Showing papers on "Surface states published in 1971"

Optical Absorption of Surface States in Ultrahigh Vacuum Cleaved (111) Surfaces of Ge and Si

Abstract: The optical absorption due to surface states on ultrahigh vacuum cleaved Ge and Si surfaces has been directly measured. Results show an absorption extending to energies lower than the edge, which disappears when the cleaved surfaces are oxidized. Possible optical transitions giving rise to this absorption are discussed. It is concluded that the dominant processes are transitions between two bands of surface states located in the gap. Combining the present results with photoelectric data, the energy position of the surface bands in Si is given.

Interpretation of surface and bulk effects using the pulsed MIS capacitor

Abstract: The interpretation of lifetimes and surface generation velocities determined from pulsed MIS-C measurements is examined. The effect of surface generation on the C-t response and ‘Zerbst’ plot is demonstrated and values for s0 are correlated with the density of fast surface states. Different kinds of surface dominated responses are analyzed and we discuss how the bulk characteristics can be retrieved. It is also shown that pulsing from inversion significantly lowers s0, but for high densities of surface states this technique does not suffice to eliminate surface effects. Finally, an approximate analysis of the C-t data is shown to agree quite well with the more exact analysis and it is then applied to lifetime maps of Si wafers.

The quantum theory of one-electron states at surfaces and interfaces

Abstract: The matching of the wavefunction at an arbitrary surface is formulated in terms of Green functions. If $G\_{1}$ and $G\_{2}$ are the resolvents for media 1 and 2, respectively, and $G\_{\text{s}}$ is the resolvent for a system consisting of 1 and 2 in contact through an interface (not necessarily abrupt), then $G\_{\text{s}}$ is fully obtained in terms of $G\_{1}$ and $G\_{2}$. By taking suitable matrix elements one obtains: (i) a secular determinant for the matching eigenvalues (surface states); (ii) a formula for the wavefunction everywhere, and (iii) a formula for the density of states. The case of a film is studied in the same way. The formalism is illustrated with a few examples. This paper deals with the physical information contained in the matrix elements of $G_{\text{s}}$ between points which are either on the surface or else on the same side, but the method yields also the matrix elements across the surface, which are important for the theory of dielectric responses in a system with an interface.

Determination of Surface States at Clean, Cleaved Silicon Surfaces from Photoconductivity

Abstract: The spectral response of photoconductivity of clean, cleaved silicon surfaces shows at 80\ifmmode^\circ\else\textdegree\fi{}K a broad shoulder for photon energies lower than the band gap. This shoulder exhibits a sequence of minima, equally spaced with 59 meV. From the spectral dependence of photoresponse and the energetic position of the minima, it is concluded that the photoconductance of the clean, cleaved surface is caused by indirect transitions from the valence band to surface states 0.5 eV above the valence-band edge.

Electronic spectra of the surfaces of alkaline earth oxides

Abstract: The surfaces of fine powder samples of MgO, CaO and SrO have been characterized by the diffuse reflectance technique over the wavelength range 200–2000 nm. Spectra due to F+s centres (electron in surface anion vacancy), SH centres (F+s centre with nearby —OH group) and adsorbed O–2 species have been identified. In powders which have been freed from surface contaminants fluorescences exist which can be quenched by O2, H2O or CO2. These fluorescences are interpreted as due to the presence of surface states which create an “effective” band gap at the oxide surfaces at significantly lower energies than the band gaps typical of the bulk oxides.

Low-energy electron diffraction

Abstract: Many investigations in metallurgy and physics require a knowledge of the chemical and physical state of the surface of a solid. For example, junction effects at semiconductor interfaces depend sensitively upon the surface states, which, in turn, depend upon the surface symmetry and chemistry; rigorous studies of epitaxial overgrowth must necessarily be performed on surfaces with known atomic arrangements. The techniques previously available for such studies have all had serious attendant disadvantages. The most commonly used method was that of reflection high-energy electron diffraction (RREED), which has proved extremely powerful. However, it requires an atomically smooth surface if the diffraction pattern is not to contain confusing features which result from surface asperities and undulations. Another powerful structural method is field-ion microscopy (FIM), but this has among its disadvantages the fact that it can cause progressive removal of the surface being studied. X-ray-fluorescence analy...

Energy Distribution in Field Emission from Krypton Covered Tungsten

Abstract: Work functions and energy distributions as functions of relative coverage have been obtained for Kr adsorbed on the (110), (100), (111), and (112) planes of a tungsten field emitter, from zero coverage to several monolayers. Work function results agree with previous measurements where overlap exists. The data could be fitted by the Topping equation for depolarization, yielding polarizabilities in reasonable agreement with the atomic value if HCP monolayer densities were used, on all but the (110) plane where a higher value resulted. Energy distribution in the submonolayer range show no deviations from free‐electron‐like behavior, except possibly on the (110) plane where a strong antiresonance seems to occur. On the (100) surface the Swanson anomaly found in the distribution from the clean surface decreases monotonically with Kr coverage, indicating that it is probably due to surface states. Work function values in the multilayer range can be interpreted to mean that the conduction band of Kr lies ∼ 1.4 eV...

Characterization of Surface States at the Si ‐ SiO2 Interface Using the Quasi‐Static Technique

Abstract: : The quasi-static technique is used to investigate the effect of processing parameters on the surface-state density at the silicon-thermally grown silicon dioxide interface. The determination of the constant required for the evaluation of surface potential from equilibrium C-V data is discussed. A rapid method of estimating the midgap density of surface states is also described. The dependence of surface-state density on substrate orientation, type of oxide growth, high-temperature annealing in nitrogen, low-temperature heat treatment in forming gas, and temperature of oxide growth are discussed. The interdependence between the fixed oxide charge and the surface-state density is also investigated. (Author)

Theory of the Field Effect in Amorphous Covalent Semiconductor Films

Abstract: The Cohen–Fritzsche–Ovshinsky model for amorphous covalently bonded semiconductors is used to calculate the electrical characteristics of a field-effect structure utilizing an amorphous covalent film as the semiconductor. The effect of surface states on the semiconductor is considered. The analysis shows that the band bending is exponentially dependent on distance from the surface. The modulation of the surface conductance as a function of transverse field, geometry, and surface-state density is calculated. These calculations indicate that the field effect should be measurable for surface-state densities up to 1.5×1014 cm−2 (eV)−1. The results of these calculations should be used in the design of field-effect experiments in order to achieve the maximum sensitivity.

MOS Capacitors for Surface Barrier Electroreflectance Measurements

Abstract: We describe a thin film technique of fabricating samples for surface barrier electroreflectance measurements. Aluminum oxide forms the dielectric spacer and semitransparent nickel is used for the field electrode. The resulting MOS capacitor is transparent from below 0.4 eV to at least 7.5 eV and has no low temperature limitation. Spectra have been obtained on a large class of semiconductor materials using this technique. Qualitative features of the optical response suggest that the surface potential is not clamped by slow surface states, even at room temperature. This method is therefore suitable for quantitative experiments in which the surface field is determined by an auxiliary measurement of surface conductance or capacitance. Application of these preparation techniques to other experiments is suggested.