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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.

A new diluted magnetic III-V semiconductor of In& -Mn"As (x~0.18) bas been produced by molecular-beam epitaxy. Films grown at 300 C are predominantly ferromagnetic and their properties suggest the presence of MnAs clusters. Films grown at 200 C, however, are predominantly paramagnetic, and the lattice constant decreases with increasing Mn composition; both are indicative of the formation of a homogeneous alloy. These films have n-type conductivity and reduced band gaps.PACS numbers: 75.50.Pp, 68.55.Bd, 73.60.Br Diluted magnetic semiconductors are semiconductors in which a sizable fraction of the component ions are replaced by those of transition metals or rare earths, leading to a variety of cooperative effects. Most importantly, the state of magnetization changes the electronic properties (and vice versa) through the spin-exchange interaction between local magnetic moments and carriers. ' Rare-earth and transition-metal chalcogenides have been the most widely studied magnetic semiconductors.For example, mixed crystals (alloys) can be formed over a wide range of compositions even if the crystal structures of the two component materials are different from each other, as exemplified by the ternary alloy Cd& "Mn"Te. Among magnetic ions, many of the transition elements, particularly Mn + which tends to assume a spherically symmetric magnetic ground state, can be accommodated in the zinc-blende structure by substituting group-II cations in the II-VI compounds. In this paper, in contrast, we are concerned with the incorporation of high concentrations of tnagnetic ions in III-V compound semiconductors. Up to now, the number of magnetic ions incorporated in III-V semiconductors has been limited to doping levels 10' -10' cm, beyond which surface segregation and, in extreme cases, phase separation occur and impede further incorporation of the magnetic ions into the crystals. These experiments imply that the preparation of ternary alloys to form diluted magnetic III-V semiconductors is an extremely difficult task. We consequently sought to study metastable solid phases using the diverse growth-parameter space provided by the molecular-beam-epitaxy technique. In this situation, the preparation of the material itself includes such fundamental subjects as solubility, stability of the resulting crystal structures, the valence state of the magnetic ions, and the associated magnetism, all of which are not usua11y encountered in isovalent semiconductor alloy systems.Through the preparation and characterization of epitaxial 61ms of InMnAs, we obtained experimental evidence for the formation of a III-V-based diluted magnetic semiconductor in which a large amount of Mn is incorporated at least up to an average composition of In/Mn/As 0.82/0. 18/1.0. Studying magnetic, metallurgical, and semiconducting properties, we 6nd that the 61ms may be classi6ed into two different groups depending on the growth temperature. Films grown at relatively high temperatures (-300'C) exhibit ferromagnetic behavior similar to that of MnAs which may ex...

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.

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