Formation and optoelectronic property of strain-relaxed Ge1−x−y Si x Sn y /Ge1−x Sn x /Ge1−x−y Si x Sn y double heterostructures on a boron-ion-implanted Ge(001) substrate

We have investigated the formation and optoelectronic properties of strain relaxed Ge1−x−y Si x Sn y /Ge1−x Sn x /Ge1−x−y Si x Sn y double heterostructures on ion-implanted Ge substrates. The strain relaxation of Ge1−x−y Si x Sn y and Ge1−x Sn x epitaxial layers was achieved using an ion-implanted Ge substrate. The maximal degree of strain relaxation (DSR) of the Ge1−x Sn x layers was evaluated to be 46%. In addition, we obtained a sharp and strong peak in the photoluminescence (PL) spectra from the sample with a DSR of 46%, while no strong peak was detected from a sample with a smaller DSR (22%). From the theoretical calculation of the energy band structure and the measurement temperature dependence of the PL intensity, the sharp and strong peak can be explained by the transition from an indirect to direct bandgap semiconductor due to the increase of the DSR and a concomitant increase of the Γ-valley electron population. Moreover, the PL intensity increases by the improvement of the crystallinity by a post deposition annealing process.