Dislocation recombination and surface passivation of Ge micro-crystals on Si

Silicon offers a compelling platform for developing hybrid architectures that exploit novel functionalities. Heteroepitaxial growth of Ge on Si is a prominent approach to tailor material properties to achieve this goal. However, designing Ge-based heterostructures, which fulfill ever-demanding photonic and electronic applications, demands crucial control over the unavoidable non-radiative recombinations occurring at free surfaces and growth defects like dislocations. Yet the mitigation over such parasitic optical activity remains an open issue. Here we tackle this problem and demonstrate a more than 2 orders of magnitude photoluminescence (PL) enhancement achieved via confinement of threading dislocations and carefully controlled surface passivation of micron-scale Ge on Si crystals. By spectrally resolving interband and dislocation-related PL, we underpin the role played by dislocations in limiting the radiative emission, and we identify effective solutions based upon bandgap engineering to further boosting light emission efficiency. Noticeably, by combining steady state and time-resolved PL we disentangle non-radiative channels due to free surfaces and dislocations, eventually shining light on their relative impact at various temperature regimes. These findings have the potential of being beneficial for numerous applications of Ge-based heterostructures, in particular for moving forward their exploitation within the fast-growing field of Si-photonics.