No abstract

Epitaxial GaN layers grown on sapphire contain a very large density of defects (threading dislocations, stacking faults, inversion domain boundaries, . . .). Among these defects, we have performed the analysis of the basal stacking faults by high resolution transmission electron microscopy. Two faults, I1 and I2, were identified. The formation of the I1 fault is based on the climb-dissociation process of the (1/3)⟨11-20⟩ or of the [0001] perfect dislocations whereas the I2 fault is due to the shear of the structure leading to a partial dislocation loop.

A diffraction analysis in the transmission electron microscope was carried out on InxGa1−xN layers grown on (0001) sapphire by metalorganic vapor phase epitaxy on top of thick GaN buffer layers. It is found that the ternary InxGa1−xN layers can be chemically ordered. The In and Ga atoms occupy, respectively, the two simple hexagonal sublattice sites related by the glide mirrors and helicoidal axes of the P63 mc symmetry group of the wurtzite GaN. The symmetry of the ordered ternary is subsequently lowered by the disappearance of these operations, and it is shown to agree with the P3ml space group.

The formation of the ͕12 10͖ stacking fault, which has two atomic configurations in wurtzite ͑Ga,Al,In͒N, has been investigated by high-resolution electron microscopy and energetic calculations. It originates from steps at the SiC surface and it can form on a flat ͑0001͒ sapphire surface. A modified Stillinger-Weber potential is used in order to investigate the relative stability of the two atomic configurations which have comparable energy in AIN, whereas the 1 2 ͗101 1͕͘12 10͖ atomic configuration should be more stable in GaN and InN.Experimental evidence is shown in the case of AIN and GaN from high-resolution electron microscopy. Observations carried out in plan-view show the 1 2 ͗101 1͕͘12 10͖ atomic configuration in GaN layers. The 1 6 ͗202 3͘ configuration was found in small areas inside the AIN buffer layer in cross-section observations. It folds rapidly to the basal plane, and when back in the prismatic plane it bears the 1 2

Transmission electron microscopy and KOH etching were used to determine the structure of the carrot defect in 4H-SiC epilayers. The defect consists of two intersecting planar faults on prismatic {11¯00} and basal {0001} planes. Both faults are connected by a stair-rod dislocation with Burgers vector 1∕n [101¯0] with n>3 at the crossover. A Frank-partial dislocation with b=1∕12[44¯03] terminates the basal fault.