L. Esaki

Tunneling in a finite superlattice

We have computed the transport properties of a finite superlattice from the tunneling point of view. The computed I‐V characteristic describes the experimental cases of a limited number of spatial periods or a relatively short electron mean free path.

Resonant tunneling in semiconductor double barriers

Resonant tunneling of electrons has been observed in double‐barrier structures having a thin GaAs sandwiched between two GaAlas barriers. The resonance manifests itself as peaks or humps in the tunneling current at voltages near the quasistationary states of the potential well. The structures have been fabricated by molecular beam epitaxy which produces extremely smooth films and interfaces.

A new semiconductor superlattice

We treat theoretically, through the use of Bloch functions, a new semiconductor superlattice where the interaction of the conduction band in one host material with the valence band of the other host material plays an important role. The result indicates that this superlattice offers new intriguing features, realizable with the In1−xGaxAs‐GaSb1−y Asy system. In addition, the tunneling probability is calculated across a barrier involving this system.

A bird's-eye view on the evolution of semiconductor superlattices and quantum wells

Following the past seventeen-year developmental path in the research of semiconductor superlattices and quantum wells, significant milestones are presented with emphasis on experimental investigations in the device physics of reduced dimensionality performed in cooperation with the materials science of heteroepitaxial growth.

Crystal orientation dependence of silicon doping in molecular beam epitaxial AlGaAs/GaAs heterostructures

Results on crystal orientation dependence of n‐ and p‐type Si doping in molecular beam epitaxial GaAs are presented. High electron and hole mobilities in AlGaAs/GaAs heterostructures on high index planes are demonstrated for the first time. The doping results should prove useful for various transistor structures and complementary circuits. Also, due to the differences in the band structure for different orientations, quantum well heterostructures are likely to exhibit many interesting phenomena which are strongly orientation dependent.

Molecular‐beam epitaxy (MBE) of In1−xGaxAs and GaSb1−yAsy

Films of In1−xGaxAs and GaSb1−yAsy over the entire composition ranges have been grown on (100) GaAs, InAs, and GaSb substrates by MBE. In situ observations by high‐energy electron diffraction have revealed a variety of surface reconstructions and correlated the growth process with the lattice mismatch. The compositions are governed by the relative rates of In and Ga in In1−xGaxAs, but primarily by that of Sb in GaSb1−yAsy because of its dominant incorporation over As. In these alloys, Sn is found to be a donor throughout In1−xGaxAs but an amphoteric impurity in GaSb1−yAsy.

In1−xGaxAs‐GaSb1−yAsy heterojunctions by molecular beam epitaxy

Smooth films of n‐In1−xGaxAs and p‐GaSb1−yAsy were grown by molecular beam epitaxy. As a function of the compositions, x and y, the lattice constants vary linearly while the energy gaps show a downward bowing. Abrupt heterojunctions made of these alloys with close lattice matching exhibit a series of current‐voltage characteristics which change from rectifying to Ohmic as x and y are reduced. The relative location of the band‐edge energies of the two semiconductors at the interface is shown to account for the unusual characteristics observed experimentally.

Electronic properties of InAsGaSb superlattices

Abstract Experimental results in InAs-GaSb superlattices are reviewed, focussing on the difference between this type of superlattice and that of GaAsGa 1− x Al x As. The emphasis is on electronic properties obtained from optical and magneto experiments, including semiconductor-semimetal transitions observed recently. The process of fabrication by molecular beam epitaxy and the characteristics of heterojunctions will also be briefly described.

Optical absorption of In1−xGaxAsGaSb1−yAsy superlattices☆

Abstract The formation of subbands in In 1−x Ga x AsGaSb 1−y As y superlattices has resulted in entirely different absorption characteristics from those of the host semiconductors. The measured absorption edges agree with the calculated energy gaps of the superlattices of various configurations, establishing that the conduction bandedge of InAs lies approximately 0.15eV below the valence bandedge of GaSb.

Resonant tunneling of holes in AlAs‐GaAs‐AlAs heterostructures

We have observed resonant tunneling of holes through double‐barrier AlAs‐GaAs‐AlAs structures sandwiched between p+‐GaAs regions. The resonances appeared as negative resistance regions in the current‐voltage characteristics perpendicular to the interface planes. A set of resonant structures was already visible at high temperatures (T≂250 K) while an additional set was observable only at low temperatures (T≤100 K). Although in principle the sets can be attributed to tunneling of light and heavy holes, respectively, an analysis of the number and relative voltage position of the resonances suggests that considerable band mixing occurs. The application of a strong magnetic field, parallel to the tunneling current, introduced shifts in the resonances which support that interpretation.