Composition-Dependent Properties of Wurtzite-Type Mg1+xSn1-xN2 Epitaxially Grown on GaN(001) Templates

The variety of wurtzite-type semiconductors with band gaps of 1.8-2.5 eV is limited, which hinders filling the green gap. This remains an unresolved problem in green light-emitting diodes (LEDs). Wurtzite-type MgSnN2 is a ternary nitride with a band gap of similar to 2 eV, and studying it as a potential candidate for green emitters in LEDs and an absorber material in tandem photovoltaics has been initiated recently; little is known about its basic properties. We examined the cation-composition dependence of its optoelectronic properties, in which the cation sites are randomly occupied by Mg and Sn. Mg1+xSn1-xN2 epitaxial layers were grown on the (001) planes of GaN by reactive co-sputtering from Mg and Sn targets. These epilayers retained the wurtzite structure in a broad x range of -0.34-0.28. All of the layers were unintentionally doped with oxygen, thereby exhibiting n-type conductivity. The Sn-rich layers had electron densities (n(e)) of the order of 10(20) cm(-3), whereas the n(e) value was suppressed to 7 x 10(18) cm(-3) in Mg-rich layers. These results suggest that the excess Sn (Mg) serves as a donor-type (acceptor-type) defect, and the electron transport properties can be tailored by varying the cation composition. The optical gap (E-g(opt)) of the Mg1+xSn1-xN2 films exhibited a blue shift due to the Burstein-Moss (B-M) effect for the Sn-rich composition; the intrinsic band gap of MgSnN2 was approximately 2.3 eV. The tunability of the transport properties and the E-g value corresponding to green light makes wurtzite-type MgSnN2 an attractive semiconductor for green emitters and photovoltaic absorbers.

Automated summary

The potential of wurtzite-type MgSnN2 as green emitters in LEDs and absorber material in photovoltaics has been studied, and the electron transport properties can be tailored by varying the cation composition. The Mg1+xSn1-xN2 films with Sn-rich composition exhibited a blue shift in their optical gap, while the intrinsic band gap of MgSnN2 was approximately 2.3 eV.