Germanium tin (GeSn) is under equilibrium a two phase (Ge+Sn) system. Single phase GeSn alloys are important for silicon based heterostructure devices as stressors for Ge channels and as candidates ...for direct/indirect band cross-over. Such alloys would allow superior Ge channel metal oxide semiconductor devices and optoelectronic infrared circuits on a Si substrate.
Preparation of GeSn layers is possible at low growth temperatures. We discuss the challenges caused by the non-equilibrium growth and the limitations of low temperature epitaxy. Main challenges and limitations are the surface segregation, precipitations and defect accumulation in low temperature epitaxy.
The problem of high lattice mismatch between Si and GeSn (>4%) can be solved using virtual substrates with strain relaxed Ge buffer layers. The lattice mismatch can be reduced to 1% and below.
Growth of pseudomorphic GeSn layers on Ge buffers/Si substrate was investigated. The samples were characterized by X-ray methods and Raman spectroscopy. High device process stability was achieved up to 600°C annealing and documented by Raman spectroscopy. Fabrication of a detector test device demonstrated feasibility for optoelectronic applications with extended infrared range.
The influence of annealing temperature on the structural and electrical properties of conjugated poly(dodecyl-quaterthiophene) (PQT-12) polymer films is exploited. The temperature induced changes of ...structural parameters are monitored by in situ grazing incident X-ray diffraction (GIXD) and the conductivity. They are complemented by studies of the dielectric properties using variable angle spectroscopic ellipsometry (VASE). An increase of the scattered intensity, the size of the crystalline domains, and the current response is observed for a first thermal cycle with stepwise heating up to 90 °C, which revealed two polymorphs with different degrees of interdigitation in PQT-12. Irreversible changes are observed for the second cycle with a higher thermal budget up to 140 °C and are connected with a transition from the highly ordered to powder-like disordered phase for the main PQT-12 form whereas the second polymorph with stronger interdigitation completely vanished. In agreement with these observations high-temperature VASE studies demonstrated a blue shift of the transitions with a reduction in the conjugation length caused by an increase in the twist and torsion of the backbone. Combined GIXD, VASE, and electrical characterizations show that PQT-12 exhibits a complex interplay between two polymorphs with a strong influence on the charge carrier transport depending on the thermal budget employed.
Here is presented raw and analysed data collected during study of the evolution, with uniaxial stretching, of the electrical and microcrystalline characteristics of polystyrene sulfonate doped ...poly(3,4-ethylenedioxythiophene) (PEDOT:PSS) organic electrochemical transistors (OECTs). X-ray diffraction data from GIWAXS measurements of the PEDOT:PSS material, performed at the SOLEIL light source are presented in raw and partially analysed forms. Current-voltage data, collected concurrently with the GIWAXS data, are also presented, and the evolution of the transconductance of the OECT devices with stretching is shown. GIWAXS data are only examined along the qz specular reflection ridge, and scans along this ridge are extracted and presented. However, the off-specular data may also be of interest to readers and is therefore made available here in its entirety.
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•2D strain maps in Si around TSV performed using high resolution fast scanning XRD.•Strains in 335 crystallographic direction are small – in the order of 10−4.•Low impact of TSV ...process on carrier mobility variations close to the TSV at RT.•3D finite element analysis of a TSV structure compare well with experimental data.•Gradient of strains in 335 direction close to the sample surface.
Fast-scanning X-ray microscopy is used to directly visualize the local strain and lattice tilt in the silicon neighboring Through Silicon Vias (TSVs). Strain variations of the order of 10−4 were detected and results show that the silicon is slightly strained at room temperature (|ε335|<0.06%) with maximum close to the oxide/copper interface, after the completion of copper filled TSVs process. Finite element analysis was carried out and compared with experimental data obtained with synchrotron X-rays. Using the elements birth and death technique with commercial software ANSYS, 3D strains are simulated in a complete TSV structure. Numerical results are in good agreement with extracted strains from diffraction data.
Thick porous silicon (PS) buffer layers are used as sacrificial layers to epitaxially grow planar and fully relaxed Ge membranes. The single crystal Ge layers have been deposited by molecular beam ...epitaxy (MBE) on PS substrate. During deposition, the pore network of PS layers has been filled with Ge. We investigate the structure and morphology of PS as fabricated and after annealing at various temperatures. We show that the PS crystalline lattice is distorted and expanded in the direction perpendicular to the substrate plane due to the presence of chemisorbed –OH. An annealing at high temperature (>500°C), greatly changes the PS morphology and structure. This change is marked by an increase of the pore diameter while the lattice parameter becomes tensily strained in the plane (compressed in the direction perpendicular). The morphology and structure of Ge layers are investigated by transmission electron microscopy, high resolution X-ray diffraction and atomic force microscopy as a function of the deposition temperature and deposited thickness. The results show that the surface roughness, level of relaxation and Si-Ge intermixing (Ge content) depend on the growth temperature and deposited thickness. Two sub-layers are distinguished: the layer incorporated inside the PS pores (high level of intermixing) and the layer on top of the PS surface (low level of intermixing). When deposited at temperature >500°C, the Ge layers are fully relaxed with a top Si1−xGex layer x=0.74 and a very flat surface. Such layer can serve as fully relaxed ultra-thin SiGe pseudo-substrate with high Ge content. The epitaxy of Ge on sacrificial soft PS pseudo-substrate in the experimental conditions described here provides an easy way to fabricate fully relaxed SiGe pseudo-substrates. Moreover, Ge thin films epitaxially deposited by MBE on PS could be used as relaxed pseudo-substrate in conventional microelectronic technology.
•We have developed a rapid and low cost growth process of relaxed Ge buffer layer.•The process was achieved using compliant porous silicon (PS) template layers.•Single crystal Ge layers have been deposited by molecular beam epitaxy on PS.•SiGe layers obtained are fully relaxed and present a high Ge content (0.74–0.96).•SiGe layers could be used as relaxed pseudosubstrate in microelectronic technology.
The retrieval of spatially resolved atomic displacements is investigated via the phases of the direct(real)‐space image reconstructed from the strained crystal's coherent X‐ray diffraction pattern. ...It is demonstrated that limiting the spatial variation of the first‐ and second‐order spatial displacement derivatives improves convergence of the iterative phase‐retrieval algorithm for displacements reconstructions to the true solution. This approach is exploited to retrieve the displacement in a periodic array of silicon lines isolated by silicon dioxide filled trenches.
The influence of local strain fields on electrical properties such as the mobility of electrons and holes in silicon is of growing concern. In this work, we consider the displacement field generated ...in a semi-infinite Si substrate by a periodic array of lines located at the surface. We focus on a model system: an array of silicon nitride lines deposited on a monocrystalline silicon substrate. Measurements with X-ray diffraction (XRD) need mechanical modeling to validate the strain field. For that purpose we use finite element modeling (FEM) for simulating the displacement field, which is then used for calculating the diffracted intensity in the kinematical approximation. Agreement between measured and calculated intensity allows for a validation of the calculated strain field in the silicon.
Stress changes in GeTe thin films on silicon have been studied in situ as a function of temperature by optical curvature measurements. Crystallization of the initially amorphous layers is evidenced ...by a steep tensile stress buildup. The crystallization temperature is shown to be thickness-dependent for the thinner films. Various annealing conditions, such as cooling/re-heating steps and isothermal stages, allow exploring the thermo-mechanical behavior of the films. A non-thermoelastic temperature-dependent behavior is observed in the amorphous phase before crystallization.
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