No abstract

The performance of a-Si:H devices is highly sensitive to the density of gap states: tail states are distributed in two exponentials and defect states are generated by dangling bonds (DB). The density of DB in a-Si:H can be evaluated with the defect pool model (DPM). Charge trapping and recombination of electron-hole pairs through tail states are described by the Shockley-Read-Hall (SRH) formalism while defect states behave as amphoteric. Equations derived with the SRH formalism can be simplified with the Simmons-Taylor's approximation (STA), especially with the "0 K" approximation (0KSTA). Amphoteric-like defect states were approximated by donor-and acceptor-like decoupled states (DSA). The accuracy of STA was tested in a-Si:H based devices when the density of DB is evaluated with the DPM for different illumination conditions, voltages, temperatures, and some key electrical parameters. Our code was modified to include both the STA and the DSA. Our results indicate that the STA is very accurate under illuminated conditions. Under dark conditions, the STA is acceptable for forward voltages but overestimates the dark current at reverse voltages. The 0KSTA can be used under illuminated conditions for any applied voltage and under dark conditions for forward voltages.

An algorithm that simplifies the evaluation of the reverse dark current–voltage (J–V) characteristic of semiconductor thin film devices is presented. This algorithm, recognized with the symbols “0KRDA”, is an approximation of the SRH formalism that can be used when the dangling bond density is modeled with either the Uniform Density Model or with the Defect Pool Model. The 0KRDA is designed to replace the 0K‐Simmons–Taylor approximation (0KSTA) in reversed biased junctions operating under dark conditions. The dependence of the current density J with respect to the applied voltage V predicted with SRH formalism is well replicated by the 0KRDA. The small differences obtained in the calculated reverse dark currents can be removed by neglecting the contribution of gap states with energies closer than kT/5 to the intrinsic trap level. The transport physic controlling the shape of reverse dark J–V curves of thin film devices can be more easily visualized with the 0KRDA.