Masters Theses in the Pure and Applied Sciences was first conceived, published, and disseminated by the Center for Information and Numerical Data Analysis and Synthesis (CINDAS)* at Purdue University in 1957, starting its coverage of theses with the academic year 1955. Beginning with Volume 13, the printing and dis semination phases of the activity were transferred to University Microfilms/Xerox of Ann Arbor, Michigan, with the thought that such an arrangement would be more beneficial to the academic and general scientific and technical community. After five years of this jOint undertaking we had concluded that it was in the interest of all concerned if the printing and distribution of the volumes were handled by an international publishing house to assure improved service and broader dissemination. Hence, starting with Volume 18, Masters Theses in the Pure and Applied Sciences has been disseminated on a worldwide basis by Plenum Publishing Corporation of New York, and in the same year the coverage was broadened to include Canadian universities. All back issues can also be ordered from Plenum. We have reported in Volume 40 (thesis year 1995) a total of 10,746 thesis titles from 19 Canadian and 144 United States universities. We are sure that this broader base for these titles reported will greatly enhance the value of this impor tant annual reference work. While Volume 40 reports theses submitted in 1995, on occasion, certain uni versities do report theses submitted in previous years but not reported at the time.

In this dissertation, GaN growth on porous templates by metalorganic chemical vapor deposition (MOCVD) was studied. The motivation of this research is pursuing an effective reduction of defects in GaN by its submicron-scale and nano-scale epitaxial lateral overgrowth (ELO) on these porous templates, which included porous TiN/GaN (P-TiN), imprint lithography patterned Ti/GaN (IL-Ti), carbon-face nano-porous SiC (C-PSC), and silicon-face nano-porous SiC (Si-PSC). The porous TiN/GaN was formed in situ in MOCVD reactor by annealing a Ti-covered GaN seed layer. This simplicity makes the GaN ELO on the P-TiN more cost-efficient than the conventional ELO which requires ex situ photolithography and/or etching. Both the GaN nano-ELO and the GaN micron-ELO could be realized on P-TiN by controlling the GaN nucleation scheme. The reduction efficacy of edge threading dislocation (TD) was ~15 times. The optical characterization indicated that the non-radiative point-defects in GaN grown were reduced significantly on the P-TiN. The imprint lithography patterned Ti/GaN had uniformly distributed submicron Ti pads on GaN seed layer. These Ti pads acted as GaN ELO masks. The TD reduction efficacy of the IL-Ti was only ~2 due to the low coverage of Ti (~25%) on the GaN seed layer and the low pressure (30 Torr) employed during GaN ELO. Even with a small reduction of TDs, the point-defects in GaN were effectively lowered by the IL-Ti. Hydrogen polishing, sacrificial oxidation, and chemical mechanical polishing were employed to remove surface damage on the PSC substrates. Nitrogen-polarity GaN grown on the C-PSC was highly dislocated because the rough surface of C-PSC induced strong misorientation between GaN nucleation islands. The efficacy of Si-PSC on defect reduction primarily depended on the GaN nucleation schemes. A high density of GaN nano-nucleation-islands was required to realize the GaN nano-ELO extensively. With such a nucleation scheme, the GaN grown on Si-PSC had a ~20 times reduction on the density of the mixed and screw TDs compared with control sample. This growth method is promising for effective defect reduction within a small GaN thickness. Reducing the GaN nucleation density further lowered the TD density but also diminished the efficacy of Si-PSC. These results were explained by a growth model based on the mosaic structure of GaN.

This book discusses the important technological aspects of the growth of GaN single crystals by HVPE, MOCVD, ammonothermal and flux methods for the purpose of free-standing GaN wafer production.

In the past ten years, heteroepitaxy has continued to increase in importance with the explosive growth of the electronics industry and the development of a myriad of heteroepitaxial devices for solid state lighting, green energy, displays, communications, and digital computing. Our ever-growing understanding of the basic physics and chemistry underlying heteroepitaxy, especially lattice relaxation and dislocation dynamic, has enabled an ever-increasing emphasis on metamorphic devices. To reflect this focus, two all-new chapters have been included in this new edition. One chapter addresses metamorphic buffer layers, and the other covers metamorphic devices. The remaining seven chapters have been revised extensively with new material on crystal symmetry and relationships, III-nitride materials, lattice relaxation physics and models, in-situ characterization, and reciprocal space maps.

Gallium nitride is an important material for the production of next-generation visible and near-UV optical devices, as well as for high temperature electronic amplifiers and circuits; however there has been no bulk method for the production of GaN substrates for device layer growth. Instead, thick GaN layers are heteroepitaxially deposited onto non-native substrates (usually sapphire) by one of two vapor phase epitaxy (VPE) techniques: MOVPE (metalorganic VPE) or HVPE (hydride VPE). Each method has its strengths and weaknesses: MOVPE has precise growth rate and layer thickness control but it is slow and expensive; HVPE is a low-cost method for high rate deposition of thick GaN, but it lacks the precise control and heterojunction layer growth required for device structures. Because of the large (14%) lattice mismatch, GaN grown on sapphire requires the prior deposition of a low temperature MOVPE nucleation layer using a second growth process in a separate deposition system. Here we present a novel hybrid VPE system incorporating elements of both techniques, allowing MOVPE and HVPE in a single growth run. In this way, a thick GaN layer can be produced directly on sapphire. GaN growth commences as small (50-100 nm diameter) coherent strained 3-dimensional islands which coalesce into a continuous film, after which 2-dimensional layer growth commences. The coalescence of islands imparts significant stress into the growing film, which increases with the film thickness until catastrophic breakage occurs, in-situ. Additionally, the mismatch in thermal expansion rates induces compressive stress upon cooling from the growth temperature of 1025°C. We demonstrate a growth technique that mitigates these stresses, by using a 2-step growth sequence: an initial high growth rate step resulting in a pitted but relaxed film, followed by a low growth rate smoothing layer. As a result, thick (> 50 [Mu]m) and freestanding films have been grown successfully. X-ray rocking curve linewidth of 105 arcseconds and 10K PL indicating no "yellow" emission indicate that the material quality is higher than that produced by conventional MOVPE. By further modifying the hybrid system to include a metallic Mn source, it is possible to grow a doped semi-insulating GaN template for use in high frequency electronics devices.