Band Gap-Tunable (Mg, Zn)SnN2 Earth-Abundant Alloys with a Wurtzite Structure

Herein, wurtzite-type MgSnN2–ZnSnN2 alloys (MgxZn1–xSnN2) are proposed as earth-abundant and band gap-tunable semiconductors with fundamental band gaps in the range of 1.5–2.3 eV. The alloys do not exhibit immiscibility, unlike the InN–GaN system, because the lattice mismatch between the endmembers is smaller than 1% in both a- and c-axis directions. The MgxZn1–xSnN2 alloys can be epitaxially grown on GaN(001) in the whole x range, and their fundamental band gap can be tuned from 1.5 to 2.3 eV with the increase in x from 0 to 1. Moreover, the MgxZn1–xSnN2 epilayers with x > 0.53 exhibit a green-light photoluminescence emission near room temperature, which indicates that they are direct-gap semiconductors. Direct-gap semiconductors with band gaps of 1.8–2.5 eV are eagerly anticipated for the development of green light-emitting diodes (LEDs) and top cells in high-efficiency tandem solar cells, though such wurtzite- or zincblende-type compounds that can be epitaxially integrated with conventional semiconductors are quite rare. Therefore, MgxZn1–xSnN2 alloys are attractive nitride semiconductors toward the development of green-LEDs and tandem solar cells.