This paper reports the proposal, design, and demonstration of ultra-thin GaAs single-junction solar cells integrated with a reflective back scattering layer to optimize light management and minimize non-radiative recombination. According to our recently developed semi-analytical model, this design offers one of the highest potential achievable efficiencies for GaAs solar cells possessing typical non-radiative recombination rates found among commercially available III-V arsenide and phosphide materials. The structure of the demonstrated solar cells consists of an In0.49Ga0.51P/GaAs/In0.49Ga0.51P double-heterostructure PN junction with an ultra-thin 300 nm thick GaAs absorber, combined with a 5 μm thick Al0.52In0.48P layer with a textured as-grown surface coated with Au used as a reflective back scattering layer. The final devices were fabricated using a substrate-removal and flip-chip bonding process. Solar cells with a top metal contact coverage of 9.7%, and a MgF2/ZnS anti-reflective coating demonstrated open-circuit voltages (Voc) up to 1.00 V, short-circuit current densities (Jsc) up to 24.5 mA/cm2, and power conversion efficiencies up to 19.1%; demonstrating the feasibility of this design approach. If a commonly used 2% metal grid coverage is assumed, the anticipated Jsc and conversion efficiency of these devices are expected to reach 26.6 mA/cm2 and 20.7%, respectively.

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Substrate orientation plays a critical role in determining SiC epilayer quality, but limited work has been done to examine the effect of offcut directions on 4H-SiC epilayers. 4H-SiC epilayers were grown on substrates offcut 8° towards either the 〈11̄00〉 or the 〈112̄0〉 crystalline direction. Epilayers up to 15.5 μm thick, possessing smooth morphologies free of large-scale step bunching, were grown on both substrate orientations. Triangular defects were observed primarily on the wafer periphery, and the triangular defect density depended only on offcut angle. Atomic force microscopy analysis confirmed smooth surfaces for epilayers up to 15.5 μm thick grown on 〈11̄00〉 offcut substrates. Low-energy electron diffraction analysis of epilayers grown on substrates offcut towards 〈11̄00〉 showed an ordered surface. Nitrogen and aluminum doping were successfully obtained for epilayers grown on substrates offcut towards 〈11̄00〉, and n-type and p-type doping control were demonstrated.

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The morphological and impurity properties of 4H-SiC epilayers grown using graphite susceptors coated with vitreous carbon, SiC, TaC, and NbC were compared. Metal carbide coated susceptors produced epilayers with smooth morphologies and no thick backside polycrystalline SiC deposition. Epilayers grown using metal carbide coated susceptors possessed more than 10 times higher intentional N 2 doping efficiencies and more than 10 times lower unintentional Al concentrations compared to epilayers grown using vitreous carbon coated susceptors. Metal carbide coated susceptors permitted doping control and abrupt p.n. junctions, and possessed more than 10 times longer lifetimes compared with vitreous carbon or SiC coated susceptors.