Cadmium telluride nanoparticles dispersed in SiO2 films have been grown by the co-sputtering of elemental Cd, Te and SiO2 targets in argon atmosphere. The role of oxygen during annealing on the structural and optical properties of CdTe nanoparticles dispersed in SiO2 films has been studied. Formation of a CdTeO3 layer around the CdTe nanoparticle core due to ambient oxygen present in air results in structural defects and thus the formation of hexagonal CdTe nanoparticles in air-annealed samples. In vacuum-annealed samples, defect free and well-crystallized cubic CdTe nanoparticles are formed which show excitonic features in the absorption spectra. These results have been confirmed by carrying out i) annealing in vacuum and air ambiences in a sequence on the same sample and ii) by depositing an additional layer of SiO2 on the CdTe:SiO2 samples to prevent the diffusion of ambient oxygen.
We propose and demonstrate a simple and unique method to fabricate the multiple-wavelength vertical-cavity surface-emitting lasers (VCSELs) emitting at 980 nm by grading only the first low-index spacer layer of SiO2/Ta2O5 dielectric mirror. A multi step exposure to UV lithography followed by selective wet chemical etching has been applied to create spacer layer gradients. We have successfully realized equally spaced four-channel VCSELs with wavelength span exceeding 30.0 nm by grading a 230.0 nm spacer layer and achieved single mode lasing with a side mode suppression ratio in excess of 30.0 dB.
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