Defect reduction in (1120) a-plane GaN by two-stage epitaxial lateral overgrowth

摘要

The authors report a two-stage epitaxial lateral overgrowth (ELO) method to get uniformly coalesced (1120) 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 X 10~8 cm~(-2), more than two orders of magnitude lower than that in the window areas (4.2 X 10~(10) cm~(-2)). However, high density of basal stacking faults of 1.2 X 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.