Optical and vibrational properties of 2H-, 4H-, and 6H-AlN: First-principle calculations

The optical and vibrational properties of 2H-, 4H-, and 6H-AlN are studied based on the ab initio pseudopotential density functional theory. Three polymorphs have similar electronic and optical properties implying that 4H- and 6H-AlN are also of importance to optoelectronics. Infrared spectra of the three polymorphs show two main modes at 660 and 690 cm−1 and an additional mode at 570 cm−1 can only be observed from 4H- and 6H-AlN. The Raman spectra of 4H- and 6H-AlN show more active modes than that of 2H-AlN. These infrared and Raman features can be used as the fingerprints to distinguish the three polymorphs.