We investigated the magnetotransport properties of high mobility InAs/GaSb antidot lattices. In addition to the usual commensurability features at low magnetic fields we found a broad maximum of classical origin around 2.5 T. The latter can be ascribed to a class of rosetta type orbits encircling a single antidot. This is shown by both a simple transport calculation based on a 'classical' Kubo formula and an analysis of the Poincaré surface of section at different magnetic field values. At low temperatures we observe weak 1/B-periodic oscillations superimposed on the classical maximum.

Modulation-doped In0.5Ga0.5As/In0.5Al0.5As quantum well structures grown by molecular beam epitaxy on GaAs substrates using a relaxed AlGaAsSb buffer showed carrier mobilities of 8500 cm2/V s for a sheet concentration of 3.5×1012 cm−2 at room temperature. The crystallinity of the quaternary buffer layer was verified by x-ray diffractometry. Transistors with 0.25×100 μm2 gates demonstrated transconductance values as high as 800 mS/mm. S-parameter measurements revealed a cutoff frequency fT of 87 GHz and a maximum oscillation frequency fMAX of 140 GHz (both extrinsic values).

We investigated niobium-AlGaSb/InAs-niobium hybrid structures using a high mobility two-dimensional electron gas as a weak link. The Josephson current observed in this structure was suppressed by an injection current driven into the weak link via an additional normal lead. Using a four-terminal configuration the supercurrent is suppressed all over the weak link. In a three-terminal configuration it was possible to suppress the supercurrent locally. ͓S0163-1829͑99͒06217-7͔The semiconductor/superconductor hybrid structure has been the subject of extensive research during the last years, to prove its suitableness as an interface between superconductor and semiconductor electronics. Especially the control of the supercurrent in a weak-link structure has attracted considerable interest in recent years. 1 One approach was to transfer the well-known semiconductor field effect transistor to superconductor/two-dimensional electron gas ͑2DEG͒ structures as proposed by Clark et al. 2 The supercurrrent flowing through the 2DEG was switched off by reducing the coherence length in the channel by applying a negative gate voltage. 3,4 Since the voltage necessary for depleting the electrons in the 2DEG channel is typically of the order of the band gap of the semiconductor and the output signal of the order of the superconducting gap of the electrodes, a voltage gain is hard to achieve. An alternative concept to avoid this problem is controlling the supercurrent by the injection of electrons via an additional nonsuperconductive contact into the weak link. [5][6][7][8] The energy of these carriers should be only of the order of the superconducting gap of the electrodes. Very recently, the control of the supercurrent by an injection current was experimentally succeeded for a Nb/Au weak link structure. 9 This system was in the diffusive regime with inelastic scattering processes thermalizing the injected carriers.In our current-controlled structure the superconductor Nb was contacted to a high-mobility two-dimensional electron gas ͑2DEG͒ in an Al 0.2 Ga 0.8 Sb/InAs heterostructure. Due to the high electron mobility the carrier transport from one Nb electrode to the opposite one can be considered to be ballistic. In addition inelastic scattering should become relevant only for higher temperatures. For weak links without inelastic scattering an even more efficient tuning of the Josephson current was predicted compared with the case of inelastic scattering present. 10 It will be shown that if a current is injected via Ohmic contacts into the 2DEG in a four-terminal configuration the supercurrent can be suppressed completely. In a three-terminal configuration it was possible to suppress the supercurrent locally, which was proven by measuring and fitting the interference patterns of the Josephson current appearing when a magnetic field is applied to the weak link.The heterostructure which forms the weak link in our structure was grown by molecular-beam epitaxy on a semiinsulating GaAs substrate. After a 1100 nm Al-Ga-Sb buffer layer, a 5...

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InAs/Al 0.2 Ga 0.8 Sb quantum well structures of high quality were grown by molecular beam epitaxy. The structural and electrical quality was characterized by x-ray diffractometry, Raman spectroscopy and Hall transport measurements. When an optimized buffer layer was used on a GaAs substrate, electron mobilities of 28 000 cm 2 V −1 s −1 at 300 K and 400 000 cm 2 V −1 s −1 at 20 K were routinely achieved for undoped structures. These excellent transport properties were utilized in a sensitive magnetoresistive sensor.

We report on a technique we have recently developed to fabricate very high quality gates and gated structures on InAs/AlxGa1−xSb quantum wells. The low thermal budget process leads to highly stable gates with extremely low leakage currents. Both electron and hole concentrations can be changed over a wide range by the application of modest gate voltages. We obtain a dn/dV value of 5×1011 cm2/V for electrons and 1.6×1012 cm2/V for holes at 1.2 K.

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