Negative contribution to the reverse bias capacitance of organic diodes due to field dependent mobility: Determination of barrier height and transport parameters

We analyse the capacitance voltage characteristics of a small molecule-based single carrier diode consisting of a p-doped/intrinsic layer interface using m-MTDATA. In such homojunction diodes, in which the intrinsic layer thickness varies between 10 and 50 nm, the capacitance in deep reverse bias falls nearly exponentially and goes below the geometrical capacitance (C-g) beyond a critical electric field. We mainly focus on this reduction of the capacitance, which is interpreted based on charge injection mechanism in reverse bias. The small signal capacitance in such cases is shown to have negative contribution which is directly related to the delay time introduced by the charge transport. Thus, the capacitance characteristics have been modelled in deep reverse bias using the charge transport mechanisms, and the barrier height so estimated is in excellent agreement with the values calculated from current density-voltage (J-V) characteristics. The technique also allows the determination of mobility, which in turn yields the disorder parameters through its temperature and field dependence. Published by AIP Publishing.