The performance enhancement of β-Ga2O3 solar-blind photodetector by pulsed laser deposition

Abstract

From the 20th century, the high-sensitivity, high-responsivity photodetectors were attracting much interest due to the rapid expansion of detecting photons. Nowadays, photodetectors gradually become one of the most ubiquitous technology with a diversity of practical applications that range from household devices to another side of the universe. Besides, the world industry is getting closer to industry 4.0 where the smart machinery, smart robots, and smart driverless transport become more popular. These technologies comprise multiple photosensors and cameras so the demand for a high-performance photodetector is necessary than ever. Along with the strong development of photodetector, the material markets become more active. Currently, silicon, germanium, and indium gallium oxides are dominating the photodetector material market. However, these materials with low band gap which is not preferred to produce high-quality ultra-violet photodetectors. In this study, as a part of the research to improve the performance of the UV photodetector, the material, the growth conditions, and the deposition technique and optimization for detector design were discussed. In this case, among wide band gap semiconductors used to fabricate UV photodetector, gallium oxide (Ga2O3) is a promising candidate because of its outstanding properties, including good thermal stability, high break down strength, and a wide band gap. The technique which is more useful in obtaining high-quality Ga2O3 thin films is pulsed laser deposition (PLD). This technique offers several attractive features, such as stoichiometric transfer of material from the target, generation of energetic species, compatibility with background pressure, and well-controlled substrate temperature and oxygen pressure during the deposition process. These outstanding features of PLD contribute a potential direction to optimize the quality of UV photodetector. The first chapter of the thesis deals with the background theories of photodetectors, and Ga2O3. The operation mechanism of photodiodes and their characteristics are discussed. In chapter 2, the methods used to characterize semiconductor materials and devices are introduced. Some common methods used are X-ray diffraction, scanning electron microscopy, atomic force microscopy, Hall measurement, ultraviolet-visible measurement, X-ray photoelectron spectroscopy, and current-voltage measurement. The working principles and their applications in characterizing materials are described. The influence of oxygen partial pressure and annealing treatment on the properties of the β- Ga2O3 thin films grown by pulsed laser deposition was discussed in chapter 3. Based on X-ray diffraction, the enhancement of crystallinity with annealing treatment, and the increase of oxygen pressure was observed. The conductivity of as-grown Ga2O3 films obtained varied from 7.9 to 2.1mScm-1 for a variation in PO2 in the range 0-50 mTorr, and that given conductivity increased after annealing at 600. Also, the optical band gap and the defects in Ga2O3 can be well-controlled by pulsed laser deposition to optimize the high-quality thin films. In chapter 4, the design and optimization of the photodetector performance were investigated. The β- Ga2O3 thin films were deposited on a glass substrate under various oxygen partial pressures from 0 to 50 mTorr by pulsed laser deposition, and the high performance of the β- Ga2O3 detector grown at the oxygen partial pressure of 50 mTorr might be due to the reduction of oxygen vacancies by increasing oxygen during the deposition. The last chapter studied the effect of the adhesion titanium layer on the ductility of Ga2O3 photodetector on the flexible substrate. With inserting the titanium adhesion layer under the electrodes, the deformation and cracks were suppressed, and then enhance sharply the photoresponsivity of the detector after several bending cycles.