Pressure studies of conduction-band N-pair-state mixing in dilute GaAs _1-xN_x alloys

High-pressure photoluminescence (PL) experiments (at 9 K) are reported for GaAs_1-xN_x/GaAs quantum wells having N compositions (x=0.0025, 0.004) in the dilute regime where the GaAs_1-xN _x alloy conduction band (CB) evolves rapidly by incorporation of N-pair states. Under increasing pressure, the PL spectra exhibit several new N-pair features that derive from CB-resonant states at 1 atm. Two of these features appear strongly at sub-band-gap energies for P≥29 kbar in the x=0.0025 sample, but are absent for all pressures in the x=0.004 sample. Several competing PL assignments due to bound-exciton recombination at NN _i pairs (i=1-4 is the anion separation) are considered in light of prior findings for N-doped (∼10¹⁷cm^-3) GaAs. The absence of certain PL features in the x=0.004 sample shows that N-pair states mix into the CB-continuum via a selective process, and this selectivity offers an important test for band-structure calculations in dilute GaAs _1-xN_x alloys.