ASSESSMENT OF DENSITY OF STATES EXTRACTION FROM THE SPACE-CHARGE LIMITED CURRENT MEASUREMENT - A NUMERICAL-SIMULATION

The den Boer analysis of single carrier space charge limited currents is commonly used to determine the density of states function within the gap of amorphous silicon hydride and other newly emerging materials. By using a device simulator, we assess the validity and accuracy of this analysis. In particular, den Boer's assumptions of 0 K occupation statistics, a spatially uniform distribution of injected charge carriers, spatially uniform material, no generation/recombination, and no contact effects are investigated. We find that in the absence of contact effects and with spatially uniform states the den Boer analysis is accurate to within a factor of 2. However, current limiting due to contact effects at higher current values and diffusion dominated current at lower applied biases should not be mistaken for features of the density of states. In addition, if the gap states are not spatially uniform, gross overestimates (by as much as an order of magnitude for the device studied here) of the density of states can result. In general, only a limited range of the gap of the semiconductor can be mapped with this technique for a single device length, although multiple device lengths can be used to increase this range.