Infrared optical constants of n-type silicon

The infrared optical constants of n-type Si are determined from reflectance and transmittance spectra. The Drude formula with empirically adjusted, concentration dependent, parameters is used. Its low-wavelength limit is in agreement with recent mobility results. A pronounced difference between As-, P-, and Sb-doped Si is found for the free electron concentration above 10¹⁹ cm^–3. Simple empirical formulae are given for the optical constants as functions of both wavenumber and concentration.     

Density of states of grain boundaries in silicon

A new spectroscopic method for the evaluation of the density of states in semiconductor grain boundaries is presented. The method is based on a measurement of the intensity and wavelength dependence of the zero-bias photo capacitance of grain boundaries under sub-bandgap illumination. Experiments are performed on p-type silicon bicrystals. Bandtails and states close to midgap are observed.     

Density of phonon states in amorphous germanium and silicon

The density of phonon states in amorphous germanium and silicon is calculated by statistically averaging the crystalline phonon density of states according to the radial distribution function. A simple rigid ion model is used to calculate the density of phonon states at various lattice spacings. The appropriate model parameters are obtained from the pressure dependent elastic constants and the Raman frequency. The calculated results compare favorably to experimental data obtained by infrared and Raman scattering and the results of other theoretical calculations.     

Density of states and charge distribution in hydrogenated amorphous silicon

The local density of states and the charge distribution in a cluster model of hydrogenated amorphous silicon is calculated using the recursion method. The results indicate an average charge transfer of 0.3 electrons from silicon to hydrogen. In addition Si-H dipoles carry small negative charges, which are neutralized by a positively charged bulk of silicon atoms. There are also static spatial charge fluctuations, which are due to the topological disorder.     

Positron annihilation in boron-implanted n-type silicon

The ion damaged effect and subsequent isothermal annealing in boron-implanted Si was studied by positron annihilation lifetime measurements. The mean positron lifetime in preimplanted n-type Si is 243 psec. The variation of mean lifetime is detectable when the implanted boron dose is greater than 1.0x10¹⁵/cm². The saturated mean positron lifetime (247 psec) occurs when the implantation dose reaches 2.5x10¹⁵/cm². The mean electron density of the positron sensitive defects is estimated to be about 85% less than that in the perfect parts of the crystal. Isothermal annealing was held in every 5-minute step at 1000°C. In the first step, the positron lifetime in the implanted sample increases slightly and then decreases completely to its initial state in the 3rd step. Sheet resistance of the sample monitored by 4-point probe method has been found closely related to the positron lifetime.     

Penetration of electronic states from silicon substrate into silicon oxide

The depth profiling of O 1s energy loss in silicon oxide near the SiO₂/Si interface was performed using extremely small probing depth. As a result, the energy loss of O 1s photoelectrons with threshold energy of 3.5 eV was found. This value of 3.5 eV is much smaller than the SiO₂ bandgap of 9.0 eV, but quite close to direct interband transition at Γ point in energy band structure of silicon. This can be explained by considering the penetration of electronic states from silicon substrate into silicon oxide up to 0.6 nm from the interface. In addition, the penetrating depth is larger than the thickness of the compositional transition layer.     

Surface states on n-type SrTiO3

We have used a model based on local density of states functions to calculate the surface electronic structure for both perfect SrTiO₃(100) surfaces and for surfaces containing O-vacancy defects. The calculations are in excellent agreement with ultraviolet photoemission spectra for both types of surfaces. A magnetic layer with μ ≈ 2.3 μ_B per surface unit cell is predicted for the O-vacancy SrTiO₃(100) surface.     

Third-order elastic constants and pressure derivatives of the second-order elastic constants of β-tin

The second- and third-order elastic constants and pressure derivatives of second-order elastic constants of tetragonal β-tin have been obtained using the deformation theory. The strain energy density derived using the deformation theory is compared with the strain dependent lattice energy obtained from the elastic continuum model approximation to get the expressions for the second- and third-order elastic constants. Higher order elastic constants are a measure of the anharmonicity of a crystal lattice. The 12 non-vanishing third-order elastic constants and the six pressure derivatives of the second-order elastic constants in tetragonal β-tin are obtained in the present work and are compared with the available experimental values. The second-order elastic constant C₃₃ obtained in the present study is in reasonable agreement with the experimental values. The third-order elastic constants are generally one order of magnitude greater than the second-order elastic constants as expected of a crystalline solid. The third-order elastic constant C₃₃₃ is higher in magnitude than all other values. This shows a greater anharmonicity of β-tin along the c-axis direction of the crystal.     

Zero-field elastic constants of uvite

The theories of Kyame [1] and Koga et al. [2] on stress wave propagation in piezoelectric media are critically studied and compared with each other. Solutions of the modified Christoffel's equations predicted by each theory for piezoelectric crystals in class 3m are derived. The velocities of ultrasonic waves propagated through a gem quality uvite specimen in particular directions were measured at 293 K using the pulse-echo overlap method. All of the independent zero-field elastic moduli were calculated from the measured wave velocities and compared with the available data in the literature. The values of the elastic constants in 10¹²$\text{dyn}\text{cm}{}^2$ were found to be C₁₁ = 3.016 ± 0.2% C₆₆ = 1.028 ± 0.3% C₃₃ = 1.698 ± 0.2% C₁₃ = 0.47 ± 3% C₄₄ = 0.655 ± 0.3% c₁₄ = ?0.089 ± 6%. The calculated bulk modulus, shear modulus and Poisson's ratio, using the Voigt-Reuss-Hill (VRH) approximation, are K_H = 1.226 × 10¹²$\text{dyn}\text{cm}{}^2$, G_H = 0.826 × 10¹²$\text{dyn}\text{cm}{}^2$ and σ_H = 0.224. The Debye temperature is 764 K.     

Resonant four wave mixing in n-type silicon

We observe a strong resonance in the third order nonlinear optical susceptibility of n-type silicon corresponding to the valley orbit splitting of the 1s-states of phoshorous and antimony donors. Cross-sections for valley orbit Raman scattering near 10 μm obtained from our data agree with calculations based on an intraband model. The expression for the cross-section resulting from this model is equivalent to that of Jain et al.     

A DLTS study of the effects of boron counterdoping on the gap states in n-type hydrogenated amorphous silicon

The technique of Deep Level Transient Spectroscopy (DLTS) and related space charge measurement techniques have been applied to a series of 300 vppm phosphine (PH₃) doped, 0–44 vppm diborane (B₂H₆) counterdoped samples of hydrogenated amorphous silicon (a-Si:H). The trends in the resulting density of states, g(E), show: (1) A large increase of g(E) at ≈0.4 to 0.6 eV from the valence band, comparable in magnitude to the total number of B atoms introduced; (2) A smaller decrease in the midgap dangling bond states on the order of ≈2.5% of the added B; (3) A drop in the number of occupied shallow states ≈0.5%; and (4) A quantitative assessment of the degree of autocompensation which shows roughly five compensating midgap states removed for every six shallow acceptor states introduced by B.     

SERS-active substrates based on n-type porous silicon

Porous silicon (PS) prepared from n-type Si crystal is proposed as a new material for the fabrication of sensitive substrates for surface-enhanced Raman scattering (SERS). The formation procedure for nanostructured silver films on the surface of PS was optimized. Maximum of SERS enhancement for rhodamine 6G probing molecule is observed for samples obtained by the immersion plating from the water solution of AgNO₃ with the 10 mM concentration during 5 min. The dependence of morphological parameters of PS and corresponding silvered surfaces on the anodization current density has been studied. It is shown that the most SERS activities possess substrates produced from PS with lower porosity. The optimum of the PS layer thickness for high Raman signal is about 5 μm. The detection limit for rhodamine 6G adsorbed on Ag-coated PS from the 100 pM solution is established to be comparable with that for p-type PS-based substrates. Thus, the n-type porous silicon is suitable material for the preparation of sensitive SERS-active substrates.     

Density of states effective mass of n-type CuInSe2 from the temperature dependence of Hall coefficient in the activation regime

The Hall coefficient R_H of n-type CuInSe₂ single crystals is measured between 10 and 300 K in pulsed magnetic field up to 35 T. The threshold field B_th, above which the magnetic freezeout starts to occur, varies linearly with temperature. From the analysis of the temperature dependence of electron concentration in the activation regime above 100 K at different field values, it is established that the density of states effective mass is independent of the magnetic field B and the activation energy E_D, above around 6 T, varies as B^1/3. Similar B^1/3 dependence of the magnetoresistance in the high magnetic field regime, reported earlier in the same material, suggests that theoretical work that could explain this coincidence is needed.     

Electrodynamics of a Coulomb glass in n-type silicon

Measurements of the complex frequency dependent conductivity of uncompensated n-type silicon are reported. The experiments are done in the quantum limit, variant Planck's over 2pi omega>k(B)T, across a broad doping range on the insulating side of the metal-insulator transition. The low energy linear frequency dependence is consistent with theories of a Coulomb glass, but discrepancies exist in the relative magnitudes of the complex components. At higher energies we observe a crossover to a quadratic frequency dependence that is sharper than expected. The concentration dependence gives evidence that the Coulomb interaction energy is the energy scale that determines this crossover.