Graduation date: 2004

Graduation date: 1998

Two methods of electro-optically characterizing alternating-current thin-film electroluminescent (ACTFEL) devices are investigated: photo-induced transferred charge (PIQ) and luminescence (PIL), and subthreshold voltage-induced transferred charge (VIQ) techniques. Both techniques provide information related to traps within the phosphor layer. PIQ/PIL experiments monitor the transport of electrons and holes across the phosphor layer which are photo-injected by a UV laser pulse. VIQ experiments monitor the optical reset of traps ionized by bipolar subthreshold voltage pulses. PIQ/PIL experiments are performed on three different SrS ACTFEL devices: ALE-deposited SrS:Ce, sputter-deposited SrS:Cu, and undoped MOCVD-deposited SrS. From the PIQ/PIL experiments, two distinct electron thresholds in the luminescent impurity doped samples at ~0.8 (weak threshold) and ~1.2 MV/cm (strong threshold) are observed. These thresholds are independent of the phosphor thickness, indicating that they arise from a bulk property of the phosphor. The ~0.8 MV/cm weak threshold is attributed to field emission of relatively shallow (~0.6 eV) electron-emitting bulk traps (e.g. cerium or oxygen for SrS:Ce; a sulfur vacancy or oxygen for SrS:Cu). The ~1.2 MV/cm strong threshold is ascribed to the onset of trap-to-band impact ionization. In contrast to electron transport, PIQ/PIL studies reveal no hole transport in SrS doped with luminescent impurities, although hole transport is observed for an undoped SrS ACTFEL device. The lack of hole transport is attributed to the efficiency of hole capture in SrS doped with luminescent impurities. VIQ experiments are performed on the same SrS ACTFEL devices. VIQ trap energy depths are estimated as ~0.1 eV for SrS:Ce; ~0.9 eV for SrS:Cu (with a capture cross-section of ,~10�������cm��), and ~0.6 eV for undoped SrS. Tenative atomic identification of traps responsible for these VIQ trends are: chlorine or a Ce shallow donor state for SrS:Ce, a sulfur vacancy for SrS:Cu, and a sulfur vacancy or an oxygen isoelectronic trap for undoped SrS. / Graduation date: 2000

Graduation date: 1996

Graduation date: 1998

Graduation date: 1995

Graduation date: 1995

Graduation date: 1993

Thin film lithium microbatteries were investigated in this project in which LiCoO₂ cathodes about 200 to 500 nm were fabricated by pulsed-laser deposition (PLD) at different processing parameters such as laser energy and fluence, substrate temperature, background gas pressure, and target-substrate distance. Structure, microstructure and composition of as-deposited LiCoO₂ films were determined by XRD, SEM and XPS. Optimal deposition parameters were identified. Relaxation of open-circuit voltage of as-prepared cells and charge-discharge cycling were conducted to characterize the electrochemical properties of microbatteries made of these LiCoO₂ films. / Singapore-MIT Alliance (SMA)

Thesis (Ph.D.)--University of Delaware, 2006. / Principal faculty advisor: Robert G. Hunsperger, Dept. of Electrical and Computer Engineering. Includes bibliographical references.