Acceptors In Silicon Research Articles

A mechanism for hole generation by octahedral B6 clusters in silicon

The electronic structure and x-ray photoelectron spectra of silicon with octahedral B6 clusters are investigated using first-principles calculations. It is found that the B6 clusters act as double acceptors in silicon and that the simulated chemical shift of the B1s orbital signals of the B6 clusters in x-ray photoelectron spectra coincides with the chemical shift of B1s experimentally observed in as-implanted silicon at an extremely high dose of boron. These results reveal that the B6 clusters are the origin of hole carriers. We propose a mechanism of hole generation and a model of B6 cluster formation at implantation-induced divacancy sites.

Stark effect in shallow impurities inSi

We have theoretically studied the effect of an electric field on the energy levels of shallow donors and acceptors in silicon. An analysis of the electric field dependence of the lowest energy states in donors and acceptors is presented, taking the band structure into account. A description as hydrogenlike impurities was used for accurate computation of energy levels and lifetimes up to large (several MV/ m) electric fields. All results are discussed in connection with atomic scale electronics and solid state quantum computation.

Dependence of the ionization energy of shallow donors and acceptors in silicon on the host isotopic mass

A comparison of the infrared absorption spectra of isotopically pure ${}^{28}\mathrm{Si}$ and ${}^{30}\mathrm{Si}$ reveals small shifts in the transition energies for both the shallow donor phosphorus and the shallow acceptor boron. The impurity binding energies for both species are slightly larger in ${}^{30}\mathrm{Si}$ than in ${}^{28}\mathrm{Si}.$ A similar effect was earlier observed for the boron acceptor in ${}^{13}\mathrm{C}$ vs ${}^{12}\mathrm{C}$ diamond, and later explained as resulting from a change in the ground and excited state binding energies due to the dependence of the hole effective mass on the host isotopic composition. Here we show that the results for both donors and acceptors in Si can be explained by the same mechanism, with the additional inclusion of the isotopic dependence of the dielectric constant.

Magnetic moment relaxation of a shallow acceptor center in heavily doped silicon

Results of studying the temperature dependence of the residual polarization of negative muons in crystalline silicon with germanium (9 × 10 19 cm -3 ) and boron (4.1 × 10 18 , 1.34 × 10 19 , and 4.9 × 10 19 cm -3 ) impurities are presented. It is found that, similarly to n - and p -type silicon samples with impurity concentrations up to 10 17 cm -3 , the relaxation rate ν of the magnetic moment of a µ Al acceptor in silicon with a high impurity con- centration of germanium (9 × 10 19 cm -3 ) depends on temperature as ν ~ T q , q ≈ 3 at T = (5-30) K. An increase in the absolute value of the relaxation rate and a weakening of its temperature dependence are observed in sam- ples of degenerate silicon in the given temperature range. Based on the experimental data obtained, the conclu- sion is made that the spin-exchange scattering of free charge carriers makes a significant contribution to the magnetic moment relaxation of a shallow acceptor center in degenerate silicon at T � 30 K. Estimates are obtained for the effective cross-section of the spin-exchange scattering of holes ( σ h ) and electrons ( σ e ) from an acceptor Al center in Si: σ h ~ 10 -13 cm 2 and σ e ~ 8 × 10 -15 cm 2 at the acceptor (donor) impurity concentration na(nd) ~ 4 × 10 18 cm -3 . © 2001 MAIK "Nauka/Interperiodica".

Competition between Long-Living and D?(A+) States of Donors and Acceptors in Silicon

Competition between Long-Living and D?(A+) States of Donors and Acceptors in Silicon

Simple Silylhydrazines as Models for Si-Nβ-Donor Interactions in SiNN Units

Two simple silylhydrazines, H3SiMeNNMe2 and (H3Si)(2)NNMe2, have been prepared by the reaction of bromosilane with the corresponding NH-functional hydrazine in the presence of a base and the appropriate lithiated hydrazine. The intermolecular attractive interactions (beta-donor-acceptor interaction) between the silicon and beta-nitrogen atoms of H3SiMeNNMe2 and (H3Si)(2)NNMe2 has been demonstrated by low-temperature X-ray crystallography and ab initio calculations (MP2/6-311G). The contributions to the strength of this two-bond interaction are discussed in the light of a new series of calculations on RSiH2NR'NR2 molecules (R=H, F; R'=H, Me, SiH3; R =H, Me), which show electronegative substituents at the silicon acceptor center to exert the largest effect, while the electronic nature of the substituent at the P-nitrogen atom is also important. As the resulting structures cannot be described satisfactorily by either the VSEPR concept or Bartell's two-bond radius model, a two-bond interatomic attraction has to be taken into account in addition; this leads to an extension of the common models for empirical structure prediction.

Electronic structure of the Er-O6 complex in silicon

The energy diagram of the Er-O6 complex in silicon is calculated. The square amplitudes of the wave functions of the complex on the erbium atom are determined. The results of our calculations show that the Er-O6 complex is an acceptor in silicon. In addition, it is possible that the electron trap energy level is located in the energy gap of silicon. On the whole, the results of our calculations correspond to the Er-O quantum dot model proposed previously.

Si:Au and Si:Pt1S3/2(Γ8)+Γphonon-assisted Fano resonance

The excitation spectra for the Au and Pt acceptors in silicon have been studied by Fourier-transform infrared spectroscopy including uniaxial-stress perturbations. The resonancelike doublet structure, previously attributed to be the ${2p}^{\ensuremath{'}}$ Coulombic line, is shown to be the ${1S}_{3/2}({\ensuremath{\Gamma}}_{8})$ phonon-assisted Fano resonance involving the zone-center $\ensuremath{\Gamma}$ optical phonon. The deformation potentials $b$ and $d$ for the Au and Pt ${1S}_{3/2}({\ensuremath{\Gamma}}_{8})$ state are in good agreement with those previously determined for the B acceptor. Stress-induced preferential alignment effects are revealed for both centers. The doublet structure is shown to be due to crystal-field splitting of the ${1S}_{3/2}({\ensuremath{\Gamma}}_{8})$ Coulomb state.

Si acceptor excited states in ion-implanted InP

Photoluminescence has been used to investigate the behavior of Si-implanted InP, submitted to a postimplantation rapid thermal annealing. Compared with the non-implanted material, the implanted crystal displays a new broad band around 1.382 eV, in the low temperature (2 K) spectra. This band appears to be made of two unresolved recombination paths ascribed to the electron–acceptor (e,A°) and donor–acceptor pair recombinations of the silicon acceptor impurity substituted on phosphorus site. Besides the Zn-related transitions to s and p excited states, the selective excitation of the donor–acceptor pairs reveals additional recombination paths, ascribed to transitions to 2s3/2 and 2p5/2 (Γ7 and Γ8) excited states of silicon. The acceptor behavior of Si in InP is hence given a definite support by this work.

Splitting of the ground state of shallow acceptors in silicon

The results of near infra-red piezo-photoluminescence, photoluminescence excitation, and absorption spectroscopy of silicon doped with Al, Ga, and In performed at 2 K and 0.4 K show that the ground state of these shallow acceptors is split by 0.10 ± 0.01, 0.10 ± 0.01, and 0.015 ± 0.03 cm −1 respectively. This splitting is shown to be a fundamental intrinsic property of shallow acceptors and it may be explained by a dynamic Jahn-Teller effect.

Spectroscopic study of beryllium related acceptors in silicon

We have investigated the level configuration of the valence subbands in GaAs/GaAs1−xPx (x = 0.23) strained-barrier quantum well structures as a function of the well width. Circularly polarized photoluminescence excitation (CPPLE) spectroscopy was used to identify the heavy- or light-hole character of the optical transitions. Distinct polarization properties were observed in the strain-split heavy- and light-hole bands in the GaAsP barriers, which indicates the photoexcited electrons in the barriers retain spin orientation well even after the capture into the well and the relaxation process. Utilizing this polarization tendency of the transitions in the barriers, we could distinguish unequivocally the heavy- and light-hole character of the quantum well-related transitions. By varying the well width systematically, we observed the level crossing between n = 1 heavy- and light-hole transitions around the well width of 4 nm. This is in good agreement with the calculation based on the effective mass approximation.

Passivation of an Al acceptor in silicon by hydrogen or muonium

We report on calculations of the electric field gradient at the site of the Al nucleus in the Si-H-Al complex in silicon. As a model for the surroundings of the complex we used a cluster consisting of 43 silicon and one aluminum atoms. The geometry of this cluster was fully optimized at the Hartree-Fock level. To discuss the dependence of our results on the level of theory, we studied a subcluster of four silicon and one aluminum atoms at the Hartree-Fock and CASSCF level.

Normal-state tunnel junction as a tunable quasimonochromatic phonon source.

The frequency distribution of the acoustic phonons emitted from a biased metal-insulator-metal normal-state tunnel junction has been studied. Electrons tunneling across the insulating layer form an excited population with a range of energies up to \ensuremath{\sim}${\mathit{eV}}_{\mathit{B}}$ above the Fermi level and then relax, producing a phonon spectrum with a frequency cutoff at the same characteristic value. Normal-state tunnel junctions made from aluminum have been produced and phonon spectra determined by using the stress-tuned splitting of boron acceptors in silicon as a spectrometer. It has been shown that, in the range \ensuremath{\sim}1--4 meV (\ensuremath{\sim}250--1000 GHz), the second differential of the signal with respect to junction bias (${\mathrm{\ensuremath{\partial}}}^{2}$P/\ensuremath{\partial}${\mathit{V}}_{\mathit{B}}^{2}$) is quasimonochromatic, having a spectrum of an approximately Gaussian form with the peak occurring at an energy of ${\mathit{eV}}_{\mathit{B}}$ and a half width of \ensuremath{\sim}6${\mathit{kT}}_{\mathit{e}}$.

Low-energy (3–100 eV) electron-bombardment-induced nitridation of thin SiO2 films: physicochemical and electrical analyses

Low-energy (3–100 eV) electrons are shown to be efficient promoters of the superficial nitridation of thin SiO 2 films grown on boron-doped Si(100) using low pure NH 3 pressures (⩽2 × 10 −4 mbar) at ambient temperature. The initial concentration (≈10 15 at. cm −3 ) of ionized acceptors in silicon near the SiO 2 /Si interface is first lowered by the nitridation process and then restored by hydrogen annealing at 450°C. The ultrahigh vacuum experimental set-up permits us to uncouple two important effects from a thermally-assisted (700–950°C) r.f. NH 3 plasma nitridation process: the role played by low-energy (3–5 eV) electrons and the temperature. It is found that the existence of charge particles near the sample surface must be taken into account in the plasma reaction process and that the main effect of thermal activation is to enhance the reaction and the diffusion of nitrogen species through the SiO 2 layer up to the SiO 2 /Si interface.

The vibrational modes of silicon acceptors in p-type GaAs grown by molecular beam epitaxy on a (111)A plane

Silicon impurities in p-type GaAs grown by molecular beam epitaxy occupy As lattice sites and give rise to an infrared active localized vibrational mode (LVM) which appears as a Fano profile near 395 cm−1 in samples with p=1019 cm−3 or 1020 cm−3. 2 MeV electron irradiation reduces p, leading to the emergence of the usual LVM absorption line of SiAs at 399 cm−1. The treatment also leads to site switching to produce SiGa donors giving an LVM at 384 cm−1.

Photoacoustic investigations of shallow acceptors in silicon by a piezoelectric transducer

Photoacoustic (PA) measurements of p-Si single crystals near an optical absorption edge were carried out by using PZT as a detector. A pronounced peak at 1.07 eV appears in addition to the plateau above 1.2 eV. A hole carrier concentration dependence and a compensation effect by thermally generated donors of the PA spectrum are investigated extensively. By considering these results, it is concluded that the observed peak is due to electron transitions involving boron acceptor impurities. Low temperature spectra down to 90 K also support this conclusion.

Linear Stark and nonlinear Zeeman coupling to the ground state of effective mass acceptors in silicon

It is shown by dielectric resonance absorption at 60 GHz that there is a linear coupling of the electric field to the ground state of effective mass acceptors in Si reflecting the lower T d symmetry in the central portion of the ground state wave function. The coupling increases strongly with increasing binding energy from B to In, i.e., with decreasing Bohr radius of the acceptor. An unexpected nonlinear Zeeman splitting is observed the magnitude of which also increases from B to In. For all acceptors a central fine structure is found which correlates with the homogeneous linewidth

The interpretation of the p3/2 spectra of group III acceptors in silicon

The p3/2 energy levels of the hydrogen-like single acceptor in silicon are calculated down to 1.4 meV from the valence band using a non-variational method. The oscillator strength of the transitions from the ground state to the excited states are calculated using an acceptor-dependent ground state wavefunction. A comparison is made with new high-resolution experimental data for group III acceptors B, Al and In. It shows that few of the predicted transitions are not observed and that the relative intensities of the lines are in reasonable agreement with the oscillator strengths. This allows an unambiguous assignment of the lines to specific transitions when the observed peaks can be resolved into individual transitions, and this constitutes an improvement over the existing situation. The calculated values of the highly excited energy levels are very close to the observed ones, but small differences due to chemical shift are found for these highly excited states. Calibration coefficients for the acceptor concentrations can be derived from the oscillator strength calculations and they are compared with those determined experimentally. The most shallow effective mass excited states observed have binding energies of approximately 0.8 and 1.0 meV for B and Al respectively.

LPE growth of undoped n-type GaAs at 636°C with extremely low compensation

Distinct growth-temperature dependence in the range of 636–795°C has been clarified in the concentrations of donor and acceptor impurities for the liquid-phase epitaxial GaAs materials grown after little solution-bakeout. To estimate the impurity concentrations correctly, photoluminescence evaluation was employed in addition to Hall measurement. At the lowest growth temperature and without solution-bakeout, the compensation ratio, N a /N d , is as low as 10 −3 . With baking at 800°C or below, the layer is still n-type despite the compensation by carbon acceptors. However, baking at 900°C or above is so influential that the epilayer is rapidly compensated by silicon acceptors. The slow growth at 636°C is effective to obtain n-type GaAs layers with extremely low compensation.

Hydrogen passivation of acceptors in silicon: a combined PAC and resistivity study

PAC measurements at 111In, yielding information on the amount of formed In-H pairs, and four point resistivity measurements were combined to study the correlation between pair formation and electrical deactivation of acceptors in p-Si samples during passivation with H and thermal reactivation. Passivation was performed by means of low energy (200 eV) H + implantation which proved to be quite efficient at 400 K. A complete passivation of the In profile with a peak concentration of 10 18 cm −3 could be achieved. The results show, that the deactivation and reactivation of the In acceptors quantitatively coincide with the formation and dissociation of In-H pairs.