ELECTRICAL AND OPTICAL CHARACTERIZATION OF CRYSTALLINE SILICON POROUSSILICON HETEROJUNCTIONS

We have investigated the photovoltage and photocurrent spectra of crys talline silicon/porous silicon heterojunctions. The porous silicon lay ers were prepared using anodic etching of p-type crystalline silicon a t a current density of 25 mA/cm(2). From the spectral dependence of th e photovoltage and photocurrent, we suggest that the photovoltaic prop erties of the junction are dominated by absorption in crystalline sili con only. We have also studied the effect of increase in the thickness of porous silicon layers on these spectra. We find that the open-circ uit voltage of the devices increases, but the short-circuit current de creases with an increase in the thickness of the porous silicon layers . We propose a qualitative explanation for this trend, based on the in crease in the series and the shunt resistance of these devices. The ef fect of hydrogen passivation on the junction properties by exposing th e devices to hydrogen plasma is also reported.