Band offset in semiconductor heterojunctions

Semiconductor heterojunctions are widely applied in solid-state device applications, including semiconductor lasers, solar cells, and transistors. In photocatalysis they are of interest due to their capability to hinder charge carriers' recombination. A key role in the performance of heterojunctions is that of the alignment of the band edges of the two units composing the junction. In this work, we compare the performances of three widely applied approaches for the simulation of semiconductors heterostructures, based on density functional theory calculations with hybrid functionals. We benchmark the band offsets of ten semiconductors heterostructures for which experimental values are available: AlP/GaP, AlP/Si, AlAs/GaAs, AlAs/Ge, GaAs/Ge, GaP/Si, ZnSe/Ge, ZnSe/AlAs, ZnSe/GaAs, and TiO2/SrTiO3. The methods considered are (i) the alternating slabs junction (ASJ), (ii) the surface terminated junction (STJ), and (iii) the independent units (IU) approach. Moreover, two different ways to determine a common reference have been considered, (i) the plane averaged electrostatic potential, and (ii) the energy of the core levels. Advantages, drawbacks and overall performances of each method are discussed. The results suggest that the accuracy in the estimation of the band offsets is ∼0.2 eV when the ASJ method is applied. The STJ approach provides a similar accuracy, while the neglection of any interface effect, as in the IU method, provides only a qualitative estimate of the band offset and can result in significant deviations from the experiment.