Single-crystal GaAs layers have been obtained by means of lateral epitaxial overgrowth seeded within stripe openings in a SiO2 mask over GaAs layers grown on Ge-coated Si substrates. Transmission electron microscope and scanning cathodoluminescence studies indicate that the laterally overgrown GaAs layers have a dislocation density of less than 104 cm−2, compared to 107–108 cm−2 for the GaAs layers grown directly on the Ge/Si substrates. Initial experiments indicate that the electrical properties of the laterally overgrown layers are comparable to those of conventional GaAs epilayers grown on single-crystal GaAs substrates.

Lateral epitaxial overgrowth of GaAs by organometallic chemical vapor deposition has been demonstrated. Pyrolytic decomposition of trimethylgallium and arsine, without the use of HCl, was used to deposit GaAs on substrates prepared by coating (110) GaAs wafers with SiO2, then using photolithography to open narrow stripes in the oxide. Lateral overgrowth was seeded by epitaxial deposits formed on the GaAs surfaces exposed by the stripe openings. The extent of lateral overgrowth was investigated as a function of stripe orientation and growth temperature. Ratios of lateral to vertical growth rates greater than 5 have been obtained. The lateral growth is due to surface-kinetic control for the two-dimensional growth geometry studied. A continuous epitaxial GaAs layer 3 μm thick has been grown over a patterned mask on a GaAs substrate and then cleaved from the substrate.

Heteroepitaxial Ge films on 〈100〉 and 〈111〉 Si substrates have been prepared by vacuum evaporation. The films were deposited in moderate vacuum (10−6 Torr) at a rate of ∼10 Å/sec, with the substrates heated to 350–750 °C. The crystalline perfection of the films depends on both substrate orientation and temperature. The best films were obtained on 〈100〉 Si substrates heated to 550 °C. Heteroepitaxial GaAs layers of excellent crystal quality have been grown by chemical vapor deposition on such Ge films. GaAs shallow-homojunction solar cells with conversion efficiencies up to 12% at AM1 have been successfully fabricated.