Shaffer, E – MSc

Shaffer, E., “EXCIMER LASER-INDUCED CRYSTALLIZATION OF AMORPHOUS CdSe THIN FILMS”, MSc in Electrical Engineering, 2007, Université de Sherbrooke, Sherbrooke, Canada. [pdf(FR)]

Semiconductor nanocrystals, more specifically quantum dots (QDs), find many and more applications in photonics and, more recently, in the rapidly growing field of biodiagnostics. Research on colloidal QDs for biomedical imagery and biodetection already occupies a very important part of QDs literature. However, due to their instability outside of the solution and the requirement of special passivation procedures, colloidal QDs pose numerous problems in biodiagnostics and they are not well-suited for device integration. Other alternatives are being studied, that are compatible with microfabrication processes and that would allow for laser-induced modification (tuning) of QDs’ surface chemistry and their physical properties by using such techniques as laser irradiation. Two-dimensional (2D) arrays of epitaxial QDs have been proposed as a promising platform for biosensing. Another solution lies in laser-induced crystallization of amorphous thin films of semiconductors or, more precisely CdSe. Excimer laser crystallization technology is already widely used, especially in the thin-films transistors (TFT) industry and is therefore entirely compatible with microfabrication processes. Actually, this technique is used to crystallized amorphous thin films of silicon and its possible application to crystallize II-VI semiconductors has yet to be demonstrated. In this work, we demonstrate that ArF (193 nm) excimer laser irradiation can successfully lead to crystallization of amorphous, 85 nm thick, films of CdSe. We show that the crystallization can be monitored during the irradiation process by a related photoluminescence (PL) emission from the irradiated films. In addition to PL measurements, our films have been characterized by Raman spectroscopy and scanning electron microscopy (SEM). Our SEM images revealed the formation of CdSe nanorods and nanobeads. The presence of such small structures makes us to believe that quantum confinement could be achieved. We demonstrate that the ArF crystallization process is compatible with the integrated circuits fabrication techniques and it allows patterning to obtain photo-luminescent regions defined by the projection mask used in our homogenized beam delivery system. Size-controlled nanobeads or quantum dots could be the key to multiple wavelength-emitting II-VI photonic integrated circuits or biosensing devices.

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