The Increased Response Time in Hydrogenated Microcrystalline Silicon - A Fermi Level Effect or a Structural Effect in a Grainy Material?

Abstract

AbstractThe typical photocurrent decay time τR in intrinsic prepared hydrogenated microcrystalline silicon (μc-Si:H) is around lms similar to its n-doped amorphous counterpart (a-Si:H:P). Depending on the crystalline fraction Xc, the μc-Si:H films show an activation energy near to or below 0.5eV. To find out if this analogy ofτR could be due to a Fermi level shift or to the grainy structure in gc-Si:H films, we have studied the behaviour of τR in doped a-Si:H and gc-Si:H films of different XC. One-dimensional numerical simulation based on the Multiple Trapping Model (MTM) can explain this increase in terms of a Fermi level shift towards the conduction band. On the other hand, detailed measurements for temperatures from 100 to 400 K point to carrier trapping in deep states, most probably located at grain boundaries.