Polarization-dependent below band-gap optical absorption of aluminum nitride bulk crystals

The polarization dependence of the below band-gap optical absorption of aluminum nitride (AlN) is investigated in detail using cuts of bulk single crystals grown by physical vapor transport. We show that optical absorption at 445nm (2.8eV) features a polarization-dependent transition which is strongest for P⊥c, while optical absorption in the range of 250–320nm (4–5eV) features a transition which is strongest for P∥c. Such information may aid in understanding the nature of the underlying electronic transitions and subsequently decreasing unwanted blue/UV optical absorption in AlN.