Band structures and optical properties of Al-doped α-Si3N4: theoretical and experimental studies

The band structures and optical properties for Al-doped α-Si3N4 have been studied combining theoretical calculations and experimental measurements. The geometry and band structures for substitutional and interstitial Al defective α-Si3N4 models have been calculated based on density functional theory. The results indicate that the location and composition of the intermediate energy level in the band gap are affected by the partial atomic environment around the Al atoms and the characteristics of Al–N and Al–Si bonds. The maximum energy gap is observably decreased to 1.99 eV because of the appearance of intermediate energy levels in the band gap for interstitial Al defective α-Si3N4. Moreover, the energy gaps deduced from the measured absorption and photoluminescence spectra of the as-prepared Al-doped α-Si3N4 sample are in good agreement with the calculated results. The significant improvement in the optical properties by doping Al makes silicon nitride a potential visible light emitting material.