Defect structure in heteroepitaxial semipolar (11¯22) (Ga, Al)N
Résumé
The defect structures in semipolar (11¯22)-GaN, AlN layers grown on m-sapphire by metal organic vapor phase epitaxy (MOVPE) and molecular beam epitaxy (MBE) are characterized by transmission electron microscopy. The epitaxial relationships are identified as [10¯10]GaN ǁ [11¯20]sap and [1¯213]GaN ǁ [0001]sap. Defects are identified as mostly partial dislocations, I1-basal and prismatic stacking faults. The density of dislocations is of the order of 5.5 × 109 cm−2. They are Frank–Shockley partial dislocations with b = 1/6〈20¯23〉 (90%), Shockley partial dislocations with b = 1/3〈10¯10〉 (8%) and perfect dislocations of a-type with b = 1/3〈11¯20〉 (2%). This is in contrast with the growth in c- or a-orientations, where the large majority of extended defects consists of perfect dislocations. Upon MBE regrowth of GaN on MOVPE GaN, no additional defects are generated, although the defects in the substrate propagate through the overgrown layer. However, in the case of MBE deposition of AlN on MOVPE GaN, new threading dislocations of the type b = 1/3〈11¯23〉 are generated taking stepped and curved structures along their lines.