ABSTRACT
Substantial increase of the upper wavelength limit to beyond 2 μm needs either intraband transition from multiquantum wells or interband transitions from heavily strained Ge or from germanium tin (GeSn) alloys. The research on GeSn is further stimulated by the predictions of a direct bandgap semiconductor at rather low Sn amounts by prospects for high-speed electronics and by challenges from material science. The composition dependence of an alloy’s bandgap can be estimated to the first degree by the linear interpolation between the values of the endpoint materials. This linear interpolation is known as generalized Vegard’s law or, specifically for band properties, as virtual crystal approximation. The heterostructure has to be combined with a dopant structure for a device application. The electrical characterization is important from a practical viewpoint and from a characterization viewpoint. The dominant photoluminescence and electroluminescence lines originated also from direct transitions.
