Enhanced Light Output of Vertical-Structured GaN-Based Light-Emitting Diodes with TiO₂/SiO₂ Reflector and Roughened GaO_x Surface Film

Abstract

GaN-based thin-film vertical-structured light-emitting diodes (VLEDs) with a GaO x film atop an n-GaN layer roughened via KrF laser irradiation and a TiO 2 /SiO 2 distributed Bragg reflector (DBR) are proposed and investigated. As compared with regular VLEDs with an Al reflector and without a roughened GaO x film, the proposed VLEDs with a chip size of 1 mm 2 show a typical increase in light output power by 68% at 350 mA and by 51% at 750 mA, which is attributed to the enhanced reflectivity and current blocking capability of the DBR layer, the surface roughening with circular GaN protrusions, and the formation of a surface GaO x film by KrF laser irradiation. #

Enhanced performance of large‐area vertical light‐emitting diodes treated by laser irradiation

“…Nevertheless, the light‐extraction efficiency of the vertical LEDs (VLEDs) is limited due to the presence of the flat surface of the n‐GaN, which results in a poor light‐extraction ratio of ∼4%. This discrepancy has the ultimate effect of causing a large refractive index difference between the GaN ( n = 2.45) layer and the surrounding air ( n = 1), which possesses a low critical angle of total internal reflection [10]. Numerous surface roughening processes, such as nanoimprint lithography [12], patterned sapphire substrates [13], surface texturing process [14], photonic crystal structures [15], and nanoparticle arrays [16], have been proposed to enhance the light‐extraction efficiency through random scattering from the roughened surface.…”

“…Recent research has proposed the use of vertically structured GaN-based LEDs [7][8][9], which are fabricated by transferring epitaxial structures to a metal or semiconductor substrate through a laser lift-off (LLO) process, followed by undoped GaN (u-GaN) removal. Such an n-side-up configuration has been demonstrated to be an effective technique for improving light output efficiency, thereby reducing the effects of current crowding and heat loss [10]. The vertical-conducting n-side-up configuration has been demonstrated to be very effective in improving device properties by reducing the current crowding effect and the heat loss [11].…”

Enhanced Performance of GaN-Based Light-Emitting Diodes by Using Al Mirror and Atomic Layer Deposition-TiO2/Al2O3Distributed Bragg Reflector Backside Reflector with Patterned Sapphire Substrate

“…10) TiO 2 and SiO 2 are widely used materials for making the backside reflector, and the TiO 2 and SiO 2 thin films are generally fabricated by electron beam (EB) evaporation. [11][12][13][14][15] Unfortunately, the quality of the backside reflector prepared by EB evaporation is limited by its poor film uniformity and accuracy in thickness control. Furthermore, in order to grow an Al mirror on the conventional TiO 2 /SiO 2 DBR, an Al 2 O 3 adhesive layer is usually used to improve the adhesion between Al and the TiO 2 /SiO 2 DBR.…”