Comparison of AC and DC constant photocurrent methods for determination of defect densities

TY - JOUR

T1 - Comparison of AC and DC constant photocurrent methods for determination of defect densities

AU - Main, C.

AU - Reynolds, S.

AU - Zrinscak, I.

AU - Merazga, A.

PY - 2004/6

Y1 - 2004/6

N2 - We propose an explanation for large discrepancies in the absorption spectrum of a-Si:H between measurements by DC and AC constant photocurrent methods (CPM). DC measurement gives a consistently higher value for the absorption coefficient a at low photon energies. A small-signal analysis of the photoconductive response to modulated sub-gap illumination reveals low frequency poles associated with thermal emission processes, which explain this discrepancy. We demonstrate with computer simulations that while DC CPM, which includes these transitions, gives a more accurate value for absorption, AC CPM provides a more accurate means of determining the distribution of occupied gap-states. Further, we show that combining DC and AC methods allows determination of the distribution of deep unoccupied gap-states. These concepts are applied to experimental results for several undoped a-Si:H films.

AB - We propose an explanation for large discrepancies in the absorption spectrum of a-Si:H between measurements by DC and AC constant photocurrent methods (CPM). DC measurement gives a consistently higher value for the absorption coefficient a at low photon energies. A small-signal analysis of the photoconductive response to modulated sub-gap illumination reveals low frequency poles associated with thermal emission processes, which explain this discrepancy. We demonstrate with computer simulations that while DC CPM, which includes these transitions, gives a more accurate value for absorption, AC CPM provides a more accurate means of determining the distribution of occupied gap-states. Further, we show that combining DC and AC methods allows determination of the distribution of deep unoccupied gap-states. These concepts are applied to experimental results for several undoped a-Si:H films.

U2 - 10.1016/j.jnoncrysol.2004.02.059

DO - 10.1016/j.jnoncrysol.2004.02.059

M3 - Article

SN - 1873-4812

VL - 338

SP - 228

EP - 231

JO - Journal of Non-Crystalline Solids

JF - Journal of Non-Crystalline Solids

ER -