INTERFACE EFFECTS ON DOUBLE INJECTION CURRENT AND PHOTOCURRENT IN A-SI-H N-I-P AND P-I-N-DIODES

I-V curves of n-i-p and p-i-n diodes have been measured under forward bias with and without light-bias. It was found that the photogain, G(p h), can be as high as 1000 in an n-i-p structure. However, G(ph) is be low the limitation of our measurements in most p-i-n structures. Both the dark- and the photo-current responses of the devices depend strong ly on the deposition sequence (n-layer before or after i-layer) which affects both n-i and p-i interfaces. One explanation of these findings is that the photogain in both n-i-p or p-i-n structures is controlled by the strength of hole trapping near the n-i interface; the current transients are fitted well if we use this hypothesis. This suggests th at the n-i interface is degraded by light-soaking, as is the bulk. It was also found that the recombination mechanism near the n-i interface is bimolecular for as-deposited devices, and becomes monomolecular af ter degradation.