The Deccan Trap basalts are the remnants of a massive series of lava flows that erupted at the K/T boundary and covered 1-2 million km2 of west-central India. This eruptive event is of global interest because of its possible link to the major mass extinction event, and there is much debate about the duration of this massive volcanic event. In contrast to isotopic or paleomagnetic dating methods, I explore an alternative approach to determine the lifecycle of the magma chambers that supplied the lavas, and extend the concept to obtain a tighter constraint on Deccan’s duration. My method relies on extracting time information from elemental and isotopic diffusion across zone boundary in an individual crystal. I determined elemental and Sr-isotopic variations across abnormally large (2-5 cm) plagioclase crystals from the Thalghat and Kashele “Giant Plagioclase Basalts” from the lowermost Jawhar and Igatpuri Formations respectively in the thickest Western Ghats section near Mumbai. I also obtained bulk rock major, trace and rare earth element chemistry of each lava flow from the two formations. Thalghat flows contain only 12% zoned crystals, with 87Sr/86Sr ratios of 0.7096 in the core and 0.7106 in the rim, separated by a sharp boundary. In contrast, all Kashele crystals have a wider range of 87Sr/86Sr values, with multiple zones. Geochemical modeling of the data suggests that the two types of crystals grew in distinct magmatic environments. Modeling intracrystalline diffusive equilibration between the core and rim of Thalghat crystals led me to obtain a crystal growth rate of 2.03x10-10 cm/s and a residence time of 780 years for the crystals in the magma chamber(s). Employing some assumptions based on field and geochronologic evidence, I extrapolated this residence time to the entire Western Ghats and obtained an estimate of 25,000 – 35,000 years for the duration of Western Ghats volcanism. This gave an eruptive rate of 30 – 40 km3/yr, which is much higher than any presently erupting volcano. This result will remain speculative until a similarly detailed analytical-modeling study is performed for the rest of the Western Ghats formations.

This dissertation is focused on the research efforts to develop the growth, processing, and modeling technologies for GaN-based Heterojunction Field Effect Transistors (HFETs). The interest in investigating GaN HFETs is motivated by the advantageous material properties of nitride semiconductor such as large band gap, large breakdown voltage, and high saturation velocity, which make it very promising for the high power and microwave applications. Although enormous progress has been made on GaN transistors in the past decades, the technologies for nitride transistors are still not mature, especially concerning the reliability and stability of the device. In order to improve the device performance, we first optimized the growth and fabrication procedures for the conventional AlGaN barrier HFET, on which high carrier mobility and sheet density were achieved. Second, the AlInN barrier HFET was successfully processed, with which we obtained improved I-V characteristics compared with conventional structure. The lattice-matched AlInN barrier is beneficial in the removal of strain, which leads to better carrier transport characteristics. Furthermore, new device structures have been examined, including recess-gate HFET with n+ GaN cap layer and gate-on-insulator HFET, among which the insertion of gate dielectrics helps to leverage both DC and microwave performances. In order to depict the microwave behavior of the HFET, small signal modeling approaches were used to extract the extrinsic and intrinsic parameters of the device. An 18-element equivalent circuit model for GaN HFET has been proposed, from which various extraction methods have been tested. Combining the advantages from the cold-FET measurements and hot-FET optimizations, a hybrid extraction method has been developed, in which the parasitic capacitances were attained from the cold pinch-off measurements while the rest of the parameters from the optimization routine. Small simulation error can be achieved by this method over various bias conditions, demonstrating its capability for the circuit level design applications for GaN HFET. Device physics modeling, on the other hand, can help us to reveal the underlying physics for the device to operate. With the development of quantum drift-diffusion modeling, the self-consistent solution to the Schrödinger-Poisson equations and carrier transport equations were fulfilled. Lots of useful information such as band diagram, potential profile, and carrier distribution can be retrieved. The calculated results were validated with experiments, especially on the AlInN layer structures after considering the influence from the parasitic Ga-rich layer on top of the spacer. Two dimensional cross-section simulation shows that the peak of electrical field locates at the gate edge towards the drain, and of different kinds of structures the device with gate field-plate was found to efficiently reduce the possibility of breakdown failure.

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根據Bass(1969)擴散模式，放寬市場特性不影響創新擴散之假設，並使創 新係數與模仿係數可隨著時間而改變，以行動電話為例，探討ぇ各國採用 行動電話之市場潛能、市場飽和時之普及率以及單年最高採用人數出現的 時間，え市場特性因素如何影響行動電話之擴散，ぉ比較各國擴散模式與 多國擴散模式之解釋能力。研究結果發現：ぇ就本研究所分析的國家，各 國行動電話的市場大小，以美國最大，日本次之，愛爾蘭為最小。而行動 電話的最高普及率以美國與瑞典最高，超過10% ；其餘國家之最高普及率 都不超過 0.4%，顯示行動電話是一種普及率較低的服務。就單年最高採 用人數出現時間來看，只有日本是超過十年，其餘國家均在十年之內，甚 至比利時在第二年就出現採用高峰，顯示行動電話之產品生命週期可能不 是很長。え「市場需求指標」高的國家，有較高的模仿效果；「流動性」 對於創新效果與模仿效果的影響均是負的；「四海胸襟」對於創新與模仿 效果的影響均是正的。ぉ多國擴散模式的解釋能力較各國擴散模式佳，因 此，將市場特性因素加入創新擴散模式中確實有其必要性。