The structural and electronic properties of (AlN)x(C2)1-x and (AlN)x(BN)1-x alloys

Abstract

The ground-state properties of (III-V)-(IV2) type alloy (AlN)x(C2)1-x and (III-V)-(III-V) type alloy AlxB1-xN have been studied by self-consistent calculations. The calculated results show that the solid solution between cubic AlN and C (diamond) and that between AlN and BN are both nonideal, and the nonideality of AlN-C2 solid solution is larger than that of AlN-BN. The bulk modulus of (AlN)x(C2)1-x (x = 0.25, 0.5, 0.75) is less than that of AlxB1-xN (x = 0.25, 0.5, 0.75), although the bulk modulus of diamond is larger than BN. The large positive formation energies of alloys (AlN)x(C2)1-x and (AlN)x(BN)1-x indicate that these solid solutions are both metastable. Band structures of bulk diamond, cubic BN and AlN show that they are all indirect wide band gap structures, where the conduction band minima are situated at the Δ k-point for diamond and the X k-point for BN and AlN. (III-V)-(IV2) type AlN-diamond mixed crystals and alloys exhibit an anomalously large band gap bowing while (IIIA-V)-(IIIB-V) type AlN-BN systems show slightly bowing. The band line-ups of (AlN)x(C2)1-x/(AlN)x (BN)1-x show that these alloy heterojunctions will change from type-II heterojunction to type-I heterojunction.