Chemical Shift Parameters For Shallow Donors In Semiconductors

A model for a shallow donor impurity in a semiconductor is used to calculate two relationships and several conditions involving the chemical shift parameters. The model is based on the standard effective mass form for the donor electron wave function, the existence of a potential in the chemical cell which may be real, pseudo, or rather general in nature, and a few somewhat restrictive approximations. The parameters, Δ, δ and Λ are theoretically calculated and are shown to be related if the approximations are valid. These parameters determine the 1S multiplet level structure and it is shown how properties of the central cell potential can be deduced from a knowledge of this structure. As an example, the inverted structure for Si(Li) is discussed. The often-neglected parameter, Λ, is shown to be quite important. A length parameter is determined by the model and is a measure of the effective range of influence of the central cell potential. The model should be useful in determining if choices for the potential and wave function in the central cell region lead to self consistent results. The agreement between the theoretical predictions and the experimental data from both silicon and germanium and five donor impurities from both Group I (lithium) and Group V (arsenic, phosphorus, antimony and bismuth) suggest the model is reasonable. © 1973

Computerized Scanning Auger Microprobe

An Auger spectrometer has been automated using a microcomputer. Fundamental considerations in the design and choice of the computerized system are presented and should be of general interest. The spectrometer was a Physical Electronics Ind. model 545 scanning Auger microprobe. The microcomputer chosen was a Southwest Technical Products 6809 computer system. Hardware details are discussed with emphasis on the four computer-spectrometer interface boards. These boards are (1) Auger energy control board, which sets the Auger detection energy with its 16 bit digital-to-analog converter (DAC); (2) read Auger signal board, which reads the Auger signal intensity with its 12 bit analog-to-digital converter; (3) multipurpose DAC board, which uses two pairs of 8 bit DAC\u27s to position the excitation beam and display the data in memory on a CRT monitor, and (4) timing and relay control board, which selects various instruments and power supplies as required during the fully automated depth profiling sputter sequences. Organizational details of the control, analysis, and output software are discussed. The operation of the main Auger control program is emphasized along with its menu driven options, which provide great versatility to the operator. Examples are shown of the various data output modes, which include displays on the CRT monitor and plots from the multicolor digital plotter. © 1985, American Vacuum Society. All rights reserved

Crystalline To Amorphous Transformation In Ion-implanted Silicon: A Composite Model

The transformation of silicon to the amorphous state by implanted ions was studied both experimentally and theoretically. Experimentally, the amount of transformed silicon and the critical ion dose necessary to amorphized the entire implanted layer were determined by ESR. How the critical dose varies with ion mass (Li, N, Ne, Ar, and Kr), ion energy (20-180 keV), and implant temperature (77-475 K) was determined. Theoretically, several phenomenological models were used to analyze these data. The overlap-damage model was used to determine the critical dose from the data, the size of the amorphous region around the ion track, and the degree of overlap damage required for amorphization. For all implants, the first ion created only predamage, while the second or third ion into the same region caused the amorphous transformation. The critical-energy-density model was in good agreement with the measured critical doses. This model assumed that a region would become amorphous if the energy density deposited into atomic processes by the ions exceeded the critical energy density of 6x1023 eV/cm3. For high-temperature implantations, out-diffusion models can explain the temperature dependence of the critical dose. Although the analysis is not completely definitive, the critical-energy-density model may also be valid at high temperature if diffusion of the damage energy is taken into account. This out-diffusion of energy from around the ion track occurs via a thermally activated process. Probably, the energy moves with the out-diffusion of the vacancies from the ion track

Calculation Of Anisotropic Hyperfine Constants For Lattice Nuclei Near A Shallow Donor

A method is presented for calculating the magnetic anisotropic (dipolar) hyperfine constants for lattice nuclei near a shallow-donor impurity. The method assumes that the wave function of the donor electron can be expressed in an effective-mass form, i.e., a slowly varying envelope function times conduction-band Bloch functions. For each dipolar hyperfine constant, two separate calculations are performed. One calculation is for a local region about the lattice nucleus of interest. The greatest part of the interaction occurs in this region (about 85 ± 10%). The second calculation is for the more distant region. The dipolar constants in the distant region are calculated without considering the details of the Bloch functions and are evaluated by an integration involving only the envelope function. In the local region, the details of the Bloch functions must be considered. The Bloch functions are expressed in terms of equivalent orbitals. Symmetry arguments using the properties of these orbitals simplify the calculation. The final results show that the local contribution can be expressed as products of a few intrinsic lattice parameters, which are the dipolar matrix elements between equivalent orbitals, and a set of coefficients that is not difficult to evaluate. The resulting dipolar constants vary a great deal from one lattice site to another. Numerical results have been computed for the shallow donors - arsenic, phosphorus, and antimony - in silicon. Comparison of theoretical values with experimental values shows qualitative and semiquantitative agreement. © 1971 The American Physical Society

Ground-state Wave Function Of Shallow Donors In Uniaxially Stressed Silicon: Piezohyperfine Constants Determined By Electron-nuclear Double Resonance

Stress-induced changes in the ENDOR spectra of a shallow donor electron interacting with various Si29 nuclei neighboring the donor have been experimentally and theoretically investigated. For each of the three measured donors - As, P, and Sb - the compressional, uniaxial stress was applied along the [001] axis and its magnitude corresponded to strains up to 10-3. To describe the observed linear and quadratic shifts and splitting\u27s of the lines in an ENDOR shell, we have defined a set of piezo hyperfine constants. One piezo hyperfine constant was measured for each axis-class shell; three independent piezo hyperfine constants were measured for each shell of the other shell symmetry classes. Piezo hyperfine constants are reported for more than 15 measured lattice shells about each donor. Analysis of the results shows that the constants for any one shell can be attributed primarily to changes in the Fermi contact hyperfine constants at the various lattice sites within that shell. Consequently, the stress-induced changes are directly related to wave-function density changes at specific points in the lattice. Calculations of these wave-function density changes have been performed using a model based on the valley-repopulation effect and on an effect due to the redistribution of the radial envelope function (RREF effect). The calculations and experimental results are qualitatively in good agreement. The quantitative theoretical accuracy is not sufficient to match all the experimental shells to the actual lattice shells, but a new match of shell Q and the (1,1,5) shell has been determined and other matchings are suggested. The theoretical and experimental results provide information on two intrinsic lattice parameters: the deformation-potential constant Ξu, and the location of the conduction-band minimum k0. Difficulties with assigning a value to Ξu because of the RREF effect are discussed. A revised spin-resonance value for Ξu was found to be 10 ± 1 eV. Applying the above model to the previously matched shells [A and (0,0,4), B and (4,4,0), K and (0,0,8)], one finds an average k0=(0.86±0.02)kmax. © 1970 The American Physical Society

Raman Studies Of Heavily Implanted, Dye-laser-annealed GaAs

Raman scattering is used to study the annealing behavior produced by 10 nsec, 565 nm dye laser pulses in high dose ion-implanted GaAs. Samples were prepared with Sn and Cd implantations of 2, 5, and 10 x 1015 cm2. The Raman spectra indicate that the threshold for epitaxial growth lies between 0.2 - 0.3 J cm2. Best carrier activation (∼ 2%), however, is achieved at ∼1.6 J cm2 for the Sn-implanted sample (n-type). For Cd implantation the electrical activation appears to be very high ({greater-than or approximate} 50%) for low pulse energies({less-than or approximate} 0.3 J cm2) but decreases for higher pulse energies. © 1985

Evaluation Of Model For The Contributin Of Phonon-induced Tunneling To Donor ESR Spectral Narrowing In Germanium

The model commonly assumed to explain the narrowing of the ESR spectra of donor impurities in germanium is examined in detail. This model combines the Anderson line-narrowing theory with the Miller and Abrahams theory for the phonon-induced tunneling (hopping) of an electron between impurities. The predictions of this model are found to be in drastic disagreement with experimental results now available. It is shown that the narrowed linewidth should depend strongly on donor concentration, acceptor concentration, and temperature. Future spin-resonance experiments in highly compensated samples may show the effects of hopping, but no evidence now exists which indicates that hopping is influencing the narrowing of the ESR spectra. © 1974 The American Physical Society

Properties Of Microwave Cavities Containing Magnetic Resonant Samples

Properties of TE011 cylindrical, microwave cavities containing cylindrical samples of various radii and dielectric constants are calculated. The properties considered are the resonant frequency, quality factor (Q), relevant magnetic filling factor for spin transitions (ε), and a signal sensitivity factor (Qε) for a lossless sample. Sample sizes range from zero radius to full cavity radius with some experimental data on less than full length samples. The choice of dielectric constants ranges from one to sixteen. The data are presented in dimensionless form since they will be of use to other ESR experimentalists. It is shown that use of large samples is undesirable even if they are lossless. Furthermore, elongated cavities (D/L ratios less than one) are to be preferred over shortened cavities. © 1973 The American Institute of Physics

Measurement of the Wear Properties of Metallic Solids with a Falex Lubricant Testing Machine

A modified Falex Lubricant Testing Machine has been used to determine wear properties of metallic solids. In particular, wear mass loss, wear volume loss, wear rates, and other parameters have been determined for a basic steel, as heat treated and after ion implantation. Wear rate improvements of more than an order of magnitude were found in a nickel-chrome steel (SAE 3135) implanted with 2.5x1017 N+2/cm2. Wear tests were conducted with a cylinder-in-groove geometry in a mild lubricating oil with loads greater than 540 N, which corresponded to pressures which exceeded 108N/m2. A detailed analysis of the data is presented