الفهرس 
Chapter one: Theoretical backgroundOnly 14 pages are availabe for public view
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Abstract
Solubility of Sn in Ge network gives it a preference for photonic
applications because of the direct transition in GeSn alloy. Their compounds
have made many interesting contributions in photodetectors (PDs) over the
last ten years, as they have a detection limit in NIR and Mid-IR region. Sn
incorporation in Ge alters the cut off wavelength. Here, we employed the
metal induced crystallization (MIC) process of amorphous Ge and Si via Sn
as a novel mechanism to incorporate Sn inside Ge and Si networks instead of
the complex and high-cost chemical vapor deposition techniques.
(Al/Si/Sn/Ge/Sn) and (Al/Ge/Sn/Ge/Sn) multilayers were deposited by
thermal vacuum evaporation on fluorine doped tin oxide substrate (FTO), ntype silicon substrate and p-type silicon substrate. These deposited layers were
annealed under low vacuum of 4×10−2 mbar at 500 ºC for 24 hours as an
optimum time for high crystallization. MIC occurred and Sn was incorporated
in Ge crystallites network. Oxygen atoms were incorporated inside the
vacancies of the Ge network. This resulted in band gap tuning because of the
different degrees of oxidation. The Ge doped nanocrystals’ structure was
investigated using X-ray diffraction, high resolution transmission electron
microscopy and Raman spectroscopy. The effect of the base substrate on the
structure micro strains was studied. The surface morphology and diffusion of
multilayers in each other were studied using field emission scanning electron
microscopy. The direct transition and band gap values have been calculated
using diffuse reflectance spectroscopy and photoluminescence (PL)
measurements. PL measurements indicated that the junctions have emissions
from visible to NIR regions that make them promise in optically pumped
white light sources as well as waveguide applications. The impact of the base
substrate on enhancing the emission has been investigated via PL
measurements. Electroluminescence measurements show that the prepared
heterostructures on fluorine doped tin oxide (FTO) substrate have sharp
random lasing spikes over the range of PL samples spectra. The samples can
lase randomly by light scattering through the Ge doped nanocrystalline
materials. A simulation study was carried out by COMSOL Multiphysics
software and confirmed the experimental data of the emission properties. The
charge carrier lifetime measurements show high lifetime for the prepared
samples. These give them the chance to be a candidate for white random laser
diode applications. p-i-n structure based on GeSn junctions were fabricated to
serve as PDs. Arsine (As) was incorporated to develop n-GeSn compounds
via metal induced crystallization (MIC) process followed by i-GeSn on p-Si
wafers. The impact of As and Sn doping on strain characteristics of GeSn has
been studied with Raman spectroscopy analyses. The direct transitions and
tuning of their band energies have been investigated using diffuse reflectance
UV-Vis spectroscopy and photoluminescence (PL). The barrier height and
spectral responsivity have been controlled with incorporation of As and was
studied using I-V characteristics under dark conditions. Variation of As
incorporation into GeSn compounds shifted the Raman peak and hence
affected the strain in Ge network. UV-Vis spectroscopy showed that the direct
transition energies were lowered as the Ge-As bonding increased as illustrated
in Raman spectroscopy investigations. PL and UV-Vis spectroscopy of the
annealed heterostructures at 500 °C showed that there are many transition
peaks from UV to NIR region as a result of oxygen vacancies in Ge network.
The calculated diode parameters showed that As incorporation leads to an
increase of the height barrier and thus dark current. Spectral response
measurements revealed that the prepared heterojunctions have spectral
response in UV and NIR region. This gives them opportunity to be utilized in
UV and NIR photodetection-applications