Structural and electronic characterization of 355 nm laser-crystallized silicon: Interplay of film thickness and laser fluence

Abstract

We present a detailed study of the laser crystallization of amorphous silicon thin films as a function of laser fluence and film thickness. Silicon films grown through plasma-enhanced chemical vapor deposition were subjected to a Q-switched, diode-pumped solid-state laser operating at 355 nm. The crystallinity, morphology, and optical and electronic properties of the films are characterized through transmission and reflectance spectroscopy, resistivity measurements, Raman spectroscopy, X-ray diffraction, atomic force microscopy, and optical and scanning-electron microscopy. Our results reveal a unique surface morphology that strongly couples to the electronic characteristics of the films, with a minimum laser fluence at which the film properties are optimized. A simple scaling model is used to relate film morphology to conductivity in the laser-processed films.

Impact of substrate composition on the morphology and conductivity of laser-crystallized silicon films

“…With these parameters, and with the beam approximated as rectangular, each point is scanned approximately 700 times by the laser. Further details of the laser setup and crystallization process can be found in a recent publication [13].…”

“…Unique morphologies, such as high-aspect-ratio pillars or flat crystals, have also been observed as a result of the laser crystallization of a-Si films, where the specific type of morphology depends on details related to the laser and processing parameters [6,[9][10][11][12][13][14][15]. As the laser fluence is increased, the silicon melts and starts to flow in response to interfacial tension coupled with substrate interactions.…”

“…As the laser fluence is increased, the silicon melts and starts to flow in response to interfacial tension coupled with substrate interactions. When the fluence reaches a thickness-dependent threshold, the film begins to dewet from the substrate, to the extent that the morphology of the resolidified film is no longer percolated [13].…”

Excimer Laser Crystallization of Nanocrystalline Silicon Thin Films

“…The ability of excimer laser to crystallize a very thin layer of a-Si:H in the order of 100 nm becomes a limitation for photovoltaics, since films of the order 1 µm are necessary for light absorption [20]. Larger thickness means higher laser fluence needed for the crystallization [21]. It is concluded that it is not possible to convert a-Si:H films thicker than 300 nm completely to polycrystalline silicon without utilizing laser energy densities in excess of 200 mJ/cm 2 [22].…”