Browsing by Subject "Ge nanocrystals"

Now showing 1 - 5 of 5

Open Access
Formation of Ge nanocrystals and SiGe in PECVD grown SiNx: Ge thin films
(Elsevier, 2006) Dana, A.; Tokay, S.; Aydınlı, Atilla
Formation of Ge nanocrystals in SiNx matrices has been studied using plasma enhanced chemical vapor deposition in both as deposited samples as well as in post-vacuum annealed samples. Low temperature and short duration anneals in vacuum resulted in Ge nanocrystals whereas prolonged anneals at higher temperatures resulted in Ge nanocrystals accompanied with SiGe formation at the SiNx/Si interface. Raman Scattering Spectroscopy was extensively used to track the formation of various phonon modes during the diffusion of Ge through SiNx and into the Si substrate.
Open Access
Formation of Ge nanocrystals with CW laser irradiation of Siox:Ge thin films
(2015) Gümüş, Melike
Germanium and silicon are the materials which have effective absorption in the visible and near infrared region of electromagnetic spectrum; therefore they are preferred for optoelectronic device and solar cell applications. Si and Ge are the material of choice when it comes to solar cell applications due to their being low cost, widely available and inert. They have indirect bandgap and the absorption coefficient of indirect bandgap materials is lower than direct ones. It is known that decreasing dimensions of materials to nanometric sizes cause transition from indirect bandgap to direct bandgap behavior along with increasing band gap. Therefore decreasing their dimensions both a shift of the band gap toward the blue as well as an increase in absorption can be achieved. In this work, thin films of SiOx:Ge were fabricated with different germanium concentrations and annealed with CW Ar+ laser operating at 488 nm that resulted in formation of Ge nanocrystals in the SiOx matrix. Composition analysis of as grown samples were done by Rutherford Backscattering Spectroscopy, optical properties were determined by ellipsometry. Nanocrystal formation within laser irradiated samples was confirmed by Raman spectroscopy. Data were also collected about crystal formation by scanning surface texture with stylus surface profilometer. As a result of all the analysis, it was shown that crystal formation depends on germanium concentration in the SiOx matrix and laser irradiation power density
Open Access
Matrix density effect on morphology of germanium nanocrystals embedded in silicon dioxide thin films
(Materials Research Society, 2011) Alagoz, A. S.; Genisel, M. F.; Foss, Steinar; Finstad, T. G.; Turan, R.
Flash type electronic memories are the preferred format in code storage at complex programs running on fast processors and larger media files in portable electronics due to fast write/read operations, long rewrite life, high density and low cost of fabrication. Scaling limitations of top-down fabrication approaches can be overcome in next generation flash memories by replacing continuous floating gate with array of nanocrystals. Germanium (Ge) is a good candidate for nanocrystal based flash memories due its small band gap. In this work, we present effect of silicon dioxide (SiO 2) host matrix density on Ge nanocrystals morphology. Low density Ge+SiO 2 layers are deposited between high density SiO 2 layers by using off-angle magnetron sputter deposition. After high temperature post-annealing, faceted and elongated Ge nanocrystals formation is observed in low density layers. Effects of Ge concentration and annealing temperature on nanocrystal morphology and mean size were investigated by using transmission electron microscopy. Positive correlation between stress development and nanocrystal size is observed at Raman spectroscopy measurements. We concluded that non-uniform stress distribution on nanocrystals during growth is responsible from faceted and elongated nanocrystal morphology.
Open Access
SiGe nanocrystal formation in PECVD grown SiOx/Si/Ge/Si/SiOx multilayers
(World Scientific Publishing, 2009) Ağan, S.; Aydınlı, Atilla
We have studied alternating gennanium-silicon-silicon oxide layers of 41 nm thickness grown on Si substrates by plasma enhanced chemically vapor deposition. The compositions of the grown films were detennined by X-ray photoelectron spectroscopy. The films were annealed at temperatures varying from 700 to 950 °C for 7.5 minutes under nitrogen atmosphere. High resolution cross section TEM images, electron diffraction and electron energy-loss spectroscopy as well as energy-dispersive X-ray analysis (EDAX) confinn presence of Ge nanocrystals in each layer. The effect of annealing on the Ge nanocrystal fonnation in multi layers was investigated by Raman spectroscopy and TEM.
Open Access
Spectroscopic ellipsometric study of Ge nanocrystals embedded in SiO 2 using parametric models
(Wiley, 2008-05) Basa, P.; Petrik, P.; Fried, M.; Dâna, Aykutlu; Aydınlı, Atilla; Foss, S.; Finstad, T. G.
Ge-rich SiO2 layers on top of Si substrates were deposited using plasma enhanced chemical vapour deposition. Ge nanocrystals embedded in the SiO2 layers were formed by high temperature annealing. The samples were measured and evaluated by spectroscopic ellipsometry. Effective medium theory (EMT) and parametric semiconductor models have been used to model the dielectric function of the layers. Systematic dependences of the layer thickness and the oscillator parameters have been found on the annealing temperature (nanocrystal size).