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We report magnetotransport measurements of InSb/Al1-xInxSb modulation doped quantum well structures and the extracted transport (τt) and quantum (τq) lifetime of carriers at low temperature (< 2 K). We consider conventional transport lifetimes over a range of samples with different doping levels and carrier densities, and deduce different transport regimes dependent on quantum well state filling calculated from self-consistent Schrödinger-Poisson modelling. For samples where only the lowest quantum well subband occupied at an electron densities of 2.13 x 1011 cm-2 and 2.54 x 1011 cm-2 quantum lifetimes of τq ≈ 0.107 ps, and τq ≈ 0.103 ps are extracted from Shubnikov-de Haas oscillations below a magnetic field of 0.8 T. The extracted ratio of transport to quantum lifetimes, τt/τq ≈ 17 and τt/τq ≈ 20 are similar to values reported in other binary quantum well two dimensional electron gas systems, but is inconsistent with predictions from a transport model which assumes that remote ionized donors are the dominant scattering mechanism. We find the low τt/τq ratio and the variation in transport mobility with carrier density cannot be explained by reasonable levels of background impurities or well width fluctuations. Thus, there is at least one additional scattering mechanism unaccounted for, most likely arising from structural defects.

We report the observation of a thermally activated resonant tunnelling feature in the current?voltage characteristics (I(V)) of triple barrier resonant tunnelling structures (TBRTS) due to the alignment of the n = 1 confined states of the two quantum wells within the active region. With great renewed interest in tunnelling structures for high frequency (THz) operation, the understanding of device transport and charge accumulation as a function of temperature is critical. With rising sample temperature, the tunnelling current of the observed low voltage resonant feature increases in magnitude showing a small negative differential resistance region which is discernible even at 293 K and is unique to multiple barrier devices. This behaviour is not observed in conventional double barrier resonant tunnelling structures where the transmission coefficient at the Fermi energy is predominantly controlled by an electric field, whereas in TBRTS it is strongly controlled by the 2D to 2D state alignment.

We report the growth of single-phase, stoichiometric polycrystalline thin films of the half-Heusler ferromagnet NiMnSb, predicted to be half-metallic, on single crystal (100) InSb substrates heated at 200 °C by pulsed laser deposition (PLD). The NiMnSb target used for the PLD deposition was synthesized by arc melting and had a saturation magnetization, MS (5K) ≤ 4μB/formula unit. The films exhibited saturation magnetization, MS (5K) ≤ 4μB/formula unit and coercive fields of 2 Oe at 300 K, indicating good structural quality. The temperature dependence of the saturation magnetization shows that at low temperature (T 200 K behaves like an itinerant ferromagnet. © 2005 IOP Publishing Ltd. 10 167 170 167-170