Contour plot of the radiative recombination rate Χ as functions of the transition rates γ₁ and γ₂. The parameters used here are γ1∼=3.5γ2 , γ∼2=3.5γ1 , p₁ = p₂ = 0.80, Γ = 0.1γ, Γ_c = 0.45γ, E_cv = 0.15 eV, E_ai,(i=1,2)c = E_bv = 0.05 eV, and the other parameters are the same as those in Fig. 2.