Numerical Modeling of Transport and Transport Measurements in Hydrogenated Amorphous Silicon Schottky Barrier Devices

This thesis describes the computer program EPRI -AMPS and its use to investigate transport measurements n hydrogenated amorphous silicon Schottky barrier structures. The computer model is used to simulate dark current density -voltage data as well as spectral response data. When compared with experimental data as a function of thickness, it is found that a bump of acceptor-like states approximately 0.55 eV below the conduction band edge is necessary to match the far forward bias current density values. To match the low forward bias current density values, positive charge, created by adding donor-like states in the upper half of the bandgap, is required near the front surface. Also, to match intermediate forward bias current density values, a relatively low midgap density of states is required ( <5 times 10^ {14} cm^{-3}eV^ {-1}). The same density of states used to match the experimental dark current density-voltage data is required to match the experimental spectral response data as a function of thickness both in the dark and with a bias light applied. Thus, a consistent density of states model is obtained which matches both current density-voltage and spectral response data. A sensitivity study of all the model input parameters is done for the spectral response measurement. It is also shown that the bias light intensity must be an order of magnitude larger than the monochromatic light intensity to avoid an ill-defined spectral response. Finally, the surface-photovoltage diffusion length measurement is shown to be invalid for amorphous materials with a midgap density of states greater than 10 ^{13} rm cm^ {-3}eV^{-1}. This is due to the importance of drift in the motion of photogenerated carriers.