Molecular Dynamics Study Of Heat Transport Characteristics In Gallium Arsenide(GaAs) Nanowires

With the increasing miniaturization and integration of microelectronic devices,the characteristic size of field effect transistors(FET)has reached to 10 nm.The thermal effect caused by high power density becomes the bottleneck of further miniaturization of FET.Low-dimensional GaAs semiconductors have important applications in solar cells,FET,light-emitting devices and other energy fields.In order to understand the microscopic heat transport mechanism of GaAs nanowires(NW),an equilibrium molecular dynamics(MD)method is used to simulate the lattice thermal conductivity.Based on the frequency-domain characteristics of the phonon vibration density of states and the time-domain characteristics of the heat current autocorrelation function,the influence of scale,temperature,point defects and additional load on the lattice thermal conductivity of GaAs NW was studied.The lattice thermal conductivity of GaAs NW has significant scale effect.The simulation results show that the lattice thermal conductivity of the GaAs NWs are always increase first and then gradually stabilizes with the increase of GaAs nanowires' length and diameter.The reason is that as the size increases,the phonon confinement effect gradually weakens,so the lattice thermal conductivity of GaAs NW raised.As the size continues to increases,the phonon wavelength reaches the phonon mean free path at that temperature,so after that the lattice thermal conductivity tends to a constant value.The lattice thermal conductivity of GaAs NW has obvious temperature effect.The simulation results show that with the rising temperature,the lattice thermal conductivity of GaAs NWs increase at the beginning and then decrease gradually,reaching the maximum value near the temperature of 300 K.The reason is that high-temperature causing more high-frequency phonons are excited.High-frequency phonons scattering process dominates the thermal transport,adding more energy transfer channels,so the lattice thermal conductivity increases.As the temperature increasing further,the process of phonon U-scattering gradually dominates,but the U-scattering is not conducive to energy transfer,therefore the lattice thermal conductivity decreases gradually.The lattice thermal conductivity of GaAs NW has clear point defect effect.The simulation results show that the lattice thermal conductivity of GaAs NWs decrease with the increase of vacancies and impurity atoms.The reason is that the increase of crystal point defects will destroy the original structure of the crystal lattice,resulting in energy transfer hindrance,causing a certain degree of surface effect,phonon confinement effect and phonon resonant scattering,so its lattice thermal conductivity will gradually decrease.Compressive stress and torsional stress can change the lattice thermal conductivity of GaAs nanowire.The simulation results show that the lattice thermal conductivity of GaAs nanowire is reduced by both compressive stress and torsional load.The reason is that both compressive stress and torsional load produce additional stress on nanowires,and the torsional force also produces strain.These stress and strain change even destroy the lattice structure of GaAs,so that stunted the energy transfer.Compressive stress also increases the phonon confinement effect of nanowires,and the surface effect of nanowires is also changed by torsional stress,so the lattice thermal conductivity of nanowires decreases.