Enhanced Tensile Strain in P-doped Ge Films Grown by Molecular Beam Epitaxy Using GaP and Sb Solid Sources

Ge emerges as a good candidate for the active layer in optoelectronic devices and is compatible with complementary metal oxide semiconductor technology. As the Ge band structure exhibits an indirect band gap with a small difference in energy between the direct and the indirect valleys (about 140 meV), the energy band structure can be modified by applying a tensile strain or by doping electrons into the film to turn Ge into a semiconductor material with a direct ban gap structure. In this work, Ge epilayers were grown on Si substrate by molecular beam epitaxy technique, and we show that the tensile strain value of the Ge epilayers increases by a factor of two by doping electrons into the films with two donor elements using GaP and Sb sources. The dopant concentration in Ge epilayers is 5.6 × 1019 at cm−3 for the P dopant and 6.4 × 1018 at cm−3 for the Sb dopant. The activated electron concentration was found to be up to 4.1019 cm−3 in the Ge film. A gain of photoluminescence (PL) intensity three times higher than the sample doped only with P atoms was obtained. This result contributes to the perspective that Ge films can be utilized in functional optoelectronic as well as photonic devices.