Porous silicon (PS) is usually prepared by the electrochemical anodization or the stain etching techniques. Recently, a new method consisting of exposing silicon substrates to acid vapours issued from a mixture of HNO 3 /HF was employed to generate highly luminescent PS layers. The so-called HNO 3 /HF vapour etching (VE) technique can be easily applied in various large area of silicon-based devices. Depending on the HNO 3 /HF volume ratio, we found that VE silicon results in the formation of PS and/or a luminescent (NH 4 ) 2 SiF 6 powder-like phase. FTIR spectra of VE-based PS layers formed at HNO 3 /HF volume ratio ranging between 1/100-1/3 contain N-H and Si-F bonds related to NH 4 + and SiF 6 2-ions in addition to the conventional SiH x species. These nitride and fluoride groups were identified to be associated to the (NH 4 ) 2 SiF 6 powder-like phase which in turn contains small Si nanoparticles embedded in a SiO x matrix. The presence of such structures was explained as being the product of the VE technique itself. For vapours rich in HNO 3 (HNO 3 /HF volume ratio > 1/4), the VE method can produce almost only the luminescent (NH 4 ) 2 SiF 6 compound. The VE-based PS is essentially composed of dot-like Si particles with sizes not exceeding 5 nm and emitting a photoluminescence (PL) band around 1.93 eV. The PL band of the VE-based PS presents a shoulder at 2.09 eV, which becomes more significant after oxidation in air. This shoulder at 2.09 eV was attributed to an excitonic emission from the energy levels of the SiO x surrounding the smallest Si nanocrystallites. The PL band emission of the (NH 4 ) 2 SiF 6 powder presents two peaks. The first one was attributed to Si nanocrystallites emitting at 1.98 eV. The second peak could be associated to the smallest nanocrystallites (≤ 1.5 nm). For these crystallites, excitons are trapped on the SiO x energy levels, leading to a maximum PL band emission around 2.1 eV. This PL band seems to have the same origin than the small shoulder observed in the PL emission of PS.

No abstract

The Schottky diode (Al/p-CuInSe 2 /FTO) was fabricated by simple deposition of pure Aluminum on the front side of the CuInSe 2 thin film. We have investigated its electrical characteristics by measuring the current-voltage (I-V), the capacitance-voltage (C-V) and the electrical impedance in the range of temperature (300 K-425 K). At room temperature, this heterostructure has shown nonideal Schottky behavior with 3.98 as ideality factor and 38 μA/cm 2 as a reverse saturated current density. The C-V measured at 100 kHz has shown non-linear behavior and an increase with temperature. Similarly, we have estimated, at room temperature, the carrier doping density, the built-in potential and the depletion layer width which are of about 8.66 × 10 15 cm −3 , 1.12 V and 0.37 μm respectively. By the impedance spectroscopy technique, we have found a decrease with temperature of all the serial resistance R s , the parallel resistance R p and the capacitance C p. The frequency dependence of the imaginary part of this impedance was carried out to characterize the carrier transport properties in the heterostructure. From the Arrhenius diagram, we have estimated the activation energy at 460 meV. An equivalent electrical circuit was used for modeling these results.

No abstract