Threading dislocation density reduction in GaN/sapphire heterostructures
Large lattice mismatch between GaN and {alpha}-Al{sub 2}O{sub 3} (15%) leads to the possibility of high threading dislocation densities in the nitride layers grown on sapphire. This investigation focused on defect reduction in GaN epitaxial thin layer was investigated as a function of processing variables. The microstructure changes from threading dislocations normal to the basal plane to stacking faults in the basal plane. The plan-view TEM and the corresponding selected-area diffraction patterns show that the film is single crystal and is aligned with a fixed epitaxial orientation to the substrate. The cross-section image of GaN film shows the density of stacking faults is highest in the vicinity of the interface and decreases markedly near the top of the layer. Inverted domain boundaries, which are almost perpendicular to the film surface, are also visible. The concentration of threading dislocation is relatively low ({approximately} 2 x 10{sup 8} cm{sup 2{minus}}), compared to misfit dislocations. The average distance between misfit dislocations was found to be 22 {angstrom}. Contrast modulations due to the strain near misfit dislocations are seen in high-resolution cross-sectional TEM micrograph of GaN/{alpha}-Al{sub 2}O{sub 3} interface. This interface is sharp and does not contain any transitional layer. The interfacial region has a high density of Shockley and Frank partial dislocations. Mechanism of accommodation of tensile, sequence and tilt disorder through partial dislocation generation is discussed. In order to achieve low concentration of threading dislocations the authors need to establish favorable conditions for some stacking disorder in thin layers above the film-substrate interface region.
- Research Organization:
- North Carolina State Univ., Raleigh, NC (US)
- OSTI ID:
- 20104556
- Resource Relation:
- Conference: 1999 Materials Research Society Fall Meeting, Boston, MA (US), 11/28/1999--12/03/1999; Other Information: PBD: 2000; Related Information: In: GaN and related alloys -- 1999. Materials Research Society symposium proceedings, Volume 595, by Myers, T.H.; Feenstra, R.M.; Shur, M.S.; Amano, Hiroshi [eds.], [1050] pages.
- Country of Publication:
- United States
- Language:
- English
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