Designs for deep ultraviolet (DUV) edge emitting laser diodes (LDs) based on the wurtzite III-nitride (III-N) material system are presented. A combination of proprietary and commercial advanced semiconductor LD simulation software is used to study the operation of III-N based DUV LDs theoretically. Critical factors limiting device performance are identified based on an extensive literature survey. A comprehensive design parameter space is investigated thoroughly with the help of advanced scripting capabilities. Several design strategies are proposed to eliminate the critical problems completely or partially. A DUV LD design is proposed based exclusively on AlInN active layers grown epitaxially on bulk AlN substrates because AlInN offers a promising alternative to AlGaN for the realization of LDs and LEDs operating in the DUV regime. The proposed AlInN-based design also features a tapered electron blocking layer (EBL) instead of a homogeneous one. Tapered EBLs redistribute the interfacial polarization charge volumetrically throughout the entire EBL thickness via compositional grading, and eliminate the parasitic inversion layer charge. AlGaN based DUV LD designs are explored also because at present, it may be difficult to grow AlInN epitaxially with superior crystalline quality. Polarization charge matching is proposed to improve electron and hole wavefunction overlap within the active region. Although the strategy of polarization charge matching has already been proposed in the literature to enhance performance of visible wavelength LEDs and LDs, the proposed design presents the first demonstration that polarization charge matching is also feasible for DUV LDs operating at sub-300 nm wavelengths. A lateral current injection (LCI) LD design is proposed featuring polarization-charge-matched barriers and regrown Ohmic contacts to avoid a group of issues related to the highly inefficient p-type doping of wide bandgap III-N materials in vertical injection designs. The proposed design partially decouples the problem of electrical injection from that of optical confinement. Although the idea of an LCI LD design has been proposed in the literature in the 90s to be used as longer wavelength active sources in optoelectronic integrated circuits using GaInAsP/InP and related material systems, the proposed design is the first theoretical demonstration that this concept can be applied to DUV LDs based on III-N material system. To solve the problem of hole transport in vertical injection designs, a DUV LD design based exclusively on AlGaN material system is presented, featuring an inverse-tapered p-waveguide layer instead of an EBL. Several EBL designs are investigated, and compared with conventionally-tapered EBL design. Through judicious volumetric redistribution of fixed negative polarization charge, inverse tapering may be exploited to achieve nearly flat valence band profiles free from barriers to hole injection into the active region, in contrast to conventional designs. Numerical simulations demonstrate that the inverse tapered strategy is a viable solution for efficient hole injection in vertical injection DUV LDs operating at shorter wavelengths (< 290 nm).

Submitted by RODRIGO DE HOLANDA SCHMIDT (rodrigohs1979@gmail.com) on 2018-01-17T18:29:25Z No. of bitstreams: 1 PROJETO Posdefesa Versão FINAL.pdf: 1906537 bytes, checksum: 3b5e67507ea1b0d7bda550480252ae26 (MD5) / Approved for entry into archive by Janete de Oliveira Feitosa (janete.feitosa@fgv.br) on 2018-01-18T18:30:52Z (GMT) No. of bitstreams: 1 PROJETO Posdefesa Versão FINAL.pdf: 1906537 bytes, checksum: 3b5e67507ea1b0d7bda550480252ae26 (MD5) / Made available in DSpace on 2018-01-30T12:08:34Z (GMT). No. of bitstreams: 1 PROJETO Posdefesa Versão FINAL.pdf: 1906537 bytes, checksum: 3b5e67507ea1b0d7bda550480252ae26 (MD5) Previous issue date: 2017-11-30 / Purpose – The aim of this study was to comprehend the main determinant factors for vertical integration in the pulp and paper sector in Brazil, from a perspective of pulp manufacturers. Design/methodology – The research adopted a qualitative approach, through a multiple case study with three of the main companies in the pulp and paper sector in Brazil. The data collection was done through semi-structured interviews of executives of the selected companies. Findings – The main competitive advantage arises from the vertical integration backward, of the pulp mill towards the forestry. The main factors for this are the exercise of the market power of oligopoly by the pulp companies, assurance of supply of their main input, the wood, asset specificity of site, shortening the distance between the forest and the pulp mill, and mitigation of uncertainty. There is tapered integration of pulp mill and forestry, mainly due the use of advantages of site specificity of forest producers near the mill, the need to mitigate social risks and to develop a mature market for the commercialization of wood in the country. Research limitations – The main limitation of this work is the fact that the pulp sector is a concentrated oligopoly, with few companies, which restricts the diversity and number of respondents. Practical implications – The results can be applied to organizations in the pulp and paper sector, as well as to other capital-intensive industries with high dependence on a particular raw material. Originality– To our knowledge, this is the first study about vertical integration in the pulp and paper sector in Brazil. / Objetivo – Este estudo pretende compreender os principais determinantes para a integração vertical no setor de papel e celulose no Brasil, a partir de uma perspectiva das fabricantes de celulose. Metodologia – A pesquisa seguiu uma abordagem qualitativa, por meio de estudo de casos múltiplos com três das principais empresas do setor de papel e celulose do Brasil. A coleta de dados foi feita por meio de entrevistas semiestruturadas de executivos das empresas selecionadas. Resultados – A principal vantagem competitiva verificada se deu na integração vertical realizada à montante pela fábrica de celulose, em direção à produção florestal. Os principais fatores para isso foram o exercício do poder de mercado de oligopólio pelas empresas de celulose, a garantia de fornecimento do seu insumo principal, a madeira, a especificidade de local dos ativos, dada pela proximidade necessária entre a floresta e a unidade de celulose, e a mitigação da incerteza. A integração vertical entre fábrica de celulose e produção florestal é realizada de forma parcial, principalmente devido ao aproveitamento de vantagens de localização de produtores florestais próximos à fabrica, à necessidade de mitigar riscos sociais e de desenvolver um mercado maduro de comercialização de madeira no país. Limitações – A principal limitação deste trabalho é o fato do setor de celulose ser um oligopólio concentrado, com poucas empresas, o que restringe a diversidade e o número de entrevistados. Aplicabilidade do trabalho – Os resultados obtidos podem ser aplicados às organizações do setor de papel e celulose, bem como a outras indústrias de capital intensivo e com alta dependência de uma matéria-prima em especial. Originalidade – Pelo que conhecemos, é o primeiro trabalho sobre integração vertical no setor de papel e celulose no Brasil.