| Summary: | 博士 === 國立成功大學 === 微電子工程研究所 === 104 === In this dissertation, the nitride based epitaxy material was grown by metalorganic chemical vapor deposition (MOCVD). Improvements of quality, efficiency, brightness and electrostatic discharge (ESD) ability on InGaN/GaN LED devices have been investigated.
Firstly, in order to improve quality on GaN-based LED, we have studied the initial growth modes of GaN on patterned sapphire substrate (PSS) with different initial TMGa flow rates. The FWHM of the (102) XRD spectrum of GaN on PSS increased from 470 to 580 arcsec when the initial TMGa flow rate was increased from 80 to 200 sccm. A low TMGa flow rate sufficiently suppresses GaN island growth on the top of the pattern and hence improves GaN crystal quality. The electrical and optical characteristics of GaN-based LEDs on PSS with low initial TMGa were also improved. More than 90% of the GaN LED chips with low initial GaN growth rate can hold the 1-kV machine-mode elec- trostatic discharge level.
Secondly, in order to improve light-extraction on GaN-based LED, step graded-refractive index (SGRI) (ZnO)x(SiO2)1-x micropillar multilayers have been introduced and demonstrated on GaN-based LEDs combined with the mesh ITO. The SGRI (ZnO)x(SiO2)1-x micropillars were produced by controlling the Zn/Zn+Si ratio of co-sputtered ZnO and SiO2. The introduced three-layered SGRI (ZnO)x(SiO2)1-x micropillars improved both critical angle inside GaN LEDs and Fresnel transmittance coefficient (ηFr) as well as had better light coupling into the micropillars. Moreover, a high number of layers of the SGRI micropillars would aid the light coupled in the pillars to escape from the side wall of the pillar. LEDs with three-layered SGRI (ZnO)x(SiO2)1-x micropillars exhibited output power enhancements of 12.2% with a 20mA–Vf of 3.19 V. The output power of the mesh ITO LEDs with SGRI (ZnO)x(SiO2)1-x micropillars was further enhanced to 15.3% by improving the current spreading.
In addition, we demonstrate aluminum nitride / gallium nitride / indium gallium nitride (AlN/GaN/InGaN) multi-quantum-well (MQW) ultraviolet (UV) light-emitting diodes (LEDs) to improve light output power. Similar to conventional UV LEDs with AlGaN/InGaN MQWs, UV LEDs with AlN/GaN/InGaN MQWs have forward voltages (Vf’s) ranging from 3.21 V to 3.29 V at 350 mA . Each emission peak wavelength of AlN/GaN/InGaN MQW UV LEDs presents 350 mA output power greater than that of the corresponding emission peak wavelength of AlGaN/InGaN MQW UV LEDs. The output power enhancement at 375 nm emission wavelength of AlN/GaN/InGaN MQW UV LEDs could reach around 26.7% in magnitude, which is greater than that of conventional AlGaN/InGaN MQWs UV LEDs; however, at 395 nm emission wavelength, AlN/GaN/InGaN MQW UV LEDs only have an output power enhancement of around 2.43% in magnitude. Moreover, AlN/GaN/InGaN MQWs present less pits than AlGaN/InGaN MQWs, causing AlN/GaN/InGaN MQW UV LEDs to have less reverse leakage currents at −20 V. Furthermore, AlN/GaN/InGaN MQW UV LEDs have the 2-kV human body mode (HBM) electrostatic discharge (ESD) pass yield of 85%, which is 15% more than the 2-kV HBM ESD pass yield of AlGaN/InGaN MQW UV LEDs of 70%
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