  The ternary nitride CaZn2N2, composed only of earth-abundant elements, is a
novel semiconductor with a band gap of 1.8 eV. First-principles calculations
predict that continuous Mg substitution at the Zn site will change the optical
band gap in a wide range from ~3.3 eV to ~1.9 eV for Ca(Mg1-xZnx)2N2 (x = 0-1).
In this study, we demonstrate that a solid-state reaction at ambient pressure
and a high-pressure synthesis at 5 GPa produce x = 0 and 0.12, and x = 0.12-1
polycrystalline samples, respectively. It is experimentally confirmed that the
optical band gap can be continuously tuned from ~3.2 eV to ~1.8 eV, a range
very close to that predicted by theory. Band-to-band photoluminescence is
observed at room temperature in the ultravioletfired region depending on x. A
2% Na doping at the Ca site of CaZn2N2 converts its highly resistive state to a
p-type conducting state. Particularly, the x = 0.50 sample exhibits intense
green emission with a peak at 2.45 eV (506 nm) without any other emission from
deep-level defects. These features meet the demands of the III-V group nitride
and arsenide/phosphide light-emitting semiconductors.
