The study investigates the effects of vanadium (V) and manganese (Mn) doping on the structural stability and electrical properties of zinc selenide (ZnSe) composites under high pressure.
Through first-principles calculations based on density functional theory (DFT), researchers explored how different concentrations of V and Mn impact the phase transition pressure of ZnSe.
Identifying the stability pressures, the team determined notable changes, including:
- The phase transition pressure for pure ZnSe transitioning from zinc blende (ZB) to rock salt (RS) structure was found to be at 14.15 GPa.
- With the introduction of V doping, this pressure decreased to 9.97 GPa at 3.13% concentration, 7.74 GPa at 6.25%, and 4.36 GPa at 12.5%. For Mn doping, the pressures were 11.07 GPa, 9.72 GPa, and 8.30 GPa, respectively.
The results suggest V doping renders ZnSe more sensitive to changes under pressure compared to Mn doping. The underlying reason relates to the electronic configurations of the elements; V2⁺, with three outer electrons, is less stable than Mn2⁺, which maintains half-filled stability. Therefore, under pressure, the necessary charge rearrangements leading to phase transitions are more pronounced with V.
Electrical properties also showed compelling variations linked to doping and pressure:
- At atmospheric pressure, all V-doped ZnSe systems exhibited metallic properties, with transition to semiconducting occurring at high pressures for the 12.5% doping concentration.
- Conversely, the Mn-doped systems retained semiconducting properties under both atmospheric and high-pressure conditions.
High pressures push the conduction band of pure ZnSe toward higher energy levels, pointing to served changes. The team noted:
"Under high pressure, pure ZnSe remains a direct bandgap semiconductor, but the conduction band shifts toward higher energy directions, resulting in an increased bandgap."
The doping concentration was noted to affect the degeneracy and position of impurity bands, with the effects substantially modulated under pressure as well. At the lower concentrations, these impurity bands shifted toward larger energy, whereas at higher doping levels, the opposite effect was seen.
Each study conducted signals not only the substantial importance of doping but the changeable nature of semiconductor materials under pressure. The future direction of research could look toward empirical validations of these findings and practical applications.