Origin of bandgap bowing in GaNP alloys

By employing photoluminescence excitation (PLE) spectroscopy, the authors provide direct evidence for N-induced strong coupling and repelling of host conduction band (CB) states in GaN_xP_1-x. This strong coupling is manifested as (i) a drastic change in the ratio of oscillator strengths between the optical transition near E_g^{/rGamma and that near the CB minimum (CBM); (ii) a strong blue shift of the a₁(Γ) state with increasing N composition accompanying a red shift of the CBM; (iii) pinning of the energies of the N-related levels; and (iv) the appearance of t₂(L) or t₂(X₃) upon N incorporation of which the energy position is insensitive to N compositions. These findings shed new light on the controversial issue of the dominant mechanism responsible for the giant bandgap bowing of dilute nitrides.}