The effect of porous silicon thickness and pore size on the electrical properties of TiO2/PS heterojunctions

Abstract

Heterojunctions made by depositing Titanium dioxide (TiO2) on porous silicon using the sol-gel method were electrically characterized. It was found that charge transfer mechanisms are dependent on the porosity and layer thickness, as well as the pore size. For the case of devices fabricated in mesoporous matrix, the current-potential curve appears like a Schottky ohmic contact, associated with the predominance of the tunneling charge transfer mechanism, depicting a reduction in current intensity as the meso-PS thickness increases. This behavior was related to the increase of TiO2 into the pores, which in turn leads to the hole concentration decrease from around 1020 to 1012 cm−3 because the compensation effect, as revealed by the Mott-Schottky analysis, while the impedance analysis shows that this reduction in holes is traduced as increase of the resistance associated with each interface. In the case of the devices yielded in macroporous layers, it was found that devices with thinner layers behaves as hole-blocking device or even as ohmic contact, depending on the amount of interface states. In addition, in hole blocking devices, the presence of at least two diodes with opposite behavior is marked.