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Direct microscopic correlation of real structure and optical properties of semipolar GaN based on pre‐patterned r ‐plane sapphire
Author(s) -
Metzner Sebastian,
Bertram Frank,
Hempel Thomas,
Meisch Tobias,
Schwaiger Stephan,
Scholz Ferdinand,
Christen Jürgen
Publication year - 2016
Publication title -
physica status solidi (b)
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.51
H-Index - 109
eISSN - 1521-3951
pISSN - 0370-1972
DOI - 10.1002/pssb.201552467
Subject(s) - cathodoluminescence , materials science , sapphire , coalescence (physics) , exciton , optoelectronics , gallium nitride , metalorganic vapour phase epitaxy , light emitting diode , luminescence , molecular physics , crystallography , optics , epitaxy , laser , condensed matter physics , nanotechnology , chemistry , physics , layer (electronics) , astrobiology
Spatially resolved cathodoluminescence (CL) microscopy is used to study semipolar { 11 2 ¯ 2 } gallium nitride (GaN) grown out of trenches with c ‐plane‐like sidewalls etched into the r ‐plane { 1 1 ¯ 02 } sapphire substrate. The beneficial effect of growing locally c ‐GaN on c ‐sapphire and subsequent switching to the semipolar growth mode manifests in bending of threading dislocations (TDs) and a + c ‐wing of excellent material properties represented by pure donor‐bound‐exciton emission. The − c ‐wing, on the other hand, is strongly affected by a huge number of stacking faults and other structural defects. An optimized growth process leads to a delayed coalescence of the single GaN stripes which allows to block the complete − c ‐wing including all the defects by a void, and coalescence occurs only between the + c ‐wings consisting of GaN with excellent material quality. The final semipolar { 11 2 ¯ 2 } GaN surface shows exclusively CL of the donor‐bound exciton (D 0 , X) recombination and no other spectral contribution of structural defects and a reduced TD density. After coalescence and further growth a significant increase of the homogeneity of the CL intensity and emission wavelength is observed for thick samples. CL of an InGaN/GaN active region deposited on top reveals homogeneous luminescence properties over the coalesced region showing no modulation related to the pre‐structured growth mode as the defect containing growth domains are effectively blocked.