Performance of a-Si:H n–i–p photodiodes on plastic substrate

This paper reports on a-Si:H n–i–p photodiodes on PEN substrates with performance characteristics suitable for imaging applications. Segmented n–i–p photodiodes were fabricated using a process sequence and design rules that are compatible with industrial technology. Low-temperature (150 °C) plasma-enhanced chemical vapor deposition (PECVD) was employed for the a-Si:H and passivation dielectric layers. Device measurements included current–voltage characteristics, dark current decay, and spectral response. To identify the sources of the reverse dark current, the measurements were performed on variable area test structures with device sizes ranging from 126 μm to 2 mm. The n–i–p photodiodes on PEN substrates demonstrate quantum efficiencies as high as 83% and reverse current density lower than 500 pA/cm2 at −3 V, as measured on 126 μm photodiodes. Thus, the performance characteristics of the n–i–p diodes on PEN substrates meet the requirements for bio-medical X-ray imaging. We also discuss the mechanisms underlying the reverse dark current and the effect of the substrate on device characteristics.