N. Goel

Anisotropic structural and electronic properties of InSb/ AlxIn1-xSb quantum wells grown on GaAs (001) substrates

InSb quantum wells (QWs) with remotely doped Al/sub x/In/sub 1-x/Sb barriers are candidates for several novel device structures that rely on a long electron mean free path. Mesoscopic magnetoresistors that take advantage of the high electron mobility in InSb QWs at room temperature are currently being developed for read-head applications. The promise of InSb QWs for spin-transistor applications has been shown recently by experiments that demonstrate a large zero-field spin splitting and ballistic transport at temperatures as high as 185 K. Since a semi-insulating substrate is required for electronic applications, the InSb/Al/sub x/In/sub 1-x/Sb structures are grown on GaAs [001] substrates. The /spl sim/14% lattice mismatch between the epilayers and the substrate results in a high defect density that partially limits the electron mean free path. We will present a detailed characterization of these defects and elucidate their role in limiting electron mobility.

Dislocation filtering by AlxIn1−xSb∕AlyIn1−ySb interfaces for InSb-based devices grown on GaAs (001) substrates

Dislocation filtering by interfaces between AlxIn1−xSb and AlyIn1−ySb layers grown on a GaAs (001) substrate has been investigated. Transmission electron microscopy analysis shows that as many as 59% of threading dislocations (TDs) can be eliminated by such an interface. An interlayer sample that contains six Al0.12In0.88Sb∕Al0.24In0.76Sb interfaces has 6.0×108TDs∕cm2 at 1.6μm thickness. Compared with an Al0.12In0.88Sb epilayer without an interlayer, this TD density is a factor of ∼4 lower for the same thickness, and about the same as for a layer that is more than twice as thick. Our results suggest that AlxIn1−xSb∕AlyIn1−ySb interfaces can be used to improve the performance of any InSb-based device in which AlxIn1−xSb is used as a buffer, insulating, or barrier layer material.

Spin-polarized reflection in a two-dimensional electron system

We present a method to create spin-polarized beams of ballistic electrons in a two-dimensional electron system in the presence of spin–orbit interaction. Scattering of a spin-unpolarized injected beam from a lithographic barrier leads to the creation of two fully spin-polarized side beams, in addition to an unpolarized specularly reflected beam. Experimental magnetotransport data on InSb∕InAlSb heterostructures demonstrate the spin-polarized reflection in a mesoscopic geometry.

Effect of micro-twin defects on InSb quantum wells

We have investigated the effect of micro-twin defects on InSb quantum wells (QWs) grown on GaAs (001) substrates. Transmission electron microscopy analysis revealed that the QW layers are intersected by micro-twins that arise from lattice mismatch with the substrate. The intersected parts of the QWs lie near or in the {111} plane, which is tilted by 15.8° with respect to the (001) substrate. Hall effect measurements indicated that the degradation of electron mobility in the QWs is well correlated with the density of the micro-twins.

Ballistic transport in InSb∕InAlSb antidot lattices

We investigate magnetotransport properties of antidot lattices fabricated on high-mobility InSb∕InAlSb heterostructures. The temperature dependencies of the ballistic magnetoresistance peaks due to the antidot lattice are studied, and compared with mobility and density data over the same temperature range. A scattering time particular to antidot lattices is deduced, with a linear dependence on temperature between 0.4 and 50K, attributed to acoustic phonon scattering. The mobility does not vary substantially over this temperature range, whereas above ∼60K a quadratic dependence of inverse mobility on temperature is noticed, attributed to optical phonon scattering. The very weak temperature dependence of the width of the ballistic magnetoresistance peaks indicates negligible thermal smearing for electrons in the InSb quantum well, a result of the small electron effective mass.

Exciton determination of strain parameters in InSb∕AlxIn1−xSb quantum wells

Excitons in semiconductors can be used as a tool to probe various material and structural properties. The authors studied strain-related materials parameters in InSb∕AlxIn1−xSb quantum well structures. By changing the Al concentration in the barrier layers (0.03<x<0.23), the strain in the quantum wells can be tuned continuously. Using infrared transmission measurements, the authors traced strain-induced shifts in the energies of the confined states. The different strain dependences of the light- and heavy-hole band edges allow us to determine deformation potentials α and β simultaneously.

Measurement of the Dresselhaus and Rashba Spin-Orbit Coupling Via Weak Anti-Localization in InSb Quantum Wells

Weak anti-localization has been observed in the magneto-resistance of both symmetrically and asymmetrically doped InSb/AlInSb quantum wells. We find that for both types of structures, the magnetic field corresponding to the conductance minimum is in good agreement with the dominant spin-orbit term, which is the cubic Dresselhaus and Rashba terms for symmetric and asymmetric samples, respectively.

Dependence of the Spin Coherence Length on Wire Width for Quasi‐1‐Dimensional InSb and InAs Wires and Bi Wire Surface States

In diffusive two‐dimensional electron systems (2DESs) with linear spin‐orbit interaction (SOI), quasi‐one‐dimensional (Q1D) confinement in narrow wires of width W is theoretically predicted to result in an enhancement of the spin relaxation length LS, such that LS∝1/W. We present our experimental data of the dependence of LS on W for three different systems: 1) ballistic InSb wires with specular boundary scattering and strong Dresselhaus SOI, 2) ballistic InAs wires with diffusive boundary scattering and Rashba SOI, and 3) diffusive bismuth wires with a large density of states at the surface. For all three systems, information on the spin relaxation is gathered from the weak‐antilocalization effect (WAL), a magnetotransport measurement sensitive to both the spin‐orbit coherence length and the phase coherence length Lφ. We find a dependence of LS on W, where LS increases with decreasing W in all three systems. However, the theory is valid for Q1D diffusive wires with linear SOI, which does not fit the prof...

Control and Probe of Carrier and Spin Relaxations in InSb Based Structures

Narrow gap semiconductors (NGS) offer several scientifically unique features important for the field of spintronics. In order to explore these features we are using standard pump-probe and magneto-optical Kerr effect (MOKE) spectroscopy at different excitation wavelengths, power densities, and temperatures. Our goal is measuring and controlling carrier/spin relaxation in a series of InSb-based quantum wells and films, and InMnSb ferromagnetic films. The dynamic effects observed in these structures demonstrate strong dependence on the photo-induced carrier density.

Spin‐dependent Transverse Magnetic Focusing in InSb‐ and InAs‐based Heterostructures

Spin‐dependent ballistic transport was observed in InSb/AlInSb and InAs/AlGaSb heterostructures. Split transverse magnetic focusing maxima in InSb are consistent with spin‐split trajectories of carriers as well as spin‐flipping events occurring when carriers reflect off a lithographic barrier. Similar results are observed in InAs. The temperature dependence reveals that the ballistic focusing maxima survive up to ∼150 K for InSb and ∼60 K for InAs, whereas the splitting in the maxima disappears at lower temperatures, indicating the latter’s separate origin.