Jing-Hui Zheng

Enhanced light output in nitride-based light-emitting diodes by roughening the mesa sidewall

In this letter, we will report on a nitride-based light emitting diode with a mesa sidewall roughening process that increases light output power. The fabricated GaN-based light-emitting diode (LED) wafers were first treated through a photoelectrochemical (PEC) process. The Ga/sub 2/O/sub 3/ layers then formed around the GaN : Si n-type mesa sidewalls and the bottoms mesa etching regions. Selective wet oxidation occurred at the mesa sidewall between the p- and the n-type GaN interface. The light output power of the PEC treated LED was seen to increase by about 82% which was caused by a reduced index reflectance of GaN-Ga/sub 2/O/sub 3/-air layers, by a rough Ga/sub 2/O/sub 3/ surface, by a microroughening of the GaN sidewall surface, and by a selective oxidation step profile of the mesa sidewall that increases the light-extraction efficiency from the mesa sidewall direction. Consequently, this wet PEC treated process is suitable for high powered nitride-based LEDs lighting applications.

High-efficiency InGaN-based light-emitting diodes with nanoporous GaN:Mg structure

In this research nanoporous structures on p-type GaN:Mg and n-type GaN:Si surfaces were fabricated through a photoelectrochemical (PEC) oxidation and an oxide-removing process. The photoluminescence (PL) intensities of GaN and InGaN∕GaN multi-quantum-well (MQW) structures were enhanced by forming this nanoporous structure to increase light extraction efficiency. The PL emission peaks of an MQW active layer have a blueshift phenomenon from 465.5nm (standard) to 456.0nm (nanoporous) measured at 300K which was caused by partially releasing the compressive strain from the top GaN:Mg layers. The internal quantum efficiency could be increased by a partial strain release that induces a lower piezoelectric field in the active layer. The thermal activation energy of a nanoporous structure (85meV) is higher than the standard one (33meV) from a temperature dependent PL measurement. The internal quantum efficiency and light extraction efficiency of an InGaN∕GaN MQW active layer are significantly enhanced by this nano...

Enhanced Light Output Power in InGaN Light-Emitting Diodes by Fabricating Inclined Undercut Structure

The InGaN-based light-emitting diode (LED) with an inclined undercut structure is fabricated through the photoelectrochemical two-step process to increase light extraction efficiency. In the first step the sidewall-undercut structure at the p-type and n-type GaN interface is created by selective wet oxidation on an n-type GaN surface in pure H 2 O solution. In the second step an inclined undercut structure through a crystallographic wet-etching process is formed by immersion in hot KOH solution. This crystallographic wet-etching process can remove the Ga 2 O 3 layer and form a {1011} p-type GaN stable plane, {1010} n-type GaN stable plane on the mesa sidewall. This inclined p-type GaN plane of LED structure can provide the higher overlap of incident light beam core and extraction core overlap on the mesa sidewall, and the total light output power of the treated LED is 2.10 times higher than the standard LED. Consequently, this inclined undercut LED structure is suitable for high-efficiency nitride-based LED application.

High-Efficiency InGaN Light-Emitting Diodes Via Sidewall Selective Etching and Oxidation

Photoelectrochemical etching and oxidation of the sidewall structures of InGaN light-emitting diodes has been utilized to significantly improve optical emission efficiency. Only with an H 2 O solution can n-type InGaN/GaN multi-quantum-well (MQW) and n-type GaN:Si layers be selectively etched off from the p-type GaN:Mg epitaxial layer. In addition, the sidewall of n-type MQW/n-type GaN layers will be oxidized and etched simultaneously. This is attributed to the interposing of a Ga 2 O 3 layer with a low reflective index between the GaN and air as well as with the rough Ga 2 O 3 /GaN structures. Under a 20 mA operating current, and after a 10 min photoelectrochemical (PEC) oxidation process, the light output power increased by 42%. This PEC oxidizing and etching process is suitable for high-power nitride-based light-emitting diode lighting applications.

Fabricated the inclined-undercut structure in high efficiency InGaN-based light emitting diodes

The high efficiency InGaN-based light emitting diodes with an inclined-undercut mesa structures are fabricated through photoelectrochemical selective oxidation process at p-n interface and following crystallographic wet etching in molten KOH solution.

Fabrication InGaN nanodisk structure in GaN reverse hexagonal pyramid

Small self-assembled inverted hexagonal pyramids consisting of GaN:Mg and InGaN/GaN multi-quantum-well (MQW) structures were fabricated using photoelectrochemical wet etching. Lateral etching, bottom-up etching, and anisotropic etching are the sequential formation mechanism of such pyramids during the wet etching. The inverted hexagonal pyramids were measured to be 245 nm in width and 184 nm in height, and the angle between the top GaN:Mg surface and the pyramid sidewall was calculated to be about 56.3°. Due to the strain relief in the nano-disk MQW structure, we induced an emission peak of photoluminescence at the tip of the inverted hexagonal pyramids, which had a strong blue shift of 244 meV measured at 100 K.