The intrinsic interface-induced gap states (IFIGS) which derive from the virtual gap states of the complex band structure are the fundamental mechanism that determines the band-structure lineup at semiconductor interfaces. The valence-band offsets of heterostructures are composed of a zero-charge-transfer term and an electrostatic-dipole contribution which are given by the difference of the p-type branch-point energies of the IFIGS and of the electronegativities, respectively, of the two semiconductors involved. The valence-band offsets of InGaZnO4, LaAlO3, and SrTiO3 heterostructures are quantitatively and consistently explained by the IFIGS-and-electronegativity concept. The analysis of the experimental InGaZnO4, LaAlO3, and SrTiO3 data yields the p-type branch-point energies as 2.37 ± 0.18 eV, 2.59 ± 0.13 eV, and 2.86 ± 0.14 eV, respectively.

Experimental capacitance–voltage data of selenium p–n heterojunctions on n-type Ge, Si, and GaN and flat-band barrier heights of selenium Schottky contacts are reanalyzed. The resulting built-in potentials of the p–n heterojunctions as well as the flat-band barrier heights of the Schottky contacts are explained by the well established concept of interface-induced gap states (IFIGS) where the interfacial electric dipoles are estimated by using the differences of the respective electronegativities. The analysis of the built-in potentials of the heterojunctions between crystalline p-Se films and n-Si and n-GaN substrates give an energy distance of 0.06 eV between the bulk Fermi level and the branch point of the IFIGS. The evaluation of the Schottky barrier heights reveals the IFIGS branch point of crystalline selenium to lie 0.03 ± 0.15 eV above the valence-band maximum. In summary, the valence-band offsets of c-Se/Si and c-Se/GaN heterostructures are estimated as 0.29 and 2.22 eV, respectively.

The interface-induced gap states (IFIGS) are the fundamental mechanism that determines the band-structure lineup at semiconductor interfaces, i.e., the band-edge offsets at semiconductor heterostructures and the barrier heights of metal–semiconductor or Schottky contacts. Both quantities are composed of a zero-charge transfer and an electrostatic-dipole term which are given by the IFIGS’s branch-point energies and the electronegativities of the two solids in contact, respectively. A respective analysis of experimental valence-band offsets of Ga2O3 and Gd2O3 heterostructures results in the empirical p-type branch-point energies of 3.57 and 2.85 eV, respectively. From experimental barrier heights of n-Ga2O3 Schottky contacts an empirical n-type branch-point energy of 1.34 eV is obtained. The p- and n-type branch point energies of Ga2O3 add up to 4.91 eV, the width of the Ga2O3 band gap, as to be expected from the theoretical IFIGS-and-electronegativity concept. The experimental valence-band offsets of Ga2O3(Gd2O3) heterostructures indicate that at their interfaces the chemical composition of the oxide differs from its nominal value in the bulk.

Ionization energies and electron affinities of clean Al x Ga 1−x N(0001) surfaces were investigated by ultraviolet photoemission spectroscopy over the whole composition range. The samples were cleaned with cycles of N + -ion sputtering and annealing partly within a Ga atom flux. The ionization energy is measured as 6.5 eV and is almost independent of the aluminum content in good agreement with the general chemical trend. The electron affinity decreases linearly with composition from 3.1 eV for GaN to 0.25 eV for AlN. No evidence for negative electron affinity at AlN(0001) surfaces was found. Adsorption of oxygen at room temperature leads to a significant increase of the ionization energy and electron affinity. With AlN(0001) surfaces, an oxygen uptake of 0.6 monolayers is observed after exposures of 10 8 Langmuirs and the ionization energy increases by approximately 2 eV.

The intrinsic interface-induced gap states are the fundamental theoretical concept which explains the band-structure lineup at all semiconductor interfaces. However, a comparison of experimental results and theoretical predictions requires data of well-characterized interfaces. With respect to the experimental input, two aspects are of importance. First, the evaluation of the measured data has to be performed critically and very carefully and, second, extrinsic and intrinsic effects have to be recognized and then separated. Some examples are given. The interpretation of the experimental data may become misleading if a physical quantity such as the Fermi-level stabilization energy of heavily radiation-damaged semiconductors is considered which derives from the complex semiconductor band-structure as the branch-point of the interface-induced gap states.

The continuum of metal-induced gap states (MIGS) determines the barrier heights of ideal metal-semiconductor or Schottky contacts. The charge transfer across such interfaces may be attributed to the partial ionic character of the covalent bonds between the metal and the semiconductor atoms right at the interface. Consequently, the barrier heights are split up into a zero-charge-transfer term, which equals the energy separation between the MIGSs branch point and the majority-carrier band edge, and an electric-dipole term, which varies proportional to the difference of the metal and the semiconductor electronegativities. For Schottky contacts on inorganic semiconductors, the respective slope parameters were found to depend on the square (ϵ∞−1)2 of the optical susceptibility of the semiconductors. It is demonstrated that experimental as well as theoretical slope parameters reported for metal contacts to organic semiconductors follow the same relationship which was observed earlier with Schottky contacts of inorganic semiconductors. This finding is not surprising as the MIGS originate from the quantum-mechanical tunnel effect of the bulk metal electrons in the energy range from the highest occupied electronic energy level of the semiconductor up to the Fermi level, irrespective of whether inorganic or organic semiconductors are considered.

The interface-induced gap states (IFIGS) are the fundamental mechanism which determines the band structure lineup at semiconductor interfaces. The valence-band offsets of semiconductor heterostructures and the barrier heights of Schottky contacts are given by the branch-point energies of the IFIGS of the semiconductors and respective electric-dipole terms. The branch-point energies of SiO2, Si3N4, and of the high-κ dielectrics Al2O3, HfO2, and ZrO2 are determined as 3.99±0.10, 1.93±0.14, 3.23±0.42, 2.62±0.18, and ≈3.2eV, respectively, from experimental valence-band offsets of heterostructures of these insulators.

The interface-induced gap states (IFIGS) are the fundamental mechanism which determines the band structure lineup at semiconductor interfaces. The valence-band offsets of semiconductor heterostructures are given by the difference of the respective IFIGS branch-point energies and electric-dipole terms which may be omitted for elemental group-IV semiconductors, SiC, as well as the III–V, II–VI, and I–III–VI2 compounds and alloys. The branch-point energy of ZnO is determined as 3.04±0.21eV from an analysis of experimental valence-band offsets reported for various ZnO heterostructures.

The excitation of B4.3C with an Ar-laser (ℏω=2.4eV) yields a photoluminescence spectrum between about 1.56 and 1.58eV with its main maximum at 1.563eV and a weaker maximum at 1.572eV. It is attributed to the indirect-allowed recombination of free excitons.

In one of his pioneering articles, Schottky [1] described the many thorny roundabout routes which finally ended in his Semiconductor Theory of the Blocking Layer [2] at metal-semiconductor or, as they are called to honor his many basic contributions to this field, Schottky contacts. The ensuing endeavors for a physical understanding of the mechanisms which determine the barrier heights in Schottky contacts were again fraught with difficulties. Heine [3] further developed Bardeen’s basic concept [4] of interface states at metal-semiconductor interfaces. He noted that for energies in the semiconductor band gap the volume states of the metal have tails in the semiconductor. Tejedor and Flores [5] applied this idea to semiconductor heterostructures where for energies in the band-edge discontinuities the volume states of the one semiconductor tunnel in the other one.

As in the bulk of semiconductors the current flow through space-charge regions of metal semiconductor contacts occurs via drift and diffusion. The semiconductors will be assumed to be doped non-degenerately n-type so that Maxwell-Boltzmann statistics applies. The temperature shall be chosen such that all donors are ionized, i.e., the semiconductors are in the exhaustion (or saturation) range. For low-level injection and moderate electric fields the current density is then given by1 3.1 $$J = {e_0}n{\mu _n}E + {e_0}{D_n}\frac{{{d_n}}}{{{d_z}}}$$ where , μ n and D n are the electron mobility and diffusion constant, respectively. The electric-field strength E(z) in the barrier region may be written as e 0 E(z) = d[W c (z) − W F ]/dz, where the conduction-band bottom W c (z) is referenced to the energy position W F of the Fermi level in the metal bulk.

Semiconductor Surfaces and Interfaces deals with structural and electronic properties of semiconductor surfaces and interfaces. The first part introduces the general aspects of space-charge layers, of

Surface states at semiconductor surfaces exhibit donor or acceptor character. Depending on their position with respect to the Fermi level they are neutral or become charged either positively or negatively, respectively. A charging of surface states necessarily results in the formation of a space-charge layer beneath the surface and, in thermal equilibrium, the surface band-bending adjusts such as to satisfy the condition of surface charge neutrality.

Cleaved Si(111) and Ge(111) surfaces exhibit 2×1 reconstructions. Initially, a buckling of the top atom-layer was thought to explain the respective atomic rearrangement in the surface. However, this simple model had to be discarded since the shifts experimentally observed with Si(2p) and Ge(3d) core levels were much smaller and the dangling-bond bands much wider than what was to be expected from calculations for buckled surfaces. Later on, the 2 × 1 reconstructions on Si and Ge(111) surfaces were proposed to consist of zigzag chains along a (110) direction which are joined to the underlying bulk by five- and seven-member rings while six-member rings are characteristic for the bulk of diamond-structure solids. The formation of such chains was proposed to proceed by a generation of stacking faults. Chains of surface atoms intuitively account for wider bands of dangling-bond surface states since the atoms are then more closely spaced. Additionally, the chains have to be tilted. This is again intuitively concluded from the surface core-level shifts experimentally observed and also resulted from evaluations of experimental I/Wp curves of LEED spots by using dynamical theories of LEED. Tilted chains as stable atomic arrangements on Si(111) surfaces were also obtained from static minimizations of the total energy as well as from a molecular-dynamics approach.