| Gallium Telluride is a Gallium sulfur compound in the layered semiconductor of group Ⅲ–Ⅵ compounds.Because of its unique optical and electrical properties,it can be widely used in field effect transistors,memory switches,photodetectors and solar cells and other fields.Adjusting the structure and band gap of GaTe by physical and chemical has become an important research direction to improve its photoelectric performance.In this thesis,GaTe is taken as the research object,the measurement microcircuit is fabricated by manual wiring with a diamond anvil cell(DAC)device.In-situ resistivity and AC impedance spectroscopy measurements are carried out in the pressure range of 0-30 GPa.Meanwhile,we studied the electrical properties of GaTe samples under high pressure by using first-principles theoretical calculation.High pressure in-situ resistivity measurements of GaTe samples were carried out.It is found that during the pressurization process in the range of 0-30 GPa,the resistivity of the sample decreases by 9 orders of magnitude,and discontinuous changes occur around 4.8 GPa,10 GPa and 11 GPa,respectively.In the range of 0-4.8 GPa,the resistivity and slope decrease gradually.After 4.8 GPa,the resistivity decreased sharply,and gradually decreased and leveled off after 11.4 GPa.The resistivity anomaly is most obvious in the range of 4.8 GPa-11.4 GPa.According to the results of Schwarz et al.’s high pressure XRD experiment in 2005,we suggested that this abnormal change is related to the change of crystal structure of the sample.In the process of pressure relief,the resistivity does not recover to the initial order of magnitude,showing an irreversible change.It is found that the resistivity decreased with the increase of temperature when the pressure is less than 10 GPa,presenting semiconductor characteristics.When the pressure is above 11.7 GPa,the resistivity increased with the increase of temperature,showing typical metallic characteristics.The experimental results show that the GaTe sample has a pressure induced metallization phase transition in the pressure range of 10 GPa-11.7 GPa.High pressure AC impedance spectrum of GaTe samples were carried out.It is found that the semi-arc diameter of grain resistance and the total resistance decrease in the range of 0 GPa-11.3 GPa.From 4.1 GPa to 5.0 GPa,the grain resistivity changes slowly.Above 5GPa,the resistance suddenly decreased to 10.9 GPa and tended to remain unchanged.The relaxation peak also showed the same trend,but the relaxation frequency moved slowly to the right between 5.0 GPa and 10.9GPa.Combined with the measurement results and analysis of in-situ resistivity,it can be inferred that the main contribution of the process of high pressure electrical transport is grain,and the conduction mechanism is electronic conduction.GaTe was in the C2/m and Fm3 m mixed phase at 4.8 GPa until the new Fm3 m phase was generated in the pressure range of 10 GPa-11.7 GPa.The high pressure resulted in the rearrangement of atomic space in the sample,the change of lattice symmetry,the change of atomic vibration frequency,and the change of total resistance and relaxation frequency.First principles calculations of GaTe are carried out.The calculations of enthalpy difference between C2/m and Fm3 m phase show that GaTe begins to undergo phase transition at 4.5 GPa.The calculations of energy band indicate that C2/m phase is a direct bandgap semiconductor.The energy band of Fm3 m phase across Fermi level,the conduction band and valence band overlap,showing metallic characteristics.At this point,it underwent a phase transition to a complete metallic phase.The calculation of protocell volume under high pressure of GaTe showed that the volume collapsed during the structural transformation,indicating that the phase transition is a first-order phase transition.The results show that the 5p,4s and 4p states of atoms across the Fermi energy level and have the strong hybridization under the action of pressure. |
PDF Full Text Request