Jules D. Levine

Structural and electronic model of negative electron affinity on the Si/Cs/O surface

Abstract Structural and electronic models are proposed which correlate Goldsteins LEED, Auger, photo-emission, plasmon, and desorption data for negative electron affinity (NEA) on Si(100) surfaces. In the structural model, the surface Si atoms group into adjacent rows of surface “pedestals” and surface “caves”. Their density is 3.4 × 10 14 cm −2 each, as inferred from the LEED 2 × 2 reconstruction pattern and other data. Adsorbed Cs resides in fourfold coordination with Si atop the pedestals. Adsorbed oxygen is completely submerged in the caves of aperture 2.98A to give a Cs-O dipole length of 2.9A. Similar structural arguments show why Cs must be adsorbed before O 2 , and why Si(111) does not exhibit NEA. In the electronic model, the surface dielectric constant, 5.3. obtained from the surface plasmon energy, 7 eV, is used to compute the dipole length from the final work function, 0.9 eV. It is 2.8A in excellent agreement with the dipole length computed from the above structural model. Some properties of the “induced” surface states in the presence of Cs and O are also described.

Polar surfaces of wurtzite and zincblende lattices

Abstract Madelung potentials are calculated at lattice sites along the [0001] wurtzite and [111] zincblende axes, both in the bulk and at the polar surfaces. The potentials are then used to compute the electrostatic surface energies of various (0001) wurtzite and (111) zincblende surface arrangements. All arrangements considered satisfy the ionic stability criterion, which requires a net charge at the polar surface. The surface energy results predict reconstructed and faceted surface structures that agree well with experimental low energy electron diffraction work reported in the literature.

Schottky‐Barrier Anomalies and Interface States

The surface‐state energy distribution at the metal‐semiconductor interface of a Schottky barrier has been deduced by combining a general theoretical analysis with one observed fact concerning the anomalous temperature dependence of the forward current on voltage. The fact, empirically found by Saxena, Padovani, and Sumner and by Padovani, is that the exponential terms of the forward‐current characteristic involve the sum of T plus T0. Here T is the absolute temperature and T0 is the empirical parameter which is essentially independent of temperature at constant current. This fact leads to the following new theoretical conclusions: (i) The surface‐state energy distribution near the Fermi level is a simple exponential with a characteristic e‐fold energy increase E0 that can be computed from T0. (ii) A plot of T0−1 vs voltage V yields essentially a straight line whose slope and intercept can be used to compute E0 and the barrier height φB. (iii) In reverse bias, φB varies as the log of the surface electric f...

Power law reverse current-voltage characteristic in Schottky barriers

Abstract A power law relationship between the reverse current and reverse voltage is computed theoretically using a model involving an exponential distribution of interface states. The model correlates Schottky barrier data on large bandgap semiconductors such as ZnO and GaP where the reverse current is proportional to the sixth power of the reverse voltage.

Si(111) 7×7 surface structure

A comparison between a kinematic analysis of the fractional‐order LEED‐pattern symmetries of the Si(111) 7×7 structure and experimental data is presented. The surface model comprises a rippling of the first two double layers so as to produce interference in the coherent scattering from this distortion. The ripple deformation is small. It is treated as a perturbation in the analysis. Thus, the surface is nearly ideally terminated; there are no vacancies or adatoms in the model. Triagonal symmetry reversals are observed in the LEED patterns at about 20‐V intervals and are also computed theoretically.

The 3-D electrostatic potential surrounding a square array of surface charges

Abstract Simple scaling laws have been derived which relate the 3-D potential to the inter-surfacestate spacing, the field-plate spacing, the dielectric constants of both insulators bordering the interface, and the dimensions x , y , z . This 3-D potential, obtained by using a pair of images and Neumann boundary conditions, contains the usual 1-D potential as the zeroth harmonic in a Fourier series. The 3-D and 1-D potentials give equivalent densities of conduction electrons in an accumulation layer only for a surface state density σ 11 /cm 2 . For higher σ, the 1-D potential seriously underestimates the amount of space charge possible. There is a low saddle point in the 3-D potential configuration which allows surface conduction electrons to transport laterally in the presence of a transverse field.

Interaction of electron beams with insulators and semiconductors

Abstract Although it is advisable to keep electrodes and electron sources away from glass surfaces, in some cases it is unavoidable, as in modern cathode-ray tube gun design. Frequently blue glows and arcs occur due to the proximity of the glass, but their cause is poorly understood. We hypothesize that electron bombardment of the glass surface can give rise to large, selfsustaining changes in the voltage spatial distribution. Continued bombardment can cause the bombarded glass to glow, and the enhanced electric fields may produce arcs. A simplified electron-current continuity equation is formulated. It takes into account the incident electron current, the concomitant secondary-electron emission, the non-zero glass conductivity, and the capacitative effect of nearby grounded surfaces. The solutions imply regions of enhanced and of diminished surface voltage along the glass, depending upon the location of the bombarded region. A criterion for significant voltage variations is given, and some numerical results are discussed.