Iron and its complexes in silicon

This article is the first in a series of two reviews on the properties of iron in silicon. It offers a comprehensive summary of the current state of understanding of fundamental physical properties of iron and its complexes in silicon. The first section of this review discusses the position of iron in the silicon lattice and the electrical properties of interstitial iron. Updated expressions for the solubility and the diffusivity of iron in silicon are presented, and possible explanations for conflicting experimental data obtained by different groups are discussed. The second section of the article considers the electrical and the structural properties of complexes of interstitial iron with shallow acceptors (boron, aluminum, indium, gallium, and thallium), shallow donors (phosphorus and arsenic) and other impurities (gold, silver, platinum, palladium, zinc, sulfur, oxygen, carbon, and hydrogen). Special attention is paid to the kinetics of iron pairing with shallow acceptors, the dissociation of these pairs, and the metastability of iron–acceptor pairs. The parameters of iron-related defects in silicon are summarized in tables that include more than 30 complexes of iron as detected by electron paramagnetic resonance (EPR) and almost 20 energy levels in the band gap associated with iron. The data presented in this review illustrate the enormous complexing activity of iron, which is attributed to the partial or complete (depending on the temperature and the conductivity type) ionization of iron as well as the high diffusivity of iron in silicon. It is shown that studies of iron in silicon require exceptional cleanliness of experimental facilities and highly reproducible diffusion and temperature ramping (quenching) procedures. Properties of iron that are not yet completely understood and need further research are outlined. Received: 14 December 1998 / Accepted: 22 February 1999 / Published online: 26 May 1999     

Hydrogen complexes in hydrogenated silicon

Experimental evidence suggests that H bonds to a fully coordinated Si network in pairs. The total energies and vibration frequencies of various possible pair configurations are calculated using a local density pseudopotential method on supercells. The H^*₂configuration, consisting of a bond centered H and a H located at an adjacent antibonding site, is found to be low in energy and more importantly, these H^*₂configurations bind together with as much as 0.4 eV/pair forming Si>{111} platelet structures. Metastability can also be accounted for when the H^*₂dissociates creating two interstitial H atoms which diffuse to form Si dangling bond-like defects at weak bond sites. Annealing occurs when the H atoms reform complexes.     

Donor-hydrogen complexes in crystalline silicon

Summary Experimental results are presented on the study of Sb-H complexes in crystalline silicon, employing¹¹⁹Sb→¹¹⁹Sn source M?ssbauer spectroscopy and a low-energy H implantation technique. In addition to a visible component, we observe a large decrease of the M?ssbauer intensity associated with the trapping of hydrogen, even at low temperatures. This is interpreted as the formation of a component with a negligible recoilless fraction. The different M?ssbauer components were studied as a function of H dose, H-implantation temperature and annealing temperature. The data show that the visible component is associated with the well-known SbH complex, whereas the invisible component is associated with the formation of SbH _n (n≥2) complexes. We show that these complexes are in thermal equilibrium with a larger hydrogen reservoir (H ₂ ^* ), which governs their thermal stability. No Sb-H complexes are observed inp-type Si after H-implantation, in agreement with the current belief that hydrogen has a deep donor level in the gap. The microscopic structure of the various Sb-H and Sn-H complexes was studied with first-principles calculations using the pseudopotentialdensity-functional approach. The structure of the Sb-H complex is found to be similar to the P-H complex, with the H in an antibonding site of a Si atom neighbouring the Sb impurity. For SbH₂ three configurations are found with energies differing by less than ≈ 0.1 eV. We find that the reaction SbH+H≠SbH₂ is exothermic. We argue that the SbH₂ complexes are shallow donors, irrespective of the structure. Therefore, the formation of SbH₂ may depassivate the sample. Paper presented at ICAME-95, Rimini, 10–16 September 1995.     

Investigation of cadmium-hydrogen complexes in silicon

Formation, stability and electric properties of (In-H) and (Cd-H) complexes in Si are studied by the perturbed angular correlation spectroscopy (PAC). The trapping of hydrogen at the acceptors results in three different defect specific electric field gradients (EFGs), which are studied as function of temperature, doping concentration and annealing time. Two of the three observed hydrogen-related EFGs are identified as different charge states of one (Cd-H) acceptor. Within the framework of a model, which takes into account the dynamics of charge fluctuations and Shockley, Read and Hall statistics, the energy level of this (Cd-H) acceptor at E = E_V + 60 meV is deduced. Furthermore, the dynamical behavior of the hydrogen atom within the (Cd-H) complexes is studied. From the relaxation of the PAC signal the hopping rate of the hydrogen atom is extracted. This rate is thermally activated with an activation energy of E = 0.20 eV.     

Photoluminescence of transition metal complexes in silicon

Results of luminescence studies on silicon doped with the 3d transition metals are reviewed. Spectra are observed after V, Cr, Mn, Fe, and Cu diffusion. We discuss the problems of center identifications, using the example of the CrB-pair luminescence. Level schemes for the optical transitions are discussed and correlated with electrical level positions of TM defects. Luminescent centers can be divided into two classes: CrB,CrGa, and Mn₄ are effective recombination centers with low quantum efficiencies, whereas Fe and Cu associated spectra show characteristics of exciton decay at isoelectronic centers, e.g. show a high quantum efficiency. The phonon structure of the spectra is discussed, and it is shown that the local mode energies of the centers follow a systematic trend.     

Structure of Ge-O complexes in Czochralski silicon

The structures of Ge-O complexes in germanium-doped Czochralski (CZ) silicon wafers have been investigated by means of density functional theory (DFT). The calculations present the fact that the Ge-O complexes can be formed with the absence of vacancy during low-temperature thermal cycles so that they can enhance oxygen precipitation. Furthermore, the total energy of different Ge-O complexes is calculated, and then optimized and stable structure of Ge-O complexes is suggested.     

EPR study of erbium-impurity complexes in silicon

Electron paramagnetic resonance (EPR) measurements have been used to characterise Er complexes formed in FZ silicon by the implantation of erbium together with either oxygen or fluorine. The samples have a 2 μm thick layer containing 10¹⁹ Er/cm³ alone or in addition 3×10¹⁹ O/cm³, 10²⁰ O/cm³ or 10²⁰ F/cm³. Various post-implantation anneals were carried out. Several different erbium centres, which have either C_1h monoclinic or trigonal symmetry, are observed and the way in which the type of centre depends on the implantation and annealing conditions is reported.     

Hyperfine interactions in muonium-impurity complexes in silicon

The properties of paramagnetic complexes formed by muonium located near acceptor and donor impurities in silicon are calculated using the quantum chemical methods. The calculated data are compared to the experimentally observed characteristics of normal and anomalous muonium centers.     

Tailoring of nickel silicide contacts on silicon carbide

Co-deposition technique by means of simultaneous ion beam sputtering of nickel and silicon onto SiC was performed for tailoring of Ni-silicide/SiC contacts. The prepared samples were analysed by means of XRD and XPS in order to obtain information about the surface and interface chemistry. Depth profiling was used in order to analyse in-depth information and chemical distribution of the specimens. XRD results showed that the main phase formed is Ni₂Si. The XPS analysis confirmed the formation of the silicide on the surface and showed details about the chemical composition of the layer and layer/substrate interface. Moreover, the XPS depth profiles with detailed analysis of XPS peaks suggested that tailoring of C distribution could be monitored by the co-deposition technique employed.     

Introduction of nickel surface layer atoms into silicon

Results of experimental studies of the process of introduction of nickel atoms into silicon upon irradiation of layered Ni-Si structures by argon ions are presented. Following irradiation, specimen composition was studied using back scattering of helium ions. Processing of the back scattering spectra was performed by an improved method using an analytical approach. The effects of annealing temperature and dosage on the process of formation of the suicide NiSi are studied.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 36–40, July, 1989.     

微锗掺杂直拉单晶硅中的锗-空位复合体

利用第一性原理研究了微锗掺杂直拉单晶硅中的锗和微缺陷的相互作用, 其中微缺陷用一个空位、两个空位和三个空位模拟. CASTEP计算了锗与一个空位、两个空位和三个空位相互作用的情况, 通过分析三种情况下锗与空位(或空位组中心)的间距及空位面积(或体积)的大小, 分别给出了三种情况下最稳定的锗-空位复合体结构模型. 计算表明在微锗掺杂硅单晶中由于锗的引入, 空位容易团聚在锗原子附近, 形成锗-空位复合体.     

Theory of magnetooptical effects in ferromagnetic nickel

A theory is developed for magnetooptical effects in ferromagnetic nickel with allowance for the topology of the Fermi surface at low temperatures, when the carriers are scattered on ionized impurity centers. The contribution to the frequency conductivity tensor due to the anisotropy of the Fermi surfaces of nickel is found and it is shown that this contribution in the first approximation of perturbation theory reduces to a decrease of the tensor . An estimate is made of the influence of the density of states of nickel on the anomalous frequency-dependent Hall current and a study is also made of the case of low and high frequencies, when, respectively, ^{2 2} « 1 and ^{2 2} » 1.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 29–33, May, 1972.     

Microstructure and magnetooptics of silicon oxide with implanted nickel nanoparticles

Metallic nickel nanoparticles of various sizes are formed in a thin near-surface layer in an amorphous SiO₂ matrix during 40-keV Ni⁺ ion implantation at a dose of (0.25−1.0) × 10¹⁷ ions/cm². The micro-structure of the irradiated layer and the crystal structure, morphology, and sizes of nickel particles formed at various irradiation doses are studied by transmission electron microscopy and electron diffraction. The magnetooptical Faraday effect and the magnetic circular dichroism in an ensemble of nickel nanoparticles are studied in the optical range. The permittivity [^(e)]\hat \varepsilon tensor components are calculated for the implanted samples using an effective medium model with allowance for the results of magnetooptical measurements. The spectral dependences of the tensor [^(e)]\hat \varepsilon components are found to be strongly different from those of a continuous metallic nickel film. These differences are related to a disperse structure of the magnetic nickel phase and to a surface plasma resonance in the metal nanoparticles.