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Study of the Growth and Dislocation Blocking Mechanisms in InxGa1−xAs Buffer Layer for Growing High-Quality In0.5Ga0.5P, In0.3Ga0.7As, and In0.52Ga0.48As on Misoriented GaAs Substrate for Inverted Metamorphic Multijunction Solar Cell Application

Abstract Effects of growth conditions and buffer structures on crystal quality of 1.9-eV In0.5G0.5P, 1-eV In0.3Ga0.7As, and 0.75-eV In0.52Ga0.48As materials on misoriented GaAs substrate for inverted metamorphic solar cell grown by metalorganic chemical vapor deposition have been studied. Large lattice mismatch issue between the two lower bandgap 1.0-eV In0.3Ga0.7As and 0.75-eV In0.52Ga0.48As epilayers and the substrate has been resolved by using optimized step-graded buffer layers. Threading dislocation blocking mechanisms have been studied and discussed. It was indicated that threading dislocations have been significantly blocked in the designed InGaAs buffer layers through annihilation reactions between threading dislocations or through the formation of misfit dislocations. As a result, smooth surface In0.3Ga0.7As and In0.52Ga0.48As epifilms with threading dislocation density of about 1 × 106 cm−2 were obtained. For the growth of InGaP, the surface morphology, crystal quality, ordering parameter, and InGaP composition were significantly affected by growth temperature, V/III ratio, and III/III ratio. The almost lattice match to the substrate, high crystal quality, and smooth surface of In0.495Ga0.505P were obtained at growth temperature of 675°C and V/III ratio above 150. The ordering parameter was strongly dependent on growth temperature. Photoluminescence measurement indicated that the bandgap of the InGaP epilayer is 1.89 eV, indicating that the solid composition in the InGaP film is more disordered.