Silicon-based lighting show promise for display and solid state lighting use. Here we demonstrate a novel thin film light emitting diode device using nanocrystalline silicon quantum dots as an emission layer, and metal oxides as charge transport layers. Sputtering deposition conditions for the nickel and zinc oxides were explored in order to balance deposition rate with minimal roughness, optical absorption, and electrical resistivity. Devices displaying characteristic diode current-voltage behavior were routinely produced, although most showed significant reverse saturation current due to the presence of shunts. Current-voltage behavior of devices made in the same batch showed high repeatability, however variations in device performance was observed between batches while the parameters of synthesis were kept constant. Some devices were observed to emit orange-colored light, consistent with photoluminescence behavior of the silicon quantum dots. Photomultiplier tube measurements shows a turn-on voltage of 5V and an exponential increase in light emission with voltage increase.

Silicon-based lighting show promise for display and solid state lighting use. Here we demonstrate a novel thin film light emitting diode device using nanocrystalline silicon quantum dots as an emission layer, and metal oxides as charge transport layers. Sputtering deposition conditions for the nickel and zinc oxides were explored in order to balance deposition rate with minimal roughness, optical absorption, and electrical resistivity. Devices displaying characteristic diode current-voltage behavior were routinely produced, although most showed significant reverse saturation current due to the presence of shunts. Current-voltage behavior of devices made in the same batch showed high repeatability, however variations in device performance was observed between batches while the parameters of synthesis were kept constant. Some devices were observed to emit orange-colored light, consistent with photoluminescence behavior of the silicon quantum dots. Photomultiplier tube measurements shows a turn-on voltage of 5V and an exponential increase in light emission with voltage increase.

The exploration of a quantum dot fluorescence resonance energy transfer (QD-FRET) based bioassay for label-free target nucleic acid detection is reported herein. This work explores the potential for developing a displacement assay for detection of nucleic acid sequences of various lengths, including one of 484 bases. Short probe oligonucleotides conjugated to QDs were allowed to hybridize to short partially mismatched dye-labelled oligonucleotide targets. The non-labelled target of interest, a 484-base segment of heat shock protein 70 (HSP 70), contained a portion that was fully complementary to the probe. Thermodynamic parameters suggested that HSP 70 would displace dye-labelled targets; however, detection was not observed. Modifications were made to this assay to reduce sterics and increase the stability of hybrids. The results obtained using this modified assay indicated that detection of non-labelled, long oligonucleotide sequences was possible using a displacement assay that relied on a short probe oligonucleotide.

The exploration of a quantum dot fluorescence resonance energy transfer (QD-FRET) based bioassay for label-free target nucleic acid detection is reported herein. This work explores the potential for developing a displacement assay for detection of nucleic acid sequences of various lengths, including one of 484 bases. Short probe oligonucleotides conjugated to QDs were allowed to hybridize to short partially mismatched dye-labelled oligonucleotide targets. The non-labelled target of interest, a 484-base segment of heat shock protein 70 (HSP 70), contained a portion that was fully complementary to the probe. Thermodynamic parameters suggested that HSP 70 would displace dye-labelled targets; however, detection was not observed. Modifications were made to this assay to reduce sterics and increase the stability of hybrids. The results obtained using this modified assay indicated that detection of non-labelled, long oligonucleotide sequences was possible using a displacement assay that relied on a short probe oligonucleotide.

If solar energy is to be a significant component of our energy supply, technologies are required which produce high efficiency solar cells using inexpensive materials and versatile manufacturing processes. Solution-processed materials have been used to create low cost, easily fabricated devices, but have suffered from low power conversion efficiencies. A lack of infrared energy capture limits their efficiency. In this work we develop solution-processed photovoltaic devices using lead sulphide quantum dots and high surface area porous oxide electrodes. The resultant devices have a spectral response from 400 to 1800 nm. In fabricating these devices we utilize crosslinking molecules. We explore the impact crosslinkers have on the mobility and morphology of quantum dot films using field effect transistors and transmission electron microscopy. We also explore a hybrid organic/inorganic route for controlling the net doping in quantum dot films. We investigate the chemical and compositional changes that lead sulphide quantum dots films undergo during crosslinker treatment and annealing. Using this information we optimize our charge separation efficiency and our open circuit voltage. The resulting devices have an infrared power conversion efficiency of 2%, four orders of magnitude higher than that in previously reported lead sulphide quantum dot devices.

The commercially available solar cells suffer from low efficiency and high cost. This would avoid presence of solar cells as a secure energy resource in the market. Problems stem from two facts. Firstly, band gap of materials deployed for cell fabrication do not match the solar spectrum. Secondly, harvesting all the generated electrons is imperfect due to presence of many non-radiative recombination processes and, thermalization of electrons. To transcend these deficiencies, third generation of solar has been introduced. This new generation renders a whole new concept both in design and materials of solar cells scope. One of new introduction to solar cell field is Quantum Dot (QD). QD offers a broad range of tunability. The optical and electrical properties of QDs can be altered by choice of material, size and shape; therefore; they have great potential for high efficiency cell fabrication. QDs are mainly grown via MBE or synthesized via Colloidal solutions. QDs could be integrated as a part of one of new and promising third generation cells, named Intermediate Band Solar Cells. QDs could be employed as the intermediate level. If MBE is the selected method for cell fabrication, QDs would grow in a matrix of barrier material accompanied with a wetting layer. Wetting layer would disturb the ideal condition predicted in theory for gaining the high efficiency. To study how wetting layer would affect IB performance two sets of simulations have been carried out. One part is done with COSMOL. In this part different number of QDs layers have been simulated with and without wetting layer. The result showed that parasitic effect of wetting layer could not be eliminated large stacks of QD are stacked together, to achieve the promised efficient wetting layer should be eliminated from the system. In MATLAB part QDs have been approximated with simple cuboid. The main aim in this part was to compare how the result of taking into the account the real shape differs from a simple approach which has been the most reported the most in literature. If all the restrains on achieving high efficiency of IBSC are met, still one major draw- back remains and, that is high cost of MBE process. This would hinder mass production of IB cell. One possible potential method to gradually replace MBE can be Colloidal QDs. Colloidal QDs are fairly low cost and easy to fabricate. In this work, colloidal crystal growth was examined. The best condition for monolayer deposition was obtained and, the feasibility of crystal growth was demonstrated. additionally, There was an attempt to grow more than one layer and investigate result of embedding QDs in a barrier of another material.

Resonance fluorescence from solid state devices have been motivated by the capability to obtain a bright source of antibunched and indistinguishable photons from a semiconductor chip. Such a photon source would be a strong candidate for applications in the quantum information field. In this thesis, an experimental setup to obtain high signal to noise resonance fluorescence from a single quantum dot is first presented. I then discuss the photon statistics, power spectrum, second-order correlation function and two-photon interference of the stream of resonance fluorescence. Particular emphasis is placed on a throughout investigation of spectral fluctuations caused by charge noise and Overhauser field generated by fluctuating nuclear spins in the quantum dot. In each case, it is found that noise can be overcome to generate single photons that exhibit high visibility two-photon interference. Finally, an interference effect caused by the interaction of a quantum dot and a nearby metal surface is presented. Preliminary analysis yields quantitative agreement with the data.

Sources of entangled pairs of photons can be used for encoding signals in quantum-encrypted communications, allowing a sender, Alice, and a receiver, Bob, to exchange keys without the possibility of eavesdropping. In fact, any quantum information system would require single and entangled photons to serve as qubits. For this purpose, semiconductor quantum dots (QD) have been extensively studied for their ability to produce entangled light and function as single photon sources. The quality of such sources is evaluated based on three criteria: high efficiency, small multi-photon probability, and quantum indistinguishability. In this work, a simple quantum dot-based LED (E-LED) was used as a quantum light source for on-demand emission, indicating the potential for use as quantum information devices. Limitations of the device include the fine-structure splitting of the quantum dot excitons, their coherence lengths and charge carrier interactions in the structure. The quantum dot-based light emitting diode was initially shown to operate in pulsed mode under AC bias frequencies of up to several hundreds of MHz, without compromising the quality of emission. In a Hong-ou-Mandel interference type experiment, the quantum dot photons were shown to interfere with dissimilar photons from a laser, achieving high two-photon interference (TPI) visibilities. Quantum entanglement from a QD photon pair was also measured in pulsed mode, where the QD-based entangled-LED (E-LED) was electrically injected at a frequency of 203 MHz. After verifying indistinguishability and good entanglement properties from the QD photons under the above conditions, a quantum relay over 1km of fibre was demonstrated, using input qubits from a laser source. The average relay fidelity was high enough to allow for error correction for this BB84-type scheme. To improve the properties of the QD emission, an E-LED was developed based on droplet epitaxy (D-E) QDs, using a different QD growth technique. The relevant chapter outlines the process of QD growth and finally demonstration of quantum entanglement from an electrically injected diode, yielding improvements compared to previous E-LED devices. For the same reason, an alternative method of E-LED operation based on resonant two-photon excitation of the QD was explored. Analysis of Rabi oscillations in a quantum dot with a bound exciton state demonstrated coupling of the ground state and the biexciton state by the external oscillating field of a laser, therefore allowing the transition between the two states. The results include a considerable improvement in the coherence length of the QD emission, which is crucial for future quantum network applications. We believe that extending this research can find application in quantum cryptography and in realising the interface of a quantum network, based on semiconductor nanotechnology.

During the past few decades, examinations of social, biological, and communication networks have taken on increased attention. While numerous models of these networks have arisen, some have lacked visual representations. This is particularly true in ecology, where scientists have often been restricted to at most three dimensions when creating graphical representations of pattern and process. I will introduce an application of dot product representation graphs that allows scientists to view the high dimensional connections in ecological networks. Using actual data, example graphs will be developed and analyzed using key measures of graph theory.

In this work, the operating characteristics of quantum dot (QD) lasers with asymmetric barrier layers (ABLs) are studied. Several different cases are examined, in particular: 1) Effect of excited states on static and dynamic operating characteristics Within QDs, in addition to the lasing ground state, carriers can be captured into excited states, where they then decay into the ground state. This excited-state-mediated capture impacts the operating characteristics, limiting the maximum output power and modulation bandwidth. Three separate cases are considered: only indirect capture with electron-hole symmetry, both direct and indirect capture with electron-hole symmetry, and both direct and indirect capture of electrons but only indirect capture of holes. The impact of different parameters on the operating characteristics is studied, with values for maximizing the output power and modulation bandwidth being found. In addition, it is found that parasitic recombination in the active region in the space between QDs causes the output power to saturate at high injection currents for the cases of indirect capture for both electrons and holes and indirect capture for holes but direct and indirect capture for electrons, although the presence of the ABLs causes it to reach saturation at much lower currents. 2) QD laser with only a single ABL To be effective, the materials for ABLs must be carefully chosen to ensure that the band edges properly align to allow one carrier to enter the active region while preventing the other from overshooting it. Due to this requirement, it may arise that a suitable material only exists for one ABL but not the other. The performance of a QD laser with only a single ABL is considered and compared to a conventional QD laser. Specifically, the output power and characteristic temperature are calculated. While the single ABL laser only offers a negligible increase in output power compared to the conventional laser, it offers a considerable increase in characteristic temperature. 3) Analytical derivation of alpha factor in QD lasers with and without ABLs The alpha factor of a semiconductor laser describes the spectral linewidth broadening that occurs in semiconductor lasers due to changes in the refractive index due to the carrier density. While it has been studied experimentally, there has been little work done on deriving the alpha factor of QD lasers analytically. An expression for the alpha factor is found in this work using the real and imaginary parts of the complex susceptibility. For QD lasers with no inhomogeneous broadening, as well as ones with equilibrium filling of QDs with narrow line of QD size distribution, the alpha factor is independent of carrier density, and is therefore the same for any QD lasers, with or without ABLs. For QD lasers with equilibrium filling without a narrow line of QD size distribution, the alpha factor depends on carrier density, allowing for a potential difference between conventional and ABL QD lasers, however the difference between the two will be lessened. / Doctor of Philosophy / Semiconductor lasers are the most widely used laser, due in part to their ability to be controlled using electricity. Semiconductor lasers are used in a wide variety of consumer electronics, such as optical drives, as well as being used in fiber optic communications, where data is transmitted using the laser's light. Fiber optic communications transmit data by controlling the laser's output, where a high output (brighter light) represents a digital one, and a low output (dimmer light) represents a digital zero. Because semiconductor lasers can be directly controlled by changing the amount of current they receive, their output can easily be changed, allowing fast transfer of data. Despite their benefits, semiconductor lasers suffer from a drawback known as parasitic recombination. Parasitic recombination is a process that makes a significant portion of the current injected to generate useful light go to waste, which negatively impacts the laser's performance. One solution to parasitic recombination is the addition of asymmetric barrier layers (ABLs). By adding ABLs, parasitic recombination can be completely removed. In this work, several different cases of semiconductor quantum dot (QD) laser with ABLs are examined. Starting from a set of equations, the operating characteristics of the lasers in the different cases are found. First, the case of excited states is examined. The presence of excited states in semiconductor lasers impacts the rate that current can be converted to light, lowering their performance. By solving the starting rate equations, which describe the way different values change over time, the performance of the laser can be calculated. Specifically, the impact of several tunable parameters on the output power and modulation bandwidth are examined. The modulation bandwidth is how fast the laser output can be changed, which is equivalent to how fast data can be transmitted. Optimum values for the DC injection current, QD surface density (number of QDs per area), and laser cavity length are found.