Low temperature surface conductivity of hydrogenated diamond

Conductivity and Hall experiments are performed on hydrogenated poly-CVD. a tomically flat homoepitaxially grown Ib and natural type IIa diamond layers in the regime 0.34 to 400 K. for all experiments hole transport is detecte d with sheet resistivities at room temperature in the range 10(4) to 10(5) Ohm/rectangle. We introduce a transport mode[ where a disorder induced tail of localized states traps holes at very low temperatures (T < 70 K). The c haracteristic energy of the tail is in the range of 6 meV. Towards higher t emperatures (T > 70 K) the hole density is approximately constant and the h ole mobility mu is increasing two orders of magnitude. In the regime 70 K < T(overdot) < 200 K. mu is exponentially activated with 22 meV. above it fo llows a similar toT(3/2) law. The activation energy of the hole density at T < 70 K is governed by the energy gap between holes trapped in the tail an d the mobility edge which they can propagate. In the temperature regime T < less than> 25 K an increasing hole mobility is detected which is attributed to transport in delocalized states at the surface.