward-bias injection of holes and ${E3}^{\ensuremath{''}}$ by illumination with band-gap light under reverse-bias conditions. During the ${E3}^{\ensuremath{'}}$ regeneration long-range migration of hydrogen occurs, whereas ${E3}^{\ensuremath{''}}$ regenerates without migration. In the space-charge layer of reverse biased diodes, ${E3}^{\ensuremath{'}}$ converts into ${E3}^{\ensuremath{''}}$ with an activation enthalpy of 0.44 eV in oxygen-rich material, whereas ${E3}^{\ensuremath{''}}$ converts into ${E3}^{\ensuremath{'}}$ with an activation enthalpy of 0.72 eV in oxygen-poor material. It is found that the density of hydrogen sites associated with ${E3}^{\ensuremath{''}}$ approximately equals the oxygen concentration, whereas the density of ${E3}^{\ensuremath{'}}$ sites is about ${10}^{23}{\mathrm{cm}}^{\mathrm{\ensuremath{-}}3}.$ These results provide further evidence for our previous assignment of ${E3}^{\ensuremath{'}}$ to isolated hydrogen at a bond center site and leads to the assignment of ${E3}^{\ensuremath{''}}$ 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.