Papers by Keyword: Strain Relaxation

Abstract: Self-diffusion in thin nanocrystalline Pt films was investigated using secondary ion mass spectrometry. Our experiments are motivated by recent investigations on stress relaxation where self-diffusion of Pt is supposed to play an important role, especially at temperatures below 250 °C and annealing times of a few hours. For the diffusion experiments, double layers of ^natPt/¹⁹⁴Pt were deposited on oxidized silicon wafers using ion beam sputtering. At 180 °C no significant diffusion induced broadening of the profiles could be observed even after an annealing time of 64 h. However, the concentration of ¹⁹⁵Pt in the top layer decreases slightly after an annealing time of 16 h and remains constant for higher annealing times. At 600 °C a broadening of the profiles was observed after an annealing time of 5 minutes. From our results we conclude that at 180 °C only atoms in the grain boundaries are mobile. After about 16 h the isotopes in the grain boundaries are completely interdiffused. From the change of the ¹⁹⁵Pt concentration in the top layer we estimate the amount of grain boundary phase in the Pt films to be about 5 %. The broadening of the profile after annealing at 600 °C is attributed to bulk diffusion.

Abstract: La_0.7Sr_0.3MnO₃(LSMO) films 35-350nm thick have been grown on (001)LaAlO₃ (LAO) substrates. The strain state evolution was examined fully by x-ray reciprocal space maps, in order to clarify its impact on the thickness-dependent properties of the films. It was found that LSMO epitaxial films have properties which is from partially strained to fully relaxed with film thickness increasing on the same substrate. Resistivity measurement shows that the relaxed film has higher resistivity than that of the strained film, because the relaxed film contains the high deficiency density. In this paper, however, the relaxed property of the same thickness LSMO epitaxial film grown on the different substrates is also discussed.

Abstract: This paper analyzes sensitivity, linearity, repeatability, strain relaxation of Carbon-coated Filaments (CCFS) in resistance tensile strain to evaluate CCFS’s sensing property. The results show that the relative resistance changes present two stages, change is stable in 0-6mm tensile range, while it amplitude increases in 6-15mm. CCFS’s linearity is better as number of filament increasing, while sensitivity is lower; if number is the same, CCFS sensitivity reduces as twist’s increasing. The 12F CCFS has poor repetitiveness and seriously flabby phenomenon when tensile change greatly.

Abstract: This paper presents an investigation of the impact of a Highly Doped Drain (HDD) implantation after epitaxial deposition on Si1-xGex S/D junction characteristics. While the no HDD diodes exhibit the usual scaling of the leakage current density with Perimeter to Area (P/A) ratio, this is not the case for the HDD diodes, showing a smaller perimeter current density JP for smaller window size structures, corresponding with larger P/A. This points to a lower density of surface states at the Shallow Trench Isolation (STI)/silicon interface, which could result from a lower compressive stress. In order to examine the role of the HDD implantation damage, Transmission Electron Microscopy (TEM) inspections have been undertaken, which demonstrate the presence of stacking faults in small active SiGe regions. These defects give rise to local strain relaxation and, therefore, could be at the origin of the lower STI/Si interface state density. The window size effect then comes from the active area dependence of the implantation defect formation.

Abstract: We have grown delta-doped In0.5Ga0.5As /In0.5Al0.5As heterostructures on GaAs substrate applying with InxAl1-xAs compositional graded-step buffers, called metamorphic structures, grown by molecular beam epitaxy. Three types of buffer layers with different compositional gradients and thicknesses have designed to investigate the influence of the strain relaxation process. We characterized the samples by using transmission electron microscopy, triple-axis X-ray diffraction and Hall measurement. Two samples with different compositional gradient show almost same results in electrical properties. On the other hand, it is found that samples with different step thicknesses had shown the large differences in epilayer tilt and mosaic spread in the step-graded buffers. These results indicate that there exists an interrelation between the strain-relaxed buffer and 2DEG transport properties.

Abstract: Strain relaxation in the GaN/AlN/6H-SiC epitaxial system grown by vicinal surface epitaxy (VSE) is investigated and compared with that in on-axis epitaxy. High resolution x-ray diffraction (HRXRD) measurements show that GaN films grown by VSE have improved crystalline quality. High resolution transmission electron microscope (HRTEM) studies reveal that there are two types of misfit dislocations (MDs) at AlN/6H-SiC interfaces: 60˚ complete dislocations along <1120 > directions with Burgers vector 1/3<1120 > and 60˚ Shockley partials along <10 10 > directions with Burgers vector 1/3<10 10 >. The latter are usually geometrical partial misfit dislocations (GPMDs) that are dominant in VSE to accommodate the lattice mismatch and stacking sequence mismatch simultaneously. In VSE, it is the high-density GPMDs formed at the vicinal surface steps that facilitate rapid strain relaxation at the initial stage of deposition and hence lead to superior crystalline quality of the subsequently grown GaN films.

Abstract: A wide variety of residual stress measurement methods can be used to measure the axial stress in a column. One of the most widely used techniques for measuring residual stress is slotting method since it is relatively simple and cost-effective to implement at vertical columns in field. However, the slotting method is considered to be semi-destructive or destructive method depending on the amount of material to be removed. Therefore, in this paper, optimal depth of slots for measuring actual stress is presented to minimize the amount of material to be removed. Finite element method is used to estimate the minimum depth of the slot in H-shaped steel column. By performing actual saw cutting, optimality of the simulated depth of the slot is investigated.

Abstract: Strain adjustment is obtained by virtual substrates which are composed of a silicon substrate and a strain relaxed buffer. The basics of strain relaxation are explained and applied to the covalent bonded Si/Ge system which shows a large regime of metastability. A solution to ultrathin strain relaxed buffers is given by the injection of point defects which nucleate to dislocation loops in the interface. Principle and injection mechanism are shown.

Abstract: Molecular beam epitaxy is employed for the growth of strained-Si layers on top of virtual substrates with highly-relaxed ultrathin SiGe buffers in a continuous procedure. An initial growth stage at a temperature-ramp down to below 200°C causes misfit-dislocation generation by nucleation from point defects and provides an early relaxation in the SiGe buffers. In situ monitoring is used for the growth control. Layer thicknesses and composition are proved by ex situ spectroscopic ellipsometry. %Raman investigations on the layer stacks reveal high degrees of relaxation (70-100%) in sub-100nm SiGe buffer layers containing from 12 to 42 % Ge. Stress in strained Si layers estimated by means of Raman-spectra shift is adjustable from 0.92 to 6.84 GPa by the Ge-content in virtual substrates. Surface morphology of strained Si and of relaxed SiGe buffers is smooth and crosshatch-free. Device test structures show substantial increase of carrier mobilities in nMOSFETs fabricated on these strained-Si layers.

Abstract: We have focused in this paper on the impact of the growth rate and of the grading rate on the structural properties of Si0.8Ge0.2 virtual substrates grown at 900°C in a commercial reduced pressure chemical vapour deposition reactor. Adopting a grading rate of 4% Ge / $m together with a growth rate around 140 nm min.-1 yields very high quality Si0.8Ge0.2 virtual substrates. Their macroscopic degree of strain relaxation is indeed very close to 100%, their surface root mean square roughness is around 2.3 nm and most importantly their field threading dislocation density is of the order of 6x104 cm-2 only, with almost no pile-ups.