Lithuanian Journal of Physics article / Lietuvos fizikos žurnalo straipsnis

REDUCTION OF SURFACE ROUGHNESS BY MODIFICATION OF STEP-BUNCHED ALUMINUM NITRIDE LAYERS TOWARDS STEP-FLOW MORPHOLOGY
Nadine Tillner^a,b, Christian Brandl^a, Marc P. Hoffmann^a, Richard Moser^a, Andreas Waag^b, and Hans-Jürgen Lugauer^a
^aOSRAM Opto Semiconductors GmbH, Leibnizstraße 4, 93055 Regensburg, Germany
^bInstitute of Semiconductor Technology, Technische Universität Braunschweig, Hans-Sommer-Straße 66, 38106 Braunschweig, Germany
Email: nadine.tillner@osram-os.com

Received 8 July 2019; accepted 30 September 2019

Conventional aluminum nitride (AlN) template fabrication techniques, like hydride vapour phase epitaxy or AlN growth on patterned sapphire substrates, usually lead to step-bunched template surfaces. The resulting macrosteps cause emission broadening or even multiple-peak characteristics of ultraviolet light-emitting diodes (UV LEDs) fabricated on such AlN templates. In order to reduce these macrosteps and to provide a smoother surface, even without the need of a thick AlN deposition, a two-layer growth procedure is reported here. A three-dimensional (3D) – two-dimensional (2D) sequential growth initiates a significant modification of the previous AlN surface morphology and simultaneously limits the evolving tensile strain. A primarily step-bunched surface with a surface roughness root mean square of 1.8 nm is successfully reduced by the two-layer growth procedure down to 0.8 nm, without any film cracking. This distinct roughness reduction of more than 50% is achieved within an AlN thickness of only 1.3 μm. With a smoother surface, the electroluminescence characteristic of a UV LED structure is substantially improved. Instead of a double-peak emission, typical for LEDs grown on step-bunched templates, a single-peak emission and lower spectral width were achieved, indicating the high potential of the suggested two-layer technique for improving performance.

Keywords: MOVPE, AlN, step-bunching

PAVIRŠIAUS ŠIURKŠTUMO MAŽINIMAS KEIČIANT ALIUMINIO NITRIDO SLUOKSNIŲ LAIPTELIŲ SANKAUPAS TOLYGIU LAIPTELIŲ IŠSIDĖSTYMU
Nadine Tillner^a,b, Christian Brandl^a, Marc P. Hoffmann^a, Richard Moser^a, Andreas Waag^b, Hans-Jürgen Lugauer^a

^aOSRAM Opto Semiconductors GmbH, Rėgensburgas, Vokietija
^bBraunšveigo technikos universiteto Puslaidininkių technologijos institutas, Braunšveigas, Vokietija

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