Optical properties of transition metal dichalcogenides on GaAs

• Autor(a) principal: Rafael Ricardo Rojas López
• Data de Publicação: 2018
• Tipo de documento: Dissertação
• Idioma: eng
• Título da fonte: Repositório Institucional da UFMG
• Texto Completo: http://hdl.handle.net/1843/41330; https://orcid.org/0000-0002-2665-8148
• topic: Transition metal dichalcogenides; GaAs; 2D materials; Monolayer; Optical properties; Propriedades ópticas; Matéria condensada; Espectros moleculares

Transition metal dichalcogenides (TMDs) are crystalline structures of the form MX2, where M is a transition metal, like Mo or W, and X is a chalcogenide, as S or Se. They are multilayer structures, with X-M-X covalent bonds within a layer and Van der Waals bonds at the interlayer interfaces. As the thickness is reduced from several layers to a single monolayer, a transition is observed from a semiconductor with indirect band gap to a direct band gap in the visible or near infrared frequencies. Therefore, the TMDs are good candidates for the implementation of ultra-thin optoelectronical devices. For this reason, and also for their interest in the study of new physical phenomena, they have been extensively investigated over the last decade. It is already well established that the optical properties of monolayer TMDs are strongly affected by the substrate. In this work, we will present how the optical properties of three different TMDs, MoS2, WS2 and WSe2, are modified by placing them on GaAs substrates. We investigate samples on three types of substrates: p-doped GaAs, n-doped GaAs and undoped GaAs. The monolayers were obtained by mechanical exfoliation and transfered to the substrates. Since the refraction indexes of GaAs and the TMDs are similar, we had to establish a procedure to locate and deal with suitable monolayers. We present a pectral analysis of the luminescence emission for each case, as well as their Raman spectra. We find that the GaAs substrates produce significant changes in the luminescence of the TMDs, which can be understood with basis on the band alignment of the TMD with GaAs. We conclude that GaAs/TMDs heterojunctions have a great potential for applications as photodetectors and solar cells.