Regensburg 2025 – scientific programme

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HL: Fachverband Halbleiterphysik

HL 33: Nitrides: Devices

HL 33.2: Talk

Wednesday, March 19, 2025, 11:30–11:45, H15

Homoepitaxy on AlN-bulk substrates with different off-cut angles — •Sebastian Krüger¹, Sarina Graupeter¹, Massimo Grigoletto^{1, 2}, Marcel Schilling¹, Sylvia Hagedorn², Carsten Hartmann³, Thomas Straubinger³, Tim Wernicke¹, and Michael Kneissl^{1, 2} — ¹Technische Universität Berlin, Institute of Solid State Physics, Berlin, Germany — ²Ferdinand-Braun-Institut (FBH), Berlin, Germany — ³Leibniz-Institut für Kristallzüchtung, Berlin, Germany

Laser diodes in the UVC spectral range require high-quality AlN and AlGaN layers with low threading dislocation densities (TDD) and smooth surfaces. AlN substrates with a TDD of < 10⁴ cm^-2 are the ideal choice. In this work we investigate the influence of substrate off-cut (0.1^∘ to 0.5^∘) and growth parameters (e.g. TMAl flow, V/III-ratio) on the morphology of homoepitaxially grown AlN buffer layers. A transition from step flow growth for a 0.2^∘ miscut AlN substrate to step bunching for miscuts of 0.39^∘ and above is observed for a growth temperature of 1070^∘C, a TMAl flow of 35 µmol/min and a V/III-ratio of 15. For a miscut of 0.27^∘ step flow growth is still present but the terrace width shows significant variation. The RMS roughness increases from 0.11 nm (on 0.2^∘) to 0.45 nm (on 0.39^∘). For 0.5^∘ miscut, the substrate terrace width is even smaller, i.e. the diffusion length must be reduced to avoid step bunching e.g. by increasing the V/III-ratio. Between V/III ratios of 15 and 60 we found morphologies such as island growth and step meandering with the lowest RMS roughness of 0.11 nm for a TMAl flow of 35 µmol/min and a V/III-ratio of 15.

Keywords: Aluminiumnitride; Homoepitaxy; Off-cut; Surface kinetics; AlN