Study on InGaN/GaN Quantum Well Structures on Si Substrate with Transmission Electron Microscopy
Date Issued
2012
Date
2012
Author(s)
Liu, Yen-Hung
Abstract
The difference of thermal expansion coefficient between GaN and Si results in a strong tensile stress on the GaN epitaxial layer during the cooling process. In our study, we create a compressive thermal stress by using an AlN buffer layer grown with graded temperatures to compensate the tensile thermal stress. The InGaN/Gan quantum well (QW) sample with the largest number of graded-temperature growth stages has the weakest residual tensile stress, shortest emission wavelength, and highest emission internal quantum efficiency. In this study, the variation trend of indium composition of the QW samples grown on Si and the control sample grown on sapphire based on strain state analysis is shown to be the same as that based on the X-ray diffraction measurement and fitting. However, the variation range becomes larger. Also, from the cross-sectional transmission electron microscopy study, it is found that the threading dislocation (TD) density decreases with decreasing residual stress. The TD density above the GaN/AlN superlattice inter-layer is lower than that below the inter-layer, indicating that the inter-layer can block the TDs.
Subjects
InGaN/GaN quantum well
Silicon substrate
Transmission Electron Microscopy
Strain State Analysis
Dislocations
Type
thesis
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