  Two-photon transition rates are investigated in resonance to the ground state
in wurtzite GaN/AlN quantum dots. The ground state transition is two-photon
allowed because of the electron-hole separation inherent to polar wurtzite
III-nitride heterostructures. We show that this built-in parity breaking
mechanism can allow deterministic triggering of single-photon emission via
coherent two-photon excitation. Radiative lifetimes obtained for single-photon
relaxation are in good agreement with available time-resolved
micro-photoluminescence experiments, indicating the reliability of the employed
computational framework based on 8-band k.p-wavefunctions. Two-photon
singly-induced emission is explored in terms of possible cavity and
non-degeneracy enhancement of two-photon processes.
