Gating of high-mobility InAs metamorphic heterostructures

Abstract

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...

Gate-defined quantum point contact in an InAs two-dimensional electron gas

“…Using an expression obtained from k · p theory [20], we can calculate the effective g-factor g * while taking into account the band-edge parameters of InAs and the quantization energies arising due to the finite quantum well width. This yields a value of g * = −13.6, which corroborates the experimental results as the quantum well investigated in this study is much wider than the ones used in previous experiments [10,21] and thus shows a larger g-factor.…”

Quantum Oscillations in a Two-Dimensional Electron Gas at the Rocksalt/Zincblende Interface of PbTe/CdTe (111) Heterostructures

“…This discrepancy indicates the coexistence of a two-dimensional electron system at the interface of PbTe/CdTe and three-dimensional bulk carriers, most likely in CdTe. This two-carrier model is also consistent with the positive MR around B = 0 T. 27 Finally, the Hall resistance R xy deviates from the linear field dependence at ∼1 T, as the 3D quantum limit is approached. 28 To further confirm that the quantum oscillations are of two-dimensional nature, we have also carried out tilted magnetic field studies in a different sample (sample C) grown under the same conditions.…”

“…We believe that this positive MR is due to a multicarriers transport. 27 At higher fields, Shubnikov de Hass (SdH) oscillations are clearly seen on a rising, roughly linear, background. The Hall resistance displays visible plateau structures at the fields where R xx shows a minimum.…”

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

“…The dominant role of remote scattering is consistent with the effective value of the dimensionless parameter in the system which is given by k F d where d is the average distance of the charged impurities from the 2DES. Here we have free carriers in InGaAs layer due to the Fermi level pinning at the surface [27,28]. In our structure, d ∼ 130 nm gives the dimensionless k F d parameter to be around 19 for n = 4×10 11 cm −2 2D carrier density.…”