Investigation of electrically active defects at the interface of high-k dielectrics and compound semiconductors

As silicon based devices in integrated circuits reach the fundamental limits of dimensional scaling there is growing research interest in the use of high electron mobility channel materials, such as indium gallium arsenide (InGaAs), in conjunction with high dielectric constant (high-k) gate oxides, for Metal-Oxide-Semiconductor Field Effect Transistor (MOSFET) based devices. The motivation for employing high mobility channel materials is to reduce power dissipation in integrated circuits while also providing improved performance. One of the primary challenges to date in the field of III-V semiconductors has been the observation of high levels of defect densities at the high-k/III-V interface, which prevents surface inversion of the semiconductor. The work presented in this PhD thesis details the characterization of MOS devices incorporating high-k dielectrics on III-V semiconductors. The analysis examines the effect of modifying the semiconductor bandgap in MOS structures incorporating InxGa1-xAs (x: 0, 0.15. 0.3, 0.53) layers, the optimization of device passivation procedures designed to reduce interface defect densities, and analysis of such electrically active interface defect states for the high-k/InGaAs system. Devices are characterized primarily through capacitance-voltage (CV) and conductance-voltage (GV) measurements of MOS structures both as a function of frequency and temperature. In particular, the density of electrically active interface states was reduced to the level which allowed the observation of true surface inversion behavior in the In0.53Ga0.47As MOS system. This was achieved by developing an optimized (NH4)2S passivation, minimized air exposure, and atomic layer deposition of an Al2O3 gate oxide. An extraction of activation energies allows discrimination of the mechanisms responsible for the inversion response. Finally a new approach is described to determine the minority carrier generation lifetime and the oxide capacitance in MOS structures. The method is demonstrated for an In0.53Ga0.47As system, but is generally applicable to any MOS structure exhibiting a minority carrier response in inversion.

Home birth in Ireland 1993-1997: a review of community midwifery practice

To date little is known about the practices of domiciliary midwives and the outcomes of home birth in Ireland. The purpose of this review is to provide some background information on the situation for women seeking a home birth and to document the outcomes of home births in Ireland between 1993 -1997. Design: Descriptive analysis of prospective data collected from domiciliary midwives regarding women who requested a home birth between 1993 and 1997. Participants: The questionnaire was distributed to 15 domiciliary midwives; this included all the domiciliary midwives known to the authors to be practising in Ireland at that time. Findings: During this period, 585 women planned to give birth in their home with the assistance of midwives, 500 women achieved this. The spontaneous vaginal delivery rate for women who commenced their labour at home was 96.9% (n = 554). These women gave birth without medications or other interventions. 544 (93%) of the women breastfed their babies and 538 (92%) were still breastfeeding at 6 weeks. This is the first review of domiciliary midwifery practice in Ireland in recent years. They obtained data from 11 independent midwives on 585 women who planned home births. Findings showed high rates of spontaneous vaginal delivery and breastfeeding. There were 500 babies born at home with three perinatal deaths, including one undiagnosed breech delivery, one infant with abnormal lungs on post-mortem and one infant with Potter's Syndrome who was stillborn.