Electronic properties of thin Au/nanoporous-Si/n-Si structures

Ultrathin nanoporous Si layers (UPSL) were prepared on n-Si(100) by anodization in aqueous NH4F solution starting from an electrochemically hydrogenated surface. The thickness of the UPSL was controlled with field emission scanning electron microscopy, The interface state density (D-it) of UPSL was measured with a field-dependent pulsed surface photovoltage technique. The value of D-it, normalized to the surface area of UPSL is about 1.3 x 10(11) eV(-1) cm(-2). Au/UPSL/n-Si structures were characterized with temperature-dependent current-voltage measurements. The room-temperature barrier height and the ideality factor at the Au/UPSL interface were 0.75 eV and 1.8, respectively. The temperature dependence of the reverse current of Au/UPSL/n-Si structures showed two regions with activation energies at 120 meV and about 60 meV for temperatures below and above 200 K, respectively. Strong near-infrared electroluminescence was observed for Au/UPSL/n-Si structures. The results are discussed on the basis of the role of Si nanostructure surface conditioning with regard to the porous Si electronic properties.