High performance InGaN LEDs on Si (1 1 1) substrates grown by MOCVD

Abstract

We report high performance InGaN multiple-quantum well (MQW) light-emitting diodes (LEDs) grown on Si (1 1 1) substrates using metalorganic chemical vapour deposition (MOCVD). A high-temperature thin AlN layer and AlN/GaN multilayers have been used for the growth of a high-quality GaN-based LED structure on Si substrates. Reduction of the high-temperature AlN layer thickness promotes the formation of a tunnel junction at the AlN/Si interface which reduces the LED operating voltage. Optical output power of the LED on Si saturates at a higher injected current density due to higher thermal conductivity of Si than that of a sapphire substrate. At a high injection current, output power of the LED on Si is higher than that of the LED on sapphire. Cross-sectional transmission electron microscopy (TEM) indicates that the active layer of these LEDs consists of a dislocation-free pyramid-shaped (quantum-dot-like) structure. Additionally, the crack-free thin-film LED epilayer region was transferred onto a copper carrier using metal-to-metal bonding and the selective lift-off technique. A LED with high output power, low operating voltage and low series resistance was realized by this technique. Furthermore, optimization of LED on Si by insertion of an Al0.06Ga0.94N/GaN strained-layer superlattice underlayer into the structure exhibits improved internal quantum efficiency (ηiqe) in the MQW, higher optical emission intensity with higher saturation current, lower operation voltage of 3.2 V at 20 mA and a series resistance of 16 Ω, as well as narrower electroluminescence spectra.