Defect structure in heteroepitaxial semipolar (11(2)over-bar2) (Ga, Al)N

The defect structures in semipolar (11 (2) over bar2)-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 (1) over bar0](GaN) parallel to [11 (2) over bar0]sap and [1 (2) over bar 13](GaN) parallel to [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 x 10(9) cm(-2). They are Frank-Shockley partial dislocations with b = 1/6 < 20 (2) over bar3 > (90%), Shockley partial dislocations with b = 1/3 < 10 (1) over bar0 > (8%) and perfect dislocations of a-type with b = 1/3 < 11 (2) over bar0 > (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 (2) over bar3 > are generated taking stepped and curved structures along their lines.