Preparation Of Ga₂O₃ Nanostructured Materials And Their UV Detectors

The responsivity of crystalline Ga₂O₃ thin film based ultra-violet(UV)detector could be significantly influenced by the massive defects induced by high temperature growth,and more efforts have been focus on one-dimensional nanomaterials due to the high specific surface area,strong scattering effects,and the built-in electric field of the nanomaterial itself,which can increase the photocurrent and responsivity of the prepared UV detecting devices.Reports show that Ga₂O₃ nanomaterials are mainly obtained by chemical vapor deposition(CVD)method,which could limit further device application due to high growth temperature.The solution method could be simply processed and low cost,but lacks of repeatability and controllability.The pulsed laser deposition(PLD)method could achieve low temperature growth,but with harsh requirement on the preparation of nanostructure growth.Thus,unclear mechanism still exist on the Ga₂O₃ nanostructured materials.In this article,we aim to fabricate Ga₂O₃nanostructured materials with good morphology and UV detecting devices with excellent performance by using both PLD method and the solution method.In this thesis,we firstly fabricated Ga₂O₃ nanorods and nanowires via PLD method and investigated the nanotopographycontroled by experimental methods by adjusting the pressure in the cavity and the flow of Ar gas,and then successfully achieved MSM-type UV detecting device with Ga₂O₃ nanostructure.Secondly,we grew Ga₂O₃ nanorod array by solution method and investigated the morphology of the nanorodsby adjusting the experimental conditions such as the annealing temperature,and then processed the study on the MSM-type UV detecting device based on Ga₂O₃ nanorod array.The main results we obtained are as follows:(1)Under low oxygen pressure conditions,we could use PLD method to obtain Ga₂O₃nanorod structures on c-Al₂O₃(0001)substrates,and the MSM-type UV detecting device based on Ga₂O₃ nanorods was obtained.Nanorods were prepared by oxygen pressure conditions of5×10^-2 Pa,due to the large specific surface area and strong scattering effect of the nanorod structure,the corresponding UV detecting device has a higher light response(with a bias voltage of 25 V,the peak response to 235 nm solar-blind UV light is 23.1 A/W).Furthermore,Ga₂O₃ nanorods of different sizes were obtained by adding argon gas to adjust the pressure,which could change the energy of the reaction particles.At the gas pressure conditions of 0.11Pa,we obtained the density of the nanorods was greater,and the corresponding UV detecting device shows that the peak response to 230 nm is 42.68 A/W,with a bias voltage of 25 V.(2)We used Au nanoparticles as seed layers to induce growth of the Ga₂O₃nanowires,by changing the thickness of the deposited Au layer,including 1 nm,3 nm,5 nm and 10 nm,as the diameter and density of the nucleation points of the Ga₂O₃nanowires are changed,so as to control the morphology of the nanowires.Moreover,by adjusting the change in the Ar flow rate in the vacuum chamber,we can also make the change in the pressure in the chamber to obtain nanowires of different sizes or densities.As the Ar flow rate increases,the diameter and density of the nanowires increase.In those ultraviolet detecting device of the obtained nanowires,the highest responsivity is 5.12 m A/W,and the minimum dark current can reach1.1×10^-9 A,and the maximum light-dark current ratio is 30.(3)We obtained the Ga OOH nanorod array by hydrothermal method and placed it in an annealing furnace for annealing treatment,so that we obtained the Ga₂O₃ nanorod array.It was found that the crystal structure of the sample obtained under annealing conditions at 500?C and 600?C was transformed into?-Ga₂O₃,and the crystal phase obtained at 700?C,800?C,900?C and 1000?C was?-Ga₂O₃.What was more,the annealed nanorods were in the shape of quadrangular prisms,and many nanoparticles appeared on the surface of the prisms.And the properties of the UV detectors prepared by them:the corresponding crystal phase under the annealing condition at 600?C is?-Ga₂O₃,and its responsivity is 0.4 m A/W,and the light-dark current ratio is 2;The corresponding crystal phase is?-Ga₂O₃ with 800?C annealing conditions,and its responsivity is the highest in a nanorod array with a crystal phase of?-Ga₂O₃,which is2.7 m A/W,and the light-dark current ratio is 40.