Kick-out Mechanism Research Articles

Diffusion models of grown-in and implanted p-type dopant in III-V semiconductor compounds

This research shows that the diffusion of grown-in and implanted Be atoms in III-V considered semiconductor materials, such as the Liquid-Encapsulated Czochralski-grown (LEC) GaAs as well as the Gas-Source Molecular Beam Epitaxy (GSMBE) In0.53Ga0.47As, In0.73Ga0.27As0.58P0.42, In0.53Ga0.47As/In0.73Ga0.27As0.58P0.42, In0.53Ga0.47As/InP compounds, taking place during the Rapid Thermal Annealing (RTA) process, is perfectly well explained by the “full” version of the kick-out mechanism operating through singly positively ionized Be interstitials and group III self-interstitial ions (Ga, In) in all their states of positive charge including neutral. Numerical solutions of the differential equations, corresponding to the considered system of diffusion reactions, have been calculated using the finite difference approach and our elaborate finite difference-Bairstow method. Such a model naturally emerges from most research works, including ours, in the considered field, over the last decades and makes it possible to “reconcile” their different diffusion models. In this study, we also present and analyze the Secondary Ion Mass Spectrometry (SIMS) profiles of the distribution of implanted Be in GaAs at an energy of 100 keV with a high dose of 1.0 ⋅ 1015cm−2 and annealed at temperatures ranging from 700 to 850 °C for à time ranging from 60 to 240s.

Theoretical and Experimental Studies of KLi6TaO6 as a Li-Ion Solid Electrolyte.

We study a hexagonal oxide KLi6TaO6 (KLTO), proposed as a Li-ion solid electrolyte, by using a recently developed screening method. First-principles calculations predict that KLTO presents a good Li-ion conductivity (σLi) and a low activation energy (Ea). Li migration is enhanced by the presence of excess Li ions in the interstitial region via a kick-out mechanism. Our experimental results demonstrate that Sn-doped KLTO presents a conductivity of 1 × 10-5 S cm-1, a σLi of 6 × 10-6 S cm-1, and a relatively low Ea of 36 kJ mol-1, which confirm the validity of the proposed screening method. Conversely, detailed analyses of the microstructure and X-ray diffraction patterns of KLTO samples indicate that a stable Li-excess condition is not achieved, therefore leaving potential improvement of the performance of KLTO as a Li-ion solid electrolyte by optimizing extrinsic doping and fabrication processes.

Large helium-vacancy clusters coalescence during helium bubble evolution under cascade in iron with edge dislocation: A MD simulation

The nucleation and growth of helium bubbles under the mutual effect of cascade and dislocation in bcc Fe was investigated by molecular dynamic simulations. The helium atoms along with primary knock-on atoms (PKA) were gradually added in the simulation system to imitate the real neutron irradiation condition. Several coalescence events of large helium-vacancy (He-V) clusters during the molecular dynamic simulation in bcc Fe were discovered. The detailed analysis of these coalescence events revealed that in the bulk region, if two helium-vacancy clusters are close enough, they are inclined to combine into one cluster by kicking out host atoms between the two clusters. However, two close helium-vacancy clusters near the dislocation line will not merge by this kick-out mechanism. Instead, it’s found that they could be promoted to combine together by cascade, even if the two clusters locate on the edge of the cascade thermal spike. The mutual influence of dislocation and cascade will lead to the formation of low content and large size helium-vacancy clusters around the dislocation line.

Stability and interaction of cation Frenkel pair in wurtzite semiconductor materials

The understanding of defects is an important issue in the development of semiconductor materials. Using ab initio calculations and ab initio molecular dynamics, the stability and interaction of cation Frenkel pairs were investigated in four wurtzite semiconductor materials, GaN, AlN, InN and ZnO. With regard to GaN material, an interesting phenomenon was found that the recombination path of Ga Frenkel pair is a kick-out mechanism which is similar to the migration of Ga interstitial. Based on the obtained path, the recombination energy barriers of different positions of Frenkel pairs were calculated respectively. The calculation results demonstrated that the recombination behavior of Ga Frenkel pair is not only determined by the distance but also the relative position of vacancy and interstitial. Meanwhile, the value of the projected interaction radius was observed to be about 7.5 Å. Compared with the small interaction range of N Frenkel pair, Ga Frenkel pair was found to be unstable, which is consistent with previous radiation experiments. Furthermore, the same phenomenon in GaN material was also found in the other three wurtzite materials and the projected interaction radius of wurtzite materials was concluded as 7/3 lattice parameter. In general, this theoretical study provides an insight of the stability of cation Frenkel pair and improves our understanding of defects in wurtzite semiconductors.

Integrated modeling of helium-vacancy clustering in Eurofer97 steel upon He+/Fe3+ dual-beam irradiation

By developing an integrated rate theory model, we studied helium-vacancy (He-V) clustering in ferritic/martensitic Eurofer97 steels under He+/Fe3+ dual-beam irradiation. Different from the known single peak concentration profile of total atomic He, the concentration of ‘solute’ He atom (interstitial He) increases and decreases twice during irradiation, showing two peaks as a function of irradiatiom time (dose). The second increase in concentration was caused by the operation of the kick-out mechanism aided by irradiation-induced self-interstitials. We show that the kicked-out interstitial He enhances the growth of He-V clusters and leads to the shift of cluster pressurization states. He-V clustering direction is also governed by the kicked-out interstitial He.

Integrated Modeling of Helium-Vacancy Clustering in Eurofer97 Steel Upon He+/Fe3+ Dual Ion Beam Irradiation

Here, by developing an integrated rate theory model, we studied helium-vacancy (He-V) clustering in ferritic/martensitic steel Eurofer97 under He + /Fe 3+ dual ion beam irradiation condition. Different from the known single peak concentration profile of total atomic He, the ‘solute’ He atom (interstitial He) concentration displays a bimodal distribution during irradiation due to the kick-out mechanism aided by irradiation-induced self-interstitials. We show that the kicked-out interstitial He enhances the He-V clustering rate and leads to the shift of cluster pressurization states. The He-V clustering direction is also governed by the kicked-out interstitial He.

Reveal the fast and charge-insensitive lattice diffusion of silver in cubic silicon carbide via first-principles calculations

The lattice diffusion of silver with various charge states in cubic silicon carbide has been investigated by means of high-fidelity spin-polarized density functional theory calculations. The migration energy barrier of the Ag interstitial diffusion is 1.09 eV and 1.11 eV for neutral and q=+1e charge state, respectively, close to the activation energy of Ag diffusion measured in the German HTR fuel program. A general trend is that the migration energy barrier reduces with respect to the increase of charge on Ag, which is much less than the increment in the oxidation energy, suggesting that the lattice diffusion of silver prefers constant neutral state without redox in transition state. Our results indicate a scenario that once Ag is deposited to interstitials via the kickout mechanism, it will highly likely perform lattice diffusion across the SiC layer leading to fast release of Ag in Tristructural-Isotropic fuel induced by irradiation.

Oxygen conduction mechanism in Ca3Fe2Ge3O12 garnet-type oxide

We investigate the oxygen conduction mechanism in a garnet-type oxide, Ca3Fe2Ge3O12, for the first time in detail by first-principle calculations. The nudged elastic band results confirm that this oxide has a lower migration barrier energy (0.45 eV) for an oxygen interstitial (Oi) with the kick-out mechanism than that (0.76 eV) for an oxygen vacancy. The migration paths for Oi are delocalized and connected to the neighboring cells in three-dimensional space. This oxide does not have a very low formation energy of Oi when the Fermi level is near the lowest unoccupied molecular orbital at a high temperature, which implies the possibility of electron doping by high-valence cations. These theoretical results suggest that the doping of Ca3Fe2Ge3O12 for generation of excess Oi provides a good oxygen-ion conductivity, along with the electronic conductivity.

Diffusion and Defect Phenomena in III-V Semiconductors and their Investigation by Transmission Electron Microscopy

This article reviews the studies of diffusion and defect phenomena induced by high-concentration zinc diffusion in the single-crystal III-V compound semiconductors GaAs, GaP, GaSb and InP by methods of transmission electron microscopy and their consequences for numerical modelling of Zn (and Cd) diffusion concentration profiles. Zinc diffusion from the vapour phase into single-crystal wafers has been chosen as a model case for interstitial-substitutional dopant diffusion in these studies. The characteristics of the formation of diffusion-induced extended defects and of the temporal evolution of the defect microstructure correlate with the experimentally determined Zn profiles whose shapes depend on the chosen diffusion conditions. General phenomena observed for all semiconductors are the formation of dislocation loops, precipitates, voids, and dislocations and of Zn-rich precipitates in the diffusion regions. The formation of extended defects near the diffusion front can be explained as result of point defect supersaturations generated by interstitial-substitutional zinc exchange via the kick-out mechanism. The defects may act as sinks for dopants and as sources and sinks for point defects during the continuing diffusion process, thereby providing a path to establishing defect-mediated local point defect equilibria. The investigations established a consistent picture of the formation and temporal evolution of defects and the mechanisms of zinc diffusion in these semiconductors for diffusion conditions leading to high-concentration Zn concentrations. Based on these results, numerical modelling of anomalously shaped dopant concentration profiles leads to satisfactory quantitative results and yields information on type and charge states of the point defect species involved, also for near-surface Zn concentration profiles and the absence of extended defects.

Redistribution of Metallic Impurities in Si during Annealing and Oxidation: W and Fe

Atomic redistribution of W and Fe in Si were studied using secondary ion mass spectrometry and transmission electron microscopy. W diffusion experiments performed during isothermal annealing and during Si oxidation show that W atoms should use at least two different diffusion mechanisms. Experimental diffusion profiles can be well simulated by considering the simultaneous use of three different W diffusion mechanisms: the dissociative and the kick-out mechanisms, as well as an original mechanism based on the formation of a W-Si self-interstitial pair located on the interstitial Si sub-lattice. Fe redistribution was studied during the oxidation of a Fe-contaminated Si wafer. Fe is shown to be first pushed-out in Si by the mobile SiO2/Si interface, and thus to form Fe silicides precipitates at this interface. The silicide precipitates, which can exhibit a core-shell structure, appear to move with the SiO2/Si interface thanks to an oxidation/dissolution mechanism in the SiO2 and a nucleation/growth mechanism in the Si matrix. Furthermore, the rate difference between Si and Fe silicide precipitate oxidation leads to the formation of Si pyramidal defects at the SiO2/Si interface.

Density functional theory calculation of diffusion mechanism of intrinsic defects in rutile TiO2

Diffusion mechanisms of four intrinsic point defects in rutile TiO2, titanium interstitial (TiI), titanium vacancy (Vti), oxygen interstitial (OI) and oxygen vacancy (VO) are studied in the framework of density functional theory with quantum ESPRESSO suite. Diffusion processes are simulated by defect movement between two stable atomic configurations through using the climbing image nudged elastic band (CI-NEB) method.The initial and final atomic structure in the minimum energy path (MEP) are constructed with 3×3×4 perfect supercell matrix of 216 atoms. Considering that oxygen atoms build up TiO6 octahedron and half of the octahedral centers are occupied by Ti atoms in rutile, interstitial defect is constructed by adding one Ti or O atom to the empty oxygen octahedral center, and vacancy defect is constructed by removing one atom from crystal lattice grid. Structural relaxation is performed before performing the NEB calculation with gamma k point sampling in irreducible Brillouin zone with an energy cutoff of 650 eV. As rutile TiO2 has tetragonal symmetry (P42/mnm), the diffusion channel along the[100] direction is equivalent to the[010] direction. Then, the diffusion paths along the direction parallel to c axis ([001] direction) and perpendicular to the c axis ([100] or[110] direction) are chosen to find the minimum diffusion energy path of TiI and OI. As for VTi and VO, diffusion paths are established from the vacancy site to nearest lattice site of the same kind.Calculation results exhibit significant anisotropy of energy barrier and diffusion mechanism. Of all defect species, TiI diffusion along the[001] direction through interstitial mechanism has the lowest activation barrier of 0.5057 eV. In addition, diffusions along the[100] and[110] direction through kick-out mechanism show higher energy barriers of 1.0024 eV and 2.7758 eV, respectively. Compared with TiI, OI shows small barrier discrepancy between different diffusion directions, which is 0.859 eV along[001] and 0.902 eV along[100] direction. For vacancy defects, diffusion can occur only through the vacancy mechanism. The activation barrier energy of symmetrically inequivalent diffusion path of VO is 0.735 eV along the[110] direction, 1.747 eV along the[001] direction, and 1.119 eV from the TiO6 apex site to the equator site. On the other hand, VTi has two inequivalent paths with much larger diffusion energy barriers:2.375 eV along the[111] direction and 3.232 eV along the[001] direction. In summary, the TiI interstitial diffusion along the[001] direction (parallel to the c axis) has the lowest activation barrier in rutile TiO2, which is in excellent agreement with former experimental and theoretical data.

Origin of the abnormal diffusion of transition metal atoms in rutile

Diffusion of dopants in rutile is the fundamental process that determines the performance of many devices in which rutile is used. The diffusion behavior is known to be highly sample-dependent, but the reasons for this are less well understood. Here, rutile is studied by using first-principles calculations, in order to unravel the microscopic origins of the diverse diffusion behaviors for different doping elements. Anomalous diffusion behavior in the open channel along [001] direction is found: larger atoms include Sc and Zr have lower energy barrier for diffusion via interstitial mechanism, apparently contradicting their known slow diffusion rate. To resolve this, we present an alternate model for the overall diffusion rate of the large-size dopants in rutile, showing that parallel to the [001] channel, it is limited by the formation of the interstitial states, whereas in the direction perpendicular to [001], it proceeds via a kick-out mechanism. By contrast, Co and Ni, prefer to stay in the interstitial site of rutile, and have conventional diffusion with a very small migration barrier in the [001] channel. This leads to highly anisotropic and fast diffusion. The diffusion mechanisms found in the present study can explain the diffusion data measured by experiments, and these findings provide novel understanding for the classic diffusion topic.

Direct observation of Li diffusion in Li-doped ZnO nanowires

The direct observation of Li diffusion in Li-doped zinc oxide nanowires (NWs) was realized by using in situ heating in the scanning transmission electron microscope (STEM). A continuous increase of low atomic mass regions within a single NW was observed between 200 °C and 600 °C when heated in vacuum, which was explained by the conversion of interstitial to substitutional Li in the ZnO NW host lattice. A kick-out mechanism is introduced to explain the migration and conversion of the interstitial Li (Lii) to Zn-site substitutional Li (LiZn), and this mechanism is verified with low-temperature (11 K) photoluminescence measurements on as-grown and annealed Li-doped zinc oxide NWs, as well as the observation of an increase of NW surface roughing with applied bias.

Response to “Comment on ‘Diffusion of n-type dopants in germanium’ ” [Appl. Phys. Rev. 2, 036101 (2015)

In this reply to the comment of Cowern et al., we demonstrate on the basis of full numerical simulations of radiation enhanced dopant diffusion via the kick-out mechanism that the g/λ analysis fails to consistently describe boron (B) diffusion in germanium (Ge) under irradiation. Cowern et al. missed to perform a consistency check with results for the diffusivity DI of Ge interstitials (I) determined from Ge self-diffusion under irradiation. Data deduced for DI from the exponential B profile reported by Cowern et al. deviate several orders of magnitude from the self-diffusion study. This clearly disproves the validity of the kick-out mechanism to control radiation enhanced B diffusion in Ge. Exponential B profiles like those established in Ge under irradiation are also reported for silicon by Venezia et al. [Phys. Rev. B 69, 125215 (2004)]. The characteristic shape is not described by the kick-out mechanism but rather explained qualitatively by the complex formation and dissolution of defect clusters. Modeling of B diffusion in Ge under irradiation performed by Schneider et al. [Phys. Rev. B 87, 115202 (2013)] is fully consistent with self-diffusion under irradiation. This constraint led us to conclude that the characteristic B profiles are additionally affected by the formation of immobile B clusters. Although a direct microscopic proof of B cluster formation is still lacking, the report of Venezia et al. on B clustering in Si during irradiation with similar exponential B profiles also supports our interpretation of B diffusion in Ge under irradiation.

Analytical boron diffusivity model in silicon for thermal diffusion from boron silicate glass film

An analytical boron diffusivity model in silicon for thermal diffusion from a boron silicate glass (BSG) film has been proposed in terms of enhanced diffusion due to boron–silicon interstitial pair formation. The silicon interstitial generation is considered to be a result of the silicon kick-out mechanism by the diffused boron at the surface. The additional silicon interstitial generation in the bulk silicon is considered to be the dissociation of the diffused pairs. The former one causes the surface boron concentration dependent diffusion. The latter one causes the local boron concentration dependent diffusion. The calculated boron profiles based on the diffusivity model are confirmed to agree with the actual diffusion profiles measured by secondary ion mass spectroscopy (SIMS) for a wide range of the BSG boron concentration. This analytical diffusivity model is a helpful tool for p+ boron diffusion process optimization of n-type solar cell manufacturing.

Identification of the dissociative and kick-out diffusion mechanisms of Zn diffusion in GaAs by photoluminescence analysis

Abstract Most investigations on Zn diffusion in GaAs were processed using the Zn–As alloy sources to prevent the As atoms from escaping GaAs wafers, while we found that the Zn diffusion would change fundamentally if Zn–Ga alloy sources were used. The Ga atoms from the diffusion sources suppressed the formation of the high-concentration surface region in Zn profiles, thus converting a kink-and-tail profile into a box profile. The photoluminescence (PL) analysis was used to identify the diffusion mechanisms. The Ga vacancy defects were found in the surface region of the kink-and-tail profile, indicating that the dissociative mechanism dominated; the PL spectrum in the tail region of kink-and-tail profile and the main region of box profile showed the same signals, no Ga vacancy defects were found, thus the kick-out mechanism dominated.

Direct observation of dopant atom diffusion in a bulk semiconductor crystal enhanced by a large size mismatch.

Diffusion is one of the fundamental processes that govern the structure, processing, and properties of materials and it plays a crucial role in determining device lifetimes. However, direct observations of diffusion processes have been elusive and limited only to the surfaces of materials. Here we use an aberration-corrected electron microscope to locally excite and directly image the diffusion of single Ce and Mn dopants inside bulk wurtzite-type AlN single crystals, identifying correlated vacancy-dopant and interstitial-dopant kick-out mechanisms. Using a 200 kV electron beam to supply energy, we observe a higher frequency of dopant jumps for the larger and heavier Ce atoms than the smaller Mn atoms. These observations confirm density-functional-theory-based predictions of a decrease in diffusion barrier for large substitutional atoms. The results show that combining depth sensitive microscopy with theoretical calculations represents a new methodology to investigate diffusion mechanisms, not restricted to surface phenomena, but within bulk materials.

A combined kick-out and dissociative diffusion mechanism of grown-in Be in InGaAs and InGaAsP. A new finite difference-Bairstow method for solution of the diffusion equations

Experimental results on the diffusion of grown-in beryllium (Be) in indium gallium arsenide (In0.53Ga0.47As) and indium gallium arsenide phosphide (In0.73Ga0.27As0.58P0.42) gas source molecular beam epitaxy alloys lattice-matched to indium phosphide (InP) can be successfully explained in terms of a combined kick-out and dissociative diffusion mechanism, involving neutral Be interstitials (Bei0), singly positively charged gallium (Ga), indium (In) self-interstitials (IIII+) and singly positively charged Ga, In vacancies (VIII+). A new numerical method of solution to the system of diffusion equations, based on the finite difference approximations and Bairstow's method, is proposed.

Oxygen vacancy formation and annihilation in lanthanum cerium oxide as a metal reactive oxide on 4H-silicon carbide

A mechanism regarding the redox reaction in lanthanum cerium oxide (LaxCeyOz) post-deposition annealed in reducing and oxidizing atmosphere was schematized and discussed in association with the presence of lanthanum as a substitutional cation. Analyses have been performed using X-ray diffraction, energy-filtered transmission electron microscopy, scanning transmission electron microscope-energy dispersive spectroscopy line scan, and capacitance-voltage measurements. The results showed the presence of an oxygen vacancy when La(3+) was in its substitution site, while annihilation of oxygen vacancy was accompanied by a displacement of La(3+) from the substitutional site to the interstitial site via a kick-out mechanism prior to its disappearance from the CeO2.

The Lattice Kinetic Monte Carlo Simulation of Boron Diffusion in SiGe

The lattice kinetic Monte Carlo simulation (kMCS) was applied to study the boron diffusion in Si-SiGe beyond nanotechnology. Both the interstitialcy and kick-out mechanisms of boron diffusion were considered, including the effects of annealing temperatures, boron dopant concentrations, Ge compositions, and concentrations of Si self-interstitial defects (SiI). The effects on boron diffusion caused by single and double layer(s) of SiGe phase with different Ge contents and varying boron concentrations in double layers of SiGe phase were also simulated. The results show that boron diffusion in Si and between SiGe-Si both largely increase as the temperature or concentration of SiI increases, but the boron diffusion between SiGe-Si is much less than in Si. Increasing the Ge contents in SiGe alloy could retard boron diffusion heavily, while increasing the boron concentration on SiGe phase would enhance boron diffusion.