Evaluation of the characteristic curves of a-Si:H based devices with the Simmons-Taylor approximation when the defect pool model is used

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 “0K” 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.