Surface texturing for wafer-bonded vertical-type GaN/mirror/Si light-emitting diodes

Abstract

An n-side-up GaN/mirror(Pd/Au)/Si light-emitting diode (LED) with surface texturing has been fabricated by a combination of wafer-bonding, laser lift-off, and surface texturing techniques. Two concentrations of KOH solution were used to roughen the n-GaN surface. In order to obtain a uniformly roughened surface, the solution was heated instead of being subjected to photoirradiation. The GaN/Pd/Au/Si LEDs with surface texturing exhibited a maximum luminance intensity of 130 mcd (at 20 mA) with a forward voltage of 3.2 V. The luminance intensity is over two times larger than that of the original planar GaN/sapphire LEDs (at 20 mA). Under high current injection, the surface textured GaN/Pd/Au/Si LEDs also showed a more stable luminance intensity. This feature is attributed to the Si substrate providing a good heat sink and surface roughening enhancing the external quantum efficiency. Furthermore, the n-side-up GaN/mirror(Pd/Au)/Si LEDs with surface texturing have been demonstrated to have high reliability.