Berlin 2018 – scientific programme

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HL: Fachverband Halbleiterphysik

HL 22: Nitrides: Preparation and characterization I

HL 22.4: Talk

Tuesday, March 13, 2018, 14:45–15:00, EW 203

Investigation of AlN layer growth evolution under a Ga surfactant effect — •Christopher Hein, Heiko Bremers, Uwe Rossow, and Andreas Hangleiter — Institute of Applied Physics, Braunschweig, Germany

A key problem for high quality growth of AlN in MBE are low growth temperatures as well as the tendency to droplet formation in a metal rich regime. The latter can be overcome by codeposition of gallium as a surfactant during growth. We will investigate the evolution of thin AlN epilayers (10nm to 40nm thickness) under gallium surfactant. The samples were grown on MOVPE 2.5µm thick GaN layers on c-oriented sapphire substrates. The MBE growth starts with a 20nm GaN buffer layer grown at 745^∘C followed by an AlN epilayer in a double-pulsed growth scheme. Metal pulses were 22s long, followed by 25s nitrogen. In case of surfactant samples, gallium was supplied in parallel to aluminum. The total ratio of gallium contributing to the group III flux was fixed at 26% in the gas phase. Symmetric 2θ-ω-scans around the (0002) and (1010) reflex for samples grown with gallium surfactant show a residual GaN surface layer, formed after growth from accumulated gallium. As a consequence a sample series was grown which implemented a desorption step for the surface gallium. AFM of samples shows the tendency to crack formation for all samples, indicative for an onset of relaxation as confirmed by XRD. The surfactant and desorption treated samples show an additional reduction in surface RMS roughness value. This is attributed to a benefiting effect of the gallium surfactant on lateral growth of the AlN layer.