Strain Engineering of InGaN/GaN Nanopillars for Optoelectronic Applications.

InGaN;LED;Quantum Dot;Electrical Engineering;Engineering;Electrical Engineering

Teng, Chu-HsiangYoon, Euisik ;

University of Michigan

关键词: InGaN;    LED;    Quantum Dot;    Electrical Engineering;    Engineering;    Electrical Engineering;   

Others  :  https://deepblue.lib.umich.edu/bitstream/handle/2027.42/120736/chteng_1.pdf?sequence=1&isAllowed=y

瑞士|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

The InGaN/GaN material system is critical for optoelectronic applications because it has direct band gap and large oscillator strength. The bandgap can be tuned by the alloy composition, and the emission wavelength covers the entire visible spectrum and extends into ultraviolet and near infrared regions. Due to the large lattice mismatch between InGaN and GaN, a large built-in strain exists in the InGaN quantum wells and induces a piezoelectric field across the wells. The piezoelectric field leads to the quantum-confined Stark effect which red-shifts the emission wavelength and degrades the recombination efficiency. It is known that nanostructures have large surface-to-volume ratio and can help relax strain via free surfaces. In this work, we present top-down InGaN/GaN nanostructures to manipulate the strain and serve as a building block to engineer the strain effect for novel optoelectronic functionalities. First, we demonstrate the emission colors from top-down nanopillars can be tuned from blue to red by changing the nanopillar diameter. The wavelength shift is well-described by an analytical model. We also demonstrate electrical nanoLED devices based on the nanopillars. It provides a simple solution to monolithic integration of multiple color pixels on a single chip. Second, we discuss the benefits of strain engineering for quantum light source applications. We focus on the intrinsic control of photon polarization states via asymmetric strain. Experimental data is provided to show that pre-defined polarization states of single photons with high degree of linear polarization can be achieved by engineering quantum dot geometry and strain. It suggests the potential of top-down InGaN quantum dots for quantum information applications. Finally, the non-ideal factors in our top-down quantum dots, including random alloy fluctuation and well-width fluctuation, are discussed. These effects modify the potential landscape and impose a fundamental limit to the quantum dot inhomogeneity, especially for ternary alloys. A methodology to model random alloy distribution and random well-width fluctuation is developed. The modeling results suggest that the strain-relaxation-induced potential is the dominant effect of lateral confinement even with the presence of random indium fluctuation and well-width fluctuation. The results are also compared to experimental data and show very good agreement.