Silicon is a pivotal material for modern electronics, but its indirect-gap nature makes it inefficient in band-to-band light emission. The realization of efficient light emission has epoch-making significance in the manufacturing of photonic chips and optical interconnect. Previous experimental studies have reported dislocation luminescence in silicon and constructed the related light-emitting devices. However, the light emission mechanism remains elusive. Here, based on large-scale first-principles calculations, we have studied the electronic structure and optical properties of different types of dislocations in silicon. It is found that the $〈110〉$ type-I edge dislocation shows a quasidirect band gap at the Γ point. The natures of the band edge states are not the dislocation states residing inside the core, rather they are bulklike states confined near the dislocation caused by strain induced by the dislocation. Due to the strong confinement, they have large optical transition dipole moments ($\sim 0.23\mathrm{eV}$), thus making them optically active. Furthermore, applying a small compressive strain ($\sim 0.5\%$) can easily change the band structure from quasidirect to direct, further enhancing the optical transition at the Γ point and improving the efficiency of the related Si-based optical devices. Finally, we also found two incognizant stable mixed-edge dislocation configurations.

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• Defects
• Density of states
• Electrical properties
• Electronic structure
• First-principles calculations
• Luminescence
• Photonics
• Pressure effects
• Structural properties