Effect Of High Concentration Of Defect States At PS/c-Si Heterointerface On Transport Properties Of Al/PS/c-Si Photodiode Structures

Current-voltage characteristics, photosensitivity, frequency dependence of impedance, and electron beam induced current were measured for Al/porous silicon/c-Si structures with porous silicon (PS) layers of 60 and 80% porosity. Al/PS/c-Si structures have photosensitivity spectra typical for Al/c-Si structures. The sign of open circuit voltage changes in these structures when the wavelength becomes less than approximately 0.4 μm. It was shown that photosensitivity of Al/PS/c-Si structures and impedance dependence on the frequency, reverse bias and thickness of PS layer are completely determined by the PS layer of high resistivity and by the space charge region in c-Si substrate on PS/c-Si heterojunction. The annealing at above 100° C leads to a decrease of the forward current at a small bias. The photosensitivity of annealed structures reaches 10 A/W for some of the structures. The experimental results lead to inevitable conclusion about opposite band bending from the two sides of the heterojunction which is caused by high concentration of charged defects at PS/c-Si heterointerface. PS photodetectors with improved device parameter were obtained.