|On 19 October 2021, Mr. Mahdiyar Nouri Rezaie defended his Ph.D. thesis under the supervision of Prof. Shahram Mohammadnejad with the title of "Design, Simulation, Fabrication and Characterization of Hybrid Heterojunction Light-Emitting Device Based on ZnO Nanotubes".
Ph.D. Thesis Abstract:
Abstract In this thesis, after a systematic survey in hybrid inorganic/organic light-emitting heterostructure devices based on ZnO in the last decay, the impact of the ZnO nanotube (NT)/polymer hybrid heterostructure for ultraviolet organic light-emitting diode (UV-OLED) application has been carefully scrutinized. The proposed structure has been fabricated, simulated and compared with conventional ZnO nanorod (NR)/MEH-PPV structure. To synthesize ZnO NTs, the as-grown chemical bath deposited ZnO NRs have been etched in KCL solution in various molar (M) concentration, etching time and etching temperature. The optimized etching condition is obtained in 1 M concentration of KCL solution, 4 h etching time and 90 ℃ temperature. The structural properties (such as strain, stress and texture coefficient), electrical properties (such as band gap energy) and optical properties (such as Urbach energy, absorbance and photoluminescence spectra) of ZnO NTs have been investigated, systematically. In continue, hybrid UV-OLEDs have been fabricated based on ZnO NRs and ZnO NTs. According to the results, ZnO NT-based OLED depicts superior electrical and optical results including lower turn-on voltage (11.2 V < 15 V) and higher UV peak in electroluminescence spectra with respect to ZnO NR-based device. To acquire more enlightenment about UV emission mechanism, the proposed devices have been simulated through Silvaco TCAD and Lumerical FDTD software. The results from simulations illustrate great agreement with experimental results. Higher radiative recombination rate, higher Purcell factor and single-mode waveguiding effect of ring-core ZnO NT lead to major superiority of the ZnO NT-based UV-OLED fabricated and simulated in this work.