Experimental and Theoretical Branch Point Energies in ZnO and MgO: A Comparison

Agreement is found between the experimentally and theoretically determined branch point level for ZnO located (2.7 ± 0.1) eV above the valence band maximum. This result is obtained on the basis of a combined study where its experimental position is extracted from temperature‐dependent capacitance versus voltage measurements on AZO/n‐Zn (1− x ) Mg x O:Al/SiO x /p‐Si heterostructures with Mg content equal to ≈0.07 and ≈0.23 combined with transmission electron microscopy and ellipsometry measurements to assess the SiO x interlayer contribution. This analysis confirms the values previously published in Schifano et al. J. Appl. Phys. 136 , 245304 (2024). In contrast, density‐functional theory calculations are used for obtaining the theoretical estimates. A similar comparison, in the MgO case, reveals a difference of ≈0.6 eV between the theoretically predicted and experimentally obtained values placed (4.3 ± 0.1) and (3.7 ± 0.4) eV above the valence band maximum, respectively. In this case, the assumption of a linear variation of the ZnMgO branch‐point level between the two binary compounds, ZnO and MgO, used for the extraction of the experimental value, is among the probable causes of the residual difference found. Overall, the presented results indicate that the whole set of p (O) related valence bands should be included for a precise determination of the branch point energies if ab‐initio methods are used.