Simulation and analysis of InP/GaInP nanowire Esaki diodes for photovoltaic device applications
Abstract: In this thesis the WKB-approximation is used to simulate the tunneling current for an Esaki nanowire diode and the result is compared to data from Esaki nanowire diodes grown with MOVPE. The WKB-approximation with triangular potential barrier predicts a strong increase of the tunneling current as a function of the doping densities and at the highest doping levels it gives lower tunneling distances than more reliable drift-diffusion simulations and is thus overestimating the current. The voltage corresponding to the peak current was found to be much higher in the measured samples than in the simulations, and it is shown that an added contact resistance cannot explain this behaviour. Band tailing is suggested as a possible explanation for the difference in the voltage between simulations and experiments. The diode characteristics of the Esaki diode samples are also studied at larger voltages. It is shown that an exponential current law fits well with the diode current at the larger voltages and the resulting contact resistance is too small to significantly change the tunnel current due to its low magnitude. An ideality factor was calculated from the fittings to be larger than 2 indicating that the excess current of the Esaki diode may be due to trap tunneling.
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