Transport properties of modulation-doped InAs-inserted-channel In0.75Al0.25As/In0.75Ga0.25As structures grown on GaAs substrates

Richter, Andreas; Koch, Maximilian; Matsuyama, T.; Heyn, Ch.; Merkt, U.

doi:10.1063/1.1326045

Cited by 63 publications

(44 citation statements)

References 12 publications

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“…A low temperature buffer layer is necessary to reduce and minimize the resulting dislocations in the active region. We utilize step graded In x Al 1−x As buffer with x =0.52 up to 0.8 and then down to x=0.75 [18,19]. The electrons are confined to a 4 nm strained InAs layer inside an In 0.75 Ga 0.25 As quantum well.…”

Section: /2mentioning

confidence: 99%

An apparent metal-insulator transition in high-mobility two-dimensional InAs heterostructures

2014

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We report on the first experimental observation of an apparent metal insulator transition in a 2D electron gas confined in an InAs quantum well. At high densities we find that the carrier mobility is limited by background charged impurities and the temperature dependence of the resistivity shows a metallic behavior with resistivity increasing with increasing temperature. At low densities we find an insulating behavior below a critical density of nc = 5 × 10 10 cm −2 with the resistivity decreasing with increasing temperature. We analyze this transition using a percolation model arising from the failure of screening in random background charged impurities. We also examine the percolation transition experimentally by introducing remote ionized impurities at the surface. Using a bias during cool-down, we modify the screening charge at the surface which strongly affects the critical density. Our study shows that transition from a metallic to an insulating phase in our system is due to percolation transition.The metallic behavior of the resistivity observed at low temperatures in low-disorder two-dimensional (2D) systems is a topic of great interest in condensed matter physics. The scaling theory of localization predicts a noninteracting two-dimensional system in the presence of finite disorder is an insulator at zero temperature in the thermodynamic limit [1]. Indeed early experiments confirmed that in highly-disordered two dimensional electron systems (2DESs) the resistivity shows an insulating logarithmic temperature dependence [2]. The scaling theory was challenged by the observation of an apparent metalinsulator transition in high-mobility electron inversion layers in Si metal-oxide-semiconductor-field-effect transistors (MOSFETs) and later in several other 2D semiconductor systems [3,4]. At higher densities, a metallic temperature dependence of the resistivity, ρ, and a concomitant transition to an insulating phase at lower densities were observed. This apparent metal insulator transition (MIT) is marked by a "critical carrier density", n c which characterizes the crossover from the higherdensity metallic temperature dependence of the resistivity to the lower-density insulating temperature dependence. For n > n c , the system exhibits a metallic behavior (dρ/dT>0) while for n < n c , the resistivity increases with decreasing temperature and dρ/dT<0 in the insulating phase.In the past twenty years, MIT has been observed in a wide variety of 2D carrier systems such as n-Si MOSFETs [3], n-GaAs [5, 6], p-GaAs [7-9], n-Si/SiGe [10, 11], pSi/SiGe [12, 13] and n-AlAs [14,15]. In the current work we present the first experimental observation of 2D MIT in a narrow gap semiconductor, namely, 2D electrons confined in InAs quantum wells. We believe that our work is also the observation of the 2D MIT phenomenon in a material with the lowest value of the dimensionless electron interaction coupling parameter r s (∼ 2). Narrow band-gap materials such as InAs are particularly interesting as they have strong spin-orbit coupling,...

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Section: /2mentioning

confidence: 99%

An apparent metal-insulator transition in high-mobility two-dimensional InAs heterostructures

2014

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“…2 However, only heterostructures of one particular composition (In 0.52 Al 0.48 As/In 0.53 Ga 0.47 As) can be grown lattice-matched to a commercial binary substrate (InP). In order to maximize the flexibility in the choice of alloy composition, several authors [3][4][5][6] report the possibility of realizing metamorphic, almost unstrained In order to reduce the threading dislocation density in the QW due to misfit dislocations generated at the heterointerface between mismatched layers, a 1.2 µm step-graded buffer layer of In x Al 1-x As (x = 0.15-0.85) was inserted below the 2DEG region to fit the GaAs lattice parameter to the In 0.75 Ga 0.25 As one (Fig 1). The In concentration of up to 0.85 in the step graded buffer is chosen in such a way that the topmost part of the buffer has a lattice parameter corresponding to the unstrained In 0.75 Ga 0.25 As due to the partial lattice relaxation of the buffer layers closer to the substrate.…”

Section: Introductionmentioning

confidence: 99%

Two-dimensional electron gas formation in undoped In0.75Ga0.25As/In0.75Al0.25As quantum wells

Capotondi¹,

Biasiol²,

Vobornik³

et al. 2004

Journal of Vacuum Science &Amp; Technology B: Microelectronics and Nanometer Structures Processing, Measurement, and Phenomena

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We report on the achievement of a two-dimensional electron gas in completely undoped In 0.75 Al 0.25 As/In 0.75 Ga 0.25 As metamorphic quantum wells. Using these structures we were able to reduce the carrier density, with respect to reported values in similar modulation-doped structures, to about 2-3×10 11 cm -2 with mobilities of up to 2.15×10 5 cm 2 (V s) -1 . We found experimentally that the electronic charge in the quantum well is likely due to a deep-level donor state in the In 0.75 Al 0.25 As barrier band gap, whose energy lies within the In 0.75 Ga 0.25 As/In 0.75 Al 0.25 As conduction band discontinuity. This result is further confirmed through a Poisson-Schrödinger simulation of the two-dimensional electron gas structure.

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“…This lower temperature buffer growth is used to reduce and minimize the influence of dislocations forming due to the lattice mismatch of the active region to the InP substrate. The indium content in In x Al 1−x As is step graded from x =0.52 to 0.85 [14,15]. We lower the indium content to x=0.75 while increasing the substrate temperature to T sub ∼ 490 o C with As 4 beam equivalent pressure (BEP) to 2.0 × 10 −5 .…”

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confidence: 99%

Gating of high-mobility InAs metamorphic heterostructures

Shabani

McFadden

Shojaei

et al. 2014

Applied Physics Letters

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We investigate the performance of gate-defined devices fabricated on high mobility InAs metamorphic heterostructures. We find that heterostructures capped with In0.75Ga0.25As often show signs of parallel conduction due to proximity of their surface Fermi level to the conduction band minimum. Here, we introduce a technique that can be used to estimate the density of this surface charge that involves cool-downs from room temperature under gate bias. We have been able to remove the parallel conduction under high positive bias, but achieving full depletion has proven difficult. We find that by using In0.75Al0.25As as the barrier without an In0.75Ga0.25As capping, a drastic reduction in parallel conduction can be achieved. Our studies show that this does not change the transport properties of the quantum well significantly. We achieved full depletion in InAlAs capped heterostructures with non-hysteretic gating response suitable for fabrication of gate-defined mesoscopic devices.Narrow band gap semiconductors such as InAs are of fundamental interest for next generation high-speed electronics due to their unique material properties of small effective mass, large dielectric constant and high room temperature mobility [1,2]. In addition, they possess strong spin orbit interaction and large g-factor which make them an ideal platform for spintronics applications [3,4]. Recently, two-dimensional electron systems (2DESs) confined to InAs layers have become the focus of renewed theoretical and experimental attention partly because of their potential applications in quantum computation [5][6][7]. However, all these applications require precise control of electrostatic potentials and carrier densities using nano-fabricated metallic gates. Unlike widely used GaAs based systems, reliable gating has proven difficult in InAs based systems due to gate leakage and hysteretic behavior. Charge traps and surface Fermi level pinning could drastically affect the device performance. Controlling surface properties in In x Ga 1−x As material has played a crucial role in achieving high quality interfaces for metal oxide semiconductor field effect transistors (MOSFETs) [2].The Fermi level pinning at semiconductor surfaces has been the subject of numerous theoretical and experimental studies [8]. In most semiconductors, such as GaAs, the Fermi level is pinned in the band gap [9]. It is well known that the surface states in case of InAs (100) can result in a two dimensional electron system [10]. The electron accumulation is due to pinning of the Fermi level above the conduction band minimum. The position of the pinning level sensitively depends on the material and the surface treatments [11]. In the case of high indium content InGaAs, the situation is similar to InAs. Experiments on In x Ga 1−x As predicts Schottky barrier height becomes negative, exhibiting an ohmic behavior, for x > 0.85 [12]. In this work, we grow InAs metamorphic heterostructures with an In 0.75 Ga 0.25 As surface layer, see Fig. 1(a). High indium content InGaAs, in this cas...

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Transport properties of modulation-doped InAs-inserted-channel In0.75Al0.25As/In0.75Ga0.25As structures grown on GaAs substrates

Cited by 63 publications

References 12 publications

An apparent metal-insulator transition in high-mobility two-dimensional InAs heterostructures

An apparent metal-insulator transition in high-mobility two-dimensional InAs heterostructures

Two-dimensional electron gas formation in undoped In0.75Ga0.25As/In0.75Al0.25As quantum wells

Gating of high-mobility InAs metamorphic heterostructures

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