Interplay of confinement, strain, and piezoelectric effects in the optical spectrum of GaN quantum dots.

We theoretically investigated excitonic states, energy and oscillator strength of optical transitions in GaN quantum dots characterized by different size, shape, interface, and substrate. On the basis of our multi-band model we determined that the piezoelectric field-induced red shift of the ground state transition, observed in recent experiments, can manifest itself only in strained GaN/AIN dots with the dot height larger than 3 nm. It was also established that the oscillator strength of the red-shifted transitions is small (< 0.05) and decreases fast with increasing the dot size, while the strength of ground state transitions in c-GaN/c-AIN and GaN/dielectric dots is large (approximately 0.4-0.7) and almost independent of the dot size.