Semiconductor/Al Interfaces The band alignment at semiconductor/metal interfaces is a key parameter for device performance because it fundamentally affects charge transport through metal contacts and contact resistances. Depending on the semiconductor band edge positions with respect to the metal work function, either an Ohmic contact or a potential step, known as a Schottky barrier, may form. It has been established, both theoretically and experimentally, that the local properties of the interface, including the crystal lattice orientation, the bonding configuration, presence of defects, charge redistribution, and dipole formation, may further affect the band alignment and Schottky barrier height (SBH). 114,117-120 First principles simulations can help interpret experiments and predict the band alignment at metal/semiconductor interfaces. To this end, the electrostatic potential alignment method, described in detail in the SI, is often used. The idea is similar to the method described above for determining the band alignment at semiconductor interfaces. To avoid expensive calculations of large slab models, and to compensate for errors caused by the underestimation of band gaps by semi-local functionals, the SBH is evaluated by referencing the average electrostatic potential difference between the semiconductor and metal, calculated using a smaller slab model, to calibrate bulk values of the Fermi energy and band edges. Similar to the band alignment at semiconductor interfaces discussed above, the SBH results can also be sensitive to geometry relaxation in the interface region. As explained above, we are ultimately interested in studying the spatial evolution of the electronic structure as a function of position across the interface. To describe local effects, such as the presence of MIGS, which manifest as a finite density of states in the gap of the semiconductor due to the penetration of exponentially decaying metallic Bloch states, 123-126 fully converged slab models are used. Below, the band alignment and SBH values extracted from the local DOS of large slab models. For completeness, we also provide values calculated using the potential alignment method. We note that the values obtained using the potential alignment method are highly sensitive to relaxation. Fig. shows the DOS as a function of position across interfaces of the three semiconductors with Al. In all three interfaces there is a significant presence of MIGS, which decay gradually with the distance from the interface, as also seen in the local DOS plots provided in the SI. In ZnTe, the MIGS decay more rapidly than in the CdSe and InAs, vanishing completely within 14 atomic layers. In the InAs and CdSe some MIGS persist about 18 layers (∼ 4 nm) deep into the semiconductor. Deep MIGS are also seen in the structurally similar GaSb/Al interface, shown in the SI. Based on Fig. , in the InAs/Al interface there is downward band bending with the conduction band minimum (CBM) lying ∼0.1 eV below the Fermi level. SBH calculations using the potential alignment method yield a negative value of -0.05 eV, which also indicates an Ohmic contact. These results are consistent with experimental observations in Ref., 127 which measured a downward band bending of around 0.3 eV for InAs(100)/Al interfaces, and with the calculations reported in Ref. for InAs(100)/Al(111). Fig. shows that in the ZnTe/Al interface there is no band bending and the Fermi level is located in the ZnTe gap with a SBH of ∼0.8 eV. The potential alignment method yields a SBH of 0.9 eV. These results are consistent with reports of a Schottky barrier of 0.9 eV for ZnTe(111) and ZnTe(110) interfaces with Al. Fig. shows that in the CdSe/Al interface there is downward band bending, similar to InAs/Al, with the CBM positioned ∼0.1 eV below the Fermi level. The potential alignment method yields a value of 0.01 eV. The similar band alignment in the CdSe/Al and InAs/Al is to be expected based on the similar conduction band edge positions of InAs and CdSe. Our results are consistent with experimental reports of Ohmic contacts for CdSe(1010) interfaced with Al. The evolution of the ZnTe and CdSe band gaps with the number of layers is similar to that of the CdTe tunnel barrier at the InSb/α-Sn interface, reported previously. On the one hand, for a thin layer of the barrier material the band gap is expected to be significantly larger than the bulk value because of the quantum size effect (see the gap convergence plot in Figure ). With 24 barrier layers the gap of the barrier approaches the expected value of 1.58 eV for ZnTe and 1.06 eV for CdSe obtained for a slab of the same thickness (see Figure ). For ZnTe the band gap reaches a maximum of 1.35 eV at a distance of 12 atomic layers from the Al interface. For CdSe the band gap reaches a maximum of 0.8 eV at a distance of 12 atomic layers from the Al interface.