Electrical Transport Properties Of GaSb Under High Pressure

Gallium antimonide (GaSb) is a very important III-V semiconductor material. Because of its larger carrier concentration and relatively narrower band gap, GaSb based devices have shown potentiality applications in optical communication devices, high fiequency electronic equipment and infrared imaging sensors. The study about the physics properties of GaSb..especially electrical properties, has to be carried out systematically and exhaustively before it can be employed for large scale device fabrication.In this thesis, we combined the technique of the magnetron sputtering film deposition and photolithography to fabricate a microcircuit which our experiment required on the diamond cell (DAC), and the pressure are generated by DAC device. We used the microcircuit and DAC device to study the electrical transport properties of GaSb under high pressure, including pressure dependence of electrical resistivity, relaxation fiequency, Hall coefficient, carrier concentration and mobility of GaSb. Moreover, we utilize theoretical calculation to analyze the band structure of GaSb.The specific results are listed as follow:1. We conducted in situ the resistivity measurement experiment on GaSb under high pressure. In the compression process, the changing curve of the resistivity with the pressure increasing occurs three discontinuous changes, which were 4.5 GPa,7.0 GPa and 10.0 GPa. Among them the resistivity shows a trend of becoming low at 4.5 GPa and 7.0 GPa, at which have been reported the metallization of GaSb.2. By carried out in situ Hall effect measurement experiment on GaSb under high pressure, we obtained the pressure dependences of Hall coefficient(RH), carrier concentration(n) and mobility(μ). From the atmospheric pressure to 4.5 GPa, the Hall coefficient of GaSb decreases with pressure increasing and changes its sign to negative at 4.5 GPa. That indicates GaSb transforming into p-type semiconductor from n-type around 4.5 GPa. From 4.5 GPa to 7.0 GPa, the carrier concentration decreases with pressure increasing which the led to the decreasing rate of resistivity become samller. From 7.0 GPa to 10.0 GPa, n and μ both Increases with pressure increasing, which result in that the resistivity of GaSb drops rapidy. Above 10,0 GPa, the variation of carrier concentration becomes gentle, indicating n trend to be saturated. So the resistivity of GaSb no longer decreases. But a slight reduction in the mobility of GaSb is observed, which led to a slight increasing of resistivity.3. We carried out in situ the temperature dependence of the resistivity measurement experiment on GaSb under high pressure in order to solve the controversial metallization transition of GsSb. From ambient pressure to 7.0 GPa, the resistivity of GaSb shows a negative reationship with temperature increasing, indicating that GaSb is asemiconductor. Above 7.0 GPa, the resistivity increases with temperature, indicating GaSb becomes metallized arround this pressure. This confirmed that GaSb undergoes a typical semiconductor-to-metal phase transition at 7.0 GPa. Meanwhile, the fitting activation energy occurs a discontinuous changes, and then trend to 0 around 7.0 GPa. They correspond to electronic structure tanasition and metallization transition, respectively.4. The TEM (transmission electron microscope) images of the ZTO samples after decompression from different pressures show that the power sample keep long-range order after 5.0 GPa compressing and the direction os the crystal lattice become disordered state after 10.0 GPa compressing. However, in the pressure range from 10.0 to 25.0 GPa, the grain doesn’t be further refined. This indicates that the refinement of the grain and an increase in boundaries led to the motion of the carrier becoming difficult. so that the resistivity rises up at 10.0 GPa.5. The result of ac impedance spectroscopy measurement at high pressure shows that the resistance of the sample GaSb is consist of the grain and boundary resistance. Before 7.4 GPa, the boundary resistance is greater than the grain resistance, but that reverses at 8.6 GPa. The relaxation frequency always move to the right. The relaxation peak of the grain and boundary change synchronized with their resistance. Because of the value of sample resistance beyond the the measurement range of instrument, we don’t get any valuable data after 8.6 GPa.