Research On Heat Conduction Control Of Silicon Germanium Nanostructure

The fast development on microelectronics technology has greatly improved the level of device integration,so the thermal management of microelectronic devices has become more and more important and drove the thermal transport study to the micro-nano scale.The silicon/germanium(Si/Ge)material system plays a key role in appli-cations such as chips,microwave devices and sensors,and good thermal properties are essential for achieving high-performance devices.Whether in the process of material preparation or device fabrication,interfaces and defects are unavoidable.Especially,in the micro-nano scale,the effects of interfaces and defects on thermal performance cannot be neglected.Although there have been many studies on the thermal transport in Si/Ge nanos-tructures,most of them are theoretical predictions,either at the micrometer scale,or at the nanoscale.A study covering from microscale to nanoscale is lacking.There have been few systematic studies on the thermal transport and its regulation from the micrometer scale to the nanometer scale,especially the heat conduction across inter-faces at the scale of 100 nanometers.Based on theoretical and practical values,we select silicon/germanium semiconductor materials as the object,design various sili-con/germanium nanostructures and use molecular beam epitaxy(MBE)to grow a se-ries of samples for this study.The out-of-plane thermal conductivity and interfacial thermal conductance are measured using the Time-domain thermal reflectance(TDTR)method.The thermal transport properties of the silicon/germanium heterostructures are studied in depth,and the following results are obtained:1.The thermal transport properties of Ge films grown on Si are systematically studied.A series of 500 nm thick Ge films were obtained by low temperature growth followed by controlling the annealing temperature.TDTR experimental results show the thermal conductivity of the Ge film is related to its quality.Debye-Callaway model was used to fit the experimental results,and demonstrated that there was a competition between dislocation scattering and alloy scattering in the Ge films.We analyzed the influence of the two different scattering mechanisms,and then discussed the scattering mechanisms in detail.Based on the results,the optimized annealing temperature for the Ge films(around 700?)is determined.By adjusting the thickness of the Ge film,we observed ballistic transport in the ultra-thin(?12 nm)Ge films.2.Benefit from the precise control of the Ge film growth,we obtained a series of Ge nanodots with different morphologies to explore the control by artificial microstruc-tures.The effect and modulation mechanism of Ge nanodots on the thermal transport properties at the Al/Si interface were studied.We first studied the effect of interface treatment and growth technique of aluminum(Al)films on the thermal transport,and found that efficient surface cleaning can increase the interfacial thermal conductance by more than two times.We used the epitaxial Al films grown by MBE on Si to obtain atomically flat interfaces,and obtained an ultra-high Al/Si interfacial thermal conduc-tance of 700 MW·m^-2·K^-1,which was much higher than the theoretical value(460MW·m^-2·K^-1)and experimental results(100 MW·m^-2·K^-1)reported so far.We fur-ther obtained Ge nanodots with different sizes and morphologies through MBE control.Interestingly,when the surface coverage is within30%,the interfacial thermal conduc-tance is almost independent to the size of the nanodots.These results provide more experimental support and research ideas for future research on the thermal transport by interface regulation.Certain nanostructures can be appropriately introduced into the silicon-germanium device structures to satisfy more performance requirements with-out affecting heat dissipation.This provides more flexibility for device integration and on-chip processes.The results have not only enriched the research of the micro-nano scale regulation on thermal transport properties,but also provide more guidance for solving key issues in nanoelectronics,nanocomposites,energy conversion,etc.,and will help to promote the microelectronic device applications.