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/sub x/P/sub 1-x/. This strong coupling is manifested as (i) a drastic change in the ratio of oscillator strengths between the optical transition near E/sub g//sup (Gamma) and that near the CB minimum (CBM); (ii) a strong blue shift of the a/sub 1/(gamma) 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 t/sub 2/(L) or t/sub 2/(X/sub 3/) 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.