Compositionally graded Ga1−xInxP buffers grown by static and dynamic hydride vapor phase epitaxy at rates up to 1 μm/min

We demonstrate Ga1−xInxP compositionally graded buffers (CGBs) grown on GaAs with lattice constants between GaAs and InP by hydride vapor phase epitaxy (HVPE). Growth rates were up to ∼1 μm/min, and the threading dislocation density (TDD) was as low as 1.0 × 106 cm−2. We studied the effect of the substrate offcut direction, growth rate, and strain grading rate on the CGB defect structure. We compared the effect of a “dynamic” grading style, which creates compositional interfaces via mechanical transfer of a substrate between two growth chambers, vs “static” grading where the CGB grows in a single chamber. Dynamic grading yielded smoother grades with higher relaxation, but TDD was not significantly different between the two styles. The substrate offcut direction was the most important factor for obtaining CGBs with low defect density. (001) substrates offcut toward (111)B yielded smoother CGBs with lower TDD compared to CGBs grown on substrates offcut toward (111)A. Transmission electron microscopy of static and dynamic CGBs grown on A- and B-offcuts only found evidence of phase separation in a static A-offcut CGB, indicating that the B-offcut limits phase separation, which, in turn, keeps TDD low. Reductions in growth rate led to the appearance of CuPt-type atomic ordering, which affected the distribution of dislocations on the active glide planes but did not alter TDD significantly. Higher growth rates led to smoother CGBs and did not appreciably increase TDD as otherwise predicted by steady-state models of plastic relaxation. These results show HVPE's promise for lattice-mismatched applications and low-cost InP virtual substrates on GaAs.