Entwicklung und Beschreibung von optoelektronischen Bauelementen auf der Basis amorphen Siliziums

Multi spectral photodiodes for the detection of the fundamental components of the visible light (blue, green, red) based on amorphous silicon (a-Si:H) were developed. The spectral sensitivity of the novel thin film color detectors (nipiin- and niipiiin-structures) are controlled by the applied bias voltage. For the optimization of these color sensitive two terminal devices a numerical model was developed and successfully applied. The model combines the simulation of both, the spatial dependence of the transport and recombination behavior and the optical generation of carriers in solar cells and color detectors. Furthermore, bias voltage switching and illumination switching-on transients as weIl as capacitance-voltage measurements are investigated to analyze the time dependent behavior of the photocurrent of thecolor detectors. The most critical parameter, the defect distribution of a-Si:H for various doping levels was determined by comparison of simulated and measured constant photocurrent method (CPM) spectra. The simulations yield information about the density of localized gap states, the defect distribution in energy and the charge state of the defects. The defect density of n- and p-type sampies increases with doping concentration and is dominated by charge states in the annealed as weIl as in the degraded state. A good agreement between simulated and measured CPM data could only be achieved when a defect state distribution resembling to the defectpool model was used. Based on the defect density determined from the sub-bandgap absorption spectra, device simulation of the temperature dependent solar cell parameter (fill factor, short circuit current, open circuit voltage, diode quality factor, reverse bias saturation current) are performed. The correlation between the Fermi level and the defect state distribution results in a spatial dependent defect density profile within the i-layer of a pin-diode. For the modeling of the temperature dependence of the dark I/V curve and spectral response an enhanced defect density at the pli-interface above midgap, as predicted by the defect-pool model, is necessary. Furthermore, numerical simulation of the nipin-structures for color detection are carried out, which show that the electronic properties of the p-layer have a major influence on the device performance and that a good color separation between green and red requires a special design of the i-layers. Therefore, structures with controlled bandgap and mobility-lifetime product were developed which extract three linearly independent spectral response curves to generate an RGB-(red-green-blue)-signal with a two terminal device. These devices exhibit a dynamic above 95 dB. The bandgap ofthe devices decreases from the front to the rear contactand the mobility-lifetime product increase from the n- to the p-Iayer. The transient behavior of nipin structures was studied using a SPICE (Simulation Program with Integrated Circuit Emphasis) model. The simulations reveal that the transient behavior of the photocurrent of the nipin-structure after bias voltage switching from the green to blue color voltage is determined by the recharging behavior of the pin-diode switching from forward to reverse bias. Based on these results optimization criteria to improve the transient behavior are discussed