Electrical characterization and carrier transport mechanisms of GaAs p/i/n devices for photovoltaic applications

GaAs p/i/n diodes made by Metal-Organic Vapour Phase Epitaxy were examined by electrical measurements for evaluating the optimum i-region for use as solar cells. Four series of samples were prepared and studied each one with a different i-region width. The performance of the devices was examined by means of Admittance spectroscopy as well as classical current–voltage and capacitance–voltage characterization, allowing the calculation of the minority carriers lifetime (τ_eff) and the diodes ideality factors. The values of the τ_eff were found to lie between 8.7 ps and 0.14 ns for i-region widths between 0 and 0.8 μm. These results were used to model the multilayer structure with the two-diode representation and explain the conductance mechanisms inside the diodes. This modeling showed that the recombination/generation currents were dominating in forward biased diodes and the ohmic loss current in reverse bias.