Room temperature lasing from electrically pumped n-type doped Ge edge emitting devices has been observed. The edge emitter is formed by cleaving Si-Ge waveguide heterodiodes, providing optical feedback through a Fabry-Perot resonator. The electroluminescence spectra of the devices showed optical bleaching and intensity gain for wavelengths between 1660 nm and 1700 nm. This fits the theoretically predicted behavior for the n-type Ge material system. With further pulsed electrical injection of 500 kA/cm² it was possible to reach the lasing threshold for such edge emitters. Different lengths and widths of devices have been investigated in order to maintain best gain-absorption ratios.

Vertical incidence GeSn/Ge multiquantum well (MQW) pin photodetectors on Si substrates were fabricated with a Sn concentration of 7%. The epitaxial structure was grown with a special low temperature molecular beam epitaxy process. The Ge barrier in the GeSn/Ge MQW was kept constant at 10 nm. The well width was varied between 6 and 12 nm. The GeSn/Ge MQW structures were grown pseudomorphically with the in-plane lattice constant of the Ge virtual substrate. The absorption edge shifts to longer wavelengths with thicker QWs in agreement with expectations from smaller quantization energies for the thicker QWs.

Multi-quantum well light-emitting diodes, consisting of ten alternating GeSn/Ge-layers, were grown by molecular beam epitaxy on Si. The Ge barriers were 10 nm thick, and the GeSn wells were grown with 7% Sn and thicknesses between 6 and 12 nm. The electroluminescence spectra measured at 300 and 80 K yield a broad and intensive luminescence band. Deconvolution revealed three major lines produced by the GeSn wells that can be interpreted in terms of quantum confinement. We interpret that the three lines represent two direct lines, formed by transitions with the light and heavy hole band, respectively, and an indirect line. Biaxial compressive strain causes a splitting of light and heavy holes in the GeSn wells. This interpretation is supported by an effective mass band structure calculation.

The optical properties and the Franz-Keldysh effect at the direct band gap of GeSn alloys with Sn concentrations up to 4.2% at room temperature were investigated. The GeSn material was embedded in the intrinsic region of a Ge heterojunction photodetector on Si substrates. The layer structure was grown by means of ultra-low temperature molecular beam epitaxy. The absorption coefficient as function of photon energy and the direct bandgap energies were determined. In all investigated samples, the Franz-Keldysh effect can be observed. A maximum absorption ratio of 1.5 was determined for 2% Sn for a voltage swing of 3 V.

As Ge 1−x Sn x is being investigated for CMOS applications, obtaining contacts to n-type Ge 1−x Sn x with low specific contact resistivity (ρ c ) is a major concern. Here, we present results on specific contact resistivities of Sb doped n-type Ge 1−x Sn x with 0 x 0.08 also with varying doping concentrations using Ni, Ag and Mn as contact metals. Our results show that Ni offers the lowest ρ c for all x values of Ge 1−x Sn x . The lowest ρ c measured for Ni contacts on highly n-doped Ge 0.92 Sn 0.08 is 2.29 × 10 −6 Ω cm 2 . We find a strong dependence of the specific contact resistivity on doping, which we attribute to the fact that strong Fermi level pinning is present in metal/n-Ge 1−x Sn x contacts.