The Thermal Transport Property Of Perovskite Oxide Thin Films And Heterointerfaces Studied By Time-domain Thermoreflectance

With the constant improvement on the electronic device integration,the reduction in dimensions and the increasing portion of the interfaces,heat management has become a critical issue.Therefore,it is important to study the thermal transport properties of materials,especially the heat transport in thin films and at interfaces.With abundant structures,oxides almost cover all the electrical properties,like conductors,semiconductors and insulators.As perovskite oxides have similar structures and abundant physical properties,they are suitable for making heterogeneous structures,and can be applied to high frequency oscillators,and complex logic units,etc.In this thesis,we have studied the thermal transport properties of several perovskite oxide thin films and their heterointerfaces.ReAlO3/SrTiO3(Re=La,Nd,Sm,Gd)heterostructures were grown using pulsed laser deposition(PLD).We use time-domain thermoreflectance(TDTR)to study the thermal transport properties.Major conclusions are summarized as follows.(1)The thermal transport properties of different ReAlO3 films with different thickness were measured by TDTR.The thermal conductivities of different batches of samples with same thickness show almost the same temperature dependence,which proves the repeatability of the TDTR measurement for this material system.For the samples with thickness under 80 u.c.,the thermal conductivities of these thin films show an size effect:the thermal conductivity decreases as the thickness decreases,indicating the ballistic phonon transport becomes more dominant as the thickness decreases.(2)The interfaces of 10 u.c.LaAlO3/SrTiO3 and 10 u.c.NdAlO3/SrTiO3 with TiO2 terminated SrTiO3 surfaces posses highly mobile two-dimensional electron gases(2DEGs),while 10 u.c.LaAlO3/SrO/SrTiO3,10 u.c.NdAlO3/SrO/SrTiO3,10 u.c.SmAlO3/SrTiO3 and 10 u.c.NdAlO3/SrTiO3 interface show insulating properties.The electron concentrations are 1.23×1014 cm-2 and 3.29×1013 cm--2 at room temperature for 10 u.c.LaAlO3/SrTiO3 and 10 u.c.NdAlO3/SrTiO3,respectively.We measured the thermal transport properties of these heterointerfaces by TDTR.Results show that the 2DEG can enhance the interfacial heat transfer,which means the interaction between two dimensional free electrons and phonons at the interface provides another channel for interfacial heat conduction.The phonon-electron coupling coefficients of 10 u.c.LaAlO3/SrTiO3 and 10 u.c.NdAlO3/SrTiO3 interfaces are 2.09×1014 W/(m3K)and 1.25×1014 W/(m3K),respectively.