The Research Of Preparation And Hydrogen Annealing Of Gallium Oxide Thin Films

Ga₂O₃ is one of the third generation wide band gap semiconductor materials with a band gap of 4.2-4.9eV. There are five crystal structure of Ga₂O₃, containing ?-Ga₂O₃,?-Ga₂O₃, ?-Ga₂O₃,?-Ga₂O₃ and ?-Ga₂O₃.The ?-Ga₂O₃ has the highest thermal stability among the five crystal, and its breakdown field strength is up to 8 MV/cm. The thermal stability of ?-Ga₂O₃ is after the ? phase. Unintentionally doped material exhibits an insulating or weak n-type nature, the n-type Ga₂O₃ can be obtained by Sn and Si doping. It has important applied potentiality in transparent conductive films, high-power devices, UV detectors and so on. There are a lot of ways to fabricate the Ga₂O₃ material, such as magnetron sputtering, pulsed laser deposition, spray pyrolysis technique, electron beam evaporation and mental organic chemical vapor deposition, etc. The MOCVD technique has been widely used, because it has the characteristics of accurate control and can be widely used in industrial production. In this paper, the ?-Ga₂O₃ and ?-Ga₂O₃ thin film were fabricated by MOCVD and studied the effect of the hydrogen annealing on the properties of ?-Ga₂O₃ film. The content includes the following two parts:1. We fabricated the ?-Ga₂O₃ thin film on GaAs substrate by the MOCVD technique and studied the effect of the growth pressure on the properties of the materials. The surface morphology, crystal quality and electrical properties were characterized by means of SEM, XRD and ?-? tests. It was found that the growth pressure affected the rate of the epitaxial growth and the preferred orientation of the Ga₂O₃. The Ga₂O₃ thin film couldn't be tested by the Hall system due to the high resistance characteristics, so we fabricated the ?-Ga₂O₃/ n-GaAs/Au structure to test its electrical characteristic. Finally, the Ga₂O₃ thin films grown by 5000Pa was found to have high crystal quality.2. The ?-Ga₂O₃ thin films were fabricated by the MOCVD technique. The samples were annealed at different temperatures in hydrogen atmosphere. The crystal quality, optical properties and electrical properties of the samples annealed were investigated by means of XRD, SEM, UV-visible spectrophotometer and semiconductor characteristic analyzer. Experimental results showed that the crystal structure of the samples began to change from ? to ? phase at 800?, and completely transformed into ? phase at 900?. The Ga₂O₃ thin film was completely decomposed in hydrogen atmosphere when the annealing temperature was increased to 1000?. The crystal grain of the film surface gradually became larger in the process of phase transformation. The surface morphology of the thin films changed from granules to thin sheets when the film was fully transformed to ? phase. The average transmittance in the visible region ?350nm-800nm? was greater than 90% before and after the annealing process, but the transmission curve shape was slightly different before and after the phase change. The electrical characteristics test of MSM device showed that the conductivity of Ga₂O₃ thin films gradually increased. We believed that this phenomenon might be due to the incremental density of oxygen vacancies formed by the reaction of hydrogen and Ga₂O₃ on the surface of the films with the increase of annealing temperature.