Electrical and optical characterizations of erbium doped MPS/PANI heterojunctions

Macroporous silicon (MPS) films were yielded by electrochemical anodization of p-type crystalline silicon in HF:DMF. Following, a Schottky structure was obtained by depositing polyaniline (PANI), which was doped with different contents of erbium (Er) using cyclic voltammetry method. The structural analysis showed the formation of pores with diameters ranging between 0.25 and 1.20 μm and length around 15 μm and, after PANI deposition, the diameter became about 17% lower. The chemical characterization by Energy dispersive X-ray spectroscopy (EDS) and Rutherford Backscattering Spectroscopy (RBS) pointed out that the erbium is primarily incorporated at polyaniline surface, but it spreads through the polymer layer and achieves the MPS/PANI interface. According to the Attenuated Total Reflectance Fourier Transform Infrared (ATR-FTIR) analysis, the presence of Er gave rise to the formation of additional functional groups besides that corresponding to polyaniline and silicon oxide phases. The optical characterization within the UV–vis region revealed a modified optical bandgap of PANI as a function of the Er doping concentration. The results of the electrical measurements pointed out to a lowering of the space charge region width in the silicon as well as a change of the PANI workfunction as a function of the Er doping. On the other hand, the current flow through the MPS/PANI Schottky junction was lowered by the increase of the Er doping and by the tunneling mechanism through a thin silicon oxide (≈1–2 nm) grown on MPS during PANI deposition in aqueous solution.