Alloy-Free Band Gap Tuning across the Visible Spectrum

Abstract

We present evidence, from theory and experiment, that ZnSnN 2 and MgSnN 2 can be used to match the band gap of InGaN without alloying-by exploiting cation disorder in a controlled fashion. We base this on the determination of S, the long-range order parameter of the cation sublattice, for a series of epitaxial thin films of ZnSnN 2 and MgSnN 2 using three different techniques: x-ray diffraction, Raman spectroscopy, and in situ electron diffraction. We observe a linear relationship between S 2 and the optical band gap of both ZnSnN 2 (1.12-1.98 eV) and MgSnN 2 (1.87-3.43 eV). The results clearly demonstrate the correlation between controlled heterovalent cation ordering and the optical band gap, which applies to a broad group of emerging ternary heterovalent compounds and has implications for similar trends in other material properties besides the band gap.

Quantitative Disorder Analysis and Particle Removal Efficiency of Polypropylene-Based Masks

“…However, it is possible to achieve such S 2 values through non-equilibrium growth conditions. For example, we have achieved S 2 close to 0 for ZnSnN2 through plasma-assisted molecular beam epitaxy at a temperature of 420 °C [5], a non-equilibrium crystal growth technique, despite the fact that the critical temperature for ZnSnN2 is predicted to be over 3000 K [16]. An example of a technique for polypropylene that can reach S 2 values corresponding to temperatures above its melting point is melt-electrospinning, a process commonly used in mask production.…”

“…Peaks in a Raman spectrum associated with the S = 1 ordered structure have integrated intensities proportional to S 2 , while peaks associated with the completely disordered structure have an integrated intensity proportional to (1 -S 2 ). The corresponding equations presented by Makin et al can then be rearranged to extract the order parameter from the Raman spectrum of a single sample [5]. Specifically,…”

“…Traditionally, the order parameter has been determined through x-ray diffraction [4]. However, we have recently extended measurements of S to other experimental techniques, including Raman spectroscopy, reflection high-energy electron diffraction, transmission electron microscopy and scanning electron microscopy (SEM) [5][6][7]. It is prudent to note here that each of these techniques directly measures S 2 instead of S, and thus we report S 2 values.…”

“…Further, as we demonstrate, it is possible to correlate disorder to system-level properties in certain situations through the application of an Ising model, where a linear relationship between the property and S 2 emerges. We have applied this approach to a wide range of materials including heterovalent semiconductors, binary and elemental semiconductors, and even biological systems such as viruses [5][6][7]. Given the contempo-rary COVID-19 pandemic and the corresponding surge in demand for personal protective equipment, we were motivated to investigate the application of this technique to materials commonly used in masks and filters.…”

A discussion on `Domain formation and phase transitions in the wurtzite-based heterovalent ternaries: a Landau theory analysis'

“…Further, it has demonstrated distinct disorder properties; to date, there have been no reported observations of ordering in ZnSnN 2 , even in material that emits light at room temperature (Quayle et al, 2015). Density functional theory (DFT) calculations suggest that the bandgap of ZnSnN 2 can be lowered by 0.85 eV in fully disordered material, with a randomized cation sublattice, compared with perfectly ordered material with the -NaFeO 2 -type structure (Makin et al, 2019).…”