Size Effect in Germanium Nanostructures Fabricated by Pulsed Laser Deposition

ABSTRACTWe have fabricated Ge nanostructures buried in AlN and Al2O3 matrices grown on Si(111) and sapphire substrates by pulsed laser deposition. Our approach involved three-dimensional island growth of low band-gap material followed by a layer of wide band-gap material. The nanodots were uniformly distributed in between alternating layers of AlN or Al2O3. It was observed that these nanodots exhibit crystalline structure when grown at 300-500 °C. The average size of Ge islands was determined to be ∼5-15 nm, which could be varied by controlling laser deposition and substrate parameters. The Raman spectrum showed a peak of the Ge-Ge vibrational mode downward shifted upto 295 cm− which is caused by quantum confinement of phonons in the Ge-dots. The photoluminescence of the Ge dots (size ∼15nm) was blue shifted by ∼0.266 eV from the bulk Ge value of 0.73 eV at 77 K, resulting in a distinct peak at ∼1.0 eV. The spectral positions of both E1 and E2 transitions in the absorption spectra at room temperature and 77K shift toward higher energy as the Ge dot size decreases. The interpretation of these behaviors in terms of quantum confinement is discussed in this work, and the importance of pulsed laser deposition in fabricating novel nanostructures is emphasized