This review covers important advances in recent years in the physics of thin-film ferroelectric oxides, the strongest emphasis being on those aspects particular to ferroelectrics in thin-film form. The authors introduce the current state of development in the application of ferroelectric thin films for electronic devices and discuss the physics relevant for the performance and failure of these devices. Following this the review covers the enormous progress that has been made in the first-principles computational approach to understanding ferroelectrics. The authors then discuss in detail the important role that strain plays in determining the properties of epitaxial thin ferroelectric films. Finally, this review ends with a look at the emerging possibilities for nanoscale ferroelectrics, with particular emphasis on ferroelectrics in nonconventional nanoscale geometries.

/pdf/physics-of-thin-film-ferroelectric-oxides-3zmqphtpv1.pdf

Physics of thin-film ferroelectric oxides

The 2D–3D growth mode transition during the initial stages of growth of highly strained InGaAs on GaAs is used to obtain quantum‐sized dot structures. Transmission electron micrographs reveal that when the growth of In0.5Ga0.5As is interrupted exactly at the onset of this 2D–3D transition, dislocation‐free islands (dots) of the InGaAs result. Size distributions indicate that these dots are ∼300 A in diameter and remarkably uniform to within 10% of this average size. The areal dot densities can be varied between 109 and 1011 cm−2. The uniformity of the dot sizes is explained by a mechanism based on reduction in adatom attachment probabilities due to strain. We unambiguously demonstrate photoluminescence at ∼1.2 eV from these islands by comparing samples with and without dots. The luminescent intensities of the dots are greater than or equal to those of the underlying reference quantum wells.

Direct formation of quantum‐sized dots from uniform coherent islands of InGaAs on GaAs surfaces

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

Semiconducting quantum dots, whose particle sizes are in the nanometer range, have very unusual properties. The quantum dots have band gaps that depend in a complicated fashion upon a number of factors, described in the article. Processing-structure-properties-performance relationships are reviewed for compound semiconducting quantum dots. Various methods for synthesizing these quantum dots are discussed, as well as their resulting properties. Quantum states and confinement of their excitons may shift their optical absorption and emission energies. Such effects are important for tuning their luminescence stimulated by photons (photoluminescence) or electric field (electroluminescence). In this article, decoupling of quantum effects on excitation and emission are described, along with the use of quantum dots as sensitizers in phosphors. In addition, we reviewed the multimodal applications of quantum dots, including in electroluminescence device, solar cell and biological imaging.

https://www.mdpi.com/1996-1944/3/4/2260/pdf

Quantum Dots and Their Multimodal Applications: A Review

This article reviews the history and current progress in high-mobility strained Si, SiGe, and Ge channel metal-oxide-semiconductor field-effect transistors (MOSFETs). We start by providing a chronological overview of important milestones and discoveries that have allowed heterostructures grown on Si substrates to transition from purely academic research in the 1980’s and 1990’s to the commercial development that is taking place today. We next provide a topical review of the various types of strain-engineered MOSFETs that can be integrated onto relaxed Si1−xGex, including surface-channel strained Si n- and p-MOSFETs, as well as double-heterostructure MOSFETs which combine a strained Si surface channel with a Ge-rich buried channel. In all cases, we will focus on the connections between layer structure, band structure, and MOS mobility characteristics. Although the surface and starting substrate are composed of pure Si, the use of strained Si still creates new challenges, and we shall also review the litera...

Strained Si, SiGe, and Ge channels for high-mobility metal-oxide-semiconductor field-effect transistors

We show that the islands formed in Stranski-Krastanow (SK) growth of Ge on Si(100) are initially dislocation free. Island formation in true SK growth should be driven by strain relaxation in large, dislocated islands. Coherent SK growth is explained in terms of elastic deformation around the islands, which partially accommodates mismatch. The limiting critical thickness, ${\mathit{h}}_{\mathit{c}}$, of coherent SK islands is shown to be higher than that for 2D growth. We demonstrate growth of dislocation-free Ge islands on Si to a thickness of \ensuremath{\approxeq}500 \AA{}, 50\ifmmode\times\else\texttimes\fi{}higher than ${\mathit{h}}_{\mathit{c}}$ for 2D Ge/Si epitaxy.

Dislocation-free Stranski-Krastanow growth of Ge on Si(100).

Single-crystal silicon films grown at 400 \ifmmode^\circ\else\textdegree\fi{}C on Si(111):B(\ensuremath{\surd}3 \ifmmode\times\else\texttimes\fi{} \ensuremath{\surd}3 ) are rotated 180\ifmmode^\circ\else\textdegree\fi{} about the surface normal with respect to the substrate. We discuss a mechanism based on chemical effects due to the boron (\ensuremath{\surd}3 \ifmmode\times\else\texttimes\fi{} \ensuremath{\surd}3 ) reconstruction that favors the film to grow with a B-type (twin) orientation. Films grown on the Si(111)-(7\ifmmode\times\else\texttimes\fi{}7) reconstruction under identical conditions have the A-type (untwinned) orientation.

D. J. Eaglesham

Papers

Dislocation-free Stranski-Krastanow growth of Ge on Si(100).

Influence of surface reconstruction on the orientation of homoepitaxial silicon films.

Buried, ordered structures: Boron in Si(111) and Si(100)