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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.
Characteristics of emission polarization in a-plane nanorods embedded with InGaN/GaN multiple quantum wells
(2010-09-15)
Li, J. C.
;
Lu, T. C.
;
Huang, H. M.
;
Chan, W. W.
;
Kuo, H. C.
Nonpolar (a-plane) GaN nanorod arrays with embedded In(x)Ga(1-x)N/GaN (x=0.09, 0.14, 0.24, and 0.30) multiple quantum wells (MQWs) grown on r-plane sapphire have been fabricated successfully by self-assembled Ni nanomasks and subsequent inductively coupled plasma reactive-ion etching. After nanorod fabrications, the polarization ratio of the emission from MQWs with lower indium composition (x=0.09 and 0.14) slightly decreases but apparently increases by at most 79% for the samples with higher indium composition (x=0.24 and 0.30). Competition between the effect of multiple scattering, strain relaxation and reduction in localized centers, expected in a-plane MQW samples, are attributed to the variations in the polarization ratios after the nanorod formation. (c) 2010 American Institute of Physics. [doi:10.1063/1.3483239]
Physical properties of amorphous InGaZnO4 films doped with Mn
(2009-03-02)
Liu, Shiu-Jen
;
Fang, Hau-Wei
;
Su, Shih-Hao
;
Li, Chia-Hung
;
Cherng, Jyh-Shiarn
Amorphous InGaZnO4 (a-IGZO) films doped with various concentrations of Mn have been fabricated by using pulsed-laser deposition technique. Optical, electrical, and magnetic properties of the prepared Mn-doped a-IGZO films were investigated. The resistivity, carrier concentration, and carrier mobility of the a-IGZO films were found to be, respectively, increased, decreased, and enhanced by Mn doping. Moreover, the optical transmission is slightly increased in the visible range and the optical band gaps are not affected in the Mn-doped films. Room-temperature ferromagnetism has been observed in the field-dependent magnetization measurements.
Particular Failure Mechanism of GaN-Based Alternating Current Light-Emitting Diode Induced by GaOx Oxidation
(2010-08-01)
Yen, Hsi-Hsuan
;
Kuo, Hao-Chung
;
Yeh, Wen-Yung
;
光電工程學系
;
光電工程研究所
This investigation describes the unique failure mechanism of the Wheatstone bridge circuit-type alternating current light-emitting diode (WB AC-LED). The micro-LEDs in WB AC-LED rectifying branches were reverse biased, and therefore, positive charges (holes) accumulated in the n-type GaN layer under the active region and combined with the GaN material and OH- ions to generate GaOx oxidation grains. The GaOx generation speed was fast with high reverse voltage applied to micro-LEDs, and the expansion of GaOx dimensions degraded the opto-electrical characteristics and eventually caused failure of the WB AC-LED. The root-mean-square reverse voltage dropped across each micro-LED from -13.1 to -6.7 V with different micro-LEDs array arrangements extended the WB AC-LED life-time from being less than 650 h to more than 1600 h, respectively.
High extraction efficiency GaN-based light-emitting diodes on embedded SiO2 nanorod array and nanoscale patterned sapphire substrate
(2010-06-28)
Huang, Hung-Wen
;
Huang, Jhi-Kai
;
Kuo, Shou-Yi
;
Lee, Kang-Yuan
;
Kuo, Hao-Chung
In this paper, GaN-based LEDs with a nanoscale patterned sapphire substrate (NPSS) and a SiO2 photonic quasicrystal (PQC) structure on an n-GaN layer using nanoimprint lithography are fabricated and investigated. The light output power of LED with a NPSS and a SiO2 PQC structure on an n-GaN layer was 48% greater than that of conventional LED. Strong enhancement in output power is attributed to better epitaxial quality and higher reflectance resulted from NPSS and PQC structures. Transmission electron microscopy images reveal that threading dislocations are blocked or bended in the vicinities of NPSS layer. These results provide promising potential to increase output power for commercial light emitting devices. (C) 2010 American Institute of Physics. [doi:10.1063/1.3456385]
Improved Performance of InGaN-GaN Light-Emitting Diode by a Periodic n-Bowl Mirror Array
(2009)
Liao, Cheng
;
Wu, YewChung Sermon
;
材料科學與工程學系
;
Department of Materials Science and Engineering
A periodic n-bowl mirror structure was introduced into light-emitting diodes with roughened p-GaN surface (RP-LED) by wafer bonding and laser lift-off technology. The performance of these n-bowl mirror light-emitting diodes (NBM-LEDs) was better than that of RP-LED. Besides, the light intensity and the output power of NBM-LEDs were increased with the decrease in n-bowl dimension. The view angle was decreased with the diameter of the n-bowl.
Output Power of AlGaInP Light Emitting Diode Improved by Double Roughening AlGaInP Surfaces
(2010)
Huang, Ping-Wei
;
Wu, YewChung Sermon
;
材料科學與工程學系
;
Department of Materials Science and Engineering
An AlGaInP-based vertical light emitting diode (LED) comprising double roughened (GaP and n-AlGaInP) surfaces and a bottom metal reflector was fabricated by surface-etching and wafer-bonding technologies. The roughened GaP surface was created by photolithography and wet etching, while the AlGaInP surface was roughened by inductively coupled plasma dry etching. The output power of the double roughened LED could reach 5.88 mW, which was 2.56 times higher than that of the conventional LED. This is because the double roughened surfaces can provide photons multiple chances to escape from the LED surface and can redirect photons.
Low Temperature Annealing with Solid-State Laser or UV Lamp Irradiation on Amorphous IGZO Thin-Film Transistors
(2010)
Zan, Hsiao-Wen
;
Chen, Wei-Tsung
;
Chou, Cheng-Wei
;
Tsai, Chuang-Chuang
;
Huang, Ching-Neng
Instead of the conventional furnace annealing process with a temperature higher than 300 degrees C, two low temperature annealing methods are successfully demonstrated to suppress the instability problem of amorphous indium gallium zinc oxide (IGZO) thin film transistors (TFTs). With adequate Nd:yttrium aluminum garnet laser (266 nm) annealing energy density or Xe excimer UV lamp (172 nm) irradiation time, the on voltage shift is greatly suppressed from over 10 to 0.1 V. The influence of laser energy density and UV lamp irradiation time on the performance of IGZO TFTs is also investigated and explained. The proposed methods are promising for the development of amorphous IGZO TFTs on flexible substrates.

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