Browsing by Author "Hung, Chih-Tsang"

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830-nm AlGaAs-InGaAs Graded Index Double Barrier Separate Confinement Heterostructures Laser Diodes With Improved Temperature and Divergence Characteristics
(2013-01-01)
Hung, Chih-Tsang
;
Lu, Tien-Chang
;
光電工程學系
;
Department of Photonics
The 830-nm AlGaAs/InGaAs laser diodes (LDs) adopting multistep-graded index double-barrier separate confinement heterostructures (GRIN-DBSCHs) with small divergence beams and improved temperature characteristics under a high-output-power operation are reported. The double-barrier separate confinement heterostructure (DBSCH) design provides good carrier confinement and prevents current leakage by adding a multistep grading layer between cladding and waveguide layers. Simultaneously, the DBSCH design can facilitate reducing the divergence angle at high-power operation and widening the transverse mode distribution to decrease the power density around emission facets. In addition, the p-side doping depth is optimized to effectively raise the barrier height for reducing the electron overflow. Gaussian-like narrow far-field patterns are measured with the full-width at half-maximum vertical divergence angle to be between 11 degrees and 13 degrees. A threshold current of 16.5 mA and a slop efficiency of 0.98 W/A are obtained in the continuous-wave operation condition at room temperature. The maxima optical power densities of 21.5 MW/cm(2) per laser facet and good characteristic temperature values of threshold current (T-0) and slope efficiency (T-1) are achieved.
830nm Graded Index Double Barrier Separate Confinement Heterostructure Laser Diodes with Small Vertical Divergence and Temperature Insensitive Characteristics
(2012)
Hung, Chih-Tsang
;
Ho, Tsong-Lin
;
Lu, Tien-Chang
;
光電工程學系
;
Department of Photonics
Asymmetric design of photonic crystal surface-emitting lasers with low-threshold characteristics
(2013-08-10)
Hung, Chih-Tsang
;
Ho, Tsung-Lin
;
Lu, Tien-Chang
;
光電工程學系
;
Department of Photonics
We present AlGaAs-InGaAs multiquantum wells photonic crystal surface-emitting lasers by using the transfer matrix method and coupled wave method to achieve a low-threshold operation. The extremely low-threshold gain is achieved by adopting an asymmetric cladding layer design to enhance both of the vertical optical confinement factors for the quantum wells and photonic crystal (PC). By modifying the composition of the AlGaAs layer to raise the refractive index in the p-type cladding, optical field distribution will obviously be shifted to the p side. Hence, it results in a significant coupling enhancement between the optical mode profile and the PC layer. The optimized value of the vertically optical confinement factor of the PC layer is 13.94%, and the corresponding threshold gain can be as low as 19.45 cm(-1). (C) 2013 Optical Society of America
Design of Low-Threshold Photonic Crystal Surface-Emitting Lasers
(2012-05-15)
Hung, Chih-Tsang
;
Syu, Yu-Cheng
;
Wu, Tzeng-Tsong
;
Lu, Tien-Chang
;
光電工程學系
We have investigated the influence of various thicknesses on different layers in GaAs-based photonic crystal surface-emitting lasers (PCSELs), by using the transfer matrix and coupled wave methods to increase the vertically optical confinement factor and to reduce the threshold gain. In addition, the relationship between the threshold gain and the filling factor has been considered. This letter provides an efficient calculation method for designing square-lattice-type PCSEL structures, which shall be useful for the fabrication of low-threshold PCSELs in the near future.
Design of Low-Threshold Photonic Crystal Surface-Emitting Lasers (vol 24, pg 866, 2012)
(2012-08-01)
Hung, Chih-Tsang
;
Syu, Yu-Cheng
;
Wu, Tzeng-Tsong
;
Lu, Tien-Chang
;
光電工程學系
"Design of Low-Threshold Photonic Crystal Surface-Emitting Lasers (vol 24, pg 866, 2012)"
(1970-01-01)
Hung, Chih-Tsang
;
Syu, Yu-Cheng
;
Wu, Tzeng-Tsong
;
Lu, Tien-Chang
;
光電工程學系
Effect of passivation layers on characteristics of AlGaInP ridge waveguide laser diodes
(2014-07-01)
Hung, Chih-Tsang
;
Huang, Shen-Che
;
Lu, Tien-Chang
;
光電工程學系
;
Department of Photonics
We investigate the effect of passivation structure on the optical mode distribution and characteristics of the edge emitting ridge waveguide AlGaInP-GaInP visible laser diodes (LDs). For conventional designs of single-layer Si3N4 or SiO2 passivation, the variation of lateral near-field confinement and the horizontal far-field (FF) divergence can be determined via the modification of dielectric layer thickness. Thin passivation layer suffers from high absorption at the metal interface while thick passivation layer suffers from poor heat dissipation in the ridge waveguide and high scattering loss, resulting in high threshold. We propose a novel design of three-pair Al2O3/Ta2O5 multilayer optical thin films as passivation on the ridge waveguide, which can improve the laser characteristics and the heat dissipation. The measured room-temperature threshold current (Ith) and characteristic temperature (T-0) are 44.5 mA and 104.2 K with a divergence angle of 16.4. (C) 2013 Elsevier Ltd. All rights reserved.
Enhancing the Emission Efficiency of In(0.2)Ga(0.8)N/GaN MQW Blue LED by Using Appropriately Misoriented Sapphire Substrates
(2009-01-01)
Li, Zhen-Yu
;
Uen, Wu-Yih
;
Lo, Ming-Hua
;
Chiu, Ching-Hua
;
Lin, Po-Chun
In this paper, we report the fabrication of an In(0.2)Ga(0.8)N/GaN multiple-quantum-well (MQW) structure on vicinal sapphire substrates with a very small offset angle of 0-1 degrees by low-pressure metallorganic chemical vapor deposition. Our study demonstrates that the quality of the In(0.2)Ga(0.8)N/GaN MQW structure is very sensitive to the offset angle of the vicinal substrate. High-resolution X-ray diffraction analyses demonstrated high-order satellite peaks and clear fringes between them for all MQW structures fabricated, from which the interface roughness (IRN) was estimated. The IRN of the In(0.2)Ga(0.8)N/GaN MQW structure fabricated on 0.2 degrees off sapphire substrate was determined as 1.36% of the quantum well layer period. Besides, reciprocal lattice mapping was employed to examine the strain status of the MQW. The lattice relaxation of the same specimen mentioned above was estimated to be 7.4x10(-5). It is therefore manifested that an In(0.2)Ga(0.8)N/GaN MQW structure with abrupt interfaces and good layer periodicity was grown. From it, a shortest radiative lifetime of 14.2 ns and a lowest fluctuation of 5.6 meV in the emission energy of micro-photoluminescence mapping were achieved. In addition, superior material qualities of the whole film fabricated on 0.2 degrees off substrate were recognized by cross-sectional transmission electron microscopy. Based on the results mentioned above, a high-quality In(0.2)Ga(0.8)N/GaN MQW blue light, emitting diode (LED) has been fabricated on 0.2 degrees off substrate, which demonstrated a strong room-temperature electroluminescence emission at the wavelength of 465 nm and with the full width at half maximum of only 19 nm. The same device also showed an output power of 13.4 mW and an external quantum efficiency of 19.2%. Both these characteristics are improved drastically compared with the devices fabricated on the substrates with other offset angles. Conclusively, the use of an appropriately misoriented sapphire substrate is suggested to be effective for elevating the emission efficiency of In(0.2)Ga(0.8)N/GaN MQW blue LED fabricated thereon.
Enhancing the Emission Efficiency of In0.2Ga0.8N/GaN MQW Blue LED by Using Appropriately Misoriented Sapphire Substrates
(2009-01-01)
Li, Zhen-Yu
;
Uen, Wu-Yih
;
Lo, Ming-Hua
;
Chiu, Ching-Hua
;
Lin, Po-Chun
In this paper, we report the fabrication of an In0.2Ga0.8N/GaN multiple-quantum-well (MQW) structure on vicinal sapphire substrates with a very small offset angle of 0-1 degrees by low-pressure metallorganic chemical vapor deposition. Our study demonstrates that the quality of the In0.2Ga0.8N/GaN MQW structure is very sensitive to the offset angle of the vicinal substrate. High-resolution X-ray diffraction analyses demonstrated high-order satellite peaks and clear fringes between them for all MQW structures fabricated, from which the interface roughness (IRN) was estimated. The IRN of the In0.2Ga0.8N/GaN MQW structure fabricated on 0.2 degrees off sapphire substrate was determined as 1.36% of the quantum well layer period. Besides, reciprocal lattice mapping was employed to examine the strain status of the MQW. The lattice relaxation of the same specimen mentioned above was estimated to be 7.4x10(-5). It is therefore manifested that an In0.2Ga0.8N/GaN MQW structure with abrupt interfaces and good layer periodicity was grown. From it, a shortest radiative lifetime of 14.2 ns and a lowest fluctuation of 5.6 meV in the emission energy of micro-photoluminescence mapping were achieved. In addition, superior material qualities of the whole film fabricated on 0.2 degrees off substrate were recognized by cross-sectional transmission electron microscopy. Based on the results mentioned above, a high-quality In0.2Ga0.8N/GaN MQW blue light, emitting diode (LED) has been fabricated on 0.2 degrees off substrate, which demonstrated a strong room-temperature electroluminescence emission at the wavelength of 465 nm and with the full width at half maximum of only 19 nm. The same device also showed an output power of 13.4 mW and an external quantum efficiency of 19.2%. Both these characteristics are improved drastically compared with the devices fabricated on the substrates with other offset angles. Conclusively, the use of an appropriately misoriented sapphire substrate is suggested to be effective for elevating the emission efficiency of In0.2Ga0.8N/GaN MQW blue LED fabricated thereon.
Optical Mode Modulation of AlGaInP Multi Quantum Well Laser Diodes
(2013)
Hung, Chih-Tsang
;
Huang, Shen-Che
;
Lu, Tien-Chang
;
光電工程學系
;
Department of Photonics
We investigate the influence of passivation structure on the optical mode distribution and LI characteristics for the edge emitting AlGaInP-GaInP visible laser diode (LD). For traditional single-layer Si3N4 or SiO2 passivation designs, the modification of dielectric layer thickness can determinate the lateral near-field confinement and change the horizontal far-field (FF) divergence. By increasing the film thickness, the non-radiation absorption come from Au-Ti can be improved and it leads to a narrow FF divergence beam. As continue to increasing the thickness, thicker passivation provides a better confinement factor and then the far-field pattern turn to be wider. For LI characteristics, it is necessary to deposit a thick enough passivation to reduce metal absorption. However, it cause much thermal energy accumulated in the ridge waveguide and deteriorate the quantum efficiency as adopting a too thick dielectric layer. Finally, we demonstrate a high power AlGaInP-GaInP multi quantum wells (MQWs) LD adopted a high-reflectivity passivation to enhance the LI characteristics and keep a suitable far-field divergence angle simultaneously. Under the design of three-pair optical thin films, it cannot only avoid the metal absorption but also enhance emitting efficiency and heat dissipation by using a high reflective and good thermal conductive three-pair optical thin films, it cannot only avoid the metal absorption but also enhance emitting efficiency and heat dissipation by using a high reflective and good thermal conductive Al2O3/Ta2O5 multilayer. The measured room-temperature threshold current (I-th) and characteristic temperature (T-0) can be arrived 44.5mA and 104.2K at 16.4 degrees far-fielddivergence.