Monte Carlo simulations of two-dimensional electron gasses in gallium nitride high electron mobility transistors via general-purpose computing on graphics processing units

Smith, Lee

Abstract

The work in this thesis covers two main topics: successfully porting an Ensemble Monte Carlo (EMC) focused on bulk III-V semiconductors on to the graphics processing unit (GPU) and investigating carrier transport in a two-dimensional electron gas (2DEG) created at an Aluminium Gallium Nitride (AlGaN) and Gallium Nit ride (GaN) heterojunction, specifically the effect of introducing non-equilibrium phonons.
The programming language used to be able to run on the GPU, NVIDIA CUDA, is introduced. The concept of highly parallel programming is explored, along with the challenges this poses to an EMC simulating semiconductor materials and devices. The changes made to the bulk EMC algorithm are explained, including architectural, memory strategies and execution optimisations. The performance increase related to each change is given, and it is found that the GPU algorithm has a run time that is approximately 30% of the original EMC algorithm. This is the first example of an EMC simulating electron transport in semiconductors on a GPU.
A two-dimensional EMC is created to simulate the behaviour of electrons confined in the 2DEG created at an AlGaN/GaN heterojunction. Results are presented for the electron velocity, momentum and energy relaxation times and mobility, which are compared to experimental results from AlGaN/GaN High Electron Mobility Transistors (HEMTs), and agreement is good. No velocity overshoot is observed, in agreement with experiments.
Finally, non-equilibrium phonons are introduced to the 2DEG simulation to study their effect on the electron transport. Non-equilibrium phonons are found to reduce the electron velocity due to diffusive heating. However, due to the confinement of electrons, the phonon distribution is only increased in a small volume of reciprocal space and the effects are shown to be weaker than in bulk. The consideration of electron confinement and a non-equilibrium phonon population has not been seen in the current literature.

Citation

Smith, L. (2020). Monte Carlo simulations of two-dimensional electron gasses in gallium nitride high electron mobility transistors via general-purpose computing on graphics processing units. (Thesis). University of Hull. Retrieved from https://hull-repository.worktribe.com/output/4223241

• Thesis Type: Thesis
• Deposit Date: Jul 8, 2021
• Publicly Available Date: Feb 23, 2023
• Keywords: Physics
• Public URL: https://hull-repository.worktribe.com/output/4223241
• Additional Information: Department of Physics and Mathematics, The University of Hull
• Award Date: Nov 1, 2020