Optical coatings for improved semiconductor diode laser performance

Abstract

<p>Optical coatings have been applied to the facets of semiconductor diode lasers using the electron cyclotron resonance plasma enhanced chemical vapour deposition technique. Processes have been developed for the fabrication of optical interference filters from silicon oxynitride thin films using both tris dimethylaminosilane and silane as the silicon precursor. An important component for the fabrication of filters with a controlled reflectance index by ellipsometry. Using the ellipsometer, it is shown that, after correcting for systematic errors, an accurate measurement of the film index of refraction can be made during a deposition. Three separate applications of these optical coatings are discussed. The fabrication of anti-reflection coatings, the fabrication of narrow band reflectance coatings which could potentially have beneficial effects on the spectral properties of the laser and the use of silicon nitride layers, in conjunction with a sulphur based passivation, to improve the reliability of high power AlGaAs based lasers. Single and double layer anti-reflection coatings have been designed for specific laser waveguide structures. An existing theoretical model of the spectral output of a semiconductor laser has been modified to include the effect of an optical filter with a highly wavelength dependent reflectance, in order to understand the limitations of this technique. Finally, improvements in the surface properties of passivated and encapsulated AlGaAs material have been observed through an increase in the yield of photoluminescence after the passivation process was applied.</p>