The Thermal Properties Of GaAs/AlAs Superlattice

In this dissertation, the research on the superlattice including the preparation, properties and application is reviewed. And then we study the thermal properties of GaAs/AlAs superlattice by lattice dynamics with force-constant matrix and first principle. The vibrational properties and thermal transport mechanisms are discussed. Based on the lattice dynamics with force-constant matrix, we investigated the vibrational properties of GaAs/AlAs superlattice. It is fount that the distinct phonons branches of ( n×n)GaAs/AlAs superlattice are 4n of which 2n modes are nondegenerate and the other2n modes are doubly degenerate. In the low frequency of densities of states of phonons, there are less Von Hove sharps than in the high frequency. The numbers the Von Hove sharps increase with increasing of the number of monolayers in a unit period. And Von Hove sharps move to the high-frequency region when the number of of monolayers in a unit period.In virtue of phonons dispersion relation, we discuss the specific heat of ( n×n)GaAs/AlAs superlattice at different temperatures. The results show that the specific heats of ( n×n)GaAs/AlAs superlattice increases dramatically with increasing of the temperature at low temperature. The specific heat would increases slowly at higher temperature and arrives the universal classical value about 24.9 J .m ol ? 1 .K? 1. The specific heat of GaAs/AlAs superlattice is not change largely with the number of monolayers in a unit period.We presented a theoretical model to calculate the thermal conductivity of GaAs/AlAs superlattice considering three-phonon Umklapp process. It is shown that thermal conductivity of GaAs/AlAs superlattice increases with the increase of temperature at low temperature, and would show a peak behaviour at about 65 K before falling off at higher temperature. It is found that the behaviour of temperature dependence of thermal conductivity can attribute to the boundary scattering and the Umklapp scattering process in GaAs/AlAs superlattice. At low temperature, thermal transport in GaAs/AlAs superlattice is dominated by the phonon boundary scattering. As temperature increases, Umklapp scattering process becomes strong to make the main contribution to the heat transfer.The dispersion relation and DOS of phonons in the cross-plane direction and the specific heat of super-thin (1×1)GaAs/AlAs superlattice are calculated by first principle. The acoustic modes of phonons dispersion relation are probability of the vector q , and their group velocities in the [001] direction are vL = 5.1k m /s and vT = 3.6 km /s, respectively. There are two frequency gap, 6.6THz-7.1THz and...