Integration of III-V devices with Si-photonics and fabrication of monolithic III-V/Si tandem solar cells require the heteroepitaxy of III-V compounds on Si. We report on the lattice tilt, mosaicity and defects content of relaxed GaAs grown by MOVPE on exactly-oriented and 4°-offcut (1 1 1)Si. Thin GaAs single-layers grown at 400 °C and annealed at 700 °C show ∼ 3 × 108 cm−2 density of surface pinholes. Double-layer samples were obtained by GaAs overgrowth at 700 °C. GaAs epilayers are tilted by (0.05–0.14)° with respect to Si. Rotational twins were observed in X-ray diffraction (XRD) pole figures: the most abundant ones originate from 60°-rotation of GaAs around the 1¯1¯1¯ growth direction and are identified as micro-twins along the GaAs/Si hetero-interface. Twins obtained by rotations around the 1¯1¯1, 11¯1¯, and 1¯11¯ directions or by combined rotations around the growth direction and one of the former, were also observed. The GaAs mosaicity and block size were studied through high-resolution XRD intensity mapping: for single-layer samples crystal blocks are ascribed to 3–5 nm thin micro-twins, whose size does not change upon annealing. In double-layer samples thicker (32–35 nm) micro-twins occur. GaAs samples grown on offcut (1 1 1)Si show less rotational twins but a reduced mosaic block size with respect to exactly-oriented Si.

GaAs hetero-epitaxial layers grown by MOVPE on exactly-oriented and off-cut (1 1 1)Si: Lattice tilt, mosaicity and defects content

Tapfer L.;
2023-01-01

Abstract

Integration of III-V devices with Si-photonics and fabrication of monolithic III-V/Si tandem solar cells require the heteroepitaxy of III-V compounds on Si. We report on the lattice tilt, mosaicity and defects content of relaxed GaAs grown by MOVPE on exactly-oriented and 4°-offcut (1 1 1)Si. Thin GaAs single-layers grown at 400 °C and annealed at 700 °C show ∼ 3 × 108 cm−2 density of surface pinholes. Double-layer samples were obtained by GaAs overgrowth at 700 °C. GaAs epilayers are tilted by (0.05–0.14)° with respect to Si. Rotational twins were observed in X-ray diffraction (XRD) pole figures: the most abundant ones originate from 60°-rotation of GaAs around the 1¯1¯1¯ growth direction and are identified as micro-twins along the GaAs/Si hetero-interface. Twins obtained by rotations around the 1¯1¯1, 11¯1¯, and 1¯11¯ directions or by combined rotations around the growth direction and one of the former, were also observed. The GaAs mosaicity and block size were studied through high-resolution XRD intensity mapping: for single-layer samples crystal blocks are ascribed to 3–5 nm thin micro-twins, whose size does not change upon annealing. In double-layer samples thicker (32–35 nm) micro-twins occur. GaAs samples grown on offcut (1 1 1)Si show less rotational twins but a reduced mosaic block size with respect to exactly-oriented Si.
2023
GaAs heteroepitaxy
High resolution X-ray diffraction
Metalorganic vapor phase epitaxy
Mosaicity
Reciprocal space mapping
Rotational twins
Silicon substrate
X-ray polar figures
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/20.500.12079/74149
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