Controlling Fermi level pinning in near-surface InAs quantum wells

Abstract

Hybrid superconductor–semiconductor heterostructures are a promising platform for quantum devices based on mesoscopic and topological superconductivity. In these structures, a semiconductor must be in close proximity to a superconductor and form an Ohmic contact. This can be accommodated in narrow bandgap semiconductors, such as InAs, where the surface Fermi level is positioned close to the conduction band. In this work, we study the structural properties of near-surface InAs quantum wells and find that surface morphology is closely connected to low-temperature transport, where electron mobility is highly sensitive to the growth temperature of the underlying graded buffer layer. By introducing an In0.81Al0.19As capping layer, we show that we change the surface Fermi level pinning of the In0.81Al0.19As thin film as compared to the In0.81Ga0.19As, giving rise to a tuning of the Fermi level in the InAs layer. Experimental measurements show a strong agreement with Schrödinger–Poisson calculations of the electron density, suggesting the conduction band energy of the In0.81Ga0.19As and In0.81Al0.19As surface is pinned to 40 and 309 meV above the Fermi level, respectively.

Tunable capacitor for superconducting qubits using an InAs/InGaAs heterostructure

“…We use a layer structure typical of gatemon qubits as in figure 1 and refer to this structure as the 'device stack' [17,20,21]. To model the device stack in COMSOL, we specified the following electronic properties of [13].…”

“…We abbreviate the fixed composition ternary III-V alloys In0.81Ga0.19As and In0.81Al0.19As, as InGaAs and InAlAs, respectively. Not shown or modeled is the superlattice graded buffer layer between InP and InAlAs [17,20,21]. the semiconductor materials and the dielectric constant of the gate oxide: electron and hole effective conduction band masses m * n(p),c , low-field mobilities µ lf n(p) , band gap energies E g , conduction band offsets ∆E c between neighboring semiconductors, dielectric constants ε r , and effective densities of states for the conduction and valence bands N c(v) .…”

“…Taking the electron affinity χ for InAs as given by the COMSOL material library, we calculated the remaining affinities using Anderson's affinity rule and the conduction band offsets of each material [22]. As in [21], we included a silicon delta-doping 6 nm below the interface between the InAlAs and lower InGasAs layers. COMSOL approximates such a doping profile with the Geometry Doping profile, which we select a Gaussian profile with a width of 0.1 nm.…”

Superconducting resonators with voltage-controlled frequency and nonlinearity

“…The devices are fabricated on a superconductorsemiconductor heterostructure grown via molecular beam epitaxy [51][52][53][54]; details of the growth are discussed in the Supplementary Material. The weak link of the JJ is a high-mobility InAs 2DEG grown near the surface and contacted in-situ by a thin aluminum film.…”

Evolution of 4π-Periodic Supercurrent in the Presence of an In-Plane Magnetic Field

“…Josephson junctions (JJs) fabricated on semiconductor structures with epitaxially grown superconductors have recently attracted attention due to their propitious characteristics − and applications in quantum computing. − In the presence of a Zeeman field − or a phase bias − and a strong spin–orbit coupling (SOC) interaction, such high-quality JJs have shown signatures of topological superconductivity, − which can host Majorana zero modes useful for fault-tolerant quantum computation. , However, robust implementation and signatures of topological superconductivity remain ambiguous. − …”