Observation of the upper branch (N′Γ) of the nitrogen isoelectronic trap in GaAs1−yPy

Luminescence data are presented on nitrogen-doped GaAs1−yPy in the composition region 0.38≲x≲0.47, near the direct-indirect crossover (yc?0.45, 77 °K), which permit the identification of the upper branch, N′Γ, of the N trap. The existence of such a state has been predicted by a recent theory of the N trap that includes both the long-range (Vl) and short-range (Vs) character of the isoelectronic impurity potential in III–V alloys. The N′Γ state is observed to lie in the band gap for 0.40≲y≲0.47 and is a resonant state in the Γ continuum for y<0.40. The identification here of laser operation on both the N′Γ and NΓ states (the latter becoming the short-range state N for y≳0.42), along with previous work demonstrating laser operation on the low-energy NX state, shows that all three N-trap states have sufficient oscillator strength for laser operation if the Γ-N separation is small enough for band-structure enhancement to be efffective.