Thermal/Mechanical/Structural Properties of Polycrystalline Diamond and Novel Layered Materials for Electronic Devices

  • Yan Zhou

Student thesis: Doctoral ThesisDoctor of Philosophy (PhD)


Under the ever-increasing requirements of higher power and higher radio-frequency in future power electronics and telecommunication applications, the thermal management of gallium nitride (GaN) based devices becomes crucial, this can be significantly improved by integrating high thermal conductivity diamond into the devices to enhance the extraction of waste heat. An important consideration is the thermal boundary resistance (TBR) of the GaN/diamond interface, which forms a bottleneck for heat transport. For incorporation as a substrate, the thermal properties of this interface and of the polycrystalline diamond (PCD) grown onto GaN using various controlled barrier layers under different growth conditions are investigated and systematically compared; SiN barrier layers were found normally producing lower TBR with a smoother interface formed. For integration of PCD as a top-side heat spreader onto AlGaN/GaN-on-Si HEMT, its thermal performance was systematically evaluated by time-domain thermoreflectance and ANSYS simulation; at best a 15% reduction in peak temperature was obtained when only the source-drain opening of a passivated AlGaN/GaN-on-Si HEMT is overgrown with PCD.
Meanwhile, next generation higher compacted electronics for future communications or computing require sub-10-nm or even atomic dimension scaling, incorporation of a new two-dimensional (2D) materials channel then has emerged as a highly attractive solution to address this challenge. Gallium telluride (GaTe) is a 2D layered material that recently raised considerable interests due to its unique optoelectronic properties but is still under extensive exploration of its fundamental properties for potential applications. The pressure-dependent solid-state properties of GaTe multilayers up to 46 GPa were firstly investigated. A strong Raman mode anisotropic splitting started at ~6.5 GPa originating from phase transition was first-time revealed and understood through first-principles calculations. Then the thermal properties of free-standing GaTe multilayers were studied mainly by micro-Raman opto-thermography, displaying an anisotropic and very low thermal conductivities along the in-plane armchair and zigzag orientations. Moreover, the mechanical properties of both SiO2/Si substrates supported and free-standing GaTe multilayers were investigated mainly through nanoindentation. Concurrence of multiple pop-ins and load-drops in the loading curve were found, likely originating from interlayer sliding within the GaTe multilayer. These pressure-tuned behaviors, thermal and mechanical properties of GaTe multilayers enable new insights for investigating and manipulating the anisotropic solid-state properties of potential device applications and other low symmetry layered materials.
Date of Award25 Sept 2018
Original languageEnglish
Awarding Institution
  • University of Bristol
SupervisorMartin H H Kuball (Supervisor)

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