Investigation of porous silicon/aliuminium structures in microwave field

Abstract

We investigate response of porous silicon/aluminium structures to 10 GHz microwave electric field. Porous silicon (por-Si) layers were fabricated by conventional electrochemical etching technique in HF - ethanol solution using p-type 0.4 Ω'cm Si substrates. Two types of samples were produced: with and without additional boron doping of the substrate surface to be etched. Bottom (ohmic) and top contacts were made by thermal aluminium evaporation. Rectifying character of the I-V dependencies was inherent for the non-doped samples. Under the action of the microwave pulses (pulse duration 2 us) these samples produced electromotive force (emf) with polarity indicating hole flow over the Schottky barrier. Crystal lattice heating was observed also in the response pulse shape. I-V characteristics of the doped samples were linear in the tested ± 5 V interval. At low values of incident microwave power a positive (with regard to grounded por-Si/Al contact) signal was detected, while at high power values there dominated emf of a negative sign. The induced emf pulse was faster than that of the previous type of samples. We consider hot carrier diffusion over the inlying potential barriers to be responsible for the signal formation.