group-V Impurities Research Articles

Interaction Rates of Group-III and Group-V Impurities with Intrinsic Point Defects in Irradiated Si and Ge

A comparative study of interactions of shallow impurities with primary defects in oxygen- and carbon-lean moderately doped Si and Ge subjected to irradiation with 0.9 MeV electrons, 60Co gamma-rays, and 15 MeV protons at room temperature is presented and discussed. For the quantitative characterization of such interactions, changes in the total concentration of the original shallow group-V donor or group-III acceptor impurities in the irradiated materials are determined by Hall effect measurements over a wide temperature range. Losses of the shallow donor or acceptor states in the irradiated Si and Ge are indicative of their removal rates that can be used for estimation of production rates of primary defects interacting with the dopants. Some important factors affecting the interactions between primary defects and shallow impurities in Si and Ge are highlighted.

Interaction rates of group-III and group-V impurities with intrinsic point defects in irradiated Si and Ge -=SUP=-*-=/SUP=-

Interaction rates of group-III and group-V impurities with intrinsic point defects in irradiated Si and Ge -=SUP=-*-=/SUP=-

Radiation-produced defects in germanium: Experimental data and models of defects

The problem of radiation-produced defects in n-Ge before and after n → p conversion is discussed in the light of electrical data obtained by means of Hall effect measurements as well as Deep Level Transient Spectroscopy. The picture of the dominant radiation defects in irradiated n-Ge before n → p conversion appears to be complicated, since they turn out to be neutral in n-type material and unobserved in the electrical measurements. It is argued that radiation-produced acceptors at ≈E C – 0.2 eV previously ascribed to vacancy-donor pairs (E-centers) play a minor role in the defect formation processes under irradiation. Acceptor defects at ≈E V + 0.1 eV are absolutely dominating in irradiated n-Ge after n → p conversion. All the radiation defects under consideration were found to be dependent on the chemical group-V impurities. Together with this, they are concluded to be vacancy-related, as evidenced positron annihilation experiments. A detailed consideration of experimental data on irradiated n-Ge shows that the present model of radiation-produced defects adopted in literature should be reconsidered.

Radiation-produced defects in germanium: experimental data and models of defects

The problem of radiation-produced defects in n-Ge before and after n-> p conversion is discussed in the light of electrical data obtained by means of Hall effect measurements as well as Deep Level Transient Spectroscopy. The picture of the dominant radiation defects in irradiated n-Ge before n-> p conversion appears to be complicated, since they turn out to be neutral in n-type material and unobserved in the electrical measurements. It is argued that radiation-produced acceptors at ~ EC-0.2 eV previously ascribed to vacancy-donor pairs (E-centers) play a minor role in the defect formation processes under irradiation. Acceptor defects at ~ EV+0.1 eV are absolutely dominating in irradiated n-Ge after n-> p conversion. All the radiation defects under consideration were found to be dependent on the chemical group-V impurities. Together with this, they are concluded to be vacancy-related, as evidenced positron annihilation experiments. A detailed consideration of experimental data on irradiated n-Ge shows that the present model of radiation-produced defects adopted in literature should be reconsidered. DOI: 10.21883/FTP.2017.12.45178.8599

Correlation between strain and defects in Bi implanted Si

The strain in Si containing group-V impurities is a topical subject of study due to its potential applications in quantum computing. In this paper we study 209Bi implanted Si concerning the correlation between the strain produced by stopped Bi ions and trapping characteristics of the defects resulted from implantation. The depths distributions of stopped ions and primary defects are simulated and the distributions of permanent defects are modelled for Si implanted with low fluence 209Bi ions of 28MeV kinetic energy. For comparison, these depths distributions were similarly calculated for 127I ions with the same fluence and energy, implanted in Si. The results are compared with each other and correlated with the characteristics of traps in these systems, previously obtained. We demonstrate that the intensity of the strain field is the most important factor in changing of trap parameters, while the superposition between the region with strain and the region where defects are located is a second order effect.

Group-V impurities inSnO2from first-principles calculations

By means of first-principles calculations we investigate the effects of N, P, As, and Sb impurities on the electrical properties of ${\text{SnO}}_{2}$. We find that N prefers to occupy the O site and unexpectedly acts as a very deep acceptor with a level closer to the conduction band than to the valence band. P, As, and Sb prefer the Sn site, where they act as shallow donors. The group-V impurities are therefore not suitable for achieving $p$-type conductivity in ${\text{SnO}}_{2}$, but P, As, and Sb may serve as $n$-type dopants. We also investigate the interaction between N and H impurities, finding that the binding energy of the N-H complex is much larger than the binding energies found for complexes involving H and group-IIIA impurities in ${\text{SnO}}_{2}$.

Effects of group-V impurities on the elastic properties of silicon

Effects of group-V impurities on the elastic properties of silicon

Effects of group-V impurities on the elastic properties of silicon

Abstract Besides reduction in device size the application of strained silicon in transistor design plays a crucial role in improving device speed and power consumption. Microscopic investigations are fundamental to understand the mechanical behaviour of strained Si layers, especially in combination with impurity atoms. In the present work, the influence of group-V impurities on strain fields in silicon was studied by means of the perturbed angular correlation method using the acceptor 111 In as probe. This nuclear technique is well suited for studying strain on an atomic scale. After ion implantation of the group-V atoms and subsequent annealing the Si samples were bent along the 〈1 1 0〉 crystal axis resulting in a uniaxial tensile strain. For nitrogen-implanted silicon the response of the crystal lattice to mechanical stress shows no difference to undoped samples, which means that nitrogen has no influence on strain fields in silicon. However, after implantation of the donors P, As and Sb a significant strain relaxation is observed which is probably due to dislocations. We show that this relaxation caused by n-doping also extends to undoped areas which are adjacent to the implanted region.

Optical absorption spectra of doped and codoped Si nanocrystallites

The effects of the incorporation of group-III (B and Al), group-IV (C and Ge), and group-V (N and P) impurities on the formation energies, electronic density of states, optical absorption spectra, and radiative lifetimes of Si nanocrystallites of different shape and with diameters up to 2 nm are studied by means of an ab initio pseudopotential method that takes into account spin polarization. The single doping with group-III or group-V impurities leads to significant changes on the onsets of the absorption spectra that are related to the minority-spin states. In contrast to the optical absorption spectra, the radiative lifetimes are sensitively influenced by the shape of the nanocrystallites, though this influence tends to disappear as the size of the nanocrystallites increase. Codoping is investigated for pairs of group-III and group-V impurities. We show that the impurity formation energies decrease significantly when the nanocrystallites are codoped with B and P or with Al and P. Additional peaks are introduced in the absorption spectra due to codoping, giving rise to a redshift of the absorption onset with respect to the undoped nanocrystallites. Those additional peaks are more intense when codoping is performed with two different species either of the group III or of the group V. The values of radiative lifetimes for the codoped nanocrystallites are mostly in between the values for the nanocrystallites doped with the impurities separately.

Structural features and electronic properties of group-III-, group-IV-, and group-V-dopedSi nanocrystallites

We investigate the incorporation of group-III (B and Al), group-IV (C and Ge), andgroup-V (N and P) impurities in Si nanocrystallites. The structural features and electronicproperties of doped Si nanocrystallites, which are faceted or spherical-like, are studiedby means of an ab initio pseudopotential method including spin polarization.Jahn–Teller distortions occur in the neighborhood of the impurity sites and the bondlengths show a dependence on size and shape of the nanocrystallites. We findthat the acceptor (group-III) and donor (group-V) levels become deep as thenanocrystallites become small. The energy difference between the spin-up andspin-down levels of group-III and group-V impurities decreases as the size of the Sinanocrystallite increases and tends to the value calculated for Si bulk. Doping with carbonintroduces an impurity-related level in the energy gap of the Si nanocrystallites.

Chemical trends of defect formation in Si quantum dots: The case of group-III and group-V dopants

Using first-principles methods, we have systematically calculated the defect formation energies and transition energy levels of group-III and group-V impurities doped in H passivated Si quantum dots (QDs) as functions of the QD size. The general chemical trends found in the QDs are similar to that found in bulk Si. We show that defect formation energy and transition energy level increase when the size of the QD decreases; thus, doping in small Si QDs becomes more difficult. ${\mathrm{B}}_{\mathrm{Si}}$ has the lowest acceptor transition energy level, and it is more stable near the surface than at the center of the H passivated Si QD. On the other hand, ${\mathrm{P}}_{\mathrm{Si}}$ has the smallest donor ionization energy, and it prefers to stay at the interior of the H passivated Si QD. We explained the general chemical trends and the dependence on the QD size in terms of the atomic chemical potentials and quantum confinement effects.

Ab-initio modeling of acceptor–hydrogen complexes in CdTe

We have investigated the hydrogenation of group-V impurities ( N Te , P Te and As Te ) in CdTe by computer modeling, using a pseudopotential density-functional method. For these complexes, we found that the lowest energy location for hydrogen is near the bond-center, closer to the acceptor atom, between a Cd atom and the acceptor. Metastable states by 0.5 eV above the ground state where found for structures where H is anti-bonding to N Te , P Te and As Te . The calculated local vibrational mode (LVM) frequencies for the bond centered configurations agree within 3% of the experimental values, i.e. 3210 cm - 1 for N Te –H and 2022 cm - 1 for As Te –H. Deuterium LVM induced shifts for As Te –D fall within 4% of the experimental data. The observed wag mode for N Te –H is reproduced within 8%. A wag mode for As Te –H and LVM frequencies for P Te –H are predicted.

Doping engineering of p-type ZnO

The formation energies of defects in ZnO taken from recently published first-principles calculations are used to simulate the incorporation and compensation of group-V impurities. A detailed analysis is carried out for the specific case of nitrogen-doped ZnO as a function of doping temperature, O/Zn stoichiometric ratio, and dopant activity. This study shows that net p-type doping of ZnO:N in thermodynamic equilibrium conditions is rather limited (∼10 16 cm −3) and involves a delicate balance between the achievement of high dopant solubility (on the Zn-rich side) and low compensation by donor defects (on the O-rich side). Efficient doping appears possible in various alternative ways: simultaneous incorporation of hydrogen as an interim compensating donor to be subsequently eliminated; use of a high activity dopant in the external phase (atomic N, NO) while preventing the formation of (N 2) O compensating donors; planar doping for separate optimization of nitrogen incorporation and a defect-free crystal. The other group-V impurities (P, As) introduce deep acceptor levels when substituted for O, but have been predicted to form a single acceptor complex in the antisite position, like [ As Zn–2V Zn], with both low formation and ionization energies. This leads to a moderate p-type behaviour. Comparison of the present theoretical modelling with experiments shows that accounting for the wide range of reported hole concentrations (10 16–10 19 cm −3) necessarily implies some departure from equilibrium.

Ab initio modeling of N–H, P–H and As–H defects in ZnSe

We have investigated the hydrogenation of group-V impurities (NSe, PSe and AsSe) in ZnSe by ab initio modeling. From the energetics, we conclude that among all sites considered for the H-atom, the bond centered location between Zn and the substitutional impurity, is the favorite. Metastable states by 0.6, 0.4 and 0.5eV were found for structures where H is antibonded to N, P and As, respectively. The calculated local vibrational mode frequencies for N–H and As–H agree well with the available experimental data, whereas a 2331cm−1 stretch and a 392cm−1 wag mode frequencies are anticipated for P–H.

Photoluminescence and optically detected magnetic resonance of Si/Si1−xGexstrained-layer superlattices grown by molecular-beam epitaxy

Photoluminescence (PL) and optically detected magnetic-resonance (ODMR) experiments have been performed on a set of Si/Si 1-x Ge x strained-layer superlattices grown by molecular-beam epitaxy. A variety of parameters was explored to expand on the results of an earlier investigation and to test models proposed for the origin of the broad emission bands. These include the dependences of the magnetic resonance on temperature, microwave power, and excitation power density. In addition, sets of samples were grown to study the PL and ODMR as a function of layer thickness, Ge composition, total superlattice thickness, and doping with group-V impurities

High-dose mixed Ga/As and Ga/P ion implantations in silicon single crystals

High-dose mixed Ga/As and Ga/P implanted silicon single crystals annealed by RTA have been studied by a combination of RBS/channeling spectrometry and TEM. Crystalline GaAs precipitates oriented with the host lattice were found in the silicon crystals after the ion implantations and RTA for both room temperature and high temperature Ga implantations. The precipitates appearing in the case of P/Ga mixed implantation were too small to be analyzed by X-ray microanalysis but are suggested to be of crystalline GaP phase coherent to the host lattice. Only slight Ga atoms redistribution takes place during high temperature implantation into the crystals containing the group-V impurities.

Microscopic mechanism of atomic diffusion in Si under pressure.

We have performed the first-principles total-energy calculations on the atomic diffusion of group-V impurities in Si, and have revealed the pressure effect on the activation energy of the diffusion. For the vacancy mechanism, the activation energies for P, As, and Sb decrease with pressure. For the interstitial mechanism, on the other hand, the formation energy of the interstitial impurity shows a general tendency to increase with pressure. Combining the results with the experimental data, we have concluded that there is a dominant contribution of the vacancy mechanism for the As diffusion. The microscopic origin of the pressure dependence is clarified in terms of the local strain around the defects. The negative pressure dependence common to the group-V impurities for the vacancy-mediated diffusion is well explained by the peculiar nature of the isolated vacancy: (a) breathing distortion of the surrounding Si atoms toward the vacancy site, which gives rise to a tensile strain around the vacancy, and (b) the characters of the wave function and the lattice distortion originating from the vacancy, which cause the weak vacancy-impurity interaction. The positive pressure dependence for the interstitial-mediated diffusion is closely related to the atomic structures of the interstitial impurities which cause compressive strain to the surrounding Si-Si bonds.

Float zone growth of high purity and high oxygen concentration silicon

Ultra-high purity silicon with high concentrations of interstitial oxygen has been prepared using the float-zone (FZ) technique. In this material, interstitial oxygen concentrations [O]∼ 9×1017 cm-3 have been achieved while maintaining good crystalline structure and a ratio of oxygen to shallow impurities greater than 105. This FZ method provides efficient oxygen “doping” by exposing only the melted zone during boule growth. Results of characterization using IR absorption, photoluminescence spectroscopy, transport and crystal quality measurements are presented. This material is of fundamental importance in the investigation of thermal donors (TDs) in silicon, where contamination from group-III and group-V impurities, and carbon, complicates the role of oxygen in the formation of TDs.

Rapid thermal annealing of high concentration mixed As/In- and P/In-implanted silicon single crystals

The effect of group-V donor impurities on the behavior of indium atoms implanted into silicon single crystals has been studied by Rutherford backscattering spectrometry/channeling spectrometry, and differential Hall-effect/resistivity measurements. Flat arsenic or phosphorus profiles of concentrations between ∼1.4×1020 cm−3 and 3×1020 cm−3 were produced by As+ or P+ implantation followed by rapid thermal annealing (RTA) (20 s, 1100 °C). Subsequently In was implanted to peak concentrations of 1.7×1020 cm−3 or 3.5×1020 cm−3 and annealed by RTA (15 s, 700–1050 °C).Compared to single indium implants, the presence of the preimplanted group-V impurities is found to reduce the redistribution of the implanted indium atoms during RTA and to increase the concentration of indium atoms incorporated on (or close to) lattice sites (up to ∼2×1020 cm−3). The value of the indium substitutional fraction is found to be dependent on anneal temperature and type of donor impurity. A reduction in the free-electron concentration is observed in both the phosphorus and arsenic predoped samples at the same depths as that of the indium atoms.

The Role of Group-V Impurities in Defect Formation in Irradiated Silicon

Direct experimental evidence is provided on the involvement of phosphorus in the structure of the defect that is associated with a prominent electron trap at Ec −0.42eV (Ec is the conduction band edge) in irradiated n-type silicon. Possible vacancy participation in the formation of the same defect is inferred from the defect production in float-zone und Czochralski-grown material. However, it may not be concluded from this study whether a single phosphorus atom and a single vacancy (i.e. the E-centre) are the only defect constituents. Similar conclusions are also arrived at for an electron trap observed at Ec −0.30eV. These two traps are metastable, a property observed here only in phosphorus-related defects. Electron traps at Ec −0.34 eV and Ec −0.51 eV are associated with defects containing arsenic and antimony, respectively. Es wird ein direkter experimenteller Hinweis geliefert fur die Beteiligung von Phosphor an der Struktur des Defekts, der mit einem vorherrschenden Elektronentrap bei Ec −0,42 eV (Ec Leitungsbandkante) verknupft ist. Eine mogliche Leerstellenbeteiligung bei der Bildung desselben Defekts wird aus der Defektbildung in zonengezogenem und Czochralski-Material abgeleitet. Jedoch kann nicht aus der Untersuchung geschlossen werden, ob ein einzelnes Phosphoratom und eine einzelne Leerstelle (d. h. das E-Zentrum) die einzigen Defektkonstituenten sind. Zu ahnlichen Schlusfolgerungen gelangt man fur ein bei Ec −0,30 eV beobachtete Haftstelle. Diese beiden Haftstellen sind metastabil, eine Eigenschaft. die hier nur in phosphorverknupften Defekten beobachtet wird. Elektronentraps bei Ec −0,34 eV und Ec −0,51 eV sind mit Defekten assoziiert, die Arsen bzw. Antimon enthalten.