Showing papers on "Effective mass (solid-state physics) published in 2008"

Nonlinear electromagnetic response of graphene: frequency multiplication and the self-consistent-field effects

Abstract: Graphene is a recently discovered carbon-based material with unique physical properties. This is a monolayer of graphite, and the two-dimensional electrons and holes in it are described by the effective Dirac equation with a vanishing effective mass. As a consequence, the electromagnetic response of graphene is predicted to be strongly nonlinear. We develop a quasi-classical kinetic theory of the nonlinear electromagnetic response of graphene, taking into account the self-consistent-field effects. The response of the system to both harmonic and pulse excitation is considered. The frequency multiplication effect, resulting from the nonlinearity of the electromagnetic response, is studied under realistic experimental conditions. The frequency upconversion efficiency is analyzed as a function of the applied electric field and parameters of the samples. Possible applications of graphene in terahertz electronics are discussed.

Tamm plasmon polaritons: Slow and spatially compact light

Abstract: We report on the first experimental observation of Tamm plasmon polaritons (TPPs) formed at the interface between a metal and a dielectric Bragg reflector (DBR). In contrast to conventional surface plasmons, TPPs have an in-plane wavevector less than the wavevector of light in vacuum, which allows for their direct optical excitation. The angular resolved reflectivity and transmission spectra of a GaAs∕AlAs DBR covered by Au films of various thicknesses show the resonances associated with the TPP at low temperatures and room temperature. The in-plane dispersion of TTPs is parabolic with an effective mass of 4×10−5 of the free electron mass.

Monte Carlo study of the two-dimensional Bose-Hubbard model

Abstract: One of the most promising applications of ultracold gases in optical lattices is the possibility to use them as quantum emulators of more complex condensed matter systems. We provide benchmark calculations, based on exact quantum Monte Carlo simulations, for the emulator to be tested against. We report results for the ground state phase diagram of the two-dimensional Bose-Hubbard model at unity filling factor. We precisely trace out the critical behavior of the system and resolve the region of small insulating gaps, $\ensuremath{\Delta}⪡J$. The critical point is found to be ${(J/U)}_{c}=0.05974(3)$, in perfect agreement with the high-order strong-coupling expansion method of Elstner and Monien [Phys. Rev. B 59, 12184 (1999)]. In addition, we present data for the effective mass of particle and hole excitations inside the insulating phase and obtain the critical temperature for the superfluid-normal transition at unity filling factor.

Bandstructure Effects in Silicon Nanowire Electron Transport

Abstract: Bandstructure effects in the electronic transport of strongly quantized silicon nanowire field-effect-transistors (FET) in various transport orientations are examined. A 10-band sp3d5s* semiempirical atomistic tight-binding model coupled to a self-consistent Poisson solver is used for the dispersion calculation. A semi-classical, ballistic FET model is used to evaluate the current-voltage characteristics. It is found that the total gate capacitance is degraded from the oxide capacitance value by 30% for wires in all the considered transport orientations ([100], [110], [111]). Different wire directions primarily influence the carrier velocities, which mainly determine the relative performance differences, while the total charge difference is weakly affected. The velocities depend on the effective mass and degeneracy of the dispersions. The [110] and secondly the [100] oriented 3 nm thick nanowires examined, indicate the best ON-current performance compared to [111] wires. The dispersion features are strong functions of quantization. Effects such as valley splitting can lift the degeneracies particularly for wires with cross section sides below 3 nm. The effective masses also change significantly with quantization, and change differently for different transport orientations. For the cases of [100] and [111] wires the masses increase with quantization, however, in the [110] case, the mass decreases. The mass variations can be explained from the non-parabolicities and anisotropies that reside in the first Brillouin zone of silicon.

Anisotropic mass density by two-dimensional acoustic metamaterials

Abstract: We show that specially designed two-dimensional arrangements of full elastic cylinders embedded in a nonviscous fluid or gas define (in the homogenization limit) a new class of acoustic metamaterials characterized by a dynamical effective mass density that is anisotropic. Here, analytic expressions for the dynamical mass density and the effective sound velocity tensors are derived in the long wavelength limit. Both show an explicit dependence on the lattice filling fraction, the elastic properties of cylinders relative to the background, their positions in the unit cell, and their multiple scattering interactions. Several examples of these metamaterials are reported and discussed.

Bandgap and effective mass of epitaxial cadmium oxide

Abstract: duced using a vapor transport technique. 3 The calculations on which this work is based used a parabolic conduction band and an electron effective mass of 0.14m0. No justification for the choice of effective mass value was given and though the author concluded that the interpretation of the thermoreflectance spectra is qualitatively correct, it was suggested that the inclusion of the effects of conduction band nonparabolicity may produce better agreement with the data. In this paper, the room temperature bandgap and the band-edge effective mass of single crystal epitaxially grown CdO are determined from infrared reflectivity, ultraviolet/ visible optical absorption and Hall effect measurements. The nonparabolicity of the conduction band and the competing effects of Moss-Burstein band-filling and bandgap renormalization are explicitly considered. Single crystal CdO samples were grown by metalorganic vapor-phase epitaxy MOVPE on r-plane sapphire substrates using the growth precursors tertiary butanol and dimethylcadmium. Further details on the growth and structural characterization of these samples can be found elsewhere. 4 The samples were annealed under ultrahigh vacuum at a temperature of 400 °C for between 2 and 24 h. As a result of this annealing, the free electron concentrations mobilites were reduced increased from 1.8 10 20 cm 3 51 cm 2 V 1 s 1 , for the as-grown samples, to as low high as 4.410 19 cm 3 113 cm 2 V 1 s 1 for the postgrowth annealed samples. Infrared reflectivity measurements were made using a Perkin Elmer Spectrum GX Fourier transform infrared spectrometer with a 35° specular reflection with respect to the surface normal. The reflectance was determined from the ratio of the reflection from the CdO sample and that of a high reflectivity optical mirror. The system employs a cadmium mercury telluride detector giving a working range of 0.05‐1.24 eV. Transmission geometry ultraviolet/visible absorption measurements were performed using a Perkin Elmer Lambda 25 spectrometer working between 1.24 and 4.00 eV. All measurements from both optical systems were taken at room temperature. Finally, single field Hall effect measurements, also conducted at room temperature, were performed using the standard van der Pauw method. The infrared reflectivity spectra of three CdO samples are shown in Fig. 1. The spectra were simulated using an expression describing the propagation and reflection of electromagnetic radiation from a two-layer stratified medium derived from the Fresnel equations. 5 This expression is dependent on the complex refractive indices n of the materials which are described in terms of the two-oscillator dielectric

Electron-phonon interaction and charge carrier mass enhancement in SrTiO3.

Abstract: We report a comprehensive THz, infrared and optical study of Nb-doped SrTiO3 as well as dc conductivity and Hall effect measurements. Our THz spectra at 7 K show the presence of an unusually narrow (<2 meV) Drude peak. For all carrier concentrations the Drude spectral weight shows a factor of three mass enhancement relative to the effective mass in the local density approximation, whereas the spectral weight contained in the incoherent midinfrared response indicates that the mass enhancement is at least a factor two. We find no evidence of a particularly large electron-phonon coupling that would result in small polaron formation.

Ab initio calculations of the mechanical and electronic properties of strained Si nanowires

Abstract: This paper reports a systematic study of the mechanical and electronic properties of strained small diameter (0.7\char21{}2.6 nm) silicon nanowires (Si NWs) using ab initio density functional theory calculations. The values of Young's modulus, Poisson ratio, band gap, effective mass, work function, and deformation potentials are calculated for $⟨110⟩$ and $⟨111⟩$ Si NWs. We find that quantum confinement in $⟨110⟩$ Si NWs splits conduction band valleys and decreases transport effective mass compared to the bulk case. Consequently, additional tensile strain should not lead to further significant electron mobility improvement. An interesting finding we report in this paper is that under compressive strain, there is a dramatic decrease in deformation potentials of $⟨110⟩$ Si NWs, which may result in a strong increase in electron mobilities, despite a concurrent increase in effective mass. We also observe a similar strain-induced counterplay of hole deformation potentials and effective masses for both $⟨110⟩$ and $⟨111⟩$ Si NWs. Finally, we do not see any significant effect of tensile or compressive strain on electron effective masses and deformation potentials in $⟨111⟩$ Si NWs. The sudden changes in effective mass and deformation potentials are concurrent with a change in the conduction and valence band edge states. In $⟨110⟩$ NWs, this change corresponds to a transition from direct-to-indirect band gap under strain.

Calculations of strain-modified anatase TiO 2 band structures

Abstract: In order to theoretically quantify a strain-inducing method that we use to engineer the material properties of anatase titania, we studied its electronic band structure over a range of biaxial strain by utilizing both the density functional theory within the generalized gradient approximation (GGA) and quasiparticle theory calculations within the GW approximation. This strain-modified material is suitable for use as a high efficiency photoanode in a photoelectrochemical cell. We track the changes to the band gap and the charge carrier effective masses versus the total pressure associated with the strained lattice. Both the GGA and the GW approximation predict a linear relationship between the change in band gap and the total pressure. However, the GGA underestimates the slope by more than 57% with respect to the GW approximation result of 0.0685 eV/GPa. We also compare our predicted band gap shift to a reported experimental result.

A defective graphene phase predicted to be a room temperature ferromagnetic semiconductor

Abstract: Theoretical calculations, based on the hybrid exchange density functional theory, are used to show that in graphene, a periodic array of defects generates a ferromagnetic ground state at room temperature for unexpectedly large defect separations. This is demonstrated for defects that consist of a carbon vacancy in which two of the dangling bonds are saturated with H atoms. The magnetic coupling mechanism is analysed and found to be due to an instability in the ?-electron system with respect to a long-range spin polarization characterized by alternation in the spin direction between adjacent carbon atoms. The disruption of the ?-bonding opens a semiconducting gap at the Fermi edge. The size of the energy gap and the magnetic coupling strength are strong functions of the defect separation and can thus be controlled by varying the defect concentration. The position of the semiconducting energy gap and the electron effective mass are strongly spin-dependent and this is expected to result in a spin asymmetry in the transport properties of the system. A defective graphene sheet is, therefore, a very promising material with an in-built mechanism for tailoring the properties of future spintronic devices.

Making Massless Dirac Fermions from Patterned Two-Dimensional Electron Gases

Abstract: Analysis of the electronic structure of an ordinary two-dimensional electron gas (2DEG) under an appropriate external periodic potential of hexagonal symmetry reveals that massless Dirac fermions are generated near the corners of the supercell Brillouin zone. The required potential parameters are found to be achievable under or close to laboratory conditions. Moreover, the group velocity is tunable by changing either the effective mass of the 2DEG or the lattice parameter of the external potential, and it is insensitive to the potential amplitude. The finding should provide a new class of systems other than graphene for investigating and exploiting massless Dirac fermions using 2DEGs in semiconductors.

First-principles study of electronic properties of biaxially strained silicon: Effects on charge carrier mobility

Abstract: Using first-principles method, we calculate the electronic band structure of biaxially strained silicon, from which we analyze the change in electron and hole effective mass as a function of strain and determine the mobility of electrons and holes in the biaxially strained silicon based on Boltzmann transport theory. We found that electron mobility increases with tensile strain and decreases with compressive strain. Such changes are mainly caused by a strain-induced change in electron effective mass, while the suppression of intervalley scattering plays a minor role. On the other hand, the hole mobility increases with both signs of strain and the effect is more significant for compressive strain because the hole effective mass decreases with compressive strain but increases with tensile strain. The strain-induced suppression of interband and intraband scatterings plays also an important role in changing the hole mobility.

Energy of K-momentum dark excitons in carbon nanotubes by optical spectroscopy.

Abstract: Phonon sideband optical spectroscopy determines the energy of the dark K-momentum exciton for (6,5) carbon nanotubes. One-phonon sidebands appear in absorption and emission, split by two zone-boundary (K-point) phonons. Their average energy locates the E 11 K-momentum exciton 36 meV above the E 11 bright level, higher than available theoretical estimates. A model for exciton-phonon coupling shows the absorbance sideband depends sensitively on the K-momentum exciton effective mass and has minimal contributions from zone-center phonons, which dominate the Raman spectra of carbon nanotubes.

Effects of position-dependent effective mass and dielectric function of a hydrogenic donor in a quantum dot

Abstract: Ionization energies of a shallow donor in a quantum dot of GaAs, using a variational procedure within the effective mass approximation, are obtained. Calculations are presented with a constant effective mass and position-dependent effective masses along with the spatially varying dielectric function. Donor binding energies are calculated using both the approximate method ( m 0 * ) and the spatially varying electron effective mass, m * ( r ) . Dielectric quantum dots are discussed and calculations are performed with the dielectric constants of the dot e1 and that of the barrier material, e2. It is found that (i) the use of a constant effective mass (0.067 m0) is justified for dot size ⩾a*, where a* is the effective Bohr radius, which is about 100 A for GaAs, in the estimation of ionization energy, (ii) the ionization energy decreases as the dot increases in both the cases of constant and variable masses, (iii) an increase of binding energy is observed when the spatially varying mass and dielectric function are included, (iv) lower binding energies are observed when the average dielectric constant is included and (v) the binding energy shows complicated behaviour when the position-dependent mass is included for the dot size ⩽a*.

Fe in III–V and II–VI semiconductors

Abstract: Many theoretical and experimental studies deal with the realization of room-temperature ferromagnetism in dilute magnetic semiconductors (DMS). However, a detailed quantitative understanding of the electronic properties of transition metal doped semiconductors has often been neglected. This article points out which issues concerning electronic states and charge transfers need to be considered using Fe as an example. Methods to address these issues are outlined, and a wealth of data on the electronic properties of Fe doped III–V and II–VI compound semiconductors that have been obtained over a few decades is reviewed thoroughly. The review is complemented by new results on the effective-mass-like state consisting of a hole bound to Fe2+ forming a shallow acceptor state. The positions of established Fe3+/2+ and Fe2+/1+ charge transfer levels are summarized and predictions on the positions of further charge transfer levels are made based on the internal reference rule. The Fe3+/4+ level has not been identified unambiguously in any of the studied materials. Detailed term schemes of the observed charge states in tetrahedral and trigonal crystal field symmetry are presented including hyperfine structure, isotope effects and Jahn–Teller effect. Particularly, the radiative transitions Fe3+(4T1 6A1) and Fe2+(5E 5T2) are analyzed in great detail. An effective-mass-like state [Fe2+, h] consisting of a hole bound to Fe2+ is of great significance for a potential realization of spin-coupling in a DMS. New insights on this shallow acceptor state could be obtained by means of stress dependent and temperature dependent absorption experiments in the mK range. The binding energy and effective Bohr radius were determined for GaN, GaP, InP and GaAs and a weak exchange interaction between the hole and the Fe2+ center was detected. With regard to the Fe3+ ground state, 6A1, in GaP and InP, the hyperfine structure level Γ8 was found to be above the Γ8 level. All results are discussed with respect to a potential realization of a ferromagnetic spin-coupling in DMSs. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Influence of bismuth incorporation on the valence and conduction band edges of GaAs1−xBix

Abstract: We investigate the electronic properties of GaAs1−xBix by photoluminescence at variable temperature (T=10–430K) and high magnetic field (B=0–30T). In GaAs0.981Bi0.019, localized state contribution to PL is dominant up to 150K. At T=180K the diamagnetic shift of the free-exciton states reveals a sizable increase in the carrier effective mass with respect to GaAs. Such an increase cannot be accounted for by an enhanced localized character of the valence band states, solely. Instead, it suggests that also the Bloch states of the conduction band are heavily affected by the presence of bismuth atoms.

Ab Initio Study of Temperature and Pressure Dependence of Energy and Phonon-Induced Dephasing of Electronic Excitations in CdSe and PbSe Quantum Dots†

Abstract: The pressure and temperature dependence of the lowest excitation energy of PbSe (Pb68Se68, d = 2.0 nm) and CdSe (Cd33Se33, d = 1.6 nm) quantum dots (QDs) were investigated by ab initio density functional theory and molecular dynamics simulation. Additionally, pure-dephasing/decoherence induced by the electron–phonon interaction was studied using optical response theory for several pairs of electronic states, including ground, excitonic and biexcitonic states. Linear dependence on temperature was observed for all quantities under consideration. The results were consistent with other theoretical and experimental reports. The ab initio data was analyzed using the effective mass approximation and the hyperbolic band model. The analysis confirmed the temperature dependence of the effective mass in the PbSe QD, as suggested in a recent experimental report [Liptay, T. J.; Ram, R. J. Appl. Phys. Lett. 2006, 89, 223132].

Theory of resonance energy transfer involving nanocrystals: The role of high multipoles

Abstract: A theory for the fluorescence resonance energy transfer (FRET) between a pair of semiconducting nanocrystal quantum dots is developed. Two types of donor-acceptor couplings for the FRET rate are described: dipole-dipole (d-d) and the dipole-quadrupole (d-q) couplings. The theory builds on a simple effective mass model that is used to relate the FRET rate to measureable quantities such as the nanocrystal size, fundamental gap, effective mass, exciton radius, and optical permittivity. We discuss the relative contribution to the FRET rate of the different multipole terms, the role of strong to weak confinement limits, and the effects of nanocrystal sizes.

Photoemission evidence for a Mott-Hubbard metal-insulator transition in VO 2

Abstract: The temperature (T) dependent metal-insulator transition (MIT) in VO2 is investigated using bulk sensitive hard x-ray (� 8 keV) valence band, core level, and V 2p-3d resonant photoemission spectroscopy (PES). The valence band and core level spectra are compared with full-multiplet cluster model calculations including a coherent screening channel. Across the MIT, V 3d spectral weight transfer from the coherent (d 1 C final) states at Fermi level to the incoherent (d 0 +d 1 L final) states, corresponding to the lower Hubbard band, lead to gap-formation. The spectral shape changes in V 1s and V 2p core levels as well as the valence band are nicely reproduced from a cluster model calculations, providing electronic structure parameters. Resonant-PES finds that the d 1 L states resonate across the V 2p-3d threshold in addition to the d 0 and d 1 C states. The results support a Mott-Hubbard transition picture for the first order MIT in VO2. PACS numbers: 79.60.-i, 71.30.+h VO2, a d 1 electron system, exhibits a sharp first-order metal-insulator transition (MIT) as a function of temperature (T), at TMI = 340 K. 1 The high-T metal phase has a rutile (R) structure, while the low-T insulating phase has a monoclinic (M1) structure with zig-zag type pairing of V atoms along the c-axis. 2 Magnetically, the metallic R phase shows enhanced susceptibility (�) with an effective mass m ∗ /m � 6, while the insulating M1 phase is non

Bose-Einstein condensation and superfluidity of magnetoexcitons in bilayer graphene

Abstract: We propose experiments to observe Bose-Einstein condensation and superfluidity of quasi-two-dimensional spatially indirect magnetoexcitons in two-layer graphene The energy spectrum of collective excitations, the sound spectrum, and the effective magnetic mass of magnetoexcitons are presented in the strong magnetic field regime The superfluid density ${n}_{S}$ and the temperature of the Kosterlitz-Thouless phase transition ${T}_{c}$ are shown to be increasing functions of the excitonic density $n$ but decreasing functions of $B$ and the interlayer separation $D$

Ultraviolet photoluminescence from 6H silicon carbide nanoparticles

Abstract: We report stable photoluminescence from 6H silicon carbide nanocrystals dispersed in three different solvents: water, hydrofluoric acid, and toluene. Transmission electron micrograph surveys reveal a size distribution that contains a significant fraction of monocrystal particles with diameters below 3nm—small enough for quantum confinement to play a role in increasing the effective bandgap energy. The ultraviolet photoluminescence band observed at 3.5eV in the colloidal solutions is consistent with quantum confinement estimates based on the effective mass model.

Band-Structure Effects on the Performance of III–V Ultrathin-Body SOI MOSFETs

Abstract: This paper examines the impact of band structure on deeply scaled III-V devices by using a self-consistent 20-band -SO semiempirical atomistic tight-binding model. The density of states and the ballistic transport for both GaAs and InAs ultrathin-body n-MOSFETs are calculated and compared with the commonly used bulk effective mass approximation, including all the valleys (, , and ). Our results show that for III-V semiconductors under strong quantum confinement, the conduction band nonparabolicity affects the confinement effective masses and, therefore, changes the relative importance of different valleys. A parabolic effective mass model with bulk effective masses fails to capture these effects and leads to significant errors, and therefore, a rigorous treatment of the full band structure is required.

Power law running of the effective gluon mass

Abstract: The dynamically generated effective gluon mass is known to depend non-trivially on the momentum, decreasing sufficiently fast in the deep ultraviolet, in order for the renormalizability of QCD to be preserved. General arguments based on the analogy with the constituent quark masses, as well as explicit calculations using the operator-product expansion, suggest that the gluon mass falls off as the inverse square of the momentum, relating it to the gauge-invariant gluon condensate of dimension four. In this article we demonstrate that the power law running of the effective gluon mass is indeed dynamically realized at the level of the non-perturbative Schwinger-Dyson equation. We study a gauge-invariant non-linear integral equation involving the gluon self-energy, and establish the conditions necessary for the existence of infrared finite solutions, described in terms of a momentum-dependent gluon mass. Assuming a simplified form for the gluon propagator, we derive a secondary integral equation that controls the running of the mass in the deep ultraviolet. Depending on the values chosen for certain parameters entering into the Ansatz for the fully dressed three-gluon vertex, this latter equation yields either logarithmic solutions, familiar from previous linear studies, or a new type of solutions, displaying power law running. In addition, it furnishes a non-trivial integral constraint, which restricts significantly (but does not determine fully) the running of the mass in the intermediate and infrared regimes. The numerical analysis presented is in complete agreement with the analytic results obtained, showing clearly the appearance of the two types of momentum dependence, well-separated in the relevant space of parameters. Several technical improvements, various open issues, and possible future directions, are briefly discussed.

Bandstructure Effects in Silicon Nanowire Hole Transport

Abstract: Bandstructure effects in p-channel MOS (PMOS) transport of strongly quantized silicon nanowire FETs in various transport orientations are examined. A 20-band sp3d5s* spin-orbit (SO) coupled atomistic tight-binding model coupled to a self-consistent Poisson solver is used for the valence-band dispersion calculation. A ballistic FET model is used to evaluate the capacitance and current-voltage characteristics. The dispersion shapes and curvatures are strong functions of device size, lattice orientation, and bias, and cannot be described within the effective mass approximation. The anisotropy of the confinement mass in the different quantization directions can cause the charge to preferably accumulate in the (110) and then on the (112) rather than on (100) surfaces, leading to significant differences in the charge distributions for different wire orientations. The total gate capacitance of the nanowire FET devices is, however, very similar for all wires in all the investigated transport orientations ([100], [110], [111]), and is degraded from the oxide capacitance by ~30%. The [111] and then the [110] oriented nanowires indicate highest carrier velocities and better on-current performance compared to [100] wires. The dispersion features and quantization behavior, although a complicated function of physical and electrostatic confinement, can be explained at first order by looking at the anisotropic shape of the heavy-hole valence band.

Low temperature thermal, thermoelectric, and thermomagnetic transport in indium rich Pb1−xSnxTe alloys

Abstract: Galvanomagnetic and thermomagnetic data of single crystal indium rich Pb1−xSnxTe are analyzed, and electronic band parameters are calculated using nonparabolic band model. Transport properties at 80K are presented as a function of Sn (x=0–0.3) and In concentrations. Our results indicate pinning of Fermi level by indium impurity levels in these alloys. Effects of interaction of band with impurity level are investigated in terms of change in effective mass and energy scattering exponent. Indium doping slightly improves the thermoelectric properties of PbSnTe alloys.

Silicon as a model ion trap: time domain measurements of donor Rydberg states

Abstract: One of the great successes of quantum physics is the description of the long-lived Rydberg states of atoms and ions. The Bohr model is equally applicable to donor impurity atoms in semiconductor physics, where the conduction band corresponds to the vacuum, and the loosely bound electron orbiting a singly charged core has a hydrogen-like spectrum according to the usual Bohr-Sommerfeld formula, shifted to the far-infrared due to the small effective mass and high dielectric constant. Manipulation of Rydberg states in free atoms and ions by single and multi-photon processes has been tremendously productive since the development of pulsed visible laser spectroscopy. The analogous manipulations have not been conducted for donor impurities in silicon. Here we use the FELIX pulsed free electron laser to perform time-domain measurements of the Rydberg state dynamics in phosphorus- and arsenic-doped silicon and we have obtained lifetimes consistent with frequency domain linewidths for isotopically purified silicon. This implies that the dominant decoherence mechanism for excited Rydberg states is lifetime broadening, just as for atoms in ion traps. The experiments are important because they represent the first step towards coherent control and manipulation of atomic-like quantum levels in the most common semiconductor and complement magnetic resonance experiments in the literature, which show extraordinarily long spin lattice relaxation times key to many well-known schemes for quantum computing qubits for the same impurities. Our results, taken together with the magnetic resonance data and progress in precise placement of single impurities, suggest that doped silicon, the basis for modern microelectronics, is also a model ion trap.