Study On Electric Transport Properties And Metallization Of InSe Under High Pressure

InSe belongs to the III-VI semiconductors. Due to the strong anisotropicbehavior presented by its chemical bonds, InSe has good photoelectric properties andtherefore has been found with many valuable applications in relevant fields and hasattracted intensive interest. In this thesis, we put more focus on the detailed study ofelectrical transport properties of InSe under high pressure. By the using of in-situresistivity measurement method based on diamond anvil cell (DAC) technique, wehave mainly studied the pressure dependence of resistivity of InSe under highpressure; through measuring the temperature dependence of resistivity under variouspressure, we have investigated the pressure induced metallization of InSe; through thein-situ Hall effect measurement, we have gained the pressure dependent charge carrierconcentration, Hall coefficient and mobility of InSe under high pressure; and we alsocalculated the energy band structure of InSe under high pressure with moduleCASTEP. Results in detail are listed as follow:1. For in-situ resistivity measurement under high pressure, we have integratedmicrocircuit on a diamond anvil by thin film deposition and photo lithographyingtechnique and obtained the pressure dependence of InSe resistivity and thetemperature dependence of InSe resistivity under different pressures, through whichwe can conclude that (1) as InSe transforms from initial rhombohedral layered phaseP1(InSe-I) to a metallic rocksalt cubic phase P3(InSe-Ⅲ) at12GPa, the pressuredependence of resistivity changed obviously, and (2) in the pressure ranges of0-5GPa and6-12GPa, the electric transport properties of InSe is of semiconductor;meanwhile (3) in the pressure range5-6GPa and after12GPa, InSe has metallictransport properties, and the pressure induced metallization of InSe at12GPa resultsfrom the pressure induced structural phase transition. 2. By using the in-situ DAC based Hall effect measurement, we have obtainedthe pressure dependent, charge carrier concentration, mobility and Hall coefficient ofInSe. The results suggested that:(1) below6.6GPa, the charge carrier concentrationand the mobility of InSe generally increased with pressure but the resistivitydecreased. Above6.6GPa, the charge carrier concentration increased very fast withthe pressure, but the mobility decreased sharply. Meanwhile, the reversal of sign ofthe Hall coefficient from positive to minus indicates that InSe transformed from aP-type semiconductor to a N-type semiconductor.(2) Above9.9GPa, the mobility ofInSe decreases to the lowest, while the carrier concentration increases to a maximum,and occurs discontinuous change. In the pressure range6.9-10GPa, the carrierconcentration increases of three orders of magnitude, and the mobility decreases oftwo orders of magnitude, while the resistivity decreases of two orders of magnitude,however, the increases of the carrier concentration is the dominant effect producingthe decrease of the resistivity.3. We conducted the theoretical calculation of energy band structure of InSe withmodule CASTEP. It was indicated that (1) at4GPa the rhombohedral layered phaseP1(InSe-I) was a direct semiconductor and band gap width was0.599eV; and (2) at7GPa, monoclinic phase P2(InSe-Ⅱ) was an indirect semiconductor and band gap was0.927eV. The analysis showed that both InSe-I and InSe-Ⅱ phases weresemiconductors, and the transition between them is a direct-to-indirect semiconductortransition.In conclusion, in-situ resistivity measurement and in-situ Hall effectmeasurement under high pressure have been conducted on InSe. In-situ resistivitymeasurement under high pressure can reflect the structural phase transition of InSefrom initial rhombohedral layered phase P1(InSe-I) to a metallic rocksalt cubic phaseP3(InSe-Ⅲ) and InSe-Ⅲ shows metallic characteristics. We have also studied thepressure dependence of carrier concentration, mobility, Hall coefficient of InSe andhave found that above6.6GPa InSe transforms from a P-type semiconductor to aN-type semiconductor. With the module CASTEP, we have theoretically calculated the energy band structure of InSe and found that both InSe-I and InSe-Ⅱaresemiconductors, and the transition between them is the type of direct-to-indirect bandgap semiconductor transition.