Positron annihilation spectroscopy of sub-surface defects in semiconductors

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Doping Silicon Nanocrystals with Boron and Phosphorus

The properties of silicon nanocrystals (Si NCs) that are usually a few nanometers in size can be exquisitely tuned by boron (B) and phosphorus (P) doping. Recent progress in the simulation of B- and P-doped Si NCs has led to improved explanation for B- and P-doping-induced changes in the optical properties of Si NCs. This is mainly enabled by comprehensive investigation on the locations of B and P in Si NCs and the electronic properties of B- and P-doped Si NCs. I remarks on the implications of newly gained insights on B- and P-doped Si NCs. Continuous research to advance the understanding of the doping of Si NCs with B and P is envisioned

Chemical modification of silicene

Silicene is a two-dimensional material, which is composed of a single layer of silicon atoms with sp2-sp3 mixed hybridization. The sp2-sp3 mixed hybridization renders silicene excellent reactive ability, facilitating the chemical modification of silicene. It has been demonstrated that chemical modification effectively enables the tuning of the properties of silicene. We now review all kind of chemical modification methods for silicene including hydrogenation, halogenation, organic surface modification, oxidation, doping and alloying. The effects of these chemical modification methods on the geometrical, electronic, optical and magnetic properties of silicene are discussed. The potential applications of chemically modified silicene in a variety of fields such as electronics, optoelectronics and magnetoelectronics are introduced. We finally envision future work on the chemical modification of silicene for the sake of further advancing the development of silicene

Phonon-limited carrier mobilities and Hall factors in 4H-SiC from first principles

Charge carrier mobility is at the core of semiconductor materials and devices optimization, and Hall measurement is one of the most important techniques for its characterization. The Hall factor, defined as the ratio between Hall and drift mobilities, is of particular importance. Here we study the effect of anisotropy by computing the drift and Hall mobility tensors of a technologically important wide-band-gap semiconductor, 4H-silicon carbide (4H-SiC) from first principles. With $GW$ electronic structure and \textit{ab initio} electron-phonon interactions, we solve the Boltzmann transport equation without fitting parameters. The calculated electron and hole mobilities agree with experimental data. The electron Hall factor strongly depends on the direction of external magnetic field $\mathbf{B}$, and the hole Hall factor exhibits different temperature dependency for $\mathbf{B}\parallel c$ and $\mathbf{B}\perp c$. We explain this by the different equienergy surface shape arising from the anisotropic and non-parabolic band structure, together with the energy-dependent electron-phonon scattering.Comment: 24 pages, 8 figure

Density functional theory study on the B doping and B/P codoping of Si nanocrystals embedded in SiO2

Doping silicon nanocrystals (Si NCs) embedded in silicon dioxide (SiO2) with boron (B) and phosphorus (P) is a promising way of tuning the properties of Si NCs. Here we take advantage of density functional theory to investigate the dependence of the structural and electronic properties of Si NCs embedded in SiO2 on the doping of B and P. The locations and energy-level schemes are examined for singularly B-doped or B/P-codoped Si NCs embedded in SiO2 with a perfect or defective Si/SiO2 interface at which a Si dangling bond exists. A dangling bond plays an important role in the doping of Si NCs with B or B/P. The doping behavior of B in Si NCs embedded in SiO2 vastly differs from that of P. The electronic structure of a B/P-codoped Si NC largely depends on the distribution of the dopants in the NC

A Silicon Cluster Based Single Electron Transistor with Potential Room-Temperature Switching

We demonstrate the fabrication of a single electron transistor device based on a single ultra-small silicon quantum dot connected to a gold break junction with a nanometer scale separation. The gold break junction is created through a controllable electromigration process and the individual silicon quantum dot in the junction is determined to be a Si_170 cluster. Differential conductance as a function of the bias and gate voltage clearly shows the Coulomb diamond which confirms that the transport is dominated by a single silicon quantum dot. It is found that the charging energy can be as large as 300meV, which is a result of the large capacitance of a small silicon quantum dot (1.8 nm). This large Coulomb interaction can potentially enable a single electron transistor to work at room temperature. The level spacing of the excited state can be as large as 10 meV, which enables us to manipulate individual spin via an external magnetic field. The resulting Zeeman splitting is measured and the lande factor of 2.3 is obtained, suggesting relatively weak electron-electron interaction in the silicon quantum dot which is beneficial for spin coherence time