Phonon mean free path - thermal conductivity relatıon of AlxGa1−xN and β-Ga2O3 semiconductors
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Date
2023
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Thesis (M.S.) - Bogazici University. Institute for Graduate Studies in Science and Engineering, 2022.
Abstract
Ultrawide-bandgap (UWBG) semiconductors like AlxGa1−xN and β- Ga2O3 emerge as a promising option for advancing next- generation high-power electronic devices. Al- GaN preserves significant attention due to its unique capability of tuning the bandgap from 3.4 (eV) to 6 eV, enabling a nonlinear increase in the critical breakdown field. β-Ga2O3, with a wide bandgap of 4.8 eV , surpasses GaN and has cost-effective substrates, making it appealing for high-power electronics. However, field-effect transistors (FET) and Schottky-barrier diodes based on AlxGa1−xN and β-Ga2O3 have shown superior performance to GaN, indicating their potential for overcoming this challenge. The pressing issue of local heat build-up and narrowing thermal pathways in such high-performance small scales devices is a significant challenge.To optimize the performance and ensure reliable operation, efficient dissipation of heat generated in the device is essential. This can be done by understanding the thermal transport of these systems at a short-length scale, in this case, lattice vibrations (i.e., phonons). One of the critical properties that characterize this behaviour is the phonon mean free path (MFP). This research offers a detailed analysis of phonon mean free path accumulation spectra in β-Ga2O3, and AlxGa1−xN alloys with different Al fractions at different lattice temperatures by utilizing ab-initio and lattice dynamics calculations based on density functional theory (DFT) along with the Boltzmann transport equation (BTE). Our results indicated that the normalized cumulative thermal conductivity of alloys is notably reduced compared to that observed in pure systems. This effect is particularly pronounced for larger mean free paths (MFPs).