Ordering effects on the electronic structures of AlN/GaN, InN/GaN and InN/AlN superlattices

The short-period group-III nitrides superlattices (SL's) are now receiving a particular intention. Depending on the technique and conditions of growth, a number of many types of chemical ordering in nitride alloys can take place. It is demonstrated that partial ordering in these new structures reduces the band gap. In this paper, we investigate the electronic structure of short-period m × n AlN/GaN superlattices (with m, n ⩽ 3) calculated in wurtzite (with (0 0 0 1) orientation) structure using a first-principles full potential linearized augmented plane waves method within the local density approximation (LDA). The calculated gaps range from 3.1 for Al-rich to 2.6 (eV) for Ga-rich m × n (0 0 1) AlN/GaN systems. We point out that ordering affects significantly the 1 × 1 (0 0 1) InN/GaN and InN/AlN electronic band structures compared to 1 × 1 (0 0 1) AlN/GaN. The 1 × 1 (0 0 1) InN/GaN and InN/AlN are found to have direct smaller band gaps of 0.4 and 1.1 (eV), respectively. The origin of the reduction in the band gaps in InN/GaN and InN/AlN is discussed, as well as the effects of increasing the monolayer number in AlN/GaN superlattices.