Characterization and control of ZnGeN2 cation lattice ordering

TL;DR

This study investigates how growth and processing conditions influence the cation lattice ordering in ZnGeN2, revealing temperature-dependent ordering and effects of annealing and alloy substrates on crystal structure.

Contribution

It provides new insights into controlling cation ordering in ZnGeN2 through temperature, annealing, and substrate choices, aiding the synthesis of heterovalent ternary semiconductors.

Findings

Higher growth temperatures increase cation ordering.

Annealing enhances cation ordering in low-temperature-grown samples.

Using a liquid alloy substrate promotes cation ordering at lower temperatures.

Abstract

ZnGeN2 and other heterovalent ternary semiconductors have important potential applications in optoelectronics, but ordering of the cation sublattice, which can affect the band gap, lattice parameters, and phonons, is not yet well understood. Here the effects of growth and processing conditions on the ordering of the ZnGeN2 cation sublattice were investigated using x-ray diffraction and Raman spectroscopy. Polycrystalline ZnGeN2 was grown by exposing solid Ge to Zn and NH3 vapors at temperatures between 758 degree C and 914 degree C. Crystallites tended to be rod-shaped, with growth rates higher along the c-axis. The degree of ordering, from disordered, wurtzite-like x-ray diffraction spectra to orthorhombic, with space group Pna21, increased with increasing growth temperature, as evidenced by the appearance of superstructure peaks and peak splittings in the diffraction patterns. Annealing disordered, low-temperature-grown ZnGeN2 at 850 degree C resulted in increased cation ordering. Growth of ZnGeN2 on a liquid Sn-Ge-Zn alloy at 758 degree C showed an increase in the tendency for cation ordering at a lower growth temperature, and resulted in hexagonal platelet-shaped crystals. The trends shown here may help to guide understanding of the synthesis and characterization of other heterovalent ternary nitride semiconductors as well as ZnGeN2.