Browsing by Author "Chang, Cheng-Yu"

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Analysis of Strain Relaxation and Emission Spectrum of A Free-Standing GaN-based Nanopillar
(2008-01-01)
Wu, Yuh-Renn
;
Yu, Peichen
;
Chiu, C. H.
;
Chang, Cheng-Yu
;
Kuo, H. C.
We have made a, GaN-based single nanopillar with a, diameter of 300nm using the focused ion beam (FB) technique. The micro-photoluminescence (mu-PL) from the embedded GaN/InGaN multi-quantum wells reveals a blue shift of 68.3 meV in energy. In order to explain the spectrum shift, we have developed a valence force field model to study the strain relaxation mechanism in a, single GaN-based nanopillar structure. The strain distribution and strain induced polarization effect inside the multiple quantum wells is added to our self-consistent Poisson, drift-diffusion, and Schrodinger solver to study the spectrum shift of mu-PL.
Size-Dependent Strain Relaxation and Optical Characteristics of InGaN/GaN Nanorod LEDs
(2009-07-01)
Wu, Yuh-Renn
;
Chiu, Chinghua
;
Chang, Cheng-Yu
;
Yu, Peichen
;
Kuo, Hao-Chung
In this paper, InGaN/GaN nanorod LEDs with various sizes are fabricated using self-assembled Ni nanomasks and inductively coupled plasma-reactive ion etching. Photoluminescence (PL) characteristics exhibit size-dependent, wavelength blue shifts of the emission spectra from the nanorod LEDs. Numerical analyses using a valence force field model and a self-consistent Poisson, Schrodinger, and drift-diffusion solver quantitatively describe the correlation between the wavelength blue shifts and the strain relaxation of multiple quantum wells embedded in nanorods with different averaged sizes. Time-resolved PL studies confirm that the array with a smaller size exhibits a shorter carrier lifetime at low temperature, giving rise to a stronger PL intensity. However, the PL intensity deteriorates at room temperature, compared to that of a larger size, possibly due to an increased number of surface states, which decreases the nonradiative lifetime, and hence reduces the internal quantum efficiency.