• Zawadzki, Paweł P.
• Schelhas, Laura T.
• Lany, Stephan
• Fioretti, Angela N.
• Zakutayev, Andriy
• Tamboli, Adele C.
• Toberer, Eric S.

Abstract

In multinary compound semiconductors, cation disorder can decisively alter the electronic properties and impact potential applications. ZnSnN₂ is a ternary nitride of interest for photovoltaics, which forms in a wurtzite-derived crystal structure. In the ground state, every N anion is coordinated by two Zn and two Sn cations, thereby observing the octet rule locally. Using a motif-based model Hamiltonian, we performed Monte Carlo simulations that provide atomistic representations of ZnSnN₂ with varying degrees of cation disorder. Subsequent electronic structure calculations describe the evolution of band gaps, optical properties, and carrier localization effects as a function of the disorder. We find that octet-rule conserving disorder is practically impossible to avoid but perfectly benign, with hardly any effects on the electronic structure. In contrast, a fully random cation distribution would be very detrimental, but fortunately it is energetically highly unfavorable. A degree of disorder that can realistically be expected for nonequilibrium thin-film deposition leads to a moderate band-gap reduction and to moderate carrier localization effects. Comparing the simulated structures with experimental samples grown by sputtering, we find evidence that these samples indeed incorporate a certain degree of octet-rule violating disorder, which is reflected in the x-ray diffraction and in the optical absorption spectra. This study demonstrates that the electronic properties of ZnSnN₂ are dominated by changes of the local coordination environments rather than long-range ordering effects.

Topics

• Deposition
• impedance spectroscopy
• compound
• x-ray diffraction
• simulation
• semiconductor
• nitride
• random