Strong white and blue photoluminescence (PL) from as-grown silicon nanocrystals (nc-Si) in SiNx films prepared by remote plasma enhanced chemical vapour deposition using SiCl4/NH3 mixtures is reported. The colour and intensity of the PL could be controlled by adjusting the NH3 flow rate. Samples with white emission were annealed at 1000 °C, obtaining a strong improvement of the PL intensity with a blue colour. The PL can be attributed to quantum confinement effect in nc-Si embedded in SiNx matrix, which is improved when a better passivation of nc-Si surface with chlorine and nitrogen atoms is obtained. The size, density and structure of the nc-Si in the as-grown and annealed films were confirmed and measured by high-resolution transmission electron microscopy.

Articles you may be interested inDistinguishing the effect of surface passivation from the effect of size on the photonic and electronic behavior of porous siliconWe have investigated the influence of the microstructure and chemistry of the surrounding host on the strong visible photoluminescence ͑PL͒ from silicon nanoclusters ͑nc-Si͒ embedded in three different silicon-based dielectric compounds: Si x N y : H , Cl, Si x N y O z : H , Cl, and Si x O z :H,Cl, obtained from silicon nitride films deposited by SiH 2 Cl 2 /NH 3 /H 2 plasma-enhanced chemical vapor deposition at different growth pressures. A blueshift is found in the PL coming from the nc-Si as the content of oxygen in the surrounding host is increased, and a significant improvement in PL intensity is achieved when the nc-Si are well passivated with O instead of H. We discuss the PL behavior in terms of the quantum confinement model and passivation state of the nc-Si surface.

In this paper, we present a comparative study of photoluminescence and its relation to the structural properties of cadmium sulphide (CdS) thin films grown by chemical bath deposition (CBD), close spaced vapour transport, laser ablation (LA) and sputtering. Taking into account that the physical properties of CdS thin films depend upon the growth technique and the optimization of the deposition conditions for each technique, we show that the best crystal perfection occurs for LA-CdS films since the main photoluminescence peak at low temperature is due to bound excitons (2.53 eV). As expected, the films with the worst crystalline quality are those grown by CBD, ascertained by the photoluminescence band around 1.72 eV due to sulfur vacancies ('red band') without the corresponding exciton band. The photoluminescence results are correlated to x-ray diffraction measurements that confirm the above results.

A study of the electrical conductivity of polypyrrole-polyoxyphenylene composites (PPy-POP and PPy-POP-MPcTS) prepared by in situ electropolymerization is presented, where MPcTS stands for tetrasulfonated tetrasodium metallophthalocyanine salts and is used as a second dopand for polypyrrole. The conductivity is studied as a function of temperature in the range 77⩽T⩽300 K. The temperature dependence of the total ac conductivity, in the frequency range 102-105 Hz, changes by approximately five orders of magnitude, showing a sub-linear dispersive behaviour. The temperature dependence of the dc conductivity gives evidence for a transport mechanism based on the Mott's variable-range hopping model in one dimension for the PPy-POP composite, which shows a crossover to three dimensions for the PPy-POP-MPcTS composites. Using this model we were able to calculate meaningful values for the density of states, hopping energy and hopping distance.

Photoluminescence (PL) studies in GaN thin films grown by infrared close space vapor transport (CSVT-IR) in vacuum are presented in this work. The growth of GaN thin films was done on a variety of substrates like silicon, sapphire and fused silica. Room temperature PL spectra of all the GaN films show near band-edge emission (NBE) and a broad blue and green luminescence (BL, GL), which can be seen with the naked eye in a bright room. The sample grown by infrared CSVT on the silicon substrate shows several emission peaks from 2.4 to 3.22 eV with a pronounced red shift with respect to the band gap energy. The sample grown on sapphire shows strong and broad ultraviolet emission peaks (UVL) centered at 3.19 eV and it exhibits a red shift of NBE. The PL spectrum of GaN films deposited on fused silica exhibited a unique and strong blue-green emission peak centered at 2.38 eV. The presence of yellow and green luminescence in all samples is related to native defects in the structure such as dislocations in GaN and/or the presence of amorphous phases. We analyze the material quality that can be obtained by CSVT-IR in vacuum, which is a high yield technique with simple equipment set-up, in terms of the PL results obtained in each case.

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