We report a unique ability to control the sign and size of the stress within Ge nanocrystals or nanodots fabricated using a complementary metal-oxide-semiconductor-compatible process within SiO2 and Si3N4 layers. Very large (as much as 4.5%), size-dependent compressive and tensile strains can be generated depending on whether the dot is embedded within either a Si3N4 or a SiO2 layer. Raman measurements reveal significant anharmonicity for smaller Ge dots and possible distortions of the diamond cubic lattice as evidenced by the measured Grünesien parameters and confirmed by their transmission electron diffraction patterns. Two completely different mechanisms are proposed to explain the formation of the tensile and compressive strain states, respectively.
One of the perspectives of the Si-based technology is the optical interconnect for data transmission and applications in optoelectronic integrated circuit. In this report, the engineered dislocation network was proposed and the atomic structure of the dislocation array was revealed by high-resolution transmission electron microscope (HRTEM) and scanning tunneling microscope (STM). The photoluminescence (PL) emission is strong and compatible with intrinsic Si characteristic peak, making it possible as light emitters in silicon. The analysis of dislocation array-induced scanning tunneling spectroscopy (STS) identified the presence of defect levels under the conduction band, compared with the occupied and unoccupied Kohn-Sham orbitals in the forbidden gap of Si derived from first-principles theoretical models. This study demonstrated the possibility of dislocation-induced optical transition from a theoretical and experimental perspective, which will be essential in the development of Si-based optoelectronic integrated circuit.
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