Quaternary Wurtzitic Nitrides in the System ZnGeN₂–GaN: Powder Synthesis, Characterization, and Potentiality as a Photocatalyst

Abstract

We developed a new quaternary wurtzitic nitride system by formation of the solid solution between ZnGeN 2 and GaN. Near stoichiometric and monophasic powder samples in the composition Zn 1−x Ge 1−x Ga 2x N 2 (x ≤ 0.50) were obtained by the reduction−nitridation synthesis conducted at 900 °C. The results of crystal structure refinement clearly revealed that the cation ordering in the structure of ZnGeN 2 (Pna2 1 ) tends to disappear by introducing Ga into the lattice, and the structure transforms to a simple wurtzite phase (P6 3 mc) with the composition of x ≥ 0.33. The observed structural evolution was further confirmed by the results of 71 Ga solid-state nuclear magnetic resonance (NMR) spectroscopy, showing an unsplit single peak observed for x ≥ 0.33. The dissolution of GaN into ZnGeN 2 also resulted in a marked narrowing of the band gap, from the ultraviolet region of 3.42 eV to the visible-light range of 3.02−3.05 eV, depending scarcely on the value of x. The results of photocatalytic test reactions for water splitting showed that the synthesized Zn 1−x Ge 1−x Ga 2x N 2 solid solution possessed the H 2 evolution rate of 2.8−3.6 μmol/h and the relatively high O 2 evolution rate of 100.4−126.6 μmol/h, as well as the capability for overall water splitting under the visible-light irradiation of λ > 400 nm.

Utilizing Site Disorder in the Development of New Energy-Relevant Semiconductors

“…Such systems are relatively unexplored, both theoretically and experimentally, and the impact of such alloying on optical and transport properties is not well-understood. Solid solutions of (ZnGeN 2 ) x –(GaN) 1– x have been demonstrated from x = 1–0.5 in powder form, and the solid solution demonstrated band gap narrowing by absorption measurements and by combined photoluminescence–photoluminescence excitation experiments . Continued investigation of these heterovalent ternary materials and their alloys is necessary to fully explore their properties and integrate them into devices.…”

Band Gaps, Band‐Offsets, Disorder, Stability Region, and Point Defects in II‐IV‐N2 Semiconductors

“…This indicates the disorder is not a thermodynamic disorder but kinetically controlled by the lower surface mobility of atoms during growth at low temperature. Similarly in ZnGeN 2 -GaN alloys, complete disordering was found by Suehiro et al [69] above a concentration of 10% Ga.…”

Experimental determination of the valence band offsets of ZnGeN2 and (ZnGe)0.94Ga0.12N2 with GaN

“…The band gap of this phase has been predicted to be within about 0.1 eV of that of GaN [1,2]. Measurements of the band gap of ZnGeN2 by photoluminescence and absorption spectroscopy are consistent with this prediction [3][4][5]. In addition, ZnGeN2 is almost lattice matched to GaN [1,2,[5][6][7].…”