Low Dislocations Density GaN/Sapphire for Optoelectronic Devices

Abstract

It is nowadays well established that threading dislocations (TDs) are degrading the performances and the operating lifetime of optoelectronic GaN-based devices (LDs and UV-LEDs). GaN/sapphire layers have been grown by Metal Organic Vapor Phase Epitaxy (MOVPE). An amorphous silicon nitride layer is deposited using a SiH4/NH3 mixture prior to the growth of the low temperature GaN buffer layer. Such a process induces a 3D nucleation at the early beginning of the growth, resulting in a kind of ELO process with intrinsic random opening sizes. This produces a significant decrease of the TDs density compared to the best GaN/sapphire templates. GaN layers with TD density as low as 7 × 107 cm-2 were obtained, as measured by atomic force microscopy (AFM), cathodoluminescence (CL) and transmission electron microscopy (TEM). The two-step epitaxial lateral overgrowth technology (2S-ELO) allows decreasing the TDs around 107 cm-2. These templates are suitable for fabricating LDs. Regrowth by HVPE on this ELO GaN/sapphire further decreases the TDs density below 106 cm-2.