Heteroepitaxial Ge films on ⟨100⟩ and ⟨111⟩ Si substrates have been prepared by vacuum evaporation. The films were deposited in moderate vacuum (10−6Torr) at a rate of ∼10 A˚/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.