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The difference between the chemical potentials of the electrons, respectively the Fermi levels in two phases in contact, produces space charge layers at the phase boundaries. At the phase boundary between a semiconductor and a gas, the gas particles are bounded and an electronic equilibrium between adsorbed particles and the solid is produced (chemisorption). The production of a space charge barrier layer at the surface of the solid, which is a consequence of this equilibrium may explain many observed effects involving the interaction of gases and semiconductors. The application of these considerations is limited to the temperature range in which an electron exchange between gas and semiconductor is possible, however, the transportation of ionic impurities in the semiconductor does not take place. The following effects related to chemisorption on semiconductors are tretaed: Change of conductivity, variation of the electron work function, kinetics of chemisorption and influence on luminescence and the electro-optical properties. In the following discussion connections with other papers were maintained, and some arguments, as well as possible extensions of the theoretical foundation, were offered. [ABSTRACT FROM AUTHOR]

Under certain conditions, an increased contact resistance and rectifier effect not only appears at the boundary between a metal and a semiconductor but—as mainly observed by Joffé—also at the boundary between two semiconductors. These zones, the conductivity of which differs from the interior of the semiconductor, are generally situated on both sides of the boundary. Therefore, this layer is called "Doppelrandschicht" (double-barrier layer) in contradistinction to the barrier layer at the metal-semiconductor boundary. This paper deals with the theory of such double-barrier layers, primarily reported earlier by Gubanow. When two semiconductors of opposite conductivity type (n-type and p-type) are in contact, a difference must be made between the two critical cases in which the electrons and holes either recombine directly at the boundary, or by means of thermal energy pass into the other semiconductor and then recombine in the interior thereof. It is shown that in accordance with the last-mentioned transition mechanism the theory contains Shockley's theory of homogeneous p—n junctions as a special case. Double-barrier layers having one semiconductor adjoining another semiconductor of the same conductivity type are dealt with by applying to this case the method used by Schottky and Spenke for metal-semiconductor contacts with altered boundary conditions. Contacts between two semiconductors may appear also in the boundary region metal-semiconductor by the growing of intermediate layers, e. g. in consequence of diffusion of proper impurities. Two cases of special interest, the theory of which is also given by Gubanow, are discussed: in the first case a metal-semiconductor arrangement, the contact potential of which is so great that in the semiconductor grows an opposite-type zone at the boundary, a so-called inversion layer, and in the second case such an arrangement having a thin opposite-type semiconducting intermediate layer with the same fundamental lattice as the semiconductor, otherwise however, chemically differing from it. Finally, using the theories developed, the question of the barrier mechanism of technical copper oxide and selenium rectifiers is discussed. [ABSTRACT FROM AUTHOR]

The usual treatment of the interaction between electrons and lattice-oscillations using pertubation-theory becomes inapplicable, if the coupling is too strong. An important example is that of an electron moving in a polar medium. If one tries to explain superconductivity with aid of the interaction between electrons and lattice oscillations, such a strong coupling is also to be taken into account. A survey of a number of recent papers is therefore given, in which other methods of approximation better than perturbation-theory have been developed. In the case of an electron in a polar medium the variational calculus predominates. The many-electron problem in superconducters on the other hand is treated by several kinds of special canonical transformations. The connection between the (exactly determined) stationary states of the whole system consisting of electrons and lattice-oscillations and a description using the conception of scattering is treated in some detail. [ABSTRACT FROM AUTHOR]

The most general type of a wave function for an electron ensemble in a periodic lattice is developed and discussed in the paper. Approximate solutions may be built up either from Bloch functions or from atomic functions of the single electrons. The relations between these two representations are discussed for a number of cases and possible extensions are outlined. The principles of the energy term structure of electron ensembles in solids may be understood in this way as well as the limitations in the applicability of the approximations used. Some applications of the results to the theory of ferromagnetism and of ionic crystals are discussed. For further progress it seems necessary to develop a theory which takes into account the Coulomb correlation of the electrons in a more satisfactory way. [ABSTRACT FROM AUTHOR]