The Electrical Transport Properties Of InN Under High Pressure

Indium nitride (InN) material exhibits the highest mobility, electronic driftvelocity and high peak drift velocity, and the lowest electron effective mass among thegroup-III nitrides semiconductor materials, which endows that InN has uniqueadvantages for the applications of High-frequency and High-rate transistors. Giventhat the physical properties of InN, especially its electrical properties is the key factorthat decides the applications worth of its devices, it is very necessary to carry out thestudy of InN systematacially and exhaustively.In our paper, we integrated the film deposition with photolithographic techniqueto fabricate a microcircuit on the diamond anvil cell (DAC), and used the microcircuitfabricated to carry out a series of researches on the electrical transport properties ofInN under high-pressure conditions generated by DAC, including pressure andtemperature dependences of electrical resistivity, Hall coefficient, carrierconcentration and mobility of InN. Meanwhile, we obtained band structures of InN byusing the first-principles calculation.Firstly, we carried out the research on the pressure dependence of electricalresistivity of InN. During the first compression, the electrical resistivity of InNappears a discontinuous change at about11.1GPa, in consistent with other studieswhere InN undergoes a structural phase transition from the wurtzite to rocksalt at12GPa. Thus, it can be concluded that InN shows the discontinuous change in itselectrical resistivity during the structural phase transition from the wurtzite to rocksalt.During the second compression, the similar discontinuous change in the electricalresistivity reoccurs at12.2GPa, which indicates that the pressure induced wurtzite torocksalt phase transition of InN is reversible.Secondly, we carried out in situ Hall effect measurement on InN under highpressure, and then obtained the pressure dependences of Hall coefficient, carrierconcentration and mobility. From ambient pressure to1.5GPa, the Hall coefficient of InN increases with pressure increasing, and then turns to decrease up to4GPa.Subsequently, the Hall coefficient maintains the increasing trend within4GPa to11GPa. Above11GPa, the Hall coefficient remains decreasing up to25GPa. Fromambient pressure to25GPa, the carrier concentration shows almost completelyconsistent trend with Hall coefficient. On the other hand, the mobility appears nearlycompletely opposite variation with Hall coefficient and carrier concentration.At11GPa, these three electrical parameters all show discontinuous changes,indicating that the wurtzite to rocksalt phase transition of InN could result in a seriesof changes in electrical transport parameters. And most particularly, these threeelectrical parameters also present the obvious anomalies at around9GPa, indicatingan isostructural phase transition of InN.Thirdly, we studied the temperature dependence of electrical resistivity of InN atseveral pressures. In the whole observed pressure region, the electrical resistivity ofInN increases with temperature increasing, in other words, InN presents anunexpected metallic-like conductive behavior. In our measured temperature region（100K—300K）, the increasing of temperature produces no effect on the carrierconcentration of InN sample, indicating that electrical resistivity is, therefore, solelydetermined by the carrier mobility. Thus, the decrease in the carrier mobility of InNsample, at last, induces the increase in its electrical resistivity. In addition, the abruptchange in the temperature coefficient of InN at10GPa is consistent with the wurtziteto rocksalt phase transition herein.Fourthly, we performed the first-principles ultrasoft pseudopotential bandstructure calculations on InN. At ambient pressure, the wurtzite phase InN is asemiconductor with a direct band gap of0.08eV, and the calculated band gap in thewurtzite phase smoothly increases with pressure increasing. After the structural phasetransition at12GPa, the rocksalt phase InN is a semiconductor with an indirect bandgap of0.33eV and the band gap shows an obvious increase with pressure increasing.Both the calculated band gap and the experimental electrical resistivity generallyshow a strikingly similar variation with pressure increasing. Before the structuralphase transition, the sluggish increase in the band gap with pressure increasing gives rise to the decrease in the electron mobility, which results in the increase in theelectrical resistivity. After the structural phase transition, the rapid increase in theband gap with pressure increasing leads to the decrease in the electron concentration,which is the dominant effect inducing the obvious increase in the electrical resistivity.