Electrical Characteristics Of The Transparent Conductive Oxide / p-a-Si:H Interface

The current-voltage (I-V) characteristics of the interfaces between boron-doped hydrogenated amorphous silicon (p-a-Si:H) and transparent conductive oxides (TCOs) such as tin oxide (SnO2) and indium tin oxide (ITO) are experimentally determined. The measurements are performed on especially developed Kelvin cross bridge structures which allow the direct sensing of the contact region. All contacts exhibit for high dopant concentrations an almost linear I-V characteristic. The values of the contact resistance depend on the TCO type and range between 0.5 and 4 Ω· cm2 at 25°C. Gradual reduction of the boron doping level leads to a remarkable increase of the contact resistance and finally to a rectifying behavior. The results indicate that tunnelling across the interface contributes significantly to the current transport. This conclusion is also supported by the behavior of the I-V characteristics at low temperatures. Regarding degradation of the contacts a systematic reduction of the contact resistance is observed after ageing them for 1000 hours at 80°C.