  BaZn2As2 is expected for a good p-type semiconductor and has two crystalline
phases of an orthorhombic alpha phase and a higher-symmetry tetragonal beta
phase. Here, we report high-quality epitaxial films of the tetragonal
beta-BaZn2As2 were grown on single-crystal MgO (001) substrates by a reactive
solid-phase epitaxy technique. Out-of-plane and in-plane epitaxial
relationships between the film and the substrate were BaZn2As2 (00l)//MgO (001)
and BaZn2As2 [200]//MgO [200], respectively. The full-widths at half maximum
were 0.082o for a 008 out-of-plane rocking curve and 0.342o for a 200 in-plane
rocking curve. A step-and-terrace structure was observed by atomic force
microscopy. The band gap of beta-BaZn2As2 was evaluated to be around 0.2 eV,
which is much smaller than that of a family compound LaZnOAs (1.5 eV). Density
functional theory calculation using the Heyd-Scuseria-Ernzerhof hybrid
functionals supports the small band gap.
