Microplasma-Driven Atomic Layer Deposition of Aluminum Oxide Etch-Free Patterning, and Gallium Oxide-Based Flexible DUV Photodetector

Aluminum oxide (Al₂O₃) and gallium oxide (Ga₂O₃) thin film have been deposited by arrays of microcavity plasmas assisted Atomic Layer Deposition (MALD). Al₂O₃ films were grown at 300 K by dissociating oxygen in an array of microcavity plasmas. Without additional etching process such as dry/wet etching, the deposition films at 300 K with patterning was accomplished by simple lift-off lithography. With this process, Al₂O₃ films having a lateral dimension of 1 - 10 µm and a thickness of ~ 68 nm were deposited. The oxygen and aluminum stoichiometric ratio for amorphous Al₂O₃ films has been measured by EDX,SIMs and RBS to be ~ 1.5 ± 0.1, demonstrating that negligible levels of impurities and oxygen vacancies exist in the films. 

In addition, Ga₂O₃ thin films were deposited on flexible PET substrate using MALD. The crystallinity of β-Ga₂O_3­ thin film after post-annealing with rapid thermal anneal system was investigated by X-ray diffraction and transmission electron microscope. From Tauc law, the optical bandgap of Ga₂O₃ thin film was calculated to be ~ 4.9eV, corresponding to 254 nm illumination. As a proof-of-concept, deep ultraviolet (DUV) photodetector was fabricated and the I-V characteristics were measured with dark current and wavelength selectivity under DUV illumination.