Stability of theDX−Center in GaAs Quantum Dots

Using a first-principles band structure method, we study how the size of quantum dots affects the stability and transition energy levels of defects in GaAs. We show that, although a negatively charged $D{X}^{-}$ center is unstable in bulk $\mathrm{GaAs}:\mathrm{Si}$ with respect to the tetrahedral coordinated ${\mathrm{Si}}_{\mathrm{Ga}}^{-}$, it becomes stable when the dot size is small enough. The critical size of the dot is about 14.5 nm in diameter. The reason for the stabilization is the strong quantum-confinement effect, which increases the formation energy of ${\mathrm{Si}}_{\mathrm{Ga}}^{-}$ more than that of the $D{X}^{-}$ defect center. Our studies show that defect properties in quantum dots could be significantly different from those in bulk semiconductors.