Band Gap-Tunable (Mg, Zn)SnN₂Earth-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.