Low dimensional structures for optical and electrical applications
Author
Akça, İmran
Advisor
Aydınlı, Atilla
Date
2008Publisher
Bilkent University
Language
English
Type
ThesisItem Usage Stats
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Abstract
Low dimensional structures such as quantum dots have been particularly attractive
because of their fundamental physical properties and their potential applications
in various devices in integrated optics and microelectronics. This thesis
presents optical and electrical applications of low dimensional structures. For this
purpose we have studied silicon and germanium nanocrystals for flash memory
applications and InAs quantum dots for optical modulators.
As a quantum dot, nanocrystals can be used as storage media for carriers in
flash memories. Performance of a nanocrystal memory device can be expressed in
terms of write/erase speed, carrier retention time and cycling durability. Charge
and discharge dynamics of PECVD grown nanocrystals were studied. Electron
and hole charge and discharge currents were observed to differ significantly and
strongly depend on annealing conditions chosen for the formation of nanocrystals.
Our experimental results revealed that, discharge currents were dominated by the
interface layer acting as a quantum well for holes and route for direct tunneling
for electrons.
On the other hand, possibility of obtaining quantum dots with enhanced
electro-optic and/or electro-absorption coefficients makes them attractive for use
in light modulation. Therefore, waveguides of multilayer InAs quantum dots
were studied. Electro-optic measurements were conducted at 1.5 µm and clear
Fabry-Perot resonances were obtained. The voltage dependent Fabry-Perot measurements
revealed that 6 V was sufficient for full on/off modulation. Electroabsorption
measurements were conducted at both 1.3 and 1.5 µm. Since the
structure lases at 1285 nm, high absorption values at 1309 nm were obtained.
The absorption spectrum of the samples was also studied under applied electric
field. Absorption spectra of all samples shift to lower photon energies with increasing electric field.
Keywords
Silicon nanocrystalsoptical waveguides
electro-absorption modulation
electro-optic modulation
quantum dots
nonvolatile memories
Germanium nanocrystals