GaAs/AlGaAs heterostructures on suspended Ge epilayers on nominal (001) deeply patterned silicon substrates

The integration of optoelectronic and photonic devices based on III–V semiconductors on Si-based integrated circuits is far from being optimized despite its technological relevance. Due to the differences in lattice parameters and thermal expansion coefficients, high density of defect is introduced. We propose a novel approach for the fabrication of GaAs/AlGaAs heterostructures on nominal (001) Si substrates based on suspended Ge epilayers. To eliminate dislocations and thermal cracks we use a patterned Si substrate on which we grow with a LEPECVD system, separated vertical Ge micro-crystals, efficient in eliminating the threading dislocations and the thermal strain. From such micro-crystals, a suspended Ge layer, hundreds of microns wide and free of thermal stress can be obtained. The suspended Ge shows a wavy surface on which double steps are formed, permitting the reduction of anti-phase domains even in absence of substrate tilt. GaAs layers were grown on such Ge/Si substrate in a MBE system. Different growth recipes were studied. We found that diffusion length of Ga adatom, which is related to the average nucleation distance of GaAs islands, has a crucial role in the determination of the average APD size. In the optimum growth conditions, it was possible to observe average dimensions of APD free area with a lateral dimension of 30 μm. Macro and Micro-PL of AlGaAs/GaAs QWs grew on top show that uniform, optical quality GaAs layers are fabricated.