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We present an inverted metamorphic rear heterojunction ∼1.0 eV GaInAs solar cell deposited by dynamic hydride vapor phase epitaxy (D-HVPE) with high growth rate. This device uses a Ga1−xInxP compositionally graded buffer (CGB) to bridge the lattice constant gap between the GaAs substrate and the Ga0.71In0.29As emitter layer. High-resolution x-ray diffraction and transmission electron microscopy confirm that the Ga0.71In0.29As emitter is grown lattice-matched to the in-plane lattice constant of the CGB with minimal generation of defects at the GaInAs/GaInP interface. The device contains a threading dislocation density of 2.3 × 106 cm−2, a level that enables high-performance minority carrier devices and is comparable to previously demonstrated GaInP CGBs grown by D-HVPE. The device exhibits an open-circuit voltage of 0.589 V under a one-sun AM1.5G illumination condition and a bandgap-voltage offset of 0.407 V, indicating metamorphic epitaxial performance nearly equal to state-of-the-art devices. We analyze the dark current of the device and determine that reducing recombination in the depletion region, which can be achieved by reducing the threading dislocation density and optimizing the device doping density, will improve the device performance. The CGB and device layers, comprising ∼8 μm of thickness, are grown in under 10 min, highlighting the ability of D-HVPE to produce high-quality metamorphic devices of all types with the potential for dramatically higher throughput compared to present technology. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]