Matching Items (2)
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- All Subjects: Bright Beams
- Genre: Doctoral Dissertation
- Creators: Drucker, Jeffery
Description
Ge1-ySny alloys represent a new class of photonic materials for integrated optoelectronics on Si. In this work, the electrical and optical properties of Ge1-ySny alloy films grown on Si, with concentrations in the range 0 ≤ y ≤ 0.04, are studied via a variety of methods. The first microelectronic devices from GeSn films were fabricated using newly developed CMOS-compatible protocols, and the devices were characterized with respect to their electrical properties and optical response. The detectors were found to have a detection range that extends into the near-IR, and the detection edge is found to shift to longer wavelengths with increasing Sn content, mainly due to the compositional dependence of the direct band gap E0. With only 2 % Sn, all of the telecommunication bands are covered by a single detector. Room temperature photoluminescence was observed from GeSn films with Sn content up to 4 %. The peak wavelength of the emission was found to shift to lower energies with increasing Sn content, corresponding to the decrease in the direct band gap E0 of the material. An additional peak in the spectrum was assigned to the indirect band gap. The separation between the direct and indirect peaks was found to decrease with increasing Sn concentration, as expected. Electroluminescence was also observed from Ge/Si and Ge0.98Sn0.02 photodiodes under forward bias, and the luminescence spectra were found to match well with the observed photoluminescence spectra. A theoretical expression was developed for the luminescence due to the direct band gap and fit to the data.
ContributorsMathews, Jay (Author) / Menéndez, Jose (Thesis advisor) / Kouvetakis, John (Thesis advisor) / Drucker, Jeffery (Committee member) / Chizmeshya, Andrew (Committee member) / Ponce, Fernando (Committee member) / Arizona State University (Publisher)
Created2011
Description
The performance of accelerator applications like X-ray free electron lasers (XFELs)and ultrafast electron diffraction (UED) and microscopy (UEM) experiments is limited
by the brightness of electron beams generated by photoinjectors. In order to
maximize the brightness of an electron beam it is essential that electrons are emitted
from photocathodes with the smallest possible mean transverse energy (MTE).
Metallic photocathodes hold the record for the smallest MTE ever measured at 5
meV from a Cu(100) single crystal photocathode operated near the photoemission
threshold and cooled to 30 K. However such photocathodes have two major limitations:
poor surface stability, and a low quantum efficiency (QE) which leads to
MTE degrading non-linear photoemission effects when extracting large charge densities.
This thesis investigates the efficacy of using a graphene protective layer in order
to improve the stability of a Cu(110) single crystalline surface. The contribution to
MTE from non-linear photoemission effects is measured from a Cu(110) single crystal
photocathode at a variety of excess energies, laser fluences, and laser pulse lengths.
To conclude this thesis, the design and research capabilities of the Photocathode and
Bright Beams Lab (PBBL) are presented. Such a lab is required to develop cathode
technology to mitigate the practical limitations of metallic photocathodes.
ContributorsKnill, Christopher John (Author) / Karkare, Siddharth (Thesis advisor) / Drucker, Jeffery (Committee member) / Kaindl, Robert (Committee member) / Teitelbaum, Samuel (Committee member) / Arizona State University (Publisher)
Created2023