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The resonances of a resonant tunneling structure are probed by a magnetic field applied parallel to the interfaces, which enables us to investigate the local band structure in k space. By rotating the magnetic field in the plane of the interfaces the energy surface at constant k∥ is investigated. Using this technique differently strained Si/Si1−xGex quantum wells were studied, where with a large anisotropy of the energy levels was seen, with the symmetry axes of light holes and heavy holes being rotated 45° with respect to each other. In the case of resonant tunneling diodes with relaxed Si1−xGex quantum wells grown on thick, relaxed Si1−xGex buffer layers, the anisotropy is smaller, and without complete symmetry between different 90° in‐plane directions, which may be due to anisotropic strain relaxation in the Si1−xGex buffer layers.

We have studied the effect of strain and strain relaxation on the band structure of Si1−xGex quantum wells. Two differently strained, molecular‐beam epitaxy grown Si/Si1−xGex hole resonant tunneling structures were studied: one fully pseudomorphic structure, with the strain in the Si1−xGex well, and the other grown on a thick relaxed Si1−xGex buffer, with the strain in the Si barriers. For the latter structure transmission electron microscopy revealed a large threading dislocation density emanating from the buffer. Using angle‐resolved magnetotunneling spectroscopy we found an anisotropy in the hole states in different in‐plane 90° directions, that was not present in fully pseudomorphically grown structures. We suggest that this is due to anisotropic strain relaxation in the buffer layer.

This paper demonstrates a novel method for fabricating two‐dimensional lateral surface superlattices. The technique involves etching a grid into a GaAs/GaAlAs modulation‐doped heterostructure using a mask consisting of an array of 50‐nm diam Ni/Au dots with a 100–150 nm period. Bias applied to a Schottky gate deposited over the structured surface varies the coupling strength between dots. The devices can be tuned to operate in the superlattice (weak and strong coupling) or the quantum dot (no coupling) regimes. Low‐temperature characterization of the superlattices fabricated specifically for transport and capacitance measurements reveal novel magnetic field effects.

This paper demonstrates a submicron trenching technique for defining low‐dimensional electron systems in GaAs/GaAlAs heterostructures for transport measurements. A variety of electron systems can be defined between trenches as narrow as 200 nm etched into a suitable heterostructure. The use of narrow trenches gives the advantages of high resolution, simplicity, and flexibility, and also avoids the complications associated with negative resists and lift‐off techniques. Using the trenching technique, we have fabricated Aharonov–Bohm ring devices with a Schottky gate over the entire ring. At 0.4 K, these devices exhibit clear interference effects which are dependent on the gate bias.

We have investigated the transport properties of (Ga,Al)Sb–InAs heterostructures grown by molecular‐beam epitaxy with the Al composition in the range of 0.3–0.5 where the alloy serves as a potential barrier for electrons in InAs. Field effect capacitors using a thick (Ga,Al)Sb barrier demonstrate the modulation of carrier densities in InAs by the application of an electric field. In the region of thin (Ga,Al)Sb, where tunneling becomes dominant, a novel negative resistance appears in InAs/(Ga,Al)Sb/InAs single‐barrier structures due to the specific band alignment of this system. The results have been further elucidated under a magnetic field.