The characteristics of GeSn p-n junction devices fabricated by molecular beam epitaxy

Germanium-tin is an emerging optoelectronic material, but its device properties are not yet well understood. To evaluate the feasibility of GeSn-based p-n junction diodes for device and circuit applications, layers of doped GeSn with Sn contents up to 10 % were grown by the method of solid source molecular beam epitaxy (MBE) at substrate temperatures near 150 °C, on Ge substrates as shown in Fig. 1 (left panel). Prior to growth, a high temperature desorption step at 850 °C for 15 minutes was used to remove the Ge surface oxides. During GeSn growth, phosphorus was used for n-type doping from a custom baffled GaP sublimation source. Boron was used as a p-type dopant from a high temperature effusion cell. The presence of dopants in the GeSn layers was verified by SIMS impurity profiling as shown in Fig. 1 (right panel). The electrical activity of the dopants was checked by the sign of the thermoelectric power and the electrical behavior of the diodes.