Electrical Propetries Study Of Compound Semiconductor Under High Pressure

In this paper, we utilize high pressure in situ electrical measurements based ondiamond anvil cell to measure multiple electrical parameters, and combine with thefirst principles calculations to systematically study the pressure dependences ofresistivity, Hall coefficient, carrier concentration, mobility, and activation energy ofcompound semiconductor SnO, Ag2S, Bi2Te3, Bi2Se3, and Sb2Te3to show the chargecarrier transport mechanism in the conduction and provide some guidance andsuggestion for the practical application of materials. Detailed experimental andtheoretical results are as follows:1. We have performed high pressure in situ resistivity, Hall-effect measurements,the temperature dependent resistivity measurements, and the first-principlescalculations in SnO under high pressure to obtain the pressure dependences ofresistivity, Hall coefficient, carrier concentration, and mobility for discussing itscharge carrier transport properties. Hall coefficient becomes negative from positive at1.3GPa, indicating that SnO undergoes a transformation from the hole-dominant toelectron-dominant conduction herein. Subsequently, a pressure-induced phasetransition of SnO at2-3GPa has also been observed by the results of the pressuredependence of electrical resistivity, Hall coefficient, carrier concentration, andmobility. Furthermore, a semiconductor-to-metal transition of SnO around5GPa hasbeen observed by the measurements of the temperature dependent resistivity at severalpressures. In addition, the calculations on band structures of SnO reveal that theclosure of the indirect fundamental gap results in the semiconductor-to-metaltransition under high pressure, and the results of total and partial density of statesindicate that the closure of the indirect fundamental gap is mostly caused by theinteraction of Sn-5s and-5p states with O-2p states at the Fermi level.2、 We have carried out high pressure in situ Hall-effect measurements,temperature dependent resistivity measurements, and the first-principles calculationson Ag2S. Hall-effect results indicate that the two structural phase transitions on Ag2Scan induce noticeable changes in the resistivity, Hall coefficient, carrier concentration, and mobility. Combining the resistivity measurement with the first-principlescalculations, we discovered that the donor level during HP2phase is gradually faraway from the conduction-band minimum, which was caused that the band-gap ofHP2phase suddenly collapses at15GPa and partial covalent bonds dissociate tomake holes play a leading role in the electrical transport process, that is Ag2Sundergoes a majority carrier-type inversion from electrons to holes. The temperaturedependent resistivity indicates that Ag2S presents a metallic-like conduction due to thecomplete ionization of impurities and defects below15.8GPa, and subsequently Ag2Stransforms into a deep acceptor semiconductor.3. We have performed high pressure in situ Hall-effect and temperaturedependent resistivity measurements on Bi2Te3, Bi2Se3, and Sb2Te3under highpressure.(1) Three high pressure structural phase transitions of Bi2Te3have been found toinduce the discontinuous changes in resistivity, Hall coefficient, carrier concentration,and mobility at8,12and17.8GPa. In addition, the electronic topological transitionand carrier-type inversion of Bi2Te3have been confirmed at4GPa and8GPa,respectively. Subsequently, the semiconductor-to-metal transition of Bi2Te3has beenobserved at9.2GPa indicating that Bi2Te3undergoes a closure of bulk gap. Beyondthe metallic pressure, the insulating gap vanishes and the gapless surface state isobscured by the metallic bulk state. Thus, the topological property of Bi2Te3disappears after the metallization.(2) High pressure structural and electronic phase transitions of Bi2Se3have beenfound to induce the discontinuous changes in resistivity, Hall coefficient, carrierconcentration, and mobility at5.8,12.9,16.8and21.7GPa. Particularly, theelectronic topological transition has been proved to derive from the topologicalchange of the band extremum near the Fermi surface. Subsequently, thesemiconductor-to-metal transition of Bi2Se3has been observed at9.7GPa, indicatingthe disappearance of topological property. Above all, the pressure-tuned physicalproperty evolution information on Bi2Se3will provide the essential guideline for thenext practical application study.(3) High pressure structural and electronic phase transitions of Sb2Te3have beenfound to induce the discontinuous changes in resistivity, Hall coefficient, carrierconcentration, and mobility at3.8,9.1,14.9, and20.8GPa. Variable-temperatureresistivity measurement has indicated that increasing pressure may enhance the insulation of Sb2Te3. And the metallization doesn’t occur in Sb2Te3. In addition, underhigh pressure the resistivity of Sb2Te3presents the obvious change, which providessome reasonable guidance for the application of PCM material.By comparing electrical properties of Bi2Te3, Bi2Se3, and Sb2Te3under highpressure, we found that every electronic and structural phase transition can inducediscontinuous changes in electrical transport parameters (resistivity, Hall coefficient,carrier concentration, and mobility) of Bi2Te3, Bi2Se3, and Sb2Te3. But the variablepressure with electrical transport parameters of Bi2Te3, Bi2Se3, and Sb2Te3in the samestructure is obvious different. Meanwhile, the temperature dependent resistivity ofBi2Te3, Bi2Se3, and Sb2Te3is also different at representative pressures.From microscopics, the above situation is due to the difference of chemicalbonds and structure stability caused by the discrepancy of Bi, Sb, Se, and Te atomicradius and electronegativity. Atomic radius of Bi, Sb, Se, and Te () is1.60,1.45,1.40, and1.45. And their electronegativity is2.02,2.05,2.10, and2.55. On the otherhand, the discrepancy of electrical transportation among them may arise from thedifferent energy gap and impurities (or defects) concentration.