Abstract
The GaN-based high-voltage flip chip light-emitting diode (HVFC-LED) is designed and developed for the purpose of efficiency enhancement. In our design, the distributed Bragg reflector (DBR) is deposited at the bonded substrate to increase the light extraction. After the flip chip process, the general current-voltage characteristics between the flip chip sample and the traditional sample are essentially the same. With the help of great thermal conductive silicon substrate and the bottom DBR, the HVFC-LED is able to enhance the power by 37.1% when compared to the traditional high-voltage LEDs. The wall-plug efficiencies of the HVFC-LED also show good droop reduction as high as 9.9% compared to the traditional devices.
Highlights
The availability of high brightness, high power, and large area of GaN-based light-emitting diodes (LEDs) has enabled their applications in exterior automotive lightings, outdoor displays, backlights for liquid crystal display (LCD) TVs, various handheld devices, printers, and rear projection TVs [1]
Two different types of packaged LED chips were prepared: the first one is the conventional high-voltage light-emitting diode (HV-LED) with patterned sapphire substrate and the other is similar to HV-LED but extra 5.5 pairs of SiO2/TiO2 and Al/Ti/Ni/Au omnidirectional reflector (ODR) layer were deposited at the bottom of sapphire substrate
Compared with conventional HV-LED and HV-LED + ODR, the light output power of HVFC-LED is found to be enhanced by 37.1% and 5.1% at the same 20 mA current injection, respectively
Summary
The availability of high brightness, high power, and large area of GaN-based light-emitting diodes (LEDs) has enabled their applications in exterior automotive lightings, outdoor displays, backlights for liquid crystal display (LCD) TVs, various handheld devices, printers, and rear projection TVs [1]. These problems are always haunting the highcurrent performance of the traditional LEDs. Recent research on high-voltage light-emitting diode (HV-LED) has shown that multiple series-connected microdiodes in a single large chip can obtain high forward voltage with a low driving current, thereby reducing current crowing and efficiency droop [20,21,22]. Another advantage brought by high-voltage/low current operation is the direct utilization of the regular wall plug outlet without further voltage conversion These features, combined with fewer wire-bonding needed, make HV-LED attractive for commercial applications. A high-voltage flip chip LED (HVFCLED) which consists of n-side up multiple series-connected diodes is demonstrated This design provides high thermal conductivity and high bottom reflection silicon submount. We will discuss fabrications and performance analysis of this device
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