A Novel Optoelectronic Device Based on Correlated Two-Dimensional Fermions

Conventional metallic contacts can be replicated by quantum two dimensional charge (of Fermion) systems (2DFS). Unlike metals, the particle concentration of these "unconventional" systems can be accurately controlled in an extensive range and by means of external electronic or optical stimuli. A 2DFS can, hence, transition from a high-density kinetic liquid into a dilute-but highly correlated-gas state, in which inter-particle Coulombic interactions are significant. Such interactions contribute negatively, by so-called exchange-correlation energies, to the overall energetics of the system, and are manifested as a series negative quantum capacitance. This dissertation investigates the capacitive performance of a class of unconventional devices based on a planar metal-semiconductor-metal structure with an embedded 2DFS. They constitute an opto-electronically controlled variable capacitor, with record breaking figures-of-merit in capacitance tuning ranges of up to 7000 and voltage sensitivities as large as 400. Internal eld manipulations by localized depletion of a dense 2DFS account for the enlarged maximum and reduced minimum capacitances. The capacitance-voltage characteristics of these devices incur an anomalous "Batman" shape capacitance enhancement (CE) of up to 200% that may be triggered optically. The CE is attributed to the release and storage of exchange-correlation energies; from the "unconventional" plate and in the dielectric, respectively. This process is enforced by density manipulation of the 2DFS by a hybrid of an external eld and light-generated carriers. Under moderate optical powers, the capacitance becomes 43 times greater than the dark value; thus a new capacitance-based photodetection method is offered. This new capacitance based photodetection method has a range of applications in optoelectronics, particularly in the next generation of photonic integrated systems.Ph.D., Electrical Engineering -- Drexel University, 201

High-Speed, High-Sensitivity Optoelectronic Device with Bilayer Electron and Hole Charge Plasma

Analogous to a drop exciting a wave in a reservoir that is detected more rapidly than the drop's transport by current flow, charge plasma confined in a semiconductor can transfer energy, hence respond much faster than the electric field-induced carrier drift current. Here we construct an optoelectronic device in which charge reservoirs respond to excitation with a speed that is impossible to achieve by transport of charge. In response to short optical pulses, this device produces electrical pulses that are almost 2 orders of magnitude shorter than the same device without the charge reservoirs. In addition to speed, the sensitivity of this process allowed us to measure, at room temperature, as low as 11 000 photons. These micro plasma devices can have a range of application such as optical communication with a fraction of a microwatt power compared to the present tens of milliwatts, ultrasensitive light detection with cryogenic cooling, photovoltaic devices capable of harvesting dim light, THz radiation detectors, and charged particle detectors

Unpacking Oakland Cemetery: Immersing Students in Atlanta History

Working with Oakland Cemetery, Georgia State and Emory Universities, and Beam Imagination are creating an experimental, public-facing digital archive that combines maps, a burial database, 3D visualizations, and curation

On absorption properties of GaAs/AlGaAs nanowire arrays

Aligned, dense arrays of GaAs/AlGaAs core-shells have been grown on variety of substrates showing very low reflectivity and hence high absorption in the solar energy range that makes them especially strong candidates for optical detection and photovoltaic applications. We analyze the reflection R(E), transmission T(E) and hence absorption A(E) spectra of periodic arrays using transfer matrix method. Simulation results compare favorably with experimental data

Performance Enhancement of a GaAs Detector with a Vertical Field and an Embedded Thin Low-Temperature Grown Layer

Low temperature growth of GaAs (LT-GaAs) near 200 °C results in a recombination lifetime of nearly 1 ps, compared with approximately 1 ns for regular temperature ~600 °C grown GaAs (RT-GaAs), making it suitable for ultra high speed detection applications. However, LT-GaAs detectors usually suffer from low responsivity due to low carrier mobility. Here we report electro-optic sampling time response measurements of a detector that employs an AlGaAs heterojunction, a thin layer of LT-GaAs, a channel of RT-GaAs, and a vertical electric field that together facilitate collection of optically generated electrons while suppressing collection of lower mobility holes. Consequently, these devices have detection efficiency near that of RT-GaAs yet provide pulse widths nearly an order of magnitude faster—~6 ps for a cathode-anode separation of 1.3 μm and ~12 ps for distances more than 3 μm

Structure and physical properties of NiO/Co3O4 nanoparticles

The thermal treatment method was employed to prepare nickel-cobalt oxide (NiO/CO3O4) nanoparticles. This method was attempted to achieve the higher homogeneity of the final product. Specimens of nickel-cobalt oxide were characterized by various experimental techniques, including X-ray diffraction (XRD), transmission electron microscopy (TEM) and Fourier transform infrared spectroscopy (FTIR). X-ray diffraction results showed that there was no crystallinity in the predecessor, and it still had the amorphous phase. The formations of the crystalline phases of the nickel-cobalt oxide nanoparticles started from 350–500 °C, and the final products had different crystallite sizes ranging from 11–35 nm. Furthermore, the variation of DC conductivity (σdc), impedance, tangent loss (tgδ) and dielectric constant (εʹ) of the calcined specimens with frequency in the range of 102–106 Hz was investigated. σdc showed a value of 1.9 × 10-6 S/m, 1.3 × 10-6 S/m and 1.6 × 10-6 S/m for the specimens calcined at 350, 400 and 450 °C, respectively. Additionally, a decrease in tgδ values with an increase in temperature was observed. Finally, the formed nanoparticles exhibited ferromagnetic behaviors, which were confirmed by using a vibrating sample magnetometer (VSM)

Structure and Physical Properties of NiO/Co3O4 Nanoparticles

The thermal treatment method was employed to prepare nickel-cobalt oxide (NiO/CO3O4) nanoparticles. This method was attempted to achieve the higher homogeneity of the final product. Specimens of nickel-cobalt oxide were characterized by various experimental techniques, including X-ray diffraction (XRD), transmission electron microscopy (TEM) and Fourier transform infrared spectroscopy (FTIR). X-ray diffraction results showed that there was no crystallinity in the predecessor, and it still had the amorphous phase. The formations of the crystalline phases of the nickel-cobalt oxide nanoparticles started from 350–500 °C, and the final products had different crystallite sizes ranging from 11–35 nm. Furthermore, the variation of DC conductivity (σdc), impedance, tangent loss (tgδ) and dielectric constant (εʹ) of the calcined specimens with frequency in the range of 102–106 Hz was investigated. σdc showed a value of 1.9 × 10-6 S/m, 1.3 × 10-6 S/m and 1.6 × 10-6 S/m for the specimens calcined at 350, 400 and 450 °C, respectively. Additionally, a decrease in tgδ values with an increase in temperature was observed. Finally, the formed nanoparticles exhibited ferromagnetic behaviors, which were confirmed by using a vibrating sample magnetometer (VSM)