Bowing of biexciton binding in AlxGa1-xN ternary alloys

Biexciton binding in AlxGa1-xN ternary alloys as a function of alloy composition is reviewed on the basis of our recent experimental observations. The biexciton binding energy in GaN and AlN was evaluated to be 5.6 and 19.3 meV, respectively. The biexciton binding energy in Ga-rich AlxGa1-xN ternary alloys (x=0.019~0.092) and Al-rich AlxGa1-xN ternary alloys (x=0.81 and 0.89) was also evaluated on the basis of two-photon absorption of biexcitons. The biexciton binding energy in Ga-rich ternary alloys increased linearly with aluminum composition and reached to 16.6 meV for x=0.092. This value was three times as large as the biexciton binding energy in GaN. Similarly, the biexciton binding energy in Al-rich ternary alloys increased with decreasing aluminum composition and reached to 56 meV for x=0.81. A strong enhancement of the biexciton binding was observed for both Ga-rich and Al-rich ternary alloys. The enhancement was attributed to the effect of localization due to alloy disorder. The results indicated that a linear interpolation between GaN and AlN did not apply to the biexciton binding energy in the ternary alloys. A large bowing existed in the biexciton binding energy in the ternary alloys.

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