Electrical Transport Properties Of GaAs Under High Pressure

In this thesis, we carried out the alternating-current impedance spectrum measurements and in situ electrical resistivity measurements of III-V compound semiconductor gallium arsenide (GaAs) under high pressure, by fabricating a microcircuit on the diamond anvil cell (DAC) which was achieved by magnetron sputtering technology and film photolithographic technique. Meanwhile, we analyzed these properties of GaAs sample by using first-principles calculations to explain the micro-mechanism of structural phase transition and metallization. Study results are listed as follow:Firstly, high-pressure AC impedance spectroscopy of GaAs sample:only observed the bulk transport property i n the experiment. From12.3GPa to13.0GPa, the resistance sharply decreased by two orders of magnitude, the bulk relaxation peaks move to significantly higher frequencies, and the relaxation strength sharply decreases. The sudden change in resistance and relaxation frequency was result from the structural phase transition from the zbâ†'Cmcm structural phase transition.Secondly, high-pressure in situ electrical resistivity of GaAs sample:during the compression process, the electrical resistivity sharply decreased by three orders of magnitude from12.0GPa to13.0GPa. The sudden change in the electrical resistivity was typical characteristic of phase transition from zb phase to Cmcm phase. The atomic position rearrangement of GaAs sample caused carrier concentration increasing and conductivity enhancing during phase transformation under high pressure. During the decompression process, a rapid resistivity increase of about three orders of magnitude was observed at approximately6.0GPa. This phenomenon was attributed to the phase-transition from Cmcm phase to zb phase.Thirdly, the temperature dependence of the electrical resistivity measurements of GaAs sample under high pressure:The results showed that the electrical resistivity decreased with increasing temperature below12.0GPa. This trend indicated that the sample showed a semiconductor behavior. Above12.0GPa, the electrical resistivity showed the positive relationship with temperature. This finding indicates that the sample showed a metallic behavior. Zb transform to Cmcm by the abnormal electrical resistivity is a typical semiconductor-to-metal transition. The activation energy can be obtained from the temperature dependence of the electrical resistivity. Between70and200K, the activation energy is relatively low; thus, the carriers are readily excited to a lower impurity level. Between200K and room temperature, further excitation of the carriers to a higher impurity level becomes difficult because of the increase in the activation energy. When the pressure close to13.0GPa, the difference value of two part activation energies close to zero, the typical behavior of a semiconductor would vanish, accompanied by the disappearance of energy barriers.Fourthly, the first-principles calculations of GaAs sample:the zb phase transforms into the Cmcm phase at12.0GPa from the changing enthalpy vs. pressure relationships of the zb and Cmcm phases. The calculated energy band structure indicated that the band gap across the Fermi level, Cmcm phase is metallic. The calculated DOS indicate the pressure-induced conduction bands cross the Fermi level and the strong hybridization among the Ga-4s, Ga-4p, As-4s, and As-4p states, in Cmcm phase. The results of the difference charge density calculations indicate that exhibits strong electron localization in the zb phase, the covalent properties are the primary contribution. In the Cmcm phase, the covalent properties exist with the metallic properties, the increase in the metallic properties as the pressure increases. Cmcm phase exhibits a metallic behavior.