Time-dependent density functional theory study on spectrum properties of Mg-doped GaN

The absorption and the emission spectra of GaN and (Ga,Mg)N were calculated by TDDFT with cluster model and CASTEP based on plate model. Ga26N26H50 cluster only has very weak absorption but has some strong emission bands in visible region. Band-to-band emission appears around 3.58 eV. Blue emission band of (Ga,Mg)N appears around 3.02 eV and it is stronger than yellow one (2.13 eV). At temperature of 0 K, the blue emission transition originates from a deep-acceptor level to a lower level in valence band or from conduction band to a shallow-acceptor level. At room temperature, the second transition is dominant.