Structure and transport mechanisms of Si/porous Si n–p junctions prepared by liquid phase epitaxy

Abstract

Heterojunction devices of n-Si/p-PSi were fabricated by growing n-Si films onto p-type porous Si substrates by liquid phase epitaxy. The structure of the grown films was checked using scanning electron microscopy and X-ray diffraction spectroscopy. X-ray diffraction measurements showed that the grown films have monocrystalline structure oriented along (111) direction with mainly cubic phase. Current–voltage (I–V) and capacitance–voltage (C–V) characteristics were measured over the temperature range from 298 to 398K. The analysis of the dark I–V characteristics of n-Si/p-PSi at several temperatures is done to elucidate the conduction mechanisms and the evaluation of the heterojunction parameters is presented. Two carrier transport mechanisms are believed to be at the origin of the forward current. At low bias voltage (V≤0.4V) the forward current is dominated by the recombination at the porous silicon side of the space charge region. In the 0.5V≤V≤1.4V region, the current transport is due to the space charge—limited current mechanism dominated by a single trapping level of energy 0.41eV. The reverse current is considered to be mainly generated in the depletion region of the porous silicon. The capacitance–voltage results confirm an abrupt junction with a homogenous distribution of the impurities inside the space charge region. Information on the depletion region, built-in voltage and net carrier concentration were obtained from the dark C–V characteristics.