The influence of the space charge on The Ohm's law conservation in CVD diamond layers

In present work we report the investigation of charge transport mechanism in thin diamonds layer grown by hot filament chemical vapor deposition (HF CVD) method. The measurements were performed in both, wide temperature and bias voltage ranges as well. In the disordered matter the variable range hopping mechanism can play a crucial role. The obtained results reveal that simultaneously holes and electrons are involved in current flow. They can be easily distinguished by their different dynamics detected by impedance spectroscopy. The diamond crystal is considered as a wide bandgap semiconductor. Hole states originated as point defects inside of the bandgap behave like usual charges in semiconductor and they obey the Ohm's law. However, the CVD diamond polycrystalline films always contains some amount of sp(2) hybridized amorphous carbon phase. This form of carbon can donate electrons to the system. Electrons gathered as space charge on diamond edges create a depletion layer with unlike properties. The Ohm's law is broken for such type of charges and their activation energy are temperature dependent. At temperature of 21 K a sudden change of surface resistivity is observed, when helium atoms are being adsorbed on slowly moving holes. (C) 2018 Elsevier Ltd. All rights reserved.