Intraband electronic processes in semiconductor devices

A Hartree-Fock approach is used to analyze both exchange and direct electron-electron interactions in quantum well heterostructures. In the case of doped quantum wells, the intra-sub-band exchange interaction can produce an energy shift which is substantially larger than the direct Coulomb energy shift. Theoretical estimates of such shifts are compared with experimental measurements of infrared photoconductivity. In addition, exchange interactions between electrons localized in selectively doped, planar quantum well heterostructures are shown to lead to a characteristic sheet density below which the conventional picture of a paramagnetic two-dimensional electron gas ground state may be inapplicable, especially at low temperatures. Estimates indicate that critical sheet densities for a possible magnetic transition may lie in a readily achievable experimental range. The effect of electron-electron interactions on localized states in quantum wells and resonant tunneling is analyzed. A Hartree-Fock model for impurity bands is used to obtain a correction to the free electron model in treatments of doped contact layers in quantum well, heterojunction and modulation doped devices.; The theoretical basis of the Tsu-Esaki tunneling current formula is examined in detail and a new set of mutually consistent equations is derived for bias voltage, tunneling current and electron densities in the emitter and collector. An operator technique of Blankenbecler is used to generate low temperature series expansions for the tunneling current and emitter-collector electron densities.; Experiments have been carried out to study the interfacing of multispectral sensors to silicon devices. First stage linear coding of input current into the pulse rate of a stereotypical neuronlike spiketrain output has been achieved for input currents ranging over more than six orders of magnitude down to about 1 picoampere. Individual network elements are shown to obey equations of the same form as equations which occur in nonlinear neural network models analyzed by Hopfield and Sejnowski. The use of extrinsic silicon injection mode infrared detectors to simulate the transient response of neurons in biological vision systems is experimentally studied. Excellent agreement is found between the experimental data and a model for the detector and the associated circuitry.