Wide and direct bandgap semiconductors (WBSs) are promising materials for many deep UV (DUV) applications. However, several challenges presently hinder the enhancement of DUV optoelectronics, such as low crystal quality, as well as complex and costly fabrication and growth processes that prevent production of high-performance devices, especially for large-scale applications. As a part of the study reported in this dissertation, I demonstrate several novel WBS-based devices with improved or novel functionalities, for the first time. The first part of work reported in this dissertation is designated for the novel, highly ordered and well-defined hexagonal ZnO nanotube (NT) arrays that were obtained without a catalyst. These arrays were grown on a p-GaN template using pulsed laser deposition (PLD), resulting in a highly bright and cost-effective UV light emitting diode (LED). In the second part, Gd-doped ZnO NRs grown on cost-effective metal substrate by PLD are presented and it is demonstrated that these can be functionalized by CH3NH3PbI3 perovskite to extend the functionality of ZnO photodetector from the ultraviolet to the infrared region (λ > 1000 nm), for the first time. The work reported in the third part demonstrates that the PLD method adopted in the present study can be extended to other high-quality metal oxide nanostructures. For this purpose, uniform p-type CuO pyramids were grown by PLD on Si substrate without a metal catalyst. Moreover, laser ablation method was advanced from vacuum based (PLD) to liquid based (femtosecond-laser ablation in liquid − FLAL) method to synthesize high-quality ZnO quantum dots (QDs). Adoption of this novel strategy allows producing high-performance self-powered DUV photodetectors based on p-CuO pyramids/n-ZnO QDs heterojunction device. In the last part, this research field is further advanced by exploring the functionality of other metal oxides synthesized by FLAL to fabricate a high-performance self-powered DUV photodetector. Such photodetector was fabricated using p-MnO QDs that were synthesized by FLAL and functionalized by high-quality mechanically exfoliated n-β-Ga2O3 nanoflakes as an active heterojunction layer grown on SiO2, confirming its superior response. All fabrication strategies, including use of heterojunction structures (mainly p−n junction), adopted in this work overcome the aforementioned issues related to the currently available WBS devices.

Orientador: Evandro Conforti / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Elétrica e de Computação / Made available in DSpace on 2018-08-21T04:49:45Z (GMT). No. of bitstreams: 1 Rocha_Peterson_M.pdf: 5254230 bytes, checksum: 811832dc531fcd6bcc9edf29f71bf219 (MD5) Previous issue date: 2012 / Resumo: Modulações ópticas avançadas como DQPSK e QAM tem sido escolhidas por serem formatos multiniveis (dois bits ou mais por símbolo), aumentando a eficiência espectral de sistemas ópticos. Entretanto, o amplificador óptico a semicondutor (SOA) indicado principalmente para aplicações de media distancia (da ordem de 20 km), pode degradar o sinal DQPSK e QAM. Sistemas de fase modulada (como o DQPSK) são afetados principalmente por SPM e XPM, devido ao ruído de fase não-linear adicionado a fase óptica do sinal. Visando analisar estes problemas, apresenta-se um estudo sobre os sinais NRZ-DQPSK e 16-QAM amplificados pelo SOA, bem como outros fatores que degradam tais sistemas, através de simulações com os softwares comerciais OptiSystem e VPItransmissionMaker. Nas simulações, resultados foram obtidos estando em acordo com a teoria e em acordo com o capitulo 3. Para o sistema DQPSK, o SOA degradou o sinal em todos cenários propostos para avaliar o sistema. O sinal NRZ-DQPSK apresentou maior penalidade quando o ganho do SOA foi de 20 dB. Efeitos não-lineares juntamente com a dispersão cromática limitam fortemente a distancia do enlace, e ao compensar a dispersão cromática no enlace com maior penalidade em 56 Gbps, o sinal NRZ-DQPSK pode trafegar por uma distancia 10 vezes maior (de 5 km para 50 km) com uma BER de 10-12. Para o sistema QAM, o sinal foi penalizado pelo SOA em todos os casos, e utilizando o SOA com ganho grampeado, os efeitos não-lineares foram minimizados, melhorando substancialmente o desempenho. Compensando a dispersão cromática e usando o SOA com ganho grampeado para o caso com maior penalidade, o sinal 16-QAM viajou a uma distancia 16 vezes maior (3 km e 50 km) / Abstract: High spectral efficiency is being achieved in modern optical fiber systems using multilevel optical modulation formats such us DQPSK and QAM, with more than one bit per symbol. However, amplifying devices such as the semiconductor optical amplifier (SOA) can degrade the DQPSK signal. In recent years SOAs have gained much attention (mainly in medium distance links, around 20 km) due to non-linear and fast switching potential applications (wavelength conversion, 3R regeneration, optical packet switching, etc.). In addition, the SOA under gain saturation further enhance deleterious nonlinear effects such as SPM, XGM, FWM, XPM. Phase modulated systems as DQPSK are affected mainly by SPM and XPM due to the nonlinear phase noise added to the controlled phase of the optical modulated signal. This work presents a study on the NRZ-DQPSK and 16-QAM signals when amplified by SOAs, analyzing the main factors degrading such systems through simulations using commercial OptiSystem and VPItransmissionMaker software. SOA showed degradation effects over DQPSK, with larger penalties to NRZ signals and optical gain over 20 dB. Non-linear effects and chromatic dispersion impose a maximum distance limit. In dispersion compensated links, 10 fold distances are achieved in relation to standard fibers (5 to 50 km) with BER= 10-12. For 16 QAM, the penalties are still high. However, gain clamped SOAs have better performance with a 16 fold distance increase (3 km to 50 km) / Mestrado / Telecomunicações e Telemática / Mestre em Engenharia Elétrica