3D Finite Element Strain Analysis of GaN based LED Nanostructures
Date Issued
2015
Date
2015
Author(s)
Hsu, Chung-Cheng
Abstract
Due to the energy crisis, GaN-based light emitting diodes (LEDs) become more popular due to their better power efficiency. However, GaN-based LEDs still have many problems. One of them is the lattice mismatch between InGaN and GaN. The strain induced by lattice mismatch between InGaN and GaN layers will make the wave functions of electron and hole separate in the InGaN quantum well (QW) by induced piezoelectric field. This is called quantum confined stark effect (QCSE) and will limit the efficiency of GaN-based LED. Thus, it is important to analyze the strain distribution in the GaN-based LED. In many researches, the fully strained approximation model is widely used in lateral grown thin film. However, it is not appropriate in nano-scale structures because the system would distribute strains to reach the minimum strain energy. In this thesis, we use 3D finite element method (FEM) continuous elastic model to analyze nano-scale structures, including indium fluctuated QWs, GaN-based LED with V-pit, and core-shell nanorod. For the first case, we analyzed how the strain distributed in the random alloy fluctuation QW and then calculated the induced polarization charges in the QW. We find that the fully strained approximation model neglects the inter-molecular interactions and the shear strains caused by random distributed indium composition. These make the fully strained approximation model has sharp strain distributions and higher total strain energy. We further analyze the strain distributions in the GaN-based LED with V-pit and core-shell nanorod. Because of the r-plane sidewall structure in the V-pit, the strain distributions might be interesting and could be an example to compare the FEM strain solver with the fully strained approximation model. At the end of this thesis, we analyze the strain distributions in a core-shell nanorod with three different diameters and investigate the strain differences. The results show that a smaller diameter nanorod has an obvious strain relaxation. In the future, with this 3D FEM continuous elastic simulation program, we can exactly analyze the strain distributions for many different nano-scale structures.
Subjects
Keywords:GaN-based light emitting diode
Strian
finite element method
Indium fluctuation
V-pit
core-shell nano rod
Type
thesis
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