Thermodynamic, electronic, and optical properties of ultra-wide bandgap zirconium-doped tin dioxide from a DFT perspective

Abstract

The effects of zirconium doping on the thermodynamic, electronic, and optical properties of tin dioxide are investigated by using density functional theory calculations combined with the cluster expansion method. In the whole composition range, the formation enthalpies of all structures are positive, indicating that SnO₂–ZrO₂ is an immiscible system and the ZrSnO₂ alloy has a tendency of phase separation at low temperature. The x-T phase diagram of ZrSnO₂ ternary alloy shows that the critical temperature is 979 K, which means that when the growth temperature of ZrSnO₂ crystal is higher than the critical temperature, it is possible to realize the full-component solid solution. The bandgaps of Zr_xSn_1−xO₂ alloys (0 ≤ x ≤ 1) are direct and increase as the Zr composition increases. Zr doping can tune the bandgap of SnO₂ from the ultraviolet-B region to the deep ultraviolet region, and has a strong optical response to deep ultraviolet light. The projected density of states and band offsets clearly reveal the reason for the increase of bandgap, which provides useful information to design relevant optoelectronic devices such as quantum wells and solar-blind deep ultraviolet photodetectors.