Investigation of Nitride Semiconductor Nanostructures with Transmission Electron Microscopy
Date Issued
2009
Date
2009
Author(s)
Li, Jen-Hung
Abstract
The objective of the proposed research uses high resolution transmission electron microscope (HRTEM) to compare the nanostructures and optical properties of single and double MOCVD-grown InGaN/GaN heterostructures as well as the nanostructures of two InGaN/GaN multi-layers of different structures. The single and double heterostructures comprised of varying InGaN thicknesses of 25, 50, 100, and 200 nm. RSM and PL measurements demonstrated the depth-dependent crystal quality and band gap due to the effects of heterostructure-induced strain and phase separation in these samples. SEM results showed that as the strain started to relax the surface roughness rose. HRTEM results of the DH samples showed formations of indium droplets depicting a trend where the density of indium droplets decreased as the InGaN thickness decreased. The second part of this research compared the crystal quality of two InGaN/GaN multi-layers of different structures. PL result implied a better optical quality in the 8nm-6P sample (thinner InGaN thickness and thicker GaN barrier) than in the 10nm-5P sample. HRTEM results showed that the indium distribution was more uniform and the interfaces between the InGaN wells and GaN barriers were clearer in the 8nm-6P sample than in the 10nm-5P sample. The SSA calibrated average indium contents and indium composition fluctuation, which gave us local information about the two samples. We find that the 8nm-6P sample has a weaker indium composition fluctuation than the 10nm-5P sample based on SSA results. EDX demonstrated the same results as SSA.
Subjects
high resolution transmission electron microscopy
InGaN thin film
strain
phase separation
InGaN/GaN multi-layers
Type
thesis
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