Influence Of Uniaxial Stress Research Articles

Uniaxial-stress-induced alignment of the B804 (J-lines) centres in silicon

The influence of uniaxial stress on the formation process of the trigonal B 80 4 centres in silicon was investigated with excitonic spectroscopy. Alignment along the [1 1 1] axis of about 70% of the centres has been obtained with application of uniaxial stress during defect formation.

Reexamination of Influence of Uniaxial Stress on the Morphology of COherent Precipitates

Reexamination of Influence of Uniaxial Stress on the Morphology of COherent Precipitates

Specific heat under uniaxial stress

An experimental approach for the adaptation of conventional calorimetric techniques for measurements under uniaxial stress is reviewed. Special attention is focused on the description of the use of the a.c. method for measuring specific heat under uniaxial stress. The application of isoperibolic calorimetry to specific heat measurements under uniaxial stress is described in detail. The method has been tested at low stress by studying the influence of uniaxial stress on the change of dimensionality of the order parameter of strontium titanate. Measurements of the specific heat and heat power exchanged by a deuterated dihydrogen potassium phosphate sample at the ferroelectric–ferroelastic phase transition are also included. These measurements show the advantages of this method for the study of first-order transitions under uniaxial stress.

The influence of uniaxial stress on ultrasonic wave propagation in ferroelastic (NH 4) 4LiH 3(SO 4) 4

The influence of uniaxial stress σ 2 on the temperature dependence of velocity and attenuation of the longitudinal ultrasonic wave propagating along the [0 0 1] direction of a ferroelastic ALHS was investigated. A distinct step-like change in velocity was observed at T c for σ 2 = 0. This anomaly was found to decrease with increasing stress. Simultaneously, an anomalous increase of attenuation coefficient was observed when the stress applied was higher than coercive stress. This fact was attributed to the local inhomogeneous deformations which are the remains of ferroelastic domain walls.

Germanium lasers in the range from far-infra red to millimetre waves

Recent experimental and theoretical achievements are reviewed on three types of laser oscillation inp-type germanium; the intervalence band (IVB) laser oscillation due to transitions between the light-hole band and the heavy-hole band, the light-hole cyclotron resonance (LHCR) laser oscillation, and the heavy hole cyclotron resonance (HHCR) maser oscillation. Described for the IVB oscillation are fundamental characteristics (such as the wavelength range of oscillation and the cooperation with higherharmonic cyclotron resonances), the polarization characteristics of radiation and influence of uniaxial stress on the oscillation. The present status of the attempt at single line oscillation is also described. As for the LHCR oscillation, the formation of population inversion and the amplification are explained on the basis of quantum mechanical calculations of the valence bands in crossed electric and magnetic fields.

Jahn-teller effect and zero-phonon line isotope shifts of transition metals in II–VI compounds

Highly resolved spectra of transition metal ions in II–VI compounds show extremely narrow zero-phonon lines to that isotope effects can be observed. An adequate description of the observed fine structures requires the inclusion of an intermediate Jahn-Teller effect using local vibrational T 2 modes. The observation of different isotope splittings at Ni impurities in CdS leads to the assumption that different local vibrational modes are coupled to the electronic states of that system and that the local vibrational modes have different dependencies on the mass of the impurity. The calculated energy shifts are in agreement with the observed isotope shifts of natural and enriched Ni and Cu doped II–VI compounds. The influence of uniaxial stress, magnetic field and temperature on the isotope shifts is also investigated.

Influence of uniaxial stress on hole effective masses in quantum wells

The hole effective masses in quantum wells under uniaxial stress are investigated. The valence subband structures are determined from a 4 × 4 Luttinger–Kohn Hamiltonian together with a 4 × 4 strain Hamiltonian with appropriate boundary conditions. The variations of the hole effective masses with well width, stress, and potential-barrier height (or the corresponding alloy composition) are discussed and found to be drastic. For example, even if the quantum well is stress free, the variations of the hole effective masses with well width can range from +∞ to −∞ and are not constant, as predicted by the infinite potential-well model. The variations with stress indicate that the effective masses can become zero, depending on the direction and the magnitude of the stress.

Far-infrared photoconductivity of uniaxially stressed germanium

The influence of uniaxial stress on the extrinsic photoconductivity of gallium-doped germanium has been investigated. It has been found that the long-wavelength cutoff is shifted from 114 μm for zero stress to 200 μm for a uniaxial stress of 6.6×103 kg/cm2 along a [100] direction. At this value of stress the responsivity was ∼2×104 V/W and the NEP was ∼2×10−11 W/Hz1/2 at 190 μm.

Acceptor ground states in nearly cubic semiconductors

AbstractThe splitting of acceptor ground states and their energy shift under the influence of uniaxial stress or noncubic crystal fields are calculated on the basis of a spherical or cubic valence band structure with large spin‐orbit splitting. The knowledge of the band parameters and the perturbation induced valence band splitting is sufficient to estimate the energies of the ground and first excited acceptor states. The experimental determination of the deformation potentials of three shallow acceptors in GaAs as well as the quadratic dependence of the acceptor ground states on the uniaxial stress provide a direct check of the calculations.

Influence of uniaxial stress and electron—electron scattering on the phenomenological conductivity relaxation time in n‐type germanium

AbstractThe dependence of the phenomenological conductivity relaxation time τσ on the compressive uniaxial stress F applied in 〈111〉 direction is investigated in n‐type Ge. The measurements at 80 K are made for two groups of samples with free carrier concentrations of 5 × 1012 cm−3 and 2.4 × 1014 cm−3. At intermediate stresses (0 to 5 kbar) a nonmonotonous dependence of τσ on F is observed. It is shown that this effect is mainly caused by the influence of stress on the inertia of the electric field‐induced electron redistribution process. At stresses F > 5 kbar τσ asymptotically approaches a saturation value which increases with electron concentration. The qualitative analysis of these data leads to the conclusion that the coupling constants for the electron scattering by the electrons of the same and of the other valleys are of the same order.

Influence of uniaxial stress on quantum effects in Si inversion layers

We show that the application of a compressional stress to the Si substrate decreases the mobility of electrons in the lowest subband and causes piezoresistance. This effect, together with the electron transfer effect and the existence of localized band-tail states in the subbands at low electron densities, account for the piezoresistance in n-channel (100)Si inversion layer at 4.2 K.

Stress Dependence of the (El, El + Δ1), Transition in Germanium

AbstractThe influence of uniaxial stress on the optical δE1, E1 + Δ1), transition of Ge is reinvestigated theoretically and experimentally. Existing theoretical approaches are extended by explicitly considering the stress dependence of spin‐orbit interaction. For comparison of the results obtained the stress dependence of the (E1, E1, + Δ1), structure is measured by means of electroreflection, where special care is given to the potential stability at the electrolytesemiconductor interface. It can be shown that the combined influence of stress‐induced valence band coupling and modification of the spin‐orbit splitting allows to explain the measured stress dependences.

Influence of uniaxial stress on the morphology of coherent precipitates during coarsening—elastic energy considerations

The theory of inclusions and inhomogeneities by Eshelby is applied to predict the influence of uniaxial applied stress on the morphology of coherent precipitates during coarsening. The case where the misfit between the matrix and the precipitates is a pure dilatation is considered. The elastic energy is calculated as a function of the particle shape, the applied stress and the ratio between the Young's modulus of the precipitates and that of the matrix. Three shapes are considered: spheres, plates perpendicular to the stress axis and needles aligned with the stress axis. The calculations are used to construct a map which gives the conditions leading to the lowest elastic energy. The results are compared with observations in Ni base alloys which have shown that a stress applied during coarsening can alter the shape of γ particles.

Influence of Uniaxial Stress on the Phenomenological Energy Relaxation Time in n‐Type Silicon

Influence of Uniaxial Stress on the Phenomenological Energy Relaxation Time in n‐Type Silicon

Influence of strain on the galvanomagnetic effect in magnetic thin films

A study of the influence of uniaxial stresses on the planar galvanomagnetic effect in thin Ni-Fe-Mo films evaporated in vacuum has been performed. Galvanomagnetic voltage was measured at different value of stress and applied field, rotated in the plane of the sample. Magnetoelastic hysteresis depending on the applied field was found.

The influence of uniaxial stress on the infrared free carrier faraday effect in n-type silicon and germanium

The dependence of the infrared free carrier faraday rotation in multivalley semiconductors on valley energy splitting under uniaxial stress is investigated both theoretically and experimentally for a configuration in which the magnetic induction, radiation propagation and uniaxial stress are all parallel, to avoid birefringence. Theoretical expressions are obtained for cases relevant to the conduction bands of silicon and germanium with the uniaxial stress in the direction of one of the valleys, that is (100) and (111) strains respectively. It is shown that measurement of the influence of uniaxial stress on the infrared free carrier faraday effect allows both the longitudinal and transverse effective masses to be determined.

Infrared Modulation and Energy Band Parameters in Multivalley Semiconductors through Uniaxial Stress Dependence of Free Carrier Contribution to Optical Constants

AbstractThe influence of uniaxial stress in 〈111〉 direction on the free carrier contribution to the optical constants of multivalley semiconductors is considered according to the electron transfer model. Calculations are made of the resulting change in absorption and shift of the wavelength for minimum reflection. It is shown that these effects may be large and experimental observation of them provides a method of determining the effective mass and relaxation time parameters and their anisotropies. The possibility of constructing infrared modulators based on these phenomena is also examined.

Das Emissionsspektrum gebundener Excitonen in Zinkoxydkristallen in Abhängigkeit von Temperatur und uniaxialer Verspannung

The recombination radiation of bound excitons in ZnO-crystals (spectral range 3,38–3,35 eV at 4.2 °K) and the adjacent phonon-assisted spectrum have been studied at temperatures between 4.2 °K and 90 °K. The phonon-assisted spectrum changes its structure at about 30 °K. With increasing temperature the exciton lines shift toward smaller quantum energies (ΔE∼T2) and their half widthH increases (H∼T2). The line shift is explained by a band gap variation due to deformation potential coupling of the holes toTA phonons. The line width is explained by broadening of an infinitely sharp line under the influence of the mean square fluctuation of thermally generated crystal deformations. The influence of uniaxial stress on the spectral positions of the lines has been studied.

The influence of uniaxial stress on the infrared free carrier Faraday rotation in n-type germanium

Measurements have been made of the effect of <111 > uniaxial stress on the infrared Faraday rotation in germanium. To avoid birefringence, an experimental configuration has been used in which the stress, magnetic field and radiation propagation are all parallel. A simple theory of the stress dependence of the free carrier contribution to the rotation is presented showing the feasibility of obtaining effective masses and their anisotropy from such experiments.

Influence of Uniaxial Stress on the Indirect Absorption Edge in Silicon and Germanium

The indirect optical absorption edge in silicon and germanium has been studied in the presence of shear strain. The splitting observed in the transmission spectrum is dependent on the direction and magnitude of the applied stress and on the polarization of the light with respect to the stress axis. The results have been interpreted in terms of changes in the valence- and conduction-band structure with strain. Neglecting strain dependence of phonon energies, various deformation potential constants have been determined from the experiments. The values are: Si, 80\ifmmode^\circ\else\textdegree\fi{}K: ${\ensuremath{\Xi}}_{u}=8.6\ifmmode\pm\else\textpm\fi{}0.2$ eV, $|b|=2.4\ifmmode\pm\else\textpm\fi{}0.2$ eV, $|d|=5.3\ifmmode\pm\else\textpm\fi{}0.4$ eV, ${\ensuremath{\Xi}}_{d}+\frac{1}{3}{\ensuremath{\Xi}}_{u}\ensuremath{-}a=3.8\ifmmode\pm\else\textpm\fi{}0.5$ eV. Si, 295\ifmmode^\circ\else\textdegree\fi{}K: ${\ensuremath{\Xi}}_{u}=9.2\ifmmode\pm\else\textpm\fi{}0.3$ eV, $|b|=2.2\ifmmode\pm\else\textpm\fi{}0.3$ eV, ${\ensuremath{\Xi}}_{d}+\frac{1}{3}{\ensuremath{\Xi}}_{u}\ensuremath{-}a=3.1\ifmmode\pm\else\textpm\fi{}0.5$ eV. Ge, 80\ifmmode^\circ\else\textdegree\fi{}K: ${\ensuremath{\Xi}}_{u}=16.2\ifmmode\pm\else\textpm\fi{}0.4$ eV, $b=\ensuremath{-}1.8\ifmmode\pm\else\textpm\fi{}0.3$ eV, $d=\ensuremath{-}3.7\ifmmode\pm\else\textpm\fi{}0.4$ eV, ${\ensuremath{\Xi}}_{d}+\frac{1}{3}{\ensuremath{\Xi}}_{u}\ensuremath{-}a=\ensuremath{-}2.0\ifmmode\pm\else\textpm\fi{}0.5$ eV. An observed nonlinear dependence of the splitting on stress has been interpreted as shifts of the exciton energies with uniaxial stress. A special experimental technique using a vibrating slit in the spectrometer was used in order to obtain an accurate determination of the fine structure in the absorption spectrum.