Impurities In Silicon Carbide Research Articles

First-Principles Study of Metal Impurities in Silicon Carbide: Structural, Magnetic, and Electronic Properties

The configurations of 10 types of metal-doped silicon carbide (SiC) systems were investigated by the first-principles calculations. The dopants include eight types of 3d-series transition metal atoms, one semi-metal Ge atom, and one other metal Al atom. For all the metal-doped SiC systems, the steadiest doping sites are fixed at the substituted Si site, while the Ti-SiC system exhibits the most potent binding activity. The properties of these new systems vary with the doping atoms. The SiC- and Al-SiC systems convert to magnetic metals. The Ti- and Ge-SiC systems remain non-magnetic semiconductors, while the V-, Cr-, Mn-, Fe-, Co-, and Zn-SiC systems turn into magnetic semiconductors with magnetic moments related to the valence electron number of dopants. Partial charge transfers from the metal atoms to the adjacent C atoms accompanied the change in the electron-emitting capacity of the new systems. The work function achieves the minimum of 3.439 eV in the Co-SiC system, just 71.6% of the original SiC system. Our analysis indicates that the potent binding energy of the Ti-SiC system is due to the complete bonding states between the transition metal Ti and the adjacent C atoms. The magnetism evolution in semiconducting metal-doped SiC is attributed to the occupation mode of the hybridization orbitals nearby the Fermi level, which are determined by the coupling of the 3d orbital of transition metal atoms and the defect states of the vacancy atoms. The adjustable magnetic and electronic properties of the metal-doped SiC systems provide a flexible method in designing more suitable SiC-based spintronics and field electron-emitting devices.

Selective Doping in Silicon Carbide Power Devices.

Silicon carbide (SiC) is the most mature wide band-gap semiconductor and is currently employed for the fabrication of high-efficiency power electronic devices, such as diodes and transistors. In this context, selective doping is one of the key processes needed for the fabrication of these devices. This paper concisely reviews the main selective doping techniques for SiC power devices technology. In particular, due to the low diffusivity of the main impurities in SiC, ion implantation is the method of choice to achieve selective doping of the material. Hence, most of this work is dedicated to illustrating the main features of n-type and p-type ion-implantation doping of SiC and discussing the related issues. As an example, one of the main features of implantation doping is the need for post-implantation annealing processes at high temperatures (above 1500 °C) for electrical activation, thus having a notable morphological and structural impact on the material and, hence, on some device parameters. In this respect, some specific examples elucidating the relevant implications on devices’ performances are reported in the paper. Finally, a short overview of recently developed non-conventional doping and annealing techniques is also provided, although these techniques are still far from being applied in large-scale devices’ manufacturing.

Solid solubility and site preference of Ti in 3C-SiC

Ti is one of characteristic background impurities in silicon carbide (SiC) crystals, and it has a significant effect on the electronic properties of SiC. Herein, the calculated C-Si-Ti phase diagrams reveal that TiC, Ti3SiC2, and TiSi2 are the most stable phases depending on the chemical potential of Si, and the solid solubilities of Ti in 3C-SiC were determined at the SiC-TiSi2 thermodynamic equilibrium. The calculated hole transition energy between L1 and M3 for different possible defects explains the observed peak shift for the experimental Ti-Lℓ soft X-ray emissions of the Ti-saturated 3C-SiC, which experimentally confirmed that the Si-site substitution by Ti is the preferred type of defects for Ti in narrower-bandgap 3C-SiC. Furthermore, theoretical calculations reveal the different effects of Ti on the Si-L2,3 and C-K emission spectra.

Identification and tunable optical coherent control of transition-metal spins in silicon carbide

Color centers in wide-bandgap semiconductors are attractive systems for quantum technologies since they can combine long-coherent electronic spin and bright optical properties. Several suitable centers have been identified, most famously the nitrogen-vacancy defect in diamond. However, integration in communication technology is hindered by the fact that their optical transitions lie outside telecom wavelength bands. Several transition-metal impurities in silicon carbide do emit at and near telecom wavelengths, but knowledge about their spin and optical properties is incomplete. We present all-optical identification and coherent control of molybdenum-impurity spins in silicon carbide with transitions at near-infrared wavelengths. Our results identify spin S = 1/2 for both the electronic ground and excited state, with highly anisotropic spin properties that we apply for implementing optical control of ground-state spin coherence. Our results show optical lifetimes of ~60 ns and inhomogeneous spin dephasing times of ~0.3 μs, establishing relevance for quantum spin-photon interfacing.

Transient model for electrical activation of aluminium and phosphorus-implanted silicon carbide

The development of novel electron devices requires a continuous support by process and device simulations in order to improve electrical properties and reduce production costs. However, an accurate description of the electrical properties of impurities in silicon carbide – a key wide bandgap semiconductor for power devices – is currently not available, which significantly limits the predictability of critical fabrication processes. Here, we introduce a transient model for electrical activation of implanted aluminium and phosphorus in silicon carbide to fill this gap. Our results suggest differences between acceptor- and donor-type dopants including activation speed, saturation limit, and activation regions. We predict acceptor and donor concentrations according to the various annealing times, temperatures, and doping concentrations. The results are used for the fabrication of PN-junction diodes, which are characterized and compared with the experimental findings. Finally, we predict improvements of various annealing steps, i.e., increased active concentration, increased carrier concentration, and decreased sheet resistance, and perform a comprehensive comparison with experimental data to evaluate the proposed model.

Empirical Model for Electrical Activation of Aluminum- and Boron-Implanted Silicon Carbide

Accurate modeling of the electrical properties of impurities in semiconductors is essential for the mandatory support of the development of novel semiconductor devices by means of simulations. An appropriate modeling approach to determine the activation rate of dopants in silicon carbide is currently not available, which limits the predictability of process simulations. To remedy this fact, we propose an empirical model for the electrical activation of aluminum and boron impurities in silicon carbide for various annealing temperatures and total doping concentrations. The differences of the two acceptor-type dopants are discussed according to the model predictions and the activation ratios for various processing parameters are presented. The model was implemented into Silvaco’s simulation platform Victory Process and evaluated with respect to published experimental findings.

Resonant optical spectroscopy and coherent control ofCr4+spin ensembles in SiC and GaN

Spins bound to point defects are increasingly viewed as an important resource for solid-state implementations of quantum information technologies. In particular, there is a growing interest in the identification of new classes of defect spin that can be controlled optically. Here we demonstrate ensemble optical spin polarization and optically detected magnetic resonance (ODMR) of the S = 1 electronic ground state of chromium (Cr4+) impurities in silicon carbide (SiC) and gallium nitride (GaN). Spin polarization is made possible by the narrow optical linewidths of these ensembles (< 8.5 GHz), which are similar in magnitude to the ground state zero-field spin splitting energies of the ions at liquid helium temperatures. We therefore are able to optically resolve individual spin sublevels within the ensembles at low magnetic fields using resonant excitation from a cavity-stabilized, narrow-linewidth laser. Additionally, these near-infrared emitters possess exceptionally weak phonon sidebands, ensuring that > 73% of the overall optical emission is contained with the defects zero-phonon lines. These characteristics make this semiconductor-based, transition metal impurity system a promising target for further study in the ongoing effort to integrate optically active quantum states within common optoelectronic materials.

Influence of Hot Implantation on Residual Radiation Damage in Silicon Carbide

Remarkable thermomechanical and electrical properties of silicon carbide (SiC) make this material very attractive for high-temperature, high-power, and high-frequency applications. Because of very low values of diffusion coefficient of most impurities in SiC, ion implantation is the best method to selectively introduce dopants over well-defined depths in SiC. Aluminium is commonly used for creating p-type regions in SiC. However, post-implantation radiation damage, which strongly deteriorates required electric properties of the implanted layers, is difficult to anneal even at high temperatures because of remaining residual damage. Therefore implantation at elevated target temperatures (hot implantation) is nowadays an accepted method to decrease the level of the residual radiation damage by avoiding ion beam-induced amorphization. The main objective of this study is to compare the results of the Rutherford backscattering spectroscopy with channeling and micro-Raman spectroscopy investigations of room temperature and 500 ◦C Al ion implantation-induced damage in 6H-SiC and its removal by high temperature (up to 1600 ◦C) thermal annealing.

Boron and nitrogen impurities in SiC nanoribbons: an ab initio investigation

Using ab initio calculations based on density-functional theory we have performed atheoretical investigation of substitutional boron and nitrogen impurities in silicon carbide(SiC) nanoribbons. We have considered hydrogen terminated SiC ribbons with zigzag andarmchair edges. In both systems we verify that the boron and nitrogen atoms energeticallyprefer to be localized at the edges of the nanoribbons. However, while boron preferentiallysubstitutes a silicon atom, nitrogen prefers to occupy a carbon site. In addition, ourelectronic-structure calculations indicate that (i) substitutional boron and nitrogenimpurities do not affect the semiconducting character of the armchair SiC nanoribbons, and(ii) the half-metallic behavior of the zigzag nanoribbons is maintained in the presenceof substitutional boron impurities. In contrast, nitrogen atoms occupying edgecarbon sites transform half-metallic zigzag nanoribbons into metallic systems.

Oxide film assisted dopant diffusion in silicon carbide

A process is described to enhance the diffusion rate of impurities in silicon carbide so that doping by thermal diffusion can be done at lower temperatures. This process involves depositing a thin film consisting of an oxide of the impurity followed by annealing in an oxidizing ambient. The process uses the lower formation energy of silicon dioxide relative to that of the impurity-oxide to create vacancies in silicon carbide and to promote dissociation of the impurity-oxide. The impurity atoms then diffuse from the thin film into the near-surface region of silicon carbide.

The influence of palladium impurities on vacancy diffusion in cubic silicon carbide

AbstractThe basic properties of palladium impurities in silicon carbide, such as solubility or diffusion mechanisms, are far from being well understood. In a recent paper I presented a systematic study of stability and kinetic properties of Pd in cubic silicon carbide using first principles calculations. In this paper I focus on the effect of the presence of palladium in silicon carbide, even in very low concentrations, on the kinetic properties of carbon vacancies. I apply a odel of Pd diffusion through a vacancy mechanism on the carbon sublattice and extract the correlation factors leading to an enhancement of vacancy migration, due to the coupling of iffusion fluxes between vacancies and palladium impurities.

Palladium in cubic silicon carbide: Stability and kinetics

Several technological applications of silicon carbide are concerned with the introduction of palladium impurities. Be it intentional or not, this may lead to the formation of silicides. Not only this process is not well understood, but the basic properties of palladium impurities in silicon carbide, such as solubility or diffusion mechanisms, are far from being known. Here the stability and kinetics of isolated Pd impurities in cubic silicon carbide are studied by first principles calculations in the framework of density functional theory. The preferential insertion sites, as well as the main migration mechanisms, are analyzed and presented here, together with the results for solution and migration energies. The early stages of nucleation are discussed based on the properties of isolated impurities and the smallest clusters.

Magnetic states of transition metal impurities in silicon carbide

Electronic properties of 3C silicon carbide with substitutional transition metalimpurities are calculated using an ab initio full-potential linearized augmented planewave technique. It is shown that transition metal atoms in an SiC host may existin both magnetic and nonmagnetic states. For different impurity species, thetransition from the nonmagnetic to the magnetic state and the correspondingchange of the atomic magnetic moments may take place either gradually as thevolume of the unit cell changes or when the energy gap between the two states isovercome. The magnetic and nonmagnetic solutions are characterized by significantlydifferent unit cell geometries, which are analysed in detail. Magnetic ordering isstudied for a number of transition metal impurities in SiC and mean-field estimatesof the Curie temperature are given. Calculated densities of states are used toanalyse the nature of the exchange interaction between the impurities. Someproperties of transition metal impurities are compared for 3C and 4H silicon carbidesubstitution.

Negative muon spin rotation study of acceptor centers in SiC

The project aims at studying aluminum and boron acceptor impurities in silicon carbide. These impurities are modeled by muonic atoms formed via negative muon capture by Si or C atoms of the host material. To distinguish between the signals from muons captured by Si and C atoms the energy of characteristic X-rays emitted during the muon transition to the 1s atomic state is measured and used for histogram routing (X-ray triggered μSR). The first experimental results with an n-type 4H–SiC are reported.

Boron, aluminum, nitrogen, and oxygen impurities in silicon carbide

Boron, aluminum, nitrogen, and oxygen impurities in silicon carbide

Laser‐doping of silicon carbide for p–n junction and LED fabrication

AbstractThe high melting point and the limited diffusion of impurities in silicon carbide have greatly restricted the use of conventional ion implantation and furnace to incorporate and activate dopants. A laser doping technique overcomes these obstacles for doping silicon carbide and other wide band gap semiconductors. This paper presents the work on fabrication of p–n junction diodes and blue light emitting diodes using laser doping technique. A p–n junction was created by laser doping a silicon carbide wafer with aluminum (p‐type) and nitrogen (n‐type). Optical interferometer profilometer scan showed that there was no damage on the surface post laser doping. Secondary ion mass spectrometry (SIMS) was carried to estimate the dopant concentration and depth. The effects of laser doping on the current–voltage characteristics were studied. The junctions were characterized by capacitance–voltage and electroluminescence measurements. A broad electroluminescence peak was observed around 498.8 nm wavelength, characterizing the p–n junction as a blue light‐emitting diode. (© 2007 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Electron Paramagnetic Resonance of Electronic‐Grade SiC Substrates

AbstractFor Abstract see ChemInform Abstract in Full Text.

Structural and electronic properties of3dtransition metal impurities in silicon carbide

We carried out a theoretical investigation on the electronic and structural properties of typical residual transition metal impurities in silicon carbide. The calculations were performed using the all electron spin-polarized full-potential linearized augmented plane-wave methodology. The results on stability, spin states, hyperfine parameters, formation and transition energies of isolated Ti, V, and Cr impurities in $3C$-SiC and $2H$-SiC were compared to available experimental data.

Structural and electronic properties of Ti impurities in SiC: an ab initio investigation

We carried a theoretical investigation on the electronic and structural properties of titanium impurities in silicon carbide. The calculations were performed using the spin-polarized full-potential linearized augmented plane-wave method in the supercell approach. The geometry and atomic structures, transition and formation energies of isolated Ti impurities in 3C-SiC were computed. For each configuration, the atoms around the impurity site were allowed to relax following the damped Newton dynamics scheme. The results were compared to available experimental data on hexagonal silicon carbide.

Finite‐cluster approximation for deep‐level impurities in silicon carbide

AbstractA series of 12 silicon carbide finite clusters has been investigated to determine a possible model for transition‐metal deep‐level impurities in several Si sites of the material. All electronic structure calculations were done using the extended Hückel method. By taking account of boundary condition effects upon the electronic structure of the pure and V‐substitutional systems, it was found that the cluster series could be classified into two groups: a large‐gap and a small‐gap group. The small‐gap group arises from spurious border Si‐3p levels that appear inside the forbidden gap. It was consequently suggested that large‐gap clusters are more suitable for describing the impurity. It is also suggested that possibly new V, Si, and C parameters could lead to both a good description of the pure and doped material. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem 95: 88–96, 2003