Browsing by Author "Chu, JY"

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Brightness enhancement of ITO/GaN LEDs by self-aligned micro-net structures
(2005)
Chang, KM
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Chu, JY
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Cheng, CC
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Chu, CF
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電子工程學系及電子研究所
Arrays of square and hexagonal holes of various dimensions were patterned on indium-tin-oxide (ITO)/GaN light-emitting diodes (LEDs) using the self-aligned method to increase the light extraction area and shorten the optical paths. The hole region was etched to give the sidewall of the active layer a sloped profile, and it was passivated by SiOxNy films to extract more light. The self-aligned micro-net LED is at least 10% brighter than the conventional structure in the normal direction without loss of operating voltage or leakage current. The ratio of luminescence to total output power is increased by 25% at a current density of 100 A/cm(2). Moreover, varying the hole dimensions and the designed density increased the peak external quantum efficiency by 5% at a current of 3 mA. The greater axial luminescence and the higher external quantum efficiency make LEDs self-aligned micro-net structures quite useful in surface-mounting and low-power-consuming devices, such as cellular phones. (c) 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Enhancement in light output of InGaN-based microhole array light-emitting diodes
(2005-06-01)
Hsueh, TH
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Shen, JK
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Huang, HW
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Chu, JY
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Kao, CC
InGaN-based microhole array light-emitting diodes (LEDs) with hole diameters (d) of 3-15 mu m were fabricated using self-aligned etching. The effects of size on the device characteristics, including current density-voltage and light output-current density, were measured and compared with those of conventional broad-area (BA) LEDs fabricated from the same wafer. The electrical characteristics of the devices are similar to those of conventional BA LEDs. The light output from the microhole array LEDs increases with d up to 7 pm. However, the light output declined as d increased further, perhaps because of the combination of the enhancement in extraction efficiency caused by the large surface areas provided by the sidewalls and the decrease in area of light generation by holes in the microhole array LEDs. The ray tracing method was used with a two-dimensional model in TracePro software. The findings indicate that an optimal design can improve the light output efficiently of the microhole array LEDs.
Highly reliable GaN-based light-emitting diodes formed by p-In0.1Ga0.9N-ITO structure
(2004-08-01)
Chang, KM
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Chu, JY
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Cheng, CC
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電子工程學系及電子研究所
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Department of Electronics Engineering and Institute of Electronics
Indium-tin-oxide (ITO) is deposited as a transparent current spreading layer of GaN-based light-emitting diodes (LEDs). To reduce the interfacial Schottky barrier height, a thin p-In0.1Ga0.9N layer is grown as an intermediate between ITO And p-GaN. The contact resistivity around 2.6 x 10(-2) Omega . cm(2) results in a moderately high forward voltage LED of 3.43 V operated at 20 mA. However, the external quantum efficiency and power efficiency are enhanced by 46% and 36%, respectively, in comparison with the conventional Ni-Au contact LEDs. In the life test, the power degradation of the p-In0.1Ga0.9N-ITO contact samples also exhibits a lower value than that of the conventional ones.
The variation of ohmic contacts and surface characteristics on p-GaN induced by reactive ion etching
(2002-07-01)
Chang, KM
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Cheng, CC
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Chu, JY
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電子工程學系及電子研究所
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Department of Electronics Engineering and Institute of Electronics
Electron cyclotron resonance (ECR) reactive ion etch (RIE) was used to etch p-type GaN under a chlorine-based plasma. Rapid thermal annealing (RTA) and nitrogen plasma were used as post-RIE treatments to investigate the variation of Ni/Au contacts on p-GaN. RIE deteriorated the contact very much due to the induced nitrogen vacancies and damage on the p-GaN surface. The poor contact was improved by RTA treatment at 700degreesC for 3 min although the current-voltage curve was still nonlinear. The results from X-ray photoelectron spectroscopy (XPS), atomic force microscopy, and grazing incidence X-ray diffraction measurements indicated that RTA at 700degreesC could reconstruct the ordered structure from the damaged p-GaN surface. Annealing at 500 or 900degreesC did not improve the contact due to the high oxygen content of the surface. ECR-N-2 plasma treatment could scarcely improve the contact. XPS and photoluminescence analyses revealed that the nitrogen plasma treatment increased the number of nitrogen vacancies as well as the nitrogen content of a p-GaN surface. These nitrogen atoms did not form tight bonds with GaN, and easily escaped from the surface by annealing. (C) 2002 The Electrochemical Society.