Abstract: ZnO nanostructures with different morphologies of nanorods, nanoneedles, nanowires,
and nanobelts have been synthesized by thermal evaporation of pure ZnO micropowder. Based on
the appearance of the as-synthesized products observed by field emission scanning electron
microscope (FE-SEM), we show that substrate temperature and catalyst are the critical factors for
the formation of different morphologies of ZnO nanostructures. The photoluminescence (PL)
properties of the ZnO nanostructures were investigated. The difference in PL spectra both in
intensity and structure for the different ZnO nanostructures are presented. We demonstrate that
under appropriate synthesis conditions, highly crystallized and defect-free ZnO nano-structures can
Abstract: Using a simple process of the deposition of ZnO thin films on SiOx/Si substrates and
subsequent thermal annealing, we fabricated ZnO quantum dots embedded in silicon oxide matrix.
The ZnO quantum dots were characterized using transmission electron microscopy and timeintegrated
photoluminescence. The photoluminescence of the quantum dots show a blue-shift of 47
meV due to the quantum confinement effect.
Abstract: Photoluminescence (PL) from silicon nanocrystals deposited on top of silica-glass
template and from silicon nanocrystals in nc_Si/SiO2 multilayer films were studied as a function of
ultraviolet (UV) laser irradiation time in vacuum. Both the films exhibit intense visible PL at room
temperature under laser excitation. It was found that upon prolong irradiation time using a He-Cd
laser (325 nm) the PL intensity of the films was spectacularly enhanced. The process is reversible
and does not happen with excitation wavelength longer than 400 nm. Upon introducing air into the
measurement chamber, a rapid decrease of the PL intensity was recorded. This observation suggests
that the UV light may lead to modification of nonradiative recombination centers in the films and
thus improves the emission yield of silicon nanocrystals.
Abstract: Photoluminescence (PL) measurement shows an additional peak with stronger and
broader emission at lower photon energy besides the energy band gap transition emission from
GaNAs epilayer grown by MOCVD. This emission is assigned as nitrogen-nitrogen interstitial
defect related emission. Effect of V/III ratio during the MOCVD growth on this defect related
emission peak has been investigated. The combination of optimum V/III ratio during the MOCVD
growth and post-growth rapid thermal anneal (RTA) can eliminate this defect emission peak and at
the same time the GaNAs’ band gap emission has been greatly improved. The PL spectra contain a
single, narrow, and high intensity GaNAs’ band gap transition emission after the RTA annealing.
The optimum V/III ratio for growing the GaNAs films with N content < 3.5% is around 20.
Abstract: Hydrogenated nanocrystalline silicon (nc-Si:H) films produced by layer-by-layer (LBL)
deposition technique were studied. The films were grown at different hydrogen to silane flow-rate
ratio on crystal silicon (111) substrate. The properties of films were investigated by X-ray
diffraction (XRD), micro-Raman scattering spectroscopy, Fourier transform infrared (FTIR)
spectroscopy, optical transmission spectroscopy, atomic force microscopy (AFM) and field
emission scanning electron microscopy (FESEM). These properties showed dependence on the
hydrogen dilution of silane. Appearance of XRD peaks at diffraction angles of 28.4 o and 56.1 o
which correspond to silicon orientation of (111) and (311) respectively, were observed in all films
indicating evidence of crystallinity in the films. Raman scattering results indicated that crystallinity
in the films was due to the presence of nanocrystallites embedded in an amorphous matrix. The
energy gap of the films showed dependence on the hydrogen content in the films. Increase in
nanocrystallite size resulted in increase in disorder at low hydrogen dilution films but films remain
homogenous with increase in nanocrystallite size for the high hydrogen dilution films.
Abstract: We report the self-assembled growth of Ge islands of different shapes and sizes on p-Si
(001) by r.f. magnetron sputtering by varying the r.f. power, growth temperature and postdeposition
annealing condition. The well known Stranski-Krastanov growth mechanism due to
lattice mismatch between Si & Ge leads to the formation of Ge islands, similar to a more
sophisticated MBE growth, albeit at a much higher pressure in our study. Ge nanocrystals
embedded in SiO2 matrix have also been grown. Optical properties of nanocrystals exhibiting
visible luminescence at room temperature are presented.
Abstract: The photoluminescence of the diverse nanostructures of nonstoichiometric ZnO grown
via carbothermal reduction at 900°C was investigated. Various formations of different structures
like wires, rods, tubes and tetrapods resulted from the inhomogeneity of the boundary diffusion
layer associated with vapor current induced in the set-up. The band gap emission of these structures
was observed at around 390 nm, which corresponds to energy of 3.20 eV. The study was extended
to measure changes of crystal habit of ZnO nanostructures in terms of its fractal dimension.
Abstract: The band structures and optical gain spectra of GaAsSbN/GaAs compressively strained
quantum well (QW) were studied using 10-band k.p approach. We found that a higher Sb and N
composition in the quantum well and a thicker well give longer emitting wavelength. The result also
shows a suitable combination of Sb and N composition, and QW thickness can achieve 1.3 μm lasing.
And, the optical gain spectra with different carrier concentrations will be obtained.