Defect reduction in ( 11 2 ¯ 0 ) a -plane GaN by two-stage epitaxiallateral overgrowth

• Published in: Applied physics letters 2006-12, Vol.89 (26), p.262105-262105-3
• Main Authors: Ni, X., Özgür, Ü., Fu, Y., Biyikli, N., Xie, J., Baski, A. A., Morkoç, H., Liliental-Weber, Z.
• Format: Article
• Language: English
• Subjects: ATOMIC FORCE MICROSCOPY; CHEMICAL VAPOR DEPOSITION; COALESCENCE; DEFECTS; DISLOCATIONS; MATERIALS SCIENCE; PHOTOLUMINESCENCE; STACKING FAULTS; TRANSMISSION ELECTRON MICROSCOPY; WINDOWS
• ISSN: 0003-6951; 1077-3118
• DOI: 10.1063/1.2423328

The authors report a two-stage epitaxial lateral overgrowth (ELO) method to get uniformly coalesced ( 11 2 ¯ 0 ) a -plane GaN using metal organic chemical vapor deposition by employing a relatively lower growth temperature in the first stage followed by conditions leading to enhanced lateral growth in the second. Using a two-stage ELO method the average Ga-polar to N-polar wing growth rate ratio has been reduced from 4-6 to 1.5-2, which consequently reduced the height difference between the two approaching wings at the coalescence front that resulted from the wing tilt (0.44° for Ga and 0.37° for N wings, measured by x-ray diffraction), thereby making their coalescence much easier. Transmission electron microscopy showed that the threading dislocation density in the wing areas was 1.0 × 10 8 cm − 2 , more than two orders of magnitude lower than that in the window areas ( 4.2 × 10 10 cm − 2 ) . However, high density of basal stacking faults of 1.2 × 10 4 cm − 1 was still present in the wing areas as compared to c -plane GaN where they are rarely observed away from the substrate. Atomic force microscopy and photoluminescence measurements on the coalesced ELO a -plane GaN sample also indicated improved material quality.