Kristal yapılarda ısınma ile tetiklenen termal boyut etkileri için basitleştirilmiş modellerin kapsamlı çalışması

High-performance nano- and microscale devices are increasingly used in advanced electronic and optical applications. The importance of accurate thermal characterization increases as their performance improves, mainly due to localized heating-induced size effects. These effects occur when the dimensions of the heated region approach the phonon mean free path, causing deviations from classical diffusive heat transport. Traditional Fourier-based models cannot adequately explain the thermal behavior under these conditions, necessitating phonon-based models, such as the solution of the phonon Boltzmann transport equation (BTE). In this thesis, we address the computational challenges of modeling thermal transport under localized heating using full Boltzmann Transport Equation (BTE), which is computationally intensive. A mesoscopic approach, such as that of Finite Volume Discrete Ordinates Method (FVDOM) and Kinetic Collective Model (KCM), is employed to evaluate their accuracy among other available methods like Monte Carlo (MC) and Lattice Boltzmann (LBM). Incorporating phonon properties from ab initio simulations further improves the accuracy of thermal predictions. KCM and gray FVDOM are compared for their capability to capture size-dependent heat transport and suitability for microscale applications. In addition, FVDOM is used to develop a semi-empirical correlation for the thermal spreading resistance, taking advantage of its numerical stability over mesh-sensitive models. Using a realistic heat generation profile in an AlGaN/GaN HEMT, we demonstrated the significance of non-diffusive transport and temperature-dependent material properties. It is evident from these findings that efficient mesoscopic models with physically accurate input are required for thermal design of advanced electronic devices.