Transmission Electron Microscopy Study of Nonpolar a-Plane GaN Grown by Pendeo-Epitaxy on (112_0) 4H-SiC

Transmission Electron Microscopy Study of Nonpolar a-Plane GaN Grown by Pendeo-Epitaxy on (1120) 4H-SiC. D.N. Zakharov 1 , Z. Liliental-Weber 1 , B. Wagner 2 , Z.J. Reitmeier 2 , E.A. Preble 2 , and R.F. Davis 2 Lawrence Berkeley National Laboratory, MS 62-203, Berkeley, CA 94720 North Carolina State University, Raleigh, NC 27695 ABSTRACT Pendeo-epitaxy has been applied to nonpolar a-plane GaN layers in order to observe if such process will lead to defect reduction in comparison with direct growth on this plane. Uncoalesced and coalesced a-plane GaN layers with thicknesses 2μm and 12μm, respectively have been studied by conventional and high resolution electron microscopy. The following structural defects have been observed in pendeo-epitaxial layers: (1) basal stacking faults, (2) threading dislocations and (3) prismatic stacking faults. Drastic decrease of threading dislocation density and stacking faults have been observed in ‘wing’ areas with respect to ‘seed’ areas. Cross-section images reveal cracks and voids at the areas where two coalesced wings meet each other. High resolution electron microscopy shows that the majority of stacking faults are low-energy planar defects of the types I 1 , I 2 and I 3 . The I 3 type basal stacking fault, predicted theoretically, has been observed experimentally for the first time. INTRODUCTION Recent studies have shown that spontaneous polarization and piezoelectric effect can be eliminated in GaN grown along non-polar directions, such as [1120] and [1100] [1,2]. These two effects were observed in GaN layers grown along [0001] direction and led to high interface charge densities and spatial separations of electron and holes wave functions in GaN-based quantum well structures [3]. Transmission electron microscopy investigations performed on (1100) (m-plane) and (1120) (a-plane) GaN layers grown by heteroepitaxial methods on different substrates revealed, however, high density of basal stacking faults (BSFs) and associated with them threading dislocations [4-6]. Since Pendeo- epitaxy (PE) was proven to be effective method for defects reduction in GaN [7], we applied this method for a-plane GaN grown by metalorganic vapor phase epitaxy on (1120) 4H-SiC substrates with AlN buffer layers. Uncoalesced and coalesced samples have been produced. These samples have been studied by transmission electron microscopy (TEM) in cross-section and plan-view configuration in order to investigate structural defects present in the layers and detect possible defects reduction. EXPERIMENTAL The epitaxial AlN buffer layers, the subsequently deposited epitaxial GaN seed films and the pendeo-epitaxial (PE) GaN layers were grown in-situ in a cold-wall, vertical,