Tilt generation and phase separation in metamorphic GaInP buffers grown on GaAs substrates by metal-organic chemical vapor deposition

Compositionally step-graded ((Al)Ga)(x)In1-xP (x=0.52-0.22) buffers and following In0.3Ga0.7As cap layers are grown by metal-organic chemical vapor deposition on (001) GaAs substrates with different miscuts toward (111)A. The tilt with respect to the substrate and phase separation in GaxIn1-xP buffer layers are investigated by x-ray reciprocal space mapping and transmission electron microscopy. It is found that a large negative tilt is generated in the [110] direction due to the preferential nucleation of alpha dislocations with tilt component along [00 (1) over bar] and that a positive tilt in the [1 (1) over bar0] direction is introduced by the wavy surface undulations along [1 (1) over bar0] when growing the GaxIn1-xP buffer and enhanced by preferential glide of the existing beta dislocations in the ((1) over bar 11) slip plane during the growth of the In0.3Ga0.7As cap layer. The phase separation in the GaxIn1 xP buffer layer, acting as the main source of threading dislocations in the In0.3Ga0.7As cap layer, has been suppressed by increasing the number of steps in the buffer layer and thickness and utilizing (Al0.3Ga0.7)(0.22)In0.78P layer as the top buffer layer. Finally, In0.3Ga0.7As layers with a low threading dislocation density are obtained on the top AlGaInP layer due to the lattice hardening effect and this improvement is confirmed by the photoluminescence measurements. (C) 2012 Elsevier B.V. All rights reserved.