Photoluminescence properties of nanocrystalline, wide band gap nitrides (C3N4, BN, AIN, GaN)

Nanocrystalline layers of C3N4, BN, AlN and GaN were grown by Impulse Plasma Assisted Chemical Vapor Deposition method on silicon substrates kept at 300K. Optical absorption studies of the layers revealed broad bands below the fundamental absorption edge, which were ascribed to transitions involving defect levels. When excited by a 3 mW He-Cd laser (325 nm line) all samples showed a wide photoluminescence spectrum (2.0 to 3.5 eV), but the disordered crystalline structure quenched the excitonic photoluminescence observed in monocrystals. The efficient visible luminescence of nanocrystalline AlN layers in the 2–3 eV region observed under non optimal excitation conditions (energy bandgap of AlN is twice the excitation energy) is promising for optoelectronic use of this material as a visible light source.