The growth of GaAs epilayers on silicon substrates with multiple layers of InAs quantum dots (QDs) as dislocation filters by metalorganic chemical vapor deposition (MOCVD) is investigated in detail. The growth conditions of single and multiple layers of QDs used as dislocation filters in GaAs/Si epilayers are optimized. It is found that the insertion of a five-layer InAs QDs into the GaAs buffer layer effectively reduces the dislocation density of GaAs/Si film. Compared with the dislocation density of 5×10 7 cm −2 in the GaAs/Si sample without QDs, a density of 2×10 6 cm −2 is achieved in the sample with QD dislocation filters.

In this study, metamorphic growth of GaAs on Si(001) substrate was investigated via three-step growth in a low-pressure metal organic chemical vapor deposition reactor. Three-step growth was achieved by simply inserting an intermediate temperature GaAs layer between the low temperature GaAs nucleation layer and the high temperature GaAs epilayer. Compared with conventional two-step growth, three-step growth could further reduce surface roughness and etch pit density. By combining three-step growth with thermal-cycle annealing, the authors have grown a 1.8-μm-thick GaAs epilayer with root mean square roughness of only 1.8 and 0.73 nm in 10 × 10 μm2 and 2 × 2 μm2 scanning areas, respectively. The threading dislocation density of the 1.8-μm-thick GaAs epilayer was as low as 1.1 × 107 cm−2, as calculated directly from the double crystal x-ray diffraction ω-scan full width at half maximum of the GaAs diffraction peak. The corresponding etch pit density was only 3 × 106 cm−2.

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Ultrathin crystalline silicon solar cells are a promising technology roadmap to achieve more cost effectiveness. However, experimental reports on ultrathin crystalline silicon cells with thickness less than 20 µm are rare. Here, we experimentally fabricate and investigate ultrathin monocrystalline silicon solar cells consisting of 16 µm-silicon base thickness and low-cost front random pyramidal texture with the feature size of 1-2 µm. The normalized light absorption is calculated to explain the measured external quantum efficiency. The achieved efficiency is 15.1% for the single-layer passivated textured solar cell. In addition, via double-layer passivation of AlO/SiN, the efficiency is further increased to 16.4% for the best textured cell, which significantly improves the absolute efficiency with Δη = 1.3%.