The authors report a study on the interface between polar high-κ materials and the Si(001)-(2×1) reconstructed surface with LaAlO3 taken as a prototype material. The construction of the interface is based on the prior growth of metal lines followed by oxidation, whose stability against oxygen coverage is studied. Electronic structure calculations within the density functional theory framework help in building the interface and understanding its bonding structure. Moreover, the authors computed a conduction band offset of 1.9eV, in agreement with the electronic application requirement. The results may provide a guidance for interface processing.

Some interfaces in semiconductors or insulators structurally cause a valence mismatch, which leads to a two-dimensional space charge that must be balanced by localised or mobile charge carriers. Screening by mobile electrons presents a lot of theoretical as well as practical interests. However it is extremely rare, so that we are aware of only one case, on which we focus here: the (0 0 1) interface between LaAlO3 and TiO2-terminated SrTiO3. Theoretically, this interface between two insulators is positively charged. Electron conductivity is observed in this system, but whether it is associated with the interface screening or an extrinsic unintended doping is not yet settled. Here, we use the literature and our own numerical and practical experiments to discuss the physics of this system.

As direct epitaxy of crystalline LaAlO3 on silicon has not been realized yet, we investigated the use of a template between the high-κ and the substrate. We performed calculations in the Density Functional Theory framework for two possible templates: a Sr0.5O monolayer and a 0.5nm thick γ-Al2O3(001) layer. We firstly found that in the Sr0.5O monolayer case, care must be taken for the LaAlO3 starting sequence in order to expect good band offsets with silicon. In the γ-Al2O3 case, a more complex engineering of the interface is needed. Nonetheless, we found stable interfaces and a surface reconstruction in agreement with experimental observations. Moreover, these interfaces exhibit insulating properties and insight calculations for a Si–γ-Al2O3–LaAlO3 superstructure lead us to a 1.9eV conduction band offset.

As the epitaxy of crystalline LaAlO3 has not been realized yet, we investigated the use of a γ-Al2O3 buffer layer between the high-κ and the substrate. We firstly studied the structural matching of γ-Al2O3(001) with a Si(001)-p(2×1) reconstructed surface. According to experimental data and computations in the density functional theory framework, we found stable interfaces between γ-Al2O3 and Si which encounters surface reconstruction changes. These interfaces satisfy the criterion of an insulating buffer layer.

The three-dimensional band structure of the III-VI layer compounds GaSe and InSe has been investigated in the tight-binding approach. The pseudo-Hamiltonian matrix elements in the sp(3)s(*) basis are fit in order to reproduce the nonlocal pseudopotential band structure, in the framework of constrained optimization techniques using the conjugate gradient method. The results are in good agreement with the optical and photoemission experimental data. The scaling laws appropriate to the covalent bonding are violated by a fraction of eV only, which suggests that the interlayer interactions are not solely of the van der Waals type.

A tight-binding calculation of the electronic properties of the semiconductor GaSe/Si(111) and InSe/Si(111) heterojunctions is performed in a charge-dependent tight binding approach where the only Coulomb effect is a shift of all the pseudoatomic levels of a given atom at site i by the same quantity U-i. The fitting parameters U-i are determined in the framework of constrained optimization techniques using the conjugate gradient method. The band offsets at the interfaces are determined and found to be in quantitative agreement with recent experiments on both heterojunctions. In addition, this optimization technique allows us to give more insight in the charge transfer between atomic planes at the heterojunction. As a result of the the strain induced by the lattice mismatch of the III-VI half layer grafted to the Si(111) surface the charge distribution does not match the simple charge neutrality condition in the case of InSe/Si(111).