Limits to mobility in InAs quantum wells with nearly lattice-matched barriers

Abstract

The growth and the density dependence of the low temperature mobility of a series of twodimensional electron systems confined to un-intentionally doped, low extended defect density InAs quantum wells with Al 1-x Ga x Sb barriers are reported. The electron mobility limiting scattering mechanisms were determined by utilizing dual-gated devices to study the dependence of mobility on carrier density and electric field independently. Analysis of the possible scattering mechanisms indicate the mobility was limited primarily by rough interfaces in narrow quantum wells and a combination of alloy disorder and interface roughness in wide wells at high carrier density within the first occupied electronic sub-band. At low carrier density the functional dependence of the mobility on carrier density provided evidence of coulombic scattering from charged defects. A gate-tuned electron mobility exceeding 750,000 cm 2 /Vs was achieved at a at a sample temperature of 2 K. The possible scattering mechanisms leading to the observed density dependence of the mobility are discussed.Heterostructures were grown by molecular beam epitaxy (MBE) on GaSb:Te (001) substrates. Growth rate and composition calibrations were performed prior to the growth of the heterostructures and verified by reflection high energy electron diffraction patterns and oscillations during the growth of the heterostructures. In a previous work it was reported the carrier mobility and single-particle lifetime in InAs/(Al,Ga)Sb heterostructures are sensitive to the dislocation density in the epitaxial layers 18 .In this work the use of the nearly lattice matched substrate and buffer layers was intended to inhibit the formation of extended defects during MBE growth. Fig. 3(a) shows the 002 x-ray diffraction curve which was measured to obtain higher contrast between the multilayers that differed by the substitution on one of the zincblende structure sites. Fig. 3(b) shows the thin film x-ray diffraction reciprocal space map in the vicinity of the 002 and asymmetric 115 Bragg reflections of the GaSb substrate of sample D. In the 115 reciprocal space map, measured in a grazing incidence configuration, the substrate peak and the peak from the AlAs 1-y Sb y buffer layer are well resolved and indicate the buffer was nearly lattice matched but slightly tensile strained 5 to the substrate (y ~ 0.9). The threading dislocation densities of the films were measured by both etch pits using a solution of HF:H 2 O 2 :H 2 SO 4 :H 2 O similar to that reported by Aifer and Maximenko 19 and by electron channeling contrast imaging (ECCI) using a backscattering geometry in a field emission scanning electron microscope. ECCI analysis was performed using several diffraction vectors to mitigate unintentionally satisfying the invisibility criterion where the Burger's vector for a given dislocation is perpendicular to the diffraction vector. Fig. 3(b) shows an ECCI micrograph measured from the surface of the MBE grown film of sample D.Several lines of enhanced contrast are interpreted ...

Materials considerations for forming the topological insulator phase in InAs/GaSb heterostructures

“…The relative to the vacuum level for changes in film thickness. The level of interface roughness that causes gap misalignments over space is well within the limits of that found in InAs/GaSb/AlSb heterostructures 23,24 .…”

Gate tuning of fractional quantum Hall states in InAs two-dimensional electron gas

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“…[23]. For both interfaces, we started with the parameters reported for InAs/AlGaSb QWs [6], roughness height of ∆ = 0.27 nm and correlation length of Λ = 13 nm. We then find that, by increasing the roughness height of the lower interface to ∆ b = 0.64 nm while keeping other parameters the same, the observed asymmetry can be reproduced reasonably well [Fig.…”

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Transistors driven by superconductors

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