Publication Date:
2014-02-12
Description:
Growing a GaN film on a patterned Al 2 O 3 substrate is one of the methods of reducing threading dislocations (TDs), which can significantly deteriorate the performance of GaN-based LEDs. In this study, the microstructural details of the GaN film grown on a cone-shaped patterned Al 2 O 3 substrate were investigated using high-resolution transmission electron microscopy and weak-beam dark-field techniques. Various defects such as misfit dislocations (MDs), recrystallized GaN (R-GaN) islands and nano-voids were observed on the patterned Al 2 O 3 surfaces, i.e. the flat surface (FS), the inclined surface (IS) and the top surface (TS), respectively. Especially, the crystallographic orientation of R-GaN between the GaN film and the inclined Al 2 O 3 substrate was identified as $[\overline 1 2\overline 1 0]_{{\rm GaN}} \hbox{//}[\overline 1 101]_{{\rm R - GaN} \,{\rm on}\,{\rm IS}} \hbox{//}[\overline 1 100]_{ {{\rm Al}} _{\rm 2} {\rm O}_{\rm 3}} $ , $(\overline 1 012)_{{\rm GaN}} \hbox{//}(1\overline 1 02)_{{\rm R - Ga}\,{\rm Non}\,{\rm IS}} \hbox{//}(\overline {11} 26)_{ {{\rm Al}} _{\rm 2} {\rm O}_{\rm 3}} $ . In addition, a rotation by 9° between $(10\overline 1 1)_{{\rm R - GaN}} $ and $(0002)_{{\rm GaN}} $ and between $(10\overline 1 1)_{{\rm R - GaN}} $ and $(0006)_{ {{\rm Al}} _{\rm 2} {\rm O}_{\rm 3}} $ was found to reduce the lattice mismatch between the GaN film and the Al 2 O 3 substrate. Many TDs in the GaN film were observed on the FS and TS of Al 2 O 3 . However, few TDs were observed on the IS. Most of the TDs generated from the FS of Al 2 O 3 were bent to the inclined facet rather than propagating to the GaN surface, resulting in a reduction in the dislocation density. Most of the TDs generated from the TS of Al 2 O 3 were characterized as edge dislocations.
Print ISSN:
0022-0744
Electronic ISSN:
1477-9986
Topics:
Electrical Engineering, Measurement and Control Technology
,
Natural Sciences in General
,
Physics
