S. Mukherjee; A. Pradhan; T. Maitra; A. Nayak; S. Bhunia
Abstract
In this paper, we report the possibility of phase-selective growth of Ge nanocrystals by changing the kinetic energy of the clusters in an ionised cluster beam deposition system. Typically, the films are of mixed phase of normal cubic and high energy tetragonal structures, the relative proportion of ...
Read More
In this paper, we report the possibility of phase-selective growth of Ge nanocrystals by changing the kinetic energy of the clusters in an ionised cluster beam deposition system. Typically, the films are of mixed phase of normal cubic and high energy tetragonal structures, the relative proportion of which could be controlled by controlling the ionisation and applied accelerating potential as has been confirmed from Raman spectroscopic study. The films deposited using neutral clusters showed higher yield of the tetragonal phase with nanocrystallites of diameter ~7 nm as evidenced from HRTEM data. The optical bandgap of the nanocrystals were observed to be blue shifted upto 1.75 eV compared to the bulk Ge attributing to the presence of Ge tetragonal ST-12 phase and the resulted quantum confinement effect inside the nanocrystals. The tetragonal-rich films were further studied by controlled photo-oxidation to tune their optical band gap. A visible photoluminescence due to excitonic transitions have been observed from the as-grown Ge film enriched in tetragonal phase with average crystallite size ~7 nm. The photoluminescence peak was further blue shifted after the course of photo-oxidation due to reduced nanocrystallite size.
V. Saikiran; N. Manikanthababu; N. Srinivasa Rao; S. V. S. Nageswara Rao; A. P. Pathak
Abstract
Trilayered HfO2/Ge/HfO2 thin films were grown on Si substrate by RF magnetron sputtering with HfO2 and Ge targets. The subsequent rapid thermal annealing (RTA) of these films at 700 & 800°C results in formation of Ge nanocrystals (NCs) in HfO2 matrix. X-ray diffraction (XRD) and micro-Raman spectroscopy ...
Read More
Trilayered HfO2/Ge/HfO2 thin films were grown on Si substrate by RF magnetron sputtering with HfO2 and Ge targets. The subsequent rapid thermal annealing (RTA) of these films at 700 & 800°C results in formation of Ge nanocrystals (NCs) in HfO2 matrix. X-ray diffraction (XRD) and micro-Raman spectroscopy measurements were performed to confirm the formation of Ge NCs in the annealed samples. XRD results indicate that the as-deposited samples show amorphous behaviour, whereas the annealed samples clearly confirm the crystallinity of the films. The average size of the Ge NCs was found to increase with an increase in annealing temperature. Raman scattering studies confirm that the annealed samples exhibit a shift in peak position corresponding to Ge-Ge optical phonon vibrations, which clearly indicates the formation of Ge NCs. Conversely, as-deposited samples were also irradiated with swift heavy ions of 150 MeV Au and 80 MeV Ni at a fluence of 3×10 13 ions/cm 2 to synthesize Ge NCs. The structural properties of pristine and irradiated samples have been studied by using X-ray diffraction, Raman spectroscopy to substantiate the growth of Ge NCs upon irradiation. The results obtained by RTA are compared with the irradiated ones.
