Graduation date: 1995

Thesis (Ph. D.)--Oregon State University, 1982. / Typescript (photocopy). Includes bibliographical references (leaves 174-179). Also available on the World Wide Web.

Alternating-current thin-film electroluminescent (ACTFEL) devices are used in the formation of pixels in flat panel displays. ACTFEL flat panel displays have many advantages over other flat panel technologies. Specifically, ACTFEL panels are emissive displays, they have high brightness, wide viewing angles, and rugged construction. Although much is already known about the operation of ACTFEL devices, several topics related to the device physics and modeling of these devices require further research. In this work, existing ACTFEL device models are refined by expanding the understanding of ACTFEL device physics and operation. Modeling is separated into three levels of increasing complexity as follows; (1) equivalent circuit modeling, (2) device physics or electrostatic modeling, or (3) Monte Carlo modeling. Each level of model is addressed in this thesis. Existing equivalent circuit models are empirically refined to account for device response to variations in the shape of the driving waveform pulse. The device physics model is expanded by presenting evidence for the formation of space charge in the phosphor layer and the equations prescribing device response are modified accordingly. Also, a new technique for measuring the distribution of interface states in ACTFEL devices is presented. This gives new insight into device operation, as the interface state distribution is one of the most difficult parameters to estimate/measure in the device physics model. Finally, an experiment is presented which attempts to measure the maximum energy of hot electrons during conduction in the phosphor. This research leads to a recommendation of the complexity of the conduction band model needed for accurate Monte Carlo simulation of ACTFEL devices. / Graduation date: 1993

Graduation date: 1994

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: 1997

Graduation date: 1996

Graduation date: 1998

Graduation date: 1995