Metal Organic Vapour Phase Epitaxy for the Growth of Semiconductor Structures and Strained Layers

The technological development of semiconductor materials started in the period following the second world war. In the electronics industry, the first transistors were fabricated from germanium, later from silicon. It was soon realized that also the AIII–BV or AII – BVI materials (most often simply termed III–V or II–VI materials) exhibited semiconductive behaviour. The energy difference between the valence band and the conduction band made them candidates for electronic devices which can absorb or emit phonons over a range of frequencies (wavelengths). Direct bandgap materials such as gallium arsenide (GaAs) were suitable for devices in which efficient electron-hole recombinations could take place and high efficiency light emitting devices were a possibility. Stimulated emission was first demonstrated in 1970 with the preparation of the single heterojunction and the double heterojunction laser diodes. These devices are multiple layer structures with a thin waveguide region contained between layers of larger bandgap and different refractive index (for confinement of carriers and radiation, respectively, in the active region). A basic laser diode chip consists of two parallel facets, (110) planes, which are prepared by cleavage and act as mirrors. The Fabry-Perot cavity is defined by these two parallel facets and the passive (cladding) layers. In the longitudinal direction current definition is by mesa etching and/or stripe-contact metallization

Osteology of the first skull of Aetosauroides scagliai Casamiquela 1960 (Archosauria: Aetosauria) from the Upper Triassic of southern Brazil (Hyperodapedon Assemblage Zone) and its phylogenetic importance.

Aetosauria, which includes 30 species, is a diverse group of armored pseudosuchian archosaurs restricted to Upper Triassic beds. Three species occur in Brazil, and one of these, Aetosauroides scagliai Casamiquela, 1960, also occurs in Argentina. The specimen UFSM 11505, found at Faixa Nova-Cerrito I Outcrop, Santa Maria Formation (Hyperodapedon Assemblage Zone), Santa Maria, Rio Grande do Sul State, Brazil, is here referred to as Aetosauroides scagliai. This specimen preserves most of the skull with both hemimandibles in association with most of the postcranium, thus representing one of the most complete aetosaur skeletons found in Brazil. The premaxilla, one of the key elements of the cranial morphology of aetosaurs, along with the posterior portion of the mandible, was not described until now for A. scagliai. In contrast to the typothoracinae aetosaurs, the premaxilla of UFSM 11505 presents a shovel-shaped tip, but it is not as prominent as the lateral expansion of desmatosuchian aetosaurs, including both species of Stagonolepis, S. robertsoni Agassiz, 1844 and S. olenkae Sulej, 2010. The retroarticular process of the mandible is elongate and not tall, as in Stenomity huangae Small & Martz, 2013 and other typothoracinae aetosaurs. Unlike previous descriptions of A. scagliai, the maxillary teeth are recurved ziphodont-like with serrations on the entire length of both margins. Premaxillary teeth are also present, being less recurved than the maxillary teeth and cylindrical. We recovered Aetosauroides scagliai as the most basal taxon within Aetosauria, like previous phylogenetic analyses. Furthermore, our analyses reinforce that recurved and unconstricted maxillary teeth, the shovel-shaped premaxilla and the presence of a tuber on the surangular are plesiomorphic features of Aetosauria