No abstract

Thick GaN bars with ͓112 គ 0͔ orientation have been sliced from GaN boules grown on freestanding films by hydride vapor phase epitaxy ͑HVPE͒ in the ͓0001͔ direction. High-resolution x-ray diffraction and transmission electron microscopy have been used to study the structural quality and defect distribution in the material in comparison to heteroepitaxially grown thick HVPE-GaN films grown in the ͓112 គ 0͔ direction on ͑11 គ 02͒-plane sapphire. It is demonstrated that while the heteroepitaxial material possesses a high density of stacking faults and partial dislocations, leading to anisotropic structural characteristics, the ͑112 គ 0͒-plane bulk GaN, sliced from boules, exhibits low dislocation density and narrow rocking curves with isotropic in-plane character.

Bulk GaN substrates grown by HVPE in the [0001] direction and sliced along the (11-20) a-plane and the (1-100) m-plane have been studied by SEM, TEM, HRXRD, CL and PL. Smooth morphology, low defect density, and narrow linewidths of the main XRD reflections and PL peaks are revealed and thus all the results demonstrate superior structural and optical quality of both a-and m-plane bulk GaN material achieved by HVPE growth of boules in the conventional [0001] direction and subsequently sliced along nonpolar planes, implying the approach as the most promising to produce nonpolar GaN substrates.