1. Low dislocations density GaN/sapphire for optoelectronic devices Low dislocations density GaN/sapphire for optoelectronic devices B. Beaumont, J-P. Faurie, E. Frayssinet, E. Aujol and P. Gibart, Lumilog, 06220-Vallauris-FRANCE It is nowadays well established that threading dislocations (TDs) are degrading the performances and the operating lifetime of optoelectronics GaN based devices (LDs and UV-LEDs). GaN/sapphire layers have been grown by Metal Organic Vapour Phase Epitaxy (MOVPE). A silicon nitride layer is deposited using a SiH 4 /NH 3 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 intrinsic random mask ELO process. This produces a significant decrease of the TDs density compared to the best GaN/sapphire templates. GaN layers with TD density as low as 7×10 7 cm -2 were obtained (as measured by atomic force microscopy (AFM), cathodoluminescence and transmission electron microscopy (TEM)). The two-step epitaxial lateral overgrowth technology (2S-ELO) allows decreasing the TDs around 10 7 cm -2. These templates are suitable for fabricating LDs. Regrowth by HVPE on these ELO GaN/sapphire further decreases the TDs density below 5×10 6 cm -2. GaN/template: The Si/N treatment of the sapphire substrate creates an intrinsic random mask, thus resulting in a micro-ELO process Comparison between reflectivity spectra recorded during the growth of GaN/sapphire standard epilayer and Ultra Low dislocation (ULD) GaN/sapphire. Arrows indicate where the growth starts High Resolution image of the interface in a ULD GaN/sapphire sample. Cross-sectional bright field image of the ULD GaN/sapphire sample showing the interface region. GaN/ELO: Two steps ELO Template 2S-ELO 1S-ELO Epitaxial growth of 2µm GaN deposition of SiN Selective Epitaxy (SAE) Lateral Overgrowth Selective Epitaxy (SAE) and Lateral Overgrowth Cross section along the [10- 10] zone axis of a 2S-ELO film at the end of the second step CL map of a GaN layer grown with the two-step process. Each dark spot corresponds to a merging TD at the surface Free standing GaN (HVPE) Characteristics SampleFWHM of near band gap PL at 10K TRPL (A exciton) TDs density measured by AFM and CL Standard<3meV80 ns 5×10 8 cm -2 ULD<2meV220 ns 7×10 7 cm -2 2S-ELO<1meV375ns 5×10 6 cm -2 Between stripes Free-standing 1×10 6 cm -2 Full wafer Devices: UV detectors and LEDs 250300350400450 10 -5 10 -4 10 -3 10 -2 10 10 0 ELOG GaN GaN / Sapphire Normalized Responsivity Wavelength, nm 250300350400450 1x10 -5 1x10 -4 1x10 -3 1x10 -2 1x10 1x10 0 Normalized Responsivity Wavelength (nm) 250300350400450 10 -5 10 -4 10 -3 10 -2 10 10 0 ELOG GaN GaN / Sapphire Normalized Responsivity Wavelength, nm 250300350400450 10 -5 10 -4 10 -3 10 -2 10 10 0 ELOG GaN GaN / Sapphire Normalized Responsivity Wavelength, nm 250300350400450 1x10 -5 1x10 -4 1x10 -3 1x10 -2 1x10 1x10 0 Normalized Responsivity Wavelength (nm) 250300350400450 10 -5 10 -4 10 -3 10 -2 10 10 0 ELOG GaN GaN / Sapphire Normalized Responsivity Wavelength, nm ELOG GaN Micro-ELO GaN GaN/Sapphire CL map of a free standing GaN grown by HVPE and separated from the sapphire substrate, TDs density 10 6 cm -2 Images from MFA, Budapest Data from U. Politechnica, Madrid From Yasan et al, APL, 81, 2151(2002)