Study of Optical Anisotropy in Polar, Nonpolar, and Semipolar AlGaN Quantum Well Deep Ultra-violet Light Emitting Diodes
Date Issued
2012
Date
2012
Author(s)
Wang, Chang-Pei
Abstract
This paper analyzes the optical polarization characteristics and internal quantum efficiency (IQE) of a AlGaN based polar, nonpolar, and semipolar deep ultra-violet (UV) light emitting diode (LED) grown on two kind of substrate. A one dimensional model is used to solve drift-diffusion, Poisson equations, and 6×6 k · p Schrodinger equations to investigate band structure and emission characteristics. The light emission polarization ratios of c-plane, nonpolar, and semipolar AlGaN based deep UV LEDs grown on AlN and AlGaN substrates with different Al compositions and injection current were studied. The study shows that the optical polarization of the c-plane AlGaN based deep UV LED grown on AlGaN substrate is dominated by the outplane polarization as the Al composition increases. For nonpolar and semipolar structures, the light polarization direction is mainly dominated by the in-plane polarized light which is good for the surface emitting. Influences of the IQE by changing the p-type activation energy, growth orientation, and nonradiatve lifetime are also studied. We find that in-plane polarization dominate the polarization ratio of c-plane deep UV LED grown on AlN substrate due to the stronger strain. Finally, the stronger strain shows small influence to the result of nonpolar and semipolar deep UV LED.
Subjects
AlGaN
c-plane
Poisson equation
Schrodinger equation
k·p method
polarization ratio
quantum well (QW)
Type
thesis
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