Despite the tremendous progress of GaN based binary and ternary III-V nitrides for applications in LEDs, challenges remain for applications in laser diodes and high power electronic devices. Therefore, it is of current interest to explore opportunities in other new wide band gap materials. We report here the growth of a novel IV-V nitride (specifically, SiCN compound) as a new addition to the family of wide bandgap nitride semiconductors.

Crystalline thin films of SiCN have been successfully grown by microwave plasma-enhanced chemical vapor deposition using H₂, CH₄, N₂ and SiH₄ gases. The new crystalline ternary compound (C; Si)_xN_y exhibits hexagonal structure and consists of a network wherein the Si and C are substitutional elements. Optical properties of the SiCN compound have been studied by photoluminescence (PL). It is found that the low-lying band gap energies of the SiCN compound is in excess of 3.1 eV. Further, a strong subband-gap emission around 2.8 eV is observed at room temperature.

Chemical vapour deposition (CVD) as well as infiltration (CVI) processes are key technologies in many industrial sectors, as for manufacturing fibre reinforced ceramic composite materials. Although the techniques are used on a technological scale, the underlying chemistry is not completely understood which seriously retards process control as well as reactor scale-up and optimisation.

Different process control concepts are discussed which are based on a multipurpose, knowledge based feedback system for monitoring the CVD/CVI process with FTIR spectroscopic data as input information. Two commonly used industrial scale CVD/CVI processes are taken as test cases: (i) a thermal high capacity CVI batch process for manufacturing carbon fibre reinforced SiC composites for high temperature applications, and (ii) a laser stimulated CVD process for continuously coating bundles of thin ceramic fibres.

(i) The process operates in a industrial scale CVI reactor near 1000oC, in the low pressure region and with CH₃SiCl₃ as a precursor for infiltrating SiC into a fibre preform. Based on FTIR emission spectroscopy, an experimental set-up has been established for in-situ monitoring the chemical composition of the gaseous atmosphere near the preform to be infiltrated. Several gaseous species have been detected among them highly reactive intermediates which are the key species of the precipitation process. Data treatment procedures have been developed for on-line monitoring the concentration of different species.

(ii) Based on an industrial 6 kW cw-CO₂- laser, a laser driven process currently runs in a prototype coater. Layers of graphitizised pyrolytic carbon and several ceramic materials (SiC, TiC_xN_y, TiB₂, BN, etc.) have been deposited on carbon fibres and on SiC fibres. The process control concept includes FTIR measurements which are carried out by rapid extraction of the gaseous reaction products.

The fabrication of thick SiO_xN_y and SiO₂ films is nowadays of great interest for many applications as coating layer, isolating substrate and optical devices^1,2. Also, being silicon compounds, they permit the integration of optical and microelectronics devices, making optoelectronic structures more plausible. On the other hand the fabrication of these materials through the conventional high temperature thermal oxidation of silicon is not reliable due to the very long times and high thermal stress that the materials have to withstand during device fabrication. In this way the deposition of good quality SiO_xN_y and SiO₂ films utilizing the Plasma Enhanced Chemical Vapor Deposition (PECVD) at low temperatures and at high deposition rates is a very promising alternative.

In previous works we have demonstrated that it is possible to produce high quality PECVD SiO₂ at temperatures as low as 320 °C and with thickness less than 1 μmm. We also showed that in this type of material is possible to control efficiently the refractive index varying the SiH₄ and N₂O concentrations in the gaseous mixture³, which is a fundamental requirement for waveguides fabrication, for example¹.

In this work we show that by the appropriate control of the gas mixture composition it is possible to obtain very thick SiO₂ and SiO_xN_y films at high deposition rates (~10 μmm), preserving the properties of the high quality thin films. The samples were characterized by Profile Measurements, Fourier Transform Infra Red Spectroscopy (FTIR) and by Scanning Electron Microscopy (SEM). The results show that the films present a structure and an etching rate very close to thermally grown SiO₂, and a well controlled refractive index when varying the composition from stoichiometric SiO₂ to SiO_xN_y.¹

¹ E. S. Bulat, M. Tabasky, B. Tweed, C. Herrick, S. Hankin, N. J. Lewis, D. Oblas, and T. Fitzgerald, J. Vac. Sci. Technol. A 11(4), 1268 (1993).

² M. S. Haque, H. A. Naseem, and W. D. Brown, J. Electrochem. Soc., 142 (11), 3864 (1995).

³ I. Pereyra and M. I. Alayo, J. Non-Cryst. Solids. 212 (2-3), 225 (1997).}

Thermal sighting systems often emply focal plane array detectors to sense radiation in 7.5 - 10.5 μm wavelength range. These detectors possess some sensitivity in lower region also which contributes as noise in the image. To ovbiate this an edge filter with a pass band in 7.5-10.5 μm wavelength region and low transmission below 7 μm has been designed following thin film multi-layer gradual evolution synthesis approach. This has shaped into a ten layer, non-quarter, alternate films of ThF₄ and Ge which has subsequently been implemented on one side of a 10 mm thick germanium substrate using electron beam gun evaporation technique. The rear side of the substrate has been provided a broad band anti-reflection coating for 7.5-10.5 μm spectral region using five layer non-quarter wave stack of the same material combination. Practically achieved transmission in the pass band is about 90% with cutoff at 6.5 um.

Basing our design ideas on gradual evolution technique we have been able to restrict the number of layers to only ten, all being very thin. This has resulted in excellent environmental stability features due to low stresses in the stack.