A New Model of Negative Photocurrent__Invited Paper

Abstract

A one-deep-energy- level impurity, space-charge neutral and steady-state model is proposed and nerified in n-type silicon N+IN+ diode samples which are overcompensated but not inverted by gold acceptors in the slightly n-type I-region. The model is as follows. If the photoionization rate of trapped holes at the impurity centeris greater than electrons, then an extrinsic monochromatic light will increase the trapped electron concentration. To maintain quasi-neutrality and a constant steady-state trapped electron concentration (equal to the concentration of the shallow level donor), the injected electron concentration into the compensated n-type I-region must decrease . Thus, the electron or the total conduction current must also decrease since the hole concentration is very low in the presence of a large sweep-out electric field and the hole conduction current may be neglected. This model has successfully predicted the observed large negative photocurrent (NPC)which is as much as 2/3 of the dark current , the large intrinsic optical gain (about 50) and the sublinearity in dark current.