This review describes recent groundbreaking results in Si, Si/SiGe, and dopant-based quantum dots, and it highlights the remarkable advances in Si-based quantum physics that have occurred in the past few years. This progress has been possible thanks to materials development of Si quantum devices, and the physical understanding of quantum effects in silicon. Recent critical steps include the isolation of single electrons, the observation of spin blockade, and single-shot readout of individual electron spins in both dopants and gated quantum dots in Si. Each of these results has come with physics that was not anticipated from previous work in other material systems. These advances underline the significant progress toward the realization of spin quantum bits in a material with a long spin coherence time, crucial for quantum computation and spintronics.

/pdf/silicon-quantum-electronics-4bxpe9czeo.pdf

Silicon quantum electronics

The ability to control matter at the atomic scale and build devices with atomic precision is central to nanotechnology. The scanning tunnelling microscope can manipulate individual atoms and molecules on surfaces, but the manipulation of silicon to make atomic-scale logic circuits has been hampered by the covalent nature of its bonds. Resist-based strategies have allowed the formation of atomic-scale structures on silicon surfaces, but the fabrication of working devices-such as transistors with extremely short gate lengths, spin-based quantum computers and solitary dopant optoelectronic devices-requires the ability to position individual atoms in a silicon crystal with atomic precision. Here, we use a combination of scanning tunnelling microscopy and hydrogen-resist lithography to demonstrate a single-atom transistor in which an individual phosphorus dopant atom has been deterministically placed within an epitaxial silicon device architecture with a spatial accuracy of one lattice site. The transistor operates at liquid helium temperatures, and millikelvin electron transport measurements confirm the presence of discrete quantum levels in the energy spectrum of the phosphorus atom. We find a charging energy that is close to the bulk value, previously only observed by optical spectroscopy.

A single-atom transistor

A system includes a semiconductor device. The semiconductor device includes a first single crystal silicon layer comprising first transistors, first alignment marks, and at least one metal layer overlying the first single crystal silicon layer, wherein the at least one metal layer comprises copper or aluminum more than other materials; and a second single crystal silicon layer overlying the at least one metal layer. The second single crystal silicon layer comprises a plurality of second transistors arranged in substantially parallel bands. Each of a plurality of the bands comprises a portion of the second transistors along an axis in a repeating pattern.

System comprising a semiconductor device and structure

A device comprising semiconductor memories, the device comprising: a first layer and a second layer of layer-transferred mono-crystallized silicon, wherein the first layer comprises a first plurality of horizontally-oriented transistors; wherein the second layer comprises a second plurality of horizontally-oriented transistors; and wherein the second plurality of horizontally-oriented transistors overlays the first plurality of horizontally-oriented transistors.

Semiconductor device and structure

The sensitive dependence of a semiconductor's electronic, optical and magnetic properties on dopants has provided an extensive range of tunable phenomena to explore and apply to devices. Recently it has become possible to move past the tunable properties of an ensemble of dopants to identify the effects of a solitary dopant on commercial device performance as well as locally on the fundamental properties of a semiconductor. New applications that require the discrete character of a single dopant, such as single-spin devices in the area of quantum information or single-dopant transistors, demand a further focus on the properties of a specific dopant. This article describes the huge advances in the past decade towards observing, controllably creating and manipulating single dopants, as well as their application in novel devices which allow opening the new field of solotronics (solitary dopant optoelectronics).

http://frg.physics.uiowa.edu/publications/review-13.pdf

Single dopants in semiconductors

A single dopant atom can dominate the subthreshold behaviour of a field-effect transistor, and this effect is enhanced if the atom is located near a dielectric.

Single-donor ionization energies in a nanoscale CMOS channel

For the first time 3D sequential CMOS integration turns up to be an actual competitor for sub 22nm technology nodes. Thanks to the original use of molecular bonding, high quality top Si active layers are obtained. Thermally robust bottom salicide goes through the whole top FET processing without any significant sheet resistance degradation. The low temperature integration of raised source and drain for top layers is demonstrated. A decrease by 4A of the Equivalent Oxide Thickness is measured when a low thermal budget process is implemented. The electrostatic coupling between stacked FETs is demonstrated thanks to an ultra thin inter layer dielectric thickness of 60nm. It leads to a threshold voltage dynamic shift of 130mV enabling SRAM stabilization.

Advances in 3D CMOS sequential integration

Although single dopant signatures have been observed at low temperature [1–2], the impact on transistor performance of a single dopant atom at room temperature is not yet well understood Here, for the first time, we provide an in-depth understanding of single dopant influence on NMOSFETs characteristics by linking low and room temperature transport We demonstrate that, for gate length of 30 nm and below (channel length down to 10 nm), the presence of a single dopant dramatically alters the subthreshold behaviour when the dopant is located in the middle of the channel Moving the dopants away from the channel leads to enhanced variability above the threshold voltage V t 

Single dopant impact on electrical characteristics of SOI NMOSFETs with effective length down to 10nm

We describe the first implementation of a coupled atom transistor where two shallow donors (P or As) are implanted in a nanoscale silicon nanowire and their electronic levels are controlled with three gate voltages Transport spectroscopy through these donors placed in series is performed both at zero and microwave frequencies The coherence of the charge transfer between the two donors is probed by Landau-Zener-Stuckelberg interferometry Single-charge transfer at zero bias (electron pumping) has been performed and the crossover between the adiabatic and non-adiabatic regimes is studied

The coupled atom transistor.

Silicon nanowire transistors are measured at low temperature in the Coulomb blockade regime. Coulomb blockade spectroscopy permits to determine the gate, source and drain capacitances. We propose a model to explain the origin of both the gate and source (drain) capacitances for quantum dots formed in gated silicon nanowires. The gate capacitance is found to be determined by the gate-wire overlap capacitor and does not depend on gate voltage. On the contrary, the source (drain) capacitances increase with gate voltage. This feature is related to the increase of the electronic polarizability in the access regions.

O. Cueto

Papers

Single-donor ionization energies in a nanoscale CMOS channel

Advances in 3D CMOS sequential integration

Single dopant impact on electrical characteristics of SOI NMOSFETs with effective length down to 10nm

The coupled atom transistor.

Capacitance measurements in nanometric silicon devices using Coulomb blockade