SI Direction Research Articles

Defect Characteristics in Different Crystallographic Directions in CzSi as a Function of Doping and Annealing

Measurements of the S-parameter as well as of lifetimes are performed as a function of thermal annealing in the 20 to 1100 °C range. CzSi with different levels of boron doping is investigated. A significant broadening of the annihilation line is found around 800 °C for the heavily doped sample. Concurrent with this a short-lived (≈ 100 ps) lifetime component is observed with an intensity up to 30%. No obvious changes in the anisotropy of the annihilation line take place. Lebensdauer- und S-Parametermessungen werden in CzSi mit unterschiedlichem Borgehalt als Funktion Von isochroner thermischer Behandlung durchgefuhrt. Eine signifikante Verbreiterung der Annihilationslinie zusammen mit dem Auftreten einer kurzlebigen Lebensdauerkomponente kann im Bereich um 800 °C festgestellt werden.

Ranges and depth distributions of 200-keV He ions channeled in Si, Ge, and GaAs crystals

We report depth distributions of 200-keV He ions channeled in the 〈100〉 and 〈110〉 directions of Si, Ge, and GaAs crystals and in a random orientation of each crystal, measured using secondary ion mass spectrometry. The 〈100〉 channeled profiles agree with the random profiles within experimental error. The 〈110〉 channeled profiles are about 1.7, 2.3, and 2.2 times as deep as the random peaks (projected range) for the three crystals, respectively. Assuming velocity-proportional electronic stopping, values of electronic stopping are calculated for He in Si, Ge, and GaAs. Fractions of He ions backscattered into the vacuum are estimated. Profiles for Ge and GaAs, with the same average atomic number, are compared. Range and profile shape parameters are tabulated.

Misoriented Epitaxial Growth of (111)CoSi 2 on Offset (111)Si Substrates

ABSTRACTSingle crystal epitaxial films of CoSi2 were grown by MBE on various (111)Si single crystal substrates, whose surfaces were purposely tilted towards the < 110>>g, direction by small angles ϕg,†, 0°, ≤ϕg, ≤, 4° measured between the surface normal and the < 111>>g, direction of Si. The actual offset angle, .ϕ8,, was determined by back Laue reflection method. The average perpendicular strain of the CoSi2 epilayer, ε┵, and the < 111 >f orientation of the epitaxial CoSi2 film were determined by double crystal diffractometry. We find that the misorientation angle, a, measured between the Si < 111>g, and CoSi2 < 111>f directions, increases linearly with the offset angle, ϕg, up to ϕg, = 4°. A simple geometrical model is developed which predicts that α = ε┵ × tan ϕg,. The model agrees quantitatively with the experimental data. The equivalent strain energy associated with the misorientation is approximated by that of a low angle tilt boundary. The misorientation angle α of the equilibrium state, determined by minimizing the total strain energy of the epitaxial film, is nonzero in general.

A b i n i t i o calculations of 29Si NMR chemical shifts for some gas phase and solid state silicon fluorides and oxides

A b initio coupled Hartree–Fock perturbation theory (CHFPT) employing near Hartree–Fock basis sets has been used to calculate the 29Si NMR chemical shifts of SiF4(Td), SiF−5 (D3h), SiF−26 (Oh), and SiO−44 (in both Td and C3v geometries). The increase in the shielding constant, σ, from SiF4 to SiF−26 is calculated to be 114 ppm, compared to an experimental value of about 75 ppm, while the decrease in σ between SiF4 to SiO−44 is calculated to be 43 ppm, compared to an experimental value of about 40 ppm. These results indicate that CHFPT applied to properly chosen molecular cluster models for solids can accurately reproduce experimental trends in solid state NMR chemical shifts. Calculations on SiF4 and SiO−44 for different internuclear distances also establish that the chemical shift is very weakly dependent on distance, suggesting that observed correlations between chemical shift and average Si–O distance in silicates arise indirectly, through the relationship between degree of polymerization and the average Si–O bond distance. By contrast, a C3v distorted SiO−44 tetrahedron (one bond 1.584 Å long and three bonds 1.651 Å long) gives an anisotropy in the chemical shift tensor of 54 ppm, with the larger value of σ occurring along the direction of the short Si–O bond, in reasonable agreement with available experiment. The calculations also support the use of the simple superimposed free atom approximation for the diamagnetic contribution to σ. For the Td species the paramagnetic contribution is shown to be dominated by excitations from the t2 σ orbitals to the σ* orbitals, as suggested previously on qualitative grounds. It may therefore be possible to interpret trends in σ by focusing on the energies and compositions of the t2 σ orbitals.

Monte carlo simulation of channeling effects near the <100> axis in silicon

Abstract Channeling effects in low-index crystallographic directions in Si near the axis are analysed with a Monte Carlo method. The theory is compared with the experimental results reported in literature.

INITIAL STAGES OF EPITAXY OF METALS ON Si(lll)-7x7 STUDIED BY UHV ELECTRON MICROSCOPY

AbstractInitial condensations of Cu, Ag and Au on Si(lll)-7x7 surface are seen continuously by video tape recording and intermittently by photographic films using an UHV electron microscope in reflection electron microscopy (REM). The growths of initial superlattice structures are found to relate with the steps of the 7x7 surface and the superlattice structures of a for Cu, for Ag and 5x2 for Au are nucleated at the upper side of the stepsand grow over the lower side terrace accompanied by the step movement. The growth of Au on Si(lll)-7x7 surface is seen in transmission electron microscopy (TEM) to supplement geometric information. It is found that the 5x2 domain of Au grows in the <llO>Si direction preferentially. The superlattice structures formed at submonolayer range are seen for the first time in TED pattern, which is useful to judge the previously proposed models from intensity distribution. REM-RHEED and TEM-TED allow us to study dynamic process of the initial growth stages of metals on Si(lll)-7x7 in real space and to analyse the geometrical structures of the superlattice structures at submonolayer.

Approximation for the surface backscattering yield from an atomic row with correlated thermal vibrations

An approximation method is given which permits rapid calculation of the surface backscattering yield from an atomic row with correlated thermal vibrations. The method has been tested by comparison with computer simulations for low index directions in Pt, Au, Mo and Si for He + beam energies between 0.5 and 2.0 MeV over the temperature range 50–500 K. Agreement was found to be good in those cases where shadow cone scaling of the yields is valid.

Phonon attenuation in heavily doped many-valley semiconductors. II. The effect of mass anisotropy

For pt.I see ibid., vol.15, p.6991 (1982). The authors have derived the phonon relaxation rate for anisotropic mass cases in heavily doped many-valley semiconductors by solving the equations of motion for the single-particle density matrices within the self-consistent field and the relaxation time approximations. Explicit expressions have been given for longitudinal and transverse waves propagating along the principal directions in Ge and Si. Numerical calculations have been performed for n-type Ge at T=0K. The following have been found. The effect of the mass anisotropy is remarkable in the high-frequency region, while in the low-frequency region it becomes negligibly small. There exist two cut-off wavenumbers in the electron-phonon interaction for the (110) and (111) longitudinal mode is qualitatively the same as in the isotropic mass case. A discussion of the recent work on phonon absorption due to the electron-hole liquid (EHL) in Ge by Dietsche et al. (1982) is also given.

Theoretical analysis of optical-phonon deformation potentials in semiconductors

A method to compute the electronic and structural properties of semiconductors self-consistently is applied to analyse the electron-phonon interaction in these crystals. The authors have calculated the optical-phonon deformation potentials along the symmetry directions in Si, Ge and GaAs. Their results confirm the previous ones obtained in more simplified approaches. Quantitative discrepancies with experimental data suggest what must be the next step to be taken in the theoretical effort.

Channeling of 20–800-keV arsenic ions in the 〈110〉 and the 〈100〉 directions of silicon, and the roles of electronic and nuclear stopping

Atom- and carrier-depth distributions have been measured for As channeled in the 〈110〉 and the 〈100〉 directions of Si in the energy range from 20 to 800 keV by secondary ion-mass spectrometry and differential C-V techniques. Maximum channeled ranges in the 〈110〉 of Si are observed up to about 6 μm. The slopes p of selected range parameters plotted versus ion energy E1 are measured and used to discuss the relative roles of electronic and nuclear stopping for the channeled and random components of the depth distributions. Values of electronic stopping Se or total stopping (electronic plus nuclear) St are calculated for ion velocity v1 = 1.5×108 cm/s and values are given for k and p in the expression Se,t = kEp1 for the energy range studied. The values of p for the maximum ranges of As channeled in the 〈110〉 and 〈100〉 directions of Si are 0.50±0.03 and 0.54±0.04, respectively. The corresponding values of Se are 5.43×10−14 and 2.18×10−13 eV cm2/atom, respectively, at v1 = 1.5×108 cm/s.

Electrical Characteristics of Depletion-Type SOS MOS Devices

(001) Si films on (1̄012) sapphire substrates have preferential dislocation arrays in the <110> Si direction. In more detailed observation, dislocation arrays in the [110] Si direction are preferential to those in the [11̄0] Si direction. A new significant anisotropy in the electron mobility of D-type SOS MOS devices is observed, and it is found to be due to the anisotropic dislocation arrays. Furthermore, the surface state density at the Si-SiO2 interface is measured as 2×1011∼8×1011/cm2·eV. These high densities of states are due to crystalline defects, mostly dislocations. Mobility humps are observed in the curves of µH vs. VG for D-type SOS MOS devices, which phenomena can be explained by a model based on a change in the quantized subband structure with strain-induced anisotropic valley configuration. The appearance of the mobility humps closely resembles those in E-type SOS MOS devices.

Cross-sectional electron microscopy of silicon on sapphire

Cross sections of (100)Si/(012)sapphire were examined by transmission electron microscopy. The foil plane was (011)Si and contained the [1̄00]Si growth direction. The number of faults (i.e., microtwins and isolated stacking faults) per cm measured in the [022]Si direction, FD, decreases with increasing distance d from the silicon/substrate growth interface according to the equations FD= (3.1×107)/d0.63 (440⩽d⩽2400 Å), and FD= (1.3×1011)/d1.7 (2400?d?4.3×104 Å). Misfit dislocations were not observed, and no evidence for the presence of an Al-bearing phase was seen in the proximity of the interface.

Anisotropy in electrical properties of {001} Si/{011̄2} Al2O3

A detailed investigation of the Hall mobility has been carried out on a series of [inverted lazy s]2-μ-thick n-type {001} Si/{011̄2} Al2O3 films. A specially designed Hall bridge pattern has been used to obtain independent measurements of mobility as a function of current direction in the plane of the film. The data show an anisotropy in the mobility of approximately 9%, with a maximum in mobility occuring along the 〈100〉 Si direction that is parallel to the 〈21̄1̄0〉 Al2O3 direction in the plane of the substrate. This behavior is found to be a consequence, through the piezoresistance effect, of the anisotropic thermal contraction of Al2O3 on cooling from the deposition temperature, which leads to an anisotropic thermally induced stress in the Si.

Temperature and Energy Dependence of Proton Dechanneling in Silicon

The dechanneled fractions of protons impinging along the $〈111〉$ and $〈110〉$ axial directions of Si have been measured for ion energies between 0.3 and 1.5 MeV and for target temperatures ranging between 80 and 423 \ifmmode^\circ\else\textdegree\fi{}K. The dechanneled fraction is a linear function of the penetration depth $z$. Its dependence on beam energy $E$ and the target temperature $T$ can be described simply through the parameter $\frac{z{\ensuremath{\rho}}^{2}}{E}$, ${\ensuremath{\rho}}^{2}$ being the mean-square vibrational amplitude normal to the row. All the experimental points follow a unique linear trend if plotted vs $\frac{z{\ensuremath{\rho}}^{2}}{E}$. The dechanneled fraction for the $〈110〉$ axis is a factor of 2 lower than that for the $〈111〉$. A theoretical model has been developed to describe the dechanneling in terms of a steady increase in the transverse energy, accounting for both electronic and nuclear reduced multiple scattering. The initial transverse-energy distribution of the particle just beneath the crystal surface has been computed including the experimental angular spread, and both scatterings produced by the amorphous layers covering the surface and by the atomic string potential. The limiting transverse energy for the channeled-to-random transition has been taken from the experimental ${\ensuremath{\psi}}_{\frac{1}{2}}(T)$ values. The computed dechanneled fractions agree reasonably well with the experimental ones and justify their temperature and energy dependence. The calculated fractions differ from the experimental ones in their having an upward curvature; the significance of this disagreement is briefly discussed together with the approximations involved.