Presence Of Compressive Strain Research Articles

Low-Frequency Noise Characterization of Strained Germanium pMOSFETs

Low-frequency noise in strained Ge epitaxial layers, which are grown on a reverse-graded relaxed SiGe buffer layer, has been evaluated for different front-end processing conditions. It has been shown that the 1/f noise in strong inversion is governed by trapping in the gate oxide (number fluctuations) and not affected by the presence of compressive strain in the channel. However, some impact has been found from the type of halo implantation used, whereby the lowest noise spectral density and the highest hole mobility are obtained by replacing the standard As halo by P implantation. At the same time, omitting the junction anneal results in poor device characteristics, which can be understood by considering the presence of a high density of nonannealed implantation damage in the channel and the gate stack near the source and the drain.

Optical study of hydrogen-irradiated GaAsN/GaAs heterostructures

The effect of hydrogen irradiation on the optical properties of GaAs1−xNx/GaAs heterostructures was investigated using photoreflectance and reflectance techniques. Systematic measurements performed on both as-grown and hydrogenated samples for N-concentrations ranging from 0.0% to 3.5% and for H-implanted doses from 3 × 1018 to 6 × 1018 ions/cm2 have shown that (a) the H-induced widening of the energy gap is accompanied by a decrease of the refractive index of the H-treated samples with respect to the as-grown ones, resulting in an index mismatch that can be as large as 2% in the subgap spectral region; and (b) the presence of compressive strain in fully passivated GaAsN determines a decrease of the refractive index even below that of GaAs that can be eliminated via moderate thermal annealing. These findings are promising for the development of heterostructures with planar geometry, in which the simultaneous confinement of both carriers and photons, even on a nanometric scale, can be obtained in a single step process.

Structural, optical and charge transport study of rutile TiO 2 nanocrystals at two calcination temperatures

In this study the influence of two different calcination temperatures 80 °C and 450 °C on the structural, optical and charge transport properties of rutile TiO 2 nanocrystals has been investigated. TiO 2 nanocrystals have been prepared at low temperature by a simple hydrolysis method using titanium tetrachloride as starting precursor. The results of X-ray diffraction (XRD) showed that the prepared nanocrystals have a rutile tetragonal crystalline structure. Specific surface area of 80 °C and 450 °C calcinated rutile TiO 2 nanocrystals are 25.38 × 10 5 cm 2/g and 7.61 × 10 5 cm 2/g respectively, which has been calculated by X-ray diffraction data. Williamson–Hall plot results indicate the presence of compressive strain at 80 °C and tensile strain at 450 °C. Ultraviolet–visible (UV–vis) absorption spectroscopy is used to calculate the band gap of the material and the shift in absorption edge and it has been observed that the absorption spectra are strongly modified by the calcination temperature. The red-shift in photoluminescence (PL) is attributed to the change in strain from compressive to tensile. Photoconductivity (PC) measurements showed that capture cross-section of 80 °C (R1) and 450 °C (R2) calcinated rutile nanocrystals are 55.10 × 10 −10 and 39.50 × 10 −10 cm 2 respectively. High value of electron life-time, low value of radiative recombination and a four order increase in photogenerated charge carriers have been reported for the rutile TiO 2 nanocrystals calcinated at 450 °C.

Source Engineering for Tunnel Field-Effect Transistor: Elevated Source with Vertical Silicon–Germanium/Germanium Heterostructure

In this work, we demonstrate by simulation and experiment that the performance of a p+ Si0.5Ge0.5 source tunnel field-effect transistor (TFET) can be improved by inserting an undoped Ge layer between source and channel. The Ge layer suppresses diffusion of boron into the Si channel and it also forms a Si0.5Ge0.5/Ge/Si hole quantum well, leading to an abrupt boron profile and a high hole concentration at the source edge. At the Ge/Si heterojunction, the presence of compressive strain in the Ge layer increases the valence band offset, while the tensile strain in the Si channel increases the conduction band offset, which effectively reduces the tunnel barrier and enhances the tunnel probability. Compared with a control device without the Ge layer, TFETs with a Si0.5Ge0.5/Ge source show a higher on-state current ION and improved threshold voltage VTH and subthreshold characteristics.

A study of ruthenium ultrathin film nucleation on pretreated SiO2 and Hf–silicate dielectric surfaces

This study explored the effects of substrate surface pretreatments on the nucleation and growth of metal–organic chemical vapor deposited ruthenium. In situ plasma (dry), featuring O2, Ar, and H2/Ar chemistries, and ex situ (wet) treatments, consisting of a standard RCA bath, were examined in the nucleation and growth of up to 50-nm-thick metallic Ru films on SiO2 and Hf–silicate surfaces. The resulting surface morphology, grain size, and roughness of the metallic films were examined by scanning electron microscopy (SEM) and atomic force microscopy (AFM), while Rutherford backscattering spectrometry (RBS) was used for compositional measurements. It was determined that an in situ plasma treatment using a H2/Ar yielded metallic Ru films with the highest nucleation density, smallest grain size, and lowest resistivity. Film buckling was also observed for the Ru films deposited on H2/Ar pretreated surfaces. The behavior was attributed to the presence of compressive strain. The films deposited on RCA-cleaned and Ar plasma treated surfaces exhibited very similar physical and electrical characteristics to the films grown on untreated substrates. Alternatively, the use of O2 plasma surface treatment adversely affected Ru nucleation on the SiO2 surface. Relevant mechanisms for Ru nucleation and growth on SiO2 and Hf–silicate nontreated surfaces are discussed in the context of the various predeposition dry and wet treatments.

Strain-dependence of the gain saturations in InGaAsP/InP quantum-well gain media

Numerical analyses of polarization-dependent optical gain saturations are given for quantum-well (QW) lasers in the presence of strain in the well regions in order to investigate the strain dependence of polarization-bistable operations. Gain saturation coefficients are obtained from nonlinear susceptibilities calculated in the perturbative analyses of density matrices. Band dispersions and dipole matrix elements, which are put into the density matrices, are calculated by diagonalizing Luttinger's Hamiltonian, including valence band mixing. The strain induces a change in band dispersions and wavefunctions, leading to strain-dependent saturation coefficients. The self-saturation coefficients and the cross-saturation coefficients (with orthogonal optical polarizations) pertinent to InGaAsP/InP QW vertical-cavity surface-emitting lasers are calculated. We find that the relative magnitudes of self- and cross-saturation coefficients are strongly dependent on the strain; in the presence of compressive strain, the cross-saturation coefficients are larger than the self-saturation in the wide range of the linear gain spectra, especially in the vicinity of the gain peak, indicating that the compressively strained structure is more favorable for the polarization-bistable operations.

Longitudinal electrooptic effects in slim-loop and linear PLZT ceramics

The longitudinal mode of operation was investigated in slim-loop PLZT 9, 10/65/35 and linear 12/40/60. Both birefringent and scattering effects were studied, using the strain-biasing technique for display applications. The results reveal strong dependence of birefringence on electric field in slim-loop materials in the presence of compressive strain and the existence of a threshold value for the field magnitude. Scattered light intensity was found to depend on stress and electric field. A similarity between the longitudinal and transverse effects in linear material was found. The feasibility of using these effects in display devices is presented.