Browsing by Author "Kao, Tsung Ting"

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Effects of Inhomogeneous Gain and Loss on Nitride-Based Vertical-Cavity Surface Emitting Lasers
(2009-04-01)
Chen, Shih Wei
;
Lo, Ming Hua
;
Kao, Tsung Ting
;
Kao, Chih Chiang
;
Chu, Jung Tang
Nitride-based vertical cavity surface emitting lasers (VCSEL) with hybrid mirror has been investigated. We further measured the as-grown samples (without top dielectric distributed Bragg reflector) by p-photoluminescence, scanning near-field optical microscopy, and cathodoluminescence (CL). By different excitation power density, the experimental results indicated that the VCSEL devices have different lasing modes and spot sizes, represented inhomogeneous gain and loss distribution in the whole structure. The non-uniform emission intensity distribution including several bright spots of about 1 to 2 pm was observed for both VCSEL devices and as-grown samples, which was obtained from CL measurement, due to the effect of indium clusters and non-uniform micro-cavity resonant in InGaN multi-quantum wells (MQWs). The results show the significant influence on commercial applications such as light emitting diodes, lasers devices and so on. (C) 2009 The Japan Society of Applied Physics
Study of GaN-Based Photonic Crystal Surface-Emitting Lasers (PCSELs) With AlN/GaN Distributed Bragg Reflectors
(2009-05-01)
Chen, Shih Wei
;
Lu, Tien Chang
;
Kao, Tsung Ting
;
光電工程學系
;
Department of Photonics
GaN-based 2-D photonic crystal (PC) surface-emitting lasers (PCSELs) with AlN/GaN distributed Bragg reflectors are fabricated and investigated. A clear threshold characteristic under the optical pumping at room temperature is observed at about 2.7 mJ/cm(2) with PC lattice constant of 234 nm. Above the threshold, only one dominant peak appears at 401.8 nm with a linewidth of 0.16 nm. The laser emission covers whole circular 2-D PC patterns of 50 mu m in diameter with a small divergence angle. The lasing wavelength emitted from 2-D PC lasers with different lattice constants occurs at the calculated band edges, showing different polarization angles due to the light diffracted in specific directions, corresponding exactly to Gamma-, K-, and M-directions in the K space. The PCSEL also shows a spontaneous emission coupling factor beta of 5 x 10(-3) and a characteristic temperature of 148 K. Furthermore, the coupled-wave model in 2-D hexagonal lattice is applied to distinguish the discrepancy in threshold power and the corresponding coupling coefficient. The results show that the lasing actions within Gamma, K, and M modes have a substantial relation between the threshold energy density and the coupling coefficient.