Hydrogen-induced transport properties of holes in diamond surface layers

Three hydrogen-terminated diamonds with different surface roughness and morphologies have been investigated by conductivity and Hall experiments in the temperature regime 0.34–350 K. The sheet hole densities are weakly temperature dependent above a critical temperature $T_c$ $\text{(20\hspace{0.05em}}\mathrm{K}{\mathrm{⩽T}}_c\text{⩽70\hspace{0.05em}}\mathrm{K}\mathrm{),}$ below $T_c$ carriers freeze out. The mobilities of holes show a minimum at $T_c$ increasing towards higher and even stronger towards lower temperatures significantly up to 400 cm²/V s. A transport model is introduced where holes propagate in the valence band where a disorder-induced tail of localized states is present.