This thesis describes the fabrication and characterization of GaN homojunction visible-blind ultraviolet (UV) p-i-n avalanche photodiodes (APDs) grown by metalorganic chemical vapor deposition (MOCVD) on free-standing bulk GaN substrates. The objective of this research is to develop GaN UV p-i-n APDs with high linear-mode avalanche gains and the Geiger-mode operation for single photon detection. Low noise, high responsivity, and high detectivity are also required for fabricated APDs used as photodiodes in the photovoltaic mode (zero bias) and the photoconductive mode (low reverse bias). High material defect density and immature fabrication technology have hampered the development of III-nitride APDs in the past. In this thesis, sidewall leakage reduction methods have been developed to achieve significant improvement in dark current density, noise performance, and photo detection performance. A record linear-mode avalanche gain > 10⁵ for GaN APDs was demonstrated at λ = 360 nm. The first Geiger-mode deep UV (DUV) APD using front-illuminated homojunction p-i-n diode structure on a free-standing bulk GaN substrate was also measured with single photo detection efficiency (SPDE) of 1.0 % and dark count probability (DCP) of 0.03 at 265 nm. The performance of fabricated homojunction GaN p-i-n photodiodes was also evaluated in the photoconductive mode as well as the photovoltaic mode. For an 80-µm-diameter device biased at - 20 V (in the photoconductive mode) the dark current density is lower than 40 pA/cm² which is the lowest value achieved for any III-nitride photodiode so far. Its responsivity is 0.140 A/W at 360 nm with an ultraviolet-visible rejection ratio of 8×10³. The room-temperature noise equivalent power is 4.27×10 ⁻¹⁷ W-Hz-[superscript 0.5] and the detectivity D* is 1.66×10¹⁴ cm-Hz[superscript 0.5]-W ⁻¹ at - 20 V. The minimum detectable optical power is as low as 100 fW. They are among the best values reported for reverse-biased GaN p-i-n photodiodes to date.

Thesis (Ph. D.)--University of Hawaii at Manoa, 2004. / Includes bibliographical references (leaves 198-219). / Also available by subscription via World Wide Web / xvii, 219 leaves, bound ill., some col. 29 cm

Excess exposure to solar ultraviolet radiation (UVR) is the only readily modifiable skin cancer risk factor, and childhood exposure is implicated in melanoma aetiology. To assist the design and evaluation of child sun protection interventions in the school and community context, this first comprehensive study used electronic monitors to record time-stamped, second-by-second UVR exposure of 325 children (from 28 randomly selected New Zealand primary schools) who kept a diary record of concurrent activities and sun-protective practices and completed a sun-related knowledge, attitudes and usual behaviours questionnaire. School principals and Health promoters (HPs) were interviewed about school and community sun protection efforts. Using the Haddon matrix and Ottawa Charter of Health Promotion to guide research, four potential domains of influence were identified: the physical and social environments, protective products, and host (child). Two key outcomes identified were child UVR exposure and sun-protective practices. A path model was developed where potential influences on these outcomes included school, community, host factors (demographics, skin type, sun-related attitudes, and sun-related knowledge), and pattern of concurrent outdoor activity. Seven specific hypotheses were defined to investigate the effects of host, school and community factors on UVR exposure, sun-protective practices, and sun-related knowledge, attitudes and behaviours. To test for the effects of host factors, day of the week and activity on UVR exposure and sun-protective practices, linear mixed models containing these factors and interactions between Year level-sex, activity-Year level and activity-sex, accounting for clustering within schools and allowing for repeated measures, were applied. Logistic regression with a random school effect was used to assess differences in scored student questionnaire items. Structural equation modelling was implemented to consider associations between sun-related knowledge, attitudes and behaviours, and other explanatory factors for variations in UVR exposure and sun-protective practices. Three of the seven specific hypotheses were supported. There were statistically significant differences in UVR exposure by sex, skin type, day of the week and activity, and sex-activity and Year level-activity interactions. Passive pursuits were associated with the highest UVR exposure rates compared to outdoor active, travel and unclassified pursuits. There were statistically significant differences in sun-protective practices by sex, ethnicity and skin type, and sex-activity and Year level-activity interactions. Girls tended to have higher sun protection scores than boys, but were more likely to sunbathe and use sunscreen. Children identifying with Pacific Island ethnicities had higher scores than children with other ethnicities, and children with Fitzpatrick skin types I and II had higher scores than children with skin types III, IV and V. School and community factors were not associated with UVR exposure, sun-protective practices, sun-related knowledge, attitudes and behaviours, but school and HPs� scores were relatively high, reflecting the significant time and effort spent promoting youth sun protection. Trends for Year level indicated that whereas child sun-related knowledge increased with Year level, attitudes and behaviours supportive of sun protection declined. When considering sun-related knowledge, attitudes and behaviours simultaneously, knowledge was only significantly associated with behaviours when mediated by attitudes. The study findings have implications for child sun protection interventions.

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Errata sheet pasted opposite Table of Contents. / Includes bibliographies. / 142, [171] leaves : ill. ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / This thesis investigates the UV-induced inhibition of oriC initiation function and the nature of the phenotype of the mutant origin of replication of Escherichia coli, oriCc. The specific aims of this study are to delineate the source of the UV-induced trans-acting inhibition of oriC function, utilizing the phage vector [lambda]poriCc, and to demonstrate the oriCc allele as an enhanced DNA replication initiator from oriC. / Thesis (Ph.D.)--University of Adelaide, Dept. of Biochemistry, 1997?

Diss. (sammanfattning) Uppsala : Sveriges lantbruksuniv. / Härtill 5 uppsatser.

Diss. (sammanfattning) Linköping : Univ. / Härtill 5 uppsatser.

Diss. (sammanfattning) Stockholm : Karol. inst., 2004. / Härtill 5 uppsatser.

Diss. (sammanfattning) Linköping : Univ., 2004. / Härtill 6 uppsatser.

Diss. (sammanfattning) Stockholm : Karolinska institutet, 2005. / Härtill 5 uppsatser.