Induced quantum dot probe for material characterization

Abstract

We propose a non-destructive means of characterizing a semiconductor wafer via measuring parameters of an induced quantum dot on the material system of interest with a separate probe chip that can also house the measurement circuitry. We show that a single wire can create the dot, determine if an electron is present, and be used to measure critical device parameters. Adding more wires enables more complicated (potentially multi-dot) systems and measurements. As one application for this concept we consider silicon metal-oxidesemiconductor and silicon/silicon-germanium quantum dot qubits relevant to quantum computing and show how to measure low-lying excited states (so-called "valley" states). This approach provides an alternative method for characterization of parameters that are critical for various semiconductor-based quantum dot devices without fabricating such devices.Semiconductor heterostructures often serve as the substrate for many solid-state devices. For quantum devices such as qubits, their quality depends crucially on the properties of these wafers. Often, these qubit characterization parameters can only be ascertained by fabricating the device and measuring it at cryogenic temperatures. Quantum dots (QDs) in silicon for quantum computing (QC) 1 are a great example. The indirect band-gap of silicon creates low-lying excited (valley) states in the QD heterostructure; if the "valley splitting" is too small, initialization, readout and even gate operation of the qubits is impeded. Optimizing the valley splitting of silicon QD qubits-in addition to other important parameters such as coherence time, charge noise, etc.-is needed for the eventual construction of quantum computers, and is limited by the design-fabrication-test cycle time.We propose a method of characterizing material properties using a separate probe chip that both creates the dot(s) and measures them. This concept was inspired by the ion trap stylus approach 2,3 where an ion qubit is trapped on a stylus-like tip that can be brought close to a material to characterize its properties, and also by the scanning nitrogen-vacancy (NV) center tip which can be used to detect magnetic fields at nanoscale for imaging or couple to spin qubits 4 . While these ideas involve putting a qubit on the scanning tip itself, our scheme uses a separate gate chip to induce a qubit in the material structure under study, then measure those material and qubit parameters of interest using the circuits on the gate chip. Indeed, scanning tunneling microscope (STM) tips have already been used to create effective dots on the surface of InAs 5,6 and, more recently, Si 7 , using tunneling to do spectroscopy. Nondestructive characterization of embedded donor atoms in a semiconductor has also been demonstrated using a scanning tip architecture 8,9 . Here, we induce the dot qubit within the material in an environment realistic to quantum computing and consider a) Electronic

Superconductor–semiconductor hybrid-circuit quantum electrodynamics

“…Scanning-probe versions of superconducting cavities (FIG. 6d) could be used to probe valley physics in silicon [153][154][155][156] and perhaps be of much broader use in investigations of two-dimensional quantum materials 157 .…”

Fabrication and Characterization of an InAs(Sb)/InxGa1−xAsySb1−y Type‐II Superlattice

“…[18,19] This requirement spreads out the electron and hole wavefunctions with a small overlap, resulting in low luminescence efficiency. [21,22] Despite the abovementioned binary or ternary alloy SL systems, no quaternary alloycontaining SL has been proposed and fabricated so far.As reported, [23] the quaternary alloy In x Ga 1Àx As y Sb 1Ày can be lattice-matched to GaSb (and InAs), which enables type II band alignment of In x Ga 1Àx As y Sb 1Ày with InAs(Sb) over a wide range…”

“…As reported, [23] the quaternary alloy In x Ga 1Àx As y Sb 1Ày can be lattice-matched to GaSb (and InAs), which enables type II band alignment of In x Ga 1Àx As y Sb 1Ày with InAs(Sb) over a wide range of In and As contents. However, the In x Ga 1Àx As y Sb 1Ày quaternary compound has an immiscibility gap.…”

“…Therefore, the InAs(Sb 0.09 )/ In 0.5 Ga 0.5 As 0.46 Sb 0.54 SLs may have longer minority carrier lifetimes. [23,34,36,37] Our FMA process can be used to optimize the localization of electrons and holes in more complex quaternary alloys. For example, we fabricated the complex InAs(Sb x )/ In x1 Ga 1Àx1 As y1 Sb 1Ày1 /In x2 Ga 1-x2 As y2 Sb 1Ày2 /In x3 Ga 1Àx3 As y3 Sb 1Ày3 system, in which we tuned the CBM and valence band maximum (VBM) positions of the mini-bandgap and the localization of electrons and holes.…”

Opinion: Democratizing Spin Qubits

“…a testbed where dots are induced and measured by a separate chip to characterize materials [27] and qubit approaches. In doing so, an acceleration of progress similar to that driven by the "wireless" 3D transmon (Figure 2b) could be replicated in the spin community.…”