Effective heat dissipation and higher light extraction efficiency of GaN vertical light emitting diodes for solid state lighting applications

Abstract

Vertical sapphire‐free GaN based LEDs (VLEDs) on metal have shown much better performance and prove to deliver an efficiency much higher than most conventional light source. In this paper we show that in addition to many advantages of VLEDs over conventional LEDs in terms of better current spreading, low operation voltage, higher drive current density, faster heat dissipation, VLEDs also enables top surface engineering for efficient light extraction to further light output. High power white LED having efficiency of 110 lumen/watt was achieved through a combination of surface engineering and optimization of the n‐GaN layer thickness underneath the corrugated pyramids surface. The low operation junction temperature of VLEDs demonstrates excellent heat dissipation capabilities. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Surface roughness of gallium nitride with volcano-like protrusions formed by KrF excimer laser etching

“…3(a). It reveals that the textured surface with curved protrusions and hexagonal cones obtained from the proposed two-step roughening scheme could effectively improve the probability of photons escaping from semiconductor to air [8,15]. …”

Improved light extraction efficiency of GaN-based vertical LEDs using hierarchical micro/subwavelength structures

“…Previously, dry etched micropatterns, KOH wet etched for rough surface, and photochemical etching methods have been used to achieve improved light extraction, which in turn has resulted in significant increases in LEE in GaN-based VLEDs. [15][16][17][18][19][20][21][22] However, GaN-based VLEDs with HSs have not yet been reported despite their important functions. 6) In this paper, we present GaN-based VLEDs with biomimetic HSs; these GaN-based VLEDs consist of coneshaped MSs and tapered SWSs (nanotips), formed using the thermal reflow and self-masked dry etching (SMDE) processes, 23,24) respectively.…”

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

“…Recently, vertically structured GaN-based LEDs (VLEDs) based on the change of a sapphire substrate to a metal or semiconductor substrate have been shown to be very promising in enhancing light output, efficiency, and power capability. 4,5) However, with the existence of a large refractive index difference between GaN (n ¼ 2:45) and air (n ¼ 1), a low critical angle of total internal reflection ($23:6 ) and a poor light extraction ratio (4%) 6) impede the light output power of VLEDs. Over the past decade, numerous surface roughening technologies, such as the use of a patterned sapphire substrate with a laser lift-off (LLO) process, 7) surface roughening using inductively coupled plasma (ICP) dry etching, 8) photoelectrochemical (PEC) etching, 9) the use of a micro-photolithographic system with dry and wet etching, 10) PEC for the roughening of oxide passivation mesa sidewalls, 11) and the use of a Ni nanomask with laser etching, 12) have been demonstrated to increase light extraction efficiency through random scattering from the roughened surface for high-power GaN-based LEDs.…”