Characterization of thin GaAs films grown on nanostructured silicon substrates

Compound semiconductor multi-junction solar cells are limited to small sizes (4-inch diameters) and are expensive due to starting wafer costs such as Ge and GaAs. High-quality GaAs films grown on Si substrates addresses many of these challenges. GaAs growth on high aspect ratio Si nanostructures has been investigated. High aspect ratio nanostructures can serve as templates for defect reduction as well as sacrificial layers. Thin (~5 μm) films of GaAs have been grown on a wide range of Si nanostructures using MBE and MOCVD methods. Both methods demonstrate effectiveness of defect density reduction with nanostructured surfaces. With MBE method, a high density of whisker growth is observed. With MOCVD growth, whisker-free relatively smooth surfaces have been produced. PL signal is also stronger with lower full width at half maximum from the MOCVD grown films. Spectral transmission measurements exhibit GaAs band edge consistent with crystalline GaAs substrates. A systematic effort aimed at growth optimization on nanostructured Si surfaces is expected to lead to defect density reduction in 10³/cm² range.