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Determination of Sapphire Off‐Cut and Its Influence on the Morphology and Local Defect Distribution in Epitaxially Laterally Overgrown AlN for Optically Pumped UVC Lasers
Author(s) -
Enslin Johannes,
Knauer Arne,
Mogilatenko Anna,
Mehnke Frank,
Martens Martin,
Kuhn Christian,
Wernicke Tim,
Weyers Markus,
Kneissl Michael
Publication year - 2019
Publication title -
physica status solidi (a)
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.532
H-Index - 104
eISSN - 1862-6319
pISSN - 1862-6300
DOI - 10.1002/pssa.201900682
Subject(s) - sapphire , epitaxy , materials science , transmission electron microscopy , optics , laser , diffraction , ultraviolet , optoelectronics , morphology (biology) , scanning electron microscope , nanotechnology , layer (electronics) , physics , biology , composite material , genetics
Herein, a systematic study of the morphology and local defect distribution in epitaxially laterally overgrown (ELO) AlN on c ‐plane sapphire substrates with different off‐cut angles ranging from 0.08° to 0.23° is presented. Precise measurements of the off‐cut angle α , using a combination of optical alignment and X‐ray diffraction with an accuracy of ±5° for the off‐cut direction and ±0.015° for the off‐cut angle, are carried out. For ELO AlN growth, a transition from step flow growth at α < 0.14° with height undulations on the surface to step bunching with step heights up to 20 nm for α > 0.14° is observed. Furthermore, the terraces of the step‐bunched surface exhibit curved steps. An analysis of the local defect distribution by scanning transmission electron microscopy and a comparison with atomic force microscopy reveal a bunching of defects in line with the ELO pattern and a roughening of step edges in highly defective regions. In addition, a reduction in the threshold excitation power density for optically pumped ultraviolet‐C (UVC) lasers with smooth surface morphologies is observed.