Defect Generation by Hydrogen at the Si- ${\mathrm{SiO}}_2$ Interface

Hydrogen is known to passivate Si dangling bonds at the $\mathrm{Si}-\mathrm{SiO}{}_2$ interface, but the subsequent arrival of $\mathrm{H}{}^{+}$ at the interface causes depassivation of Si-H bonds. Here we report first-principles density functional calculations, showing that, contrary to conventional assumptions, depassivation is not a two-step process, namely, neutralization of ${\mathrm{H}}^{+}$ by a Si electron and subsequent formation of an $\mathrm{H}{}_2$ molecule. Instead, we establish that $\mathrm{H}{}^{+}$ is the only stable charge state at the interface and that ${\mathrm{H}}^{+}$ reacts directly with Si-H, forming an $\mathrm{H}{}_2$ molecule and a positively charged dangling bond ( $P_b$ center). As a result, H-induced interface-trap formation does not depend on the availability of Si electrons.