Characterization of the absorption edges of epitaxial AlGaN grown by plasma-induced molecular beam epitaxy

The dependence of the absorption edge of wurtzite AlxGa(1-x)N on the AIN mo le fraction was studied. The Al mole fraction was varied from 0 to 1. The a bsorption coefficient at room temperature was determined by transmission an d photothermal deflection spectroscopy. Photothermal deflection spectroscop y can be applied to determine the low absorbance values. With those results , the effective bandgaps of the AlxGa1-xN alloys were defined as the photon energy E-4.8 at an absorption coefficient of 10(4.8) cm(-1). From the ener gy position of the absorption edge versus AIN mole fraction, a bowing param eter of 1.3 eV could be determined. The bowing parameter agreed quite well with the measured effective bandgaps of AlGaN alloys.