xGex Single Crystals Research Articles

Behavior of Phosphorus Donors in Bulk Single-Crystal Monoisotopic 28Si1 – x72Gex Alloys

The behavior of phosphorus donors in bulk single-crystal monoisotopic Si1 – xGex alloys (x = 0.0039–0.05) enriched by zero-spin isotopes 28Si (99.998%) and 72Ge (99.984%) by the electron-spin-resonance method is investigated. The hyperfine structure of the donor-electron spectrum giving information on the density of the donor wave function in the ground state on the 31P nucleus (I = 1/2) as well as the temperature dependences of the spin-relaxation rate (T = 3.5–30 K), which make it possible to analyze the longitudinal component T1 relaxation mechanism and magnitude of the valley–orbit splitting of the donor state, are investigated. Interest in these investigations is also caused by the fact that the Si1 – xGex alloy enriched by zero-spin isotopes (28SiisoGe, iso = 70, 72, 74, 76) is a poorly known material when compared with 28Si. The irregular arrangement of germanium atoms in the lattice of the SiGe solid solution and local distortions formed by it can level isotopic effects under isotopic enrichment. However, despite broadening of the lines of the electron-spin resonance of donor electrons due to random deformations formed by dissolved germanium atoms in silicon, narrower lines of the spectra of the electron-spin resonance are observed in isotopically pure Si1 – xGex single crystals at x = 0.39, 1.2, 2.9 at % when compared with similar crystals with the natural composition of silicon and germanium isotopes.

Automated Growth of Si1−xGex Single Crystals with Constant Axial Gradient by Czochralski Technique

AbstractThis contribution presents the growth of Si1−xGex crystals with constant gradient of composition for X‐ray or γ‐ray diffraction optics using automated control of the crystal shape during the growth process. The key idea is to achieve a constant concentration gradient by continuously decreasing the crystal diameter during the main crystal growth phase. For this purpose a concept has been developed for a proper planning of the radius trajectory matching all technological requirements. Si1−xGex single crystals with constant gradients between 0.10 and 0.16 at% cm−1 have been grown using an automated control system.

Si1−xGex (x≥0.2) crystal growth in the absence of a crucible

In this work we made a first attempt to grow Si1−xGex single crystals by the so called modified float zone technique [1], without contact of container walls, using a modified AHP (axial heat flux close to the phase interface) heater. This method was derived from the “modified Bridgman” technique using a submerged heater [2]. Some advantages of this method are the improvement in crystal quality [3,4], the reduction of the radial temperature gradient and with it the reduced radial segregation during the growth experiment. For comparison another Si1−xGex crystal was grown by the conventional float zone method, using a residual spark plasma sintered feed rod from the initially described growth experiment. Spark plasma sintering is a synthesis and consolidation technique using a pulsed current and an axial pressure to activate the sintering process [5]. Both samples were characterized by EDX, ICM, Raman and Photoluminescence spectroscopy for the purpose of analyzing the crystal quality. The use of spark plasma sintered raw material as feed material was investigated.

Si_{1-x}Ge_{x} Single Crystals Grown by the Czochralski Method: Defects and Electrical Properties

Si1−xGex Single Crystals Grown by the Czochralski Method: Defects and Electrical Properties T.S. Argunova, J.H. Jeb,∗, L.S. Kostina, A.V. Rozhkov and I.V. Grekhov Io e Physical-Technical Institute, RAS, Polytekhnicheskaya st. 26, 194021 St. Petersburg, Russia X-ray Imaging Center, Department of Materials Science and Engineering, Pohang University of Science and Technology, San 31 Hyoja-dong, Namku, 790-784 Pohang, Republic of Korea

X-ray imaging of structural defects in Si1−x Ge x single crystals using a white synchrotron beam

Nonmonochromatic (white) synchrotron radiation with a high spatial coherence makes it possible to use different types of interaction of X-rays with matter simultaneously: diffraction, refraction, absorption, and fluorescence. In this case, the structure of materials is studied by the real-time recording of high-resolution images of different types under the same conditions. The use of X-ray images for studying the structural quality is demonstrated by the example of Czochralski-grown Si1 −xGex single crystals. The effect that the germanium content has on the formation and evolution of the defect structure is analyzed and the relationship between the structure and properties is investigated. The experiments were performed on the Pohang Light Source (Pohang, Republic of Korea).

Growth and properties of single crystals of Si1 − x Ge x (0 < x < 0.35) solid solutions

Single-crystalline Si1 − xGex ingots with a germanium content of up to 35 at. %, a diameter of 10mm, and a length of up to 10 cm were grown using the crucibleless float-zone melting technique. The ingots had a homogeneous distribution of germanium and a low density of dislocations. The material was characterized with respect to the structure and electrical properties. The resistivity and the carrier lifetime, mobility, and concentration in Si1 − xGex single crystals have been studied as functions of the germanium content.

Investigation of dislocations in Czochralski grown Si1−xGex single crystals

Dislocations in p-type Si1−xGex single crystals (2–8 at% Ge) grown with the Czochralski technique are investigated by synchrotron white beam topography in transmission geometry. As the Ge concentration increases, the dislocation structure evolves from individual dislocations to slip bands and sub-grain boundaries, and the dislocation density increases from <102 cm−2 to 105–106 cm−2 at 8 at%. We discuss the effect of dislocations on the electrical characteristics such as resistivity ρv, Hall hole mobility μp, carrier lifetime τe and I–V characteristics. Here τe and I–V characteristics are measured from the diodes fabricated by bonding the p-Si1−xGex to n-Si wafers. I–V characteristics are not deteriorated in spite of a five times decrease in τe with the Ge concentration.

Magnetoelastic coupling in Fe100−xGex single crystals with 4&amp;lt;x&amp;lt;18

In this paper we examine the elastic (c′ and c44) and magnetostrictive (λ100 and λ111) behaviors of Fe100−xGex for 4&amp;lt;x&amp;lt;18, quantities used further to find the fundamental magnetoelastic coupling constants b1 and b2 at room temperature. The x dependence of b1 and b2 for Fe100−xGex is contrasted to those of Fe100−xGax and Fe100−xAlx. While the rhombohedral shear elastic constant c44 is almost insensitive to the type and amount of solute, the tetragonal shear constant c′ shows a pronounced and rapid softening with increasing x for all three alloys but with different decreasing slopes. Similarly, while the rhombohedral magnetostriction λ111 behavior is analogous for all three alloy systems, showing a sign change from negative to positive at the onset of chemical order, the tetragonal magnetostriction λ100 behavior differs. For the Ga and Al alloys, λ100 maintains positive values over the entire x range, both curves showing large peak values, whereas λ100 of Fe100−xGex exhibits a moderate positive peak followed by a negative dip, both of comparable magnitude. Finally the tetragonal coupling constant −b1 of Fe–Ge shows a marked, sharp decrease as chemical order occurs at x∼12 at. % Ge. The decline continues until the ordered D03 phase is fully established at x∼18 at. % Ge. The peak value of |b1| for Fe–Ge is approximately half of those for Fe–Ga and Fe–Al. This smaller value of |b1|, obtained for the higher electron concentration Ge alloy, is consistent with predictions based on band structure calculations. The rhombohedral coupling constant −b2 shows a consistent sign change at the occurrence of chemical ordering in both Fe–Ga and Fe–Ge.

Magnetostriction of iron-germanium single crystals

The addition of nonmagnetic Ga into body-centered cubic Fe enhances the magnetostriction constant λ100 over tenfold. Literature reports for substitution of Ge at low concentrations suggest that the addition of Ge also enhances the magnetostriction. In this work, the magnetostriction and microstructure of Fe–Ge were investigated to correlate magnetostriction with microstructure. The magnetostriction of Fe100−xGex single crystals with x between 0.05 and 0.18 varies with Ge concentration and correlates with phase changes. The value of (3∕2)λ100 increases with Ge additions in the A2 single phase region (up to x∼10), reaching a maximum of 94ppm at the solubility limit of the disordered A2 phase. Further increases in Ge in the A2+D03 two-phase region (12&amp;lt;x&amp;lt;16) result in a decrease in magnetostriction which changes from positive to negative. For Ge contents with x&amp;gt;16, magnetostriction remains negative with an absolute value of strain of 129ppm at 18at.% Ge. This behavior is similar to that observed for Fe–Si alloys.

Origin of an absorption band peaked at 5560 cm−1 and related to divacancies in Si1−x Gex

It is found that two types of centers are formed in Si1−xGex single crystals as a result of irradiation with fast electrons: divacancies (V2) characteristic of silicon and the V2* centers; the latter are complexes of divacancies V2 with germanium atoms (V2Ge). It is shown that an absorption band peaked at about 5560 cm−1 is a superposition of two absorption bands that correspond to the above centers. The V2 divacancies diffuse during isochronous heat treatment and interact with germanium atoms, thus giving rise to additional V2* centers. The latter have a higher thermal stability than the V2 centers do, and their annealing temperature increases with increasing content of germanium.

Single crystal growth of Si1 − xGex by the Czochralski technique

(111)- and (100)-Si1 − xGex single crystals (0 < x < 0.1) with diameters of up to 48 mm were grown by Czochralski technique using a crystal puller with resistance heating. An automated control system based on crystal weighing has been developed. Software provides feedback control as well as the program changes of some process parameters to optimize crystal growth conditions. Ge distribution and crystal quality were investigated by infrared transmission measurements at the absorption edge and X-ray Lang topography, respectively.

No-Phonon and Phonon-Assisted Indirect Transitions in Si1−xGex Single Crystals

ABSTRACTThe absorption properties of high quality bulk Si1−xGex single crystals (0 ≤ × ≤ 0.16) are studied. Transmission measurements were performed at the indirect absorption edge. The shape of the absorption edge is characterized by structures attributed to the onset of no-phonon and phonon-assisted indirect optical transitions. Threshold energies have been determined using a differential method. A corrected calibration function for the dependence of the excitonic energy gap on composition is presented for the compositions, where x ranges from 0 to 0.16. The presented calibration function can be used for the composition analysis by an optical method. The analysis is independent of absolute transmission values.A simulation of the absorption spectra by calculations based on second order perturbation theory was used to fit the experimental data This procedure allows to estimate the oscillator strength of the no-phonon transition in dependence on x.