In this work, we utilized resonant energy X-ray diffraction (REXD) to quantify cation ordering in ZnGeP2 thin films. ZnGeP2 thin films are promising for their potential applications in LED and solar cell devices. Controlling the extent of cation ordering in ZnGeP2 would enable properties to be tuned at nearly fixed compositions and would be invaluable in device fabrication. 

Due to the similar atomic number of Zn and Ge, the diffraction patterns of ordered and disordered ZnGeP2 are nearly indistinguishable, making it impossible to distinguish these with traditional X-ray diffraction. REXD allows for enhanced sensitivity to a specific element as diffraction patterns are collected across that element's absorption edge. We demonstrated here that REXD enabled accurate quantification of cation order in ZnGeP2 thin films.

By effectively characterizing the cation site order in ZnGeP2, we have demonstrated an example of the tunability of properties in II-IV-V2 materials at nearly fixed lattice parameters—making these materials promising for integration into current technologies. This could have a beneficial impact on devices such as LEDs and solar cells.

The REXD technique used in this work also serves to better demonstrate the capabilities of this growing characterization method and can be an example for future work involving REXD. We have provided detailed descriptions of our data collection and analysis procedures and have provided the code for the input file used in our refinement. We expect that by providing access to our REXD data analysis, this technique can be more broadly used by the scientific community.