Unraveling Optoelectronic Properties of 2D Materials

• Ano de defesa: 2019
• Autor(a) principal: Andreij de Carvalho Gadelha
• Tipo de documento: Tese
• Tipo de acesso: Acesso aberto
• Idioma: eng
• Instituição de defesa: Universidade Federal de Minas Gerais
• Palavras-chave em Português: Optoeletrônica; Memórias ópticas de MoS2; Campos eletricos
• Link de acesso: https://hdl.handle.net/1843/SMRA-BDWH9G

 2D materials have emerged as an exciting platform to investigate optoelectronics phenomena. On the other hand, the employment of external fields in matter reveals intriguing physical effects. Here, we tune the optoelectronic properties of 2D materials, MoS2 and talc, by applying electric fields, unraveling interesting possibilities. In MoS2, from the combined actions of electric field applications and laser exposures, we obtain a photomemory effect, which is non-volatile, gate-tunable, and is obtained in a simple architecture. The photomemory is due to a modulation with the gate voltage of the persistent photocurrent in MoS2 transistors. This effect, in turn, is entirely gate-tunable. In this way, we use gate voltages, during laser exposures, to ¿record¿ distinct photomemory states, with possible applications for multilevel memories. On the other hand, we can also use the gate voltage, with the laser off, to adjust the memory gains. Furthermore, we predict that our devices store the photomemory information for more than ten years, indicating a non-volatile memory effect. We also propose a phenomenological model to explain the photomemory and the persistent photocurrent, which we ascribe to a photodoping effect. We conclude this part by showing that the photodoping modifies the spatial distribution of the photocurrent. Next, for the first time, we investigate atomic-like photoluminescence emissions from defect states in 2D talc. We use the electric field to control these emissions by two different mechanisms. First, we can shift the energies of the emissions by a linear Stark effect. By further investigating this phenomenon, we get an insight into the nature of the defects in talc. Besides, the electric field can control the intensity of the emissions, leading to a reversible annihilation of some of the photoluminescence peaks. This quenching effect has rich physical explanations, so we discuss them, and from our interpretations, we elaborate which mechanism describes better our results. In summary, our work uncovers exciting and novel possibilities to study and control the optoelectronics of 2D materials.