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

Abstract

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,...

Gating of two-dimensional electron systems in InGaAs/InAlAs heterostructures: the role of the intrinsic InAlAs deep donor defects

“…The gate controllability can thus be expected to strongly depend on the electrostatic situation before the cooldown as well as on the gate sweep history of the sample. While this is rarely commented on in the literature, we find these observations to be experimentally in line with the state of the art: when compared, quite different gating properties are reported for similarly designed heterostructures [16][17][18][19][20][21][22], seemingly making a correlation between the gating behavior and the heterostructure layout elusive. Given that most of the previous reports used heterostructures with 75% indium and to further illustrate this point, we show the gate response of sample B in Fig.…”

“…These QW heterostructures allow an engineering and control of the Rashba-type spin-orbit interaction [1][2][3][4][5][6][7][8], opening perspectives [9] for the realization of all-electrical spintransistors [10] or topological superconductivity including the observation of Majorana zero modes [11][12][13][14][15]. Gating of two-dimensional carrier systems represents a key functionality of these applications and has been frequently used in this context [2][3][4][5][6][16][17][18][19][20][21][22]. Interestingly, reports on the microscopic mechanisms of the capacitive coupling between the gates and the two-dimensional systems are scarce, while at the same time similarly designed heterostructures seem to deliver diverse gate responses [16][17][18][19][20][21][22], posing the question of the origin of these discrepancies.…”

“…Gating of two-dimensional carrier systems represents a key functionality of these applications and has been frequently used in this context [2][3][4][5][6][16][17][18][19][20][21][22]. Interestingly, reports on the microscopic mechanisms of the capacitive coupling between the gates and the two-dimensional systems are scarce, while at the same time similarly designed heterostructures seem to deliver diverse gate responses [16][17][18][19][20][21][22], posing the question of the origin of these discrepancies.…”

Two-dimensional epitaxial superconductor-semiconductor heterostructures: A platform for topological superconducting networks

“…4d). For V g < −3 V the I c R n decreases rapidly as the critical current vanishes with the junction becoming insulating [32].…”

Gating of high-mobility InAs metamorphic heterostructures

“…The Hall bars are cooled down to 2 K with no bias applied on the top gate, V P = 0 V. At T = 2 K, magnetoresistance exhibits Shubnikov de Haas oscillations and well defined integer quantum Hall states in strong magnetic field [18]. The typical electron mobility is measured to be µ ∼ 2 × 10 5 cm 2 /Vs at n ∼ 4 × 10 11 cm −2 .…”