This paper presents the development of low dark current amorphous silicon (a-Si:H) based heterojunction photodiodes. A series of p-i-n and n-i-p structures have been deposited by plasma-enhanced chemical vapor deposition (PECVD). Junction properties and carrier transport are investigated in terms of dark and light current-voltage characteristics, time dependence of the dark current, and spectral photoresponse measurements. It is demonstrated that a thin (∼4 nm) undoped a-SiC:H buffer layer introduced between the p and i layers reduces the leakage current and improves the diode ideality factor. A dark current density of ∼10 pA/cm2 at reverse bias of 1 V was achieved for the n-i-p structure. Optimization of device design for further improvement of dark current and photoresponse is discussed.
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