Optical characterization of wide (WBS) and ultrawide (UWBS) bandgap semiconductors

• Autor(a) principal: Duarte, Teresa Filipa Alexandre Baptista
• Data de Publicação: 2022
• Tipo de documento: Dissertação
• Idioma: eng
• Título da fonte: Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos)
• Texto Completo: http://hdl.handle.net/10773/34525
• topic: β-Ga₂O₃; GaN; 4H-SiC; Diamond; Luminescence; Defects; Optical centres

With the current growing energy needs arises the need to obtain more efi cient electronic and optoelectronic devices. Ultrawide and wide bandgap semiconductors (UWBS, WBS) are promising materials to meet the requirements of these devices. In this thesis we characterized optically active centres in di erent UWBS and WBS samples, which include epitaxial layers grown by chemical vapour phase deposition (CVD) of β-Ga₂O₃, GaN and 4H-SiC, as well as Bulk diamond. To this end, different optical spectroscopy techniques were used: Raman, transmittance, photoluminescence (PL) and PL excitation (PLE). Raman measurements allowed the determination of the crystalline phase of the semiconductors under analysis and the identification of stress states in the epilayers. The GaN (grown on Al₂O₃) and the 4H-SiC samples evidenced compressive stress effects. For the β-Ga₂O₃ it was not possible to exclude stress effects, but it was not possible to identify the type. The Bulk diamond sample was revealed to be of high crystalline quality. The bandgap energies of the epitaxially grown samples were determined by transmittance. For the identification of the luminescent defects in the samples and the identi- fication of the emitting electronic states, PL and PLE measurements at room temperature were performed. The PL analysis of the samples was complemented with studies at 14 K. In the β-Ga₂O₃ emission bands were observed in the ultraviolet (UVL) and blue (BL) region. In parallel, a red emission was detected due to the presence of the Crᶟ⁺ contaminant in the structure. In the GaN sample, it was possible to identify the presence of recombination of free and bound excitons, and a yellow band (YL1). In 4HSiC, at room temperature, two recombination bands were identified in the blue (BL) and green (GL) donor acceptor pair (DAP). At 14 K N-bounded excitons were observed, which allowed us to assume that the observed BL may be an overlap of different DAP recombinations. In addition to this, an emission band was observed in red (RL) attributed to the spectral overlap of several centres. Two Bulk diamonds (Bulk 1 and 2) were also studied. In the Bulk 1 sample the N3 centre was identified in the spectral region of blue. In Bulk 2 it was possible to identify in the green spectral region the H3 centre and in the red one the NV° defect. In summary, the work carried out allowed us to infer about the structural and optical properties of the UWBS and WBS samples under analysis, to recognize the optically active defects in the samples, some of which assume a relevant role in terms of the conductivity of materials and can condition the response of semiconductors in various electronic and optoelectronic applications.