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Carrier mobilities and concentrations were measured for different p- and n-type silicon materials in the temperature range 0.3–300 K. Simulations show that experimentally determined carrier mobilities are best described in this temperature range by Klaassen’s model. Freeze-out reduces the carrier concentration with decreasing temperature. Freeze-out, however, depends on the dopant type and initial concentration. Semi-classical calculations are useful only for temperatures above 100 K. Otherwise quantum mechanical calculations are required.

For mono-crystalline Ge the indirect luminescence intensity declines upon growing temperature from 80 to 300 K, whereas for dislocated Ge structures the opposite behavior occurs. These findings are comparable to earlier observations on Si. The drop of the luminescence in dislocated material upon lowering temperature was attributed to the increase of the competing non-radiative recombination due to shallow dislocation states. In opposition to the indirect luminescence, the character of the direct Ge luminescence, i.e. incline of intensity upon growing temperature, is not converted by dislocations. The measured behavior of the direct peak position of Ge, in the temperature range between 80 and 300 K, is in accordance with calculated dependence and reflects the direct bandgap energy. The observed red shifts in dislocated Ge structures are shown to be produced by tensile strain, bandgap narrowing and by the Sn-content of GeSn quantum wells, respectively. A direct influence of dislocations could not be observed. Satisfying understanding of the existing temperature behavior of the indirect Ge peak position is on embryonic stage.

A significant increase of the drain current is verified if defined numbers and types of dislocations are present in the channel of MOSFETs. For pMOSFETs, analysed here, an enhancement by a factor of eight exists if mixed dislocations are placed in the channel. The drain current increase is caused by higher concentration and higher mobility of holes on dislocations. It is shown that cores of mixed dislocations possess uniaxial compressive strain components in the order of e ≅ –0.1 which are significantly higher than in the strain field surrounding a dislocation. The exceptional high uniaxial strain results in dramatic alterations of the silicon band structure. Upward shifts of the upper valence bands appear forming a quantum wire. The generation of the quantum wire forces hole confinement along dislocations and generates a one-dimensional hole gas (1DHG). Confinement and energy quantization are assumed to be most important for the increased carrier transport along dislocations. (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

In conjunction with the two-level model the temperature behaviour of the dislocation-related D1-peak follows the T-behaviour of the band gap. Based on luminescence observations in our laboratory and on literature data we propose a ∼30 meV wide domain of the D1 peak. Altogether, the D1-peak position ranges between about 0.76 eV at 300 K and nearly 0.84 eV at a few K. It was shown that the energetic shift for a certain temperature is caused by external electric fields, by excitation level, that affects the intrinsic dislocation field, and by elastic stress. The luminescence of oxygen-related defects / precipitates might be described by a line at ∼ 0.77 eV (P-line) that does not depend on temperature. (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Dislocations are basic crystal defects and represent one-dimensional native nanostructures embedded in a perfect crystalline matrix. Their structure is predefined by crystal symmetry. Two- dimensional, self-organized arrays of such nanostructures are realized reproducibly using specific preparation conditions (semiconductor wafer direct bonding). This technique allows separating dislocations up to a few hundred nanometers which enables electrical measurements of only a few, or, in the ideal case, of an individual dislocation. Electrical properties of dislocations in silicon were measured using MOSFETs as test structures. It is shown that an increase of the drain current results for nMOSFETs which is caused by a high concentration of electrons on dislocations in p-type material. The number of electrons on a dislocation is estimated from device simulations. This leads to the conclusion that metallic-like conduction exists along dislocations in this material caused by a one-dimensional carrier confinement. On the other hand, measurements of pMOSFETs prepared in n-type silicon proved the dominant transport of holes along dislocations. The experimentally measured increase of the drain current, however, is here not only caused by an higher hole concentration on these defects but also by an increasing hole mobility along dislocations. All the data proved for the first time the ambipolar behavior of dislocations in silicon. Dislocations in p-type Si form efficient one-dimensional channels for electrons, while dislocations in n-type material cause one- dimensional channels for holes.

The influence of GBs contained in the channel of MOS-FETs - fabricated in thin SOI layers - is demonstrated. The drain current measured at room temperature increases about 50 times for nFETs and about 10 times for pFETs, respectively, as compared to reference devices. The observations might be interpreted as a strong increase of the mobility of charge carriers. Moreover, the observed stepwise changes of the drain current at 5 K may point to Coulomb blockades.

The electrical behaviour of only a few dislocations was analysed. Such small numbers of defined dislocations were produced by hydrophobic semiconductor wafer direct bonding. The dislocation networks were placed in the channel of SOI MOSFETs where the source and drain regions of these devices act as contacts. Varying the channel width allows one to control the number of dislocations measured. Analyses of nMOSFETs proved an increase of the drain current caused by dislocations by more than one order of magnitude, while a decrease of the current is obtained for pMOSFETs. This indicates that electrons are present on the dislocation core in p-type material. The concentration of electrons on dislocations was estimated to be about 200 electrons per micrometer dislocation length, corresponding to a distance of about 5 nm between free electrons. This distance agrees with the space between Coulomb islands proved by low-temperature measurements. The investigations refer to a metallic-like conductance along dislocations caused by a two-dimensional carrier confinement. (© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Dislocations exhibit a number of exceptional electronic properties resulting in a significant increase of the drain current of metal-oxide-semiconductor field-effect transistors (MOSFETs) if defined numbers of these defects are placed in the channel. Measurements on individual dislocations in Si refer to a supermetallic conductivity. A model of the electronic structure of dislocations is proposed based on experimental measurements and tight binding simulations. It is shown that the high strain level on the dislocation core—exceeding 10% or more—causes locally dramatic changes of the band structure and results in the formation of a quantum well along the dislocation line. This explains experimental findings (two-dimensional electron gas and single-electron transitions). The energy quantization within the quantum well is most important for supermetallic conductivity.

A major challenge for the application of strain engineering to enhance the performance of electronic devices is the quantification of strain on the nanoscale. Besides other techniques (Raman spectroscopy, X-ray diffraction) electron beam techniques allow strain analyses with a spatial resolution of a few nanometers and a reasonable strain sensitivity of 1x10 -3 (relative to the lattice constant of silicon). In the present work, we address practical issues in the application of nano-beam electron diffraction (NBED) to probe the strain in strained silicon layers and sub-100 nm structures. The investigated specimens were prepared on biaxially tensile strained silicon-on- insulator substrates with an initial strain of = 0.6% or 0.8%. Results of the NBED experiments were compared to data obtained by other strain measurement techniques; amongst them the strain mapping by peak-pairs analysis of high-angle annular dark field (HAADF) images was especially considered. NBED can be easily performed by use of STEM with a small aperture of the 2 nd condenser lens in the micro- or nanoprobe mode. The NBED principle consists in illuminating a nanometer-sized area of the specimen (being in zone axis orientation) with a nearly parallel electron beam and acquiring series of diffraction patterns at points along previously defined lines. The strain components of interest are generally calculated using a dedicated software package which is based on procedures for the analysis of electron diffraction patterns. The spatial resolution of NBED is determined by the beam diameter to a few nanometers. The

Schottky diodes prepared on silicon bonded wafers with dislocation network (DN) lying parallel to the sample surface at the depth of ∼2 μm were investigated by means of capacitance-voltage (CV), current-voltage (IV) measurements at 80 K under optical illumination. A model of the interpretation of CV and IV data is presented and discussed. It is shown that electron-beam induced current (EBIC) mapping under the proper chosen forward bias voltages allows one to trace the inhomogeneities of the potential barrier at DN. The observed non-uniformity of the DN barrier heights was ascribed to inhomogeneous distribution of small oxide precipitates lying at the dislocation network plane (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

We report on electro-luminescence from metal-insulator-semiconductor diodes (MISLED). MISLEDs prepared on silicon with HfO2 layers of different thicknesses were investigated and their properties compared with such prepared by using SiO2 insulator layer. The role of the insulator layer was studied in view of the efficiency of the band-to-band radiation from silicon. We show that the luminescence efficiency depends on the dielectric constant of the insulator as well as on its ability to conduct carriers by tunnelling. Efficiency enhancement of 3.3 times was detected when the SiO2 insulator was substituted by HfO2 in the MIS emitter. Optimal injection current exists, which leads to a maximal efficiency of the luminescence. The optimal current depends strongly on the thickness of the oxide. We relate the existence of an optimal current with the depth at which the injected minority carriers recombine radiatively. Thus the electric field in the semiconductor and the surface recombination are the factors determining the optimal injection (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Strained silicon channels are one of the most important Technology Boosters for further Si CMOS developments. The mobility enhancement obtained by applying appropriate strain provides higher carrier velocity in MOS channels, resulting in higher current drive under a fixed supply voltage and gate oxide thickness. The physical mechanism of mobility enhancement, methods of strain generation and their application for advanced VLSI devices is reviewed.

The investigation of regular dislocation networks (DN) formed by direct wafer bonding suggests that the D1 and D2 peaks of dislocation-related luminescence (DRL) in silicon is linked to screw dislocations, whereas edge dislocations are responsible for D3 and D4 DRL peaks. Non-radiative recombination activity in DN could be attributed to edge dislocations and could be related to enhanced ability of these dislocations to getter impurity atoms. Obtained relation of DRL intensity with the density of screw dislocations suggests existence of the optimum twist angle for the wafer-bonding geometry for which the DRL intensity has a maximum. The dependence of DRL intensity on the spacing between screw dislocations has the maximum at about 7 nm. Reported radiative and non-radiative recombination properties of DN present substantial interest not only for possible LED applications in all-Si photonics but also for photovoltaics, since DNs represent a model system for grain boundaries controlling carrier lifetime in microcrystalline-Si material.

Incorporation of optical components into microelectronic devices will significantly improve their performance. Absence of effective Si-based light emitter hampers such integration. In the present work light emitting Si diodes, fabricated by dopant (boron or phosphorous) implantation and annealing are investigated. Different implantation doses and annealing temperatures were employed. The efficiency of the electroluminescence (EL), obtained from such structures was measured and correlated with the fabrication process parameters. As previously reported, the EL of band-to-band radiative transition in Si is strongly influenced, by the dopant implantation dose, i.e. higher doses usually enhance EL. Our results suggest that the effect is mainly related to the increase of minority carrier lifetime in the substrate. Distinct measurements showed that the higher implantation doses lead longer carrier lifetimes in the samples. The correlation between lifetime and the EL efficiency could be satisfactory explained in the frame of a classical model, considering the carrier-injection dependence of the rates of the three main recombination mechanisms in silicon, i.e. multi-phonon, radiative and Auger recombination. We suppose that the increase in the implantation dose improves minority carrier lifetime due to the gettering of impurity atoms from the substrate material to the highly doped emitter region.

The direct bonding of Si wafers reproducibly forms dislocation networks (DN) with a microscopic structure defined by the mutual crystallographic orientation between the pair of wafers used for the bonding procedure. This allows studying the electrical and optical properties of specific dislocations. In the present work three different DN structures were investigated using transmission electron microscopy (TEM), photoluminescence (PL) and deep level transient spectroscopy (DLTS). The results show close correlation between the structural, electrical and optical properties of dislocations and opens a possibility to identify structural peculiarities of the dislocations responsible for the high intensity of photoluminescence. Namely, the obtained results suggest that PL at ∼0.8 eV is related to screw dislocations in DN. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The electrical and optical properties of dislocations in Si are reviewed, namely dislocation-related recombination and luminescence, transport of minority and majority carriers along dislocations or the electric field around dislocations. It is shown that Si wafer direct bonding allows well-controlled formation of dislocation networks, giving rise to adjustable dislocation properties. Ideas for novel Si devices utilizing dislocations as active components are presented. In particular, dislocation-based light emitters at about 1.5 μm wavelength are demonstrated. Concepts for dislocation-based conductive channels and fast FETs, manipulators of biomolecules or thermo-electric generators are sketched.

Dislocation networks (DNs) formed by silicon wafer bonding were studied by means of Electron Beam Induced Current (EBIC) and Photoluminescence (PL). The measurements were performed on p–n junction diode structures prepared by ion implantation. EBIC signal was observed not only inside the diode structure, but also far outside the diode area. This finding demonstrates the ability of the bonding interface to efficiently collect minority carriers and indicates a high electrical conductivity of the dislocation network. In addition, circular inhomogeneities of charge collection were observed. The contrast of those regions was bright at high beam energies and turned dark or vanished at lower energies. The contrast behavior of the circular areas can be explained by local variations of collection efficiency and recombination at the DN, which might be a result of different density of oxide precipitates. PL mappings at 0.794 and 1.081 eV revealed similar circular areas.

A new concept for Si-based light emitting diodes (LED) capable of emitting at 1.5 μm is proposed. It utilizes D-band radiation from dislocations in Si. Whether a dislocation network created in a reproducible manner by Si wafer direct bonding or dislocation loops produced by Si ion implantation are employed. It is also stated that dislocation loops do not lead to the strong band-to-band electroluminescence at 1.1 μm of p-n diodes, as it was predicted in the literature. A MOS-LED (Fig. A) and p-n LEDs emitting at 1.5 μm are demonstrated by the authors. The maximum efficiency that could be achieved at room temperature is close to 1%. Levels in the bandgap which are probably involved in the formation of the D1-line at 1.5 μm are revealed. Moreover, the observation of the Stark effect for the D1-line is reported. Namely, a red/blue-shift of peak position was observed in electro- and photo-luminescence when the electric field in the p-n LED was increased/lowered. This effect may allow realization of a novel Si-based light emitter with electric field modulated emission wavelength. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Semiconductor wafer bonding offers a new degree of freedom in the design of material combinations without the common restrictions of the structure of the materials bonded. It is already an established method for the industrial production of advanced substrates (SOI) applied as basic material in high-performance device fabrication. SOI, i.e. a thin device layer on an insulator, is a promising concept for further device developments. The advantages of SOI can be combined with mobility enhancing materials such as strained silicon (SSOI) or germanium on insulator (GOI). The bonding process is not limited to a certain wafer diameter and is applicable to different material combinations which are important to integrate different functions on a chip (system on a chip, SoC). (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Dislocation rich regions can be controllably formed at a certain location inside a silicon wafer. We studied the light emission properties of such regions located in an electric field of a p–n junction under different excitation conditions. It was found that the luminescence spectra of the dislocations are significantly influenced by the presence of the junction. The dislocation-related luminescence peak position appears red-shifted due to the built-in electric field. A suppression of that field by photogeneration of carriers or by applying a forward bias voltage at the junction leads to a gradual decrease in the energy position of the peaks. The dependence of the peak position on the electric field was found to be a quadratic function, similar to that observed for semiconductor nanostructures. We show that the shift of the peak position is due to the Stark effect on dislocation-related excitonic states. The characteristic constant of the shift, obtained by fitting the data with the quadratic Stark effect equation, was 0.0186 meV/(kV/cm)2. The observed effect opens new possibilities for integration of a silicon based light emitter, combining the radiation from dislocations with a Stark effect based modulator.

The paper reviews methods of hydrophobic wafer bonding. Hydrophobic surfaces are obtained by removing the oxide layer from the surfaces of crystalline silicon substrates. Bonding such surfaces causes the formation of a dislocation network in the interface. The structure of the dislocation network depends only on the misalignment (twist and tilt components). The different dislocation structures are discussed. Because wafer bonding offers a method to the reproducible formation of such networks, different applications are possible

Spectroscopic Ellipsometry was employed to study the etching process of uniaxially strained Si (sSi) layers obtained by direct wafer bonding of Si wafers in a mechanically benstate followed by thinning one of the Si wafers, the donor wafer, by the smart-cut process, keeping the other, the handle wafer intact The smart-cut process requires a high dose hydrogen implantation into the donor wafer prior to bonding. As a result of the implantation conditions a ∼600 nm uniaxially sSi layer could be transferred onto the handle wafer. In order to thin down and smooth the surface damage of the transferred layer induced by the implantation and splitting process, the samples were dipped in a solution of tetra-methyl ammonium hydroxide (TMAH). The thicknesses of the transferred sSi layers determined from ellipsometry were in good agreement with those obtained from Transmission Electron Microscopy (TEM), while the roughness values were matching those obtained from Atomic Force Microscopy (AFM). The etching rate has also been determined.

Dislocation networks obtained by hydrophobic wafer bonding of Si (100) are investigated. The twist and tilt misorientations induce two interacting dislocation networks. Advanced bonding techniques are applied and optimized allowing to eliminate the tilt and to control the twist misorientation. At very low twist angles the interfaces no longer exhibit regular dislocation networks. Properties of dislocation networks are discussed.

Regular dislocation networks formed as a result of the direct bonding of Cz-Si wafers with oxide remnants on the pre-bonding surfaces were investigated. Besides the dislocation network, oxide precipitates were detected at the bonding interface. The precipitate density across the network was ~5×1010 cm-2, except small irregularly distributed circular areas, several mm in diameter, where the density was remarkably lower (

In order to investigate the electrical properties at the surface of dislocation rich silicon, we conducted Electrostatic Force Microscopy on cross-sections of samples prepared by Wafer Direct Bonding. The applied methods, namely Scanning Kelvin Probe Microscopy and non-contact Scanning Capacitance Microscopy, yield a distinct contrast at the position of the dislocation area, i.e. the bonding interface, indicating strong electrical activity. For an explanation of the explicit electrostatic potential extracted from the experiment a simple model taking into account only an intrinsic charge distribution at the dislocation area appears to be insufficient. Instead, a more complex approach has to be used considering carrier generation and recombination by additional, dynamic mechanisms. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Electrical levels of the dislocation network in Si and recombination processes via these levels were studied by means of the combination of grain-boundary deep level transient spectroscopy, grain-boundary electron beam induced current (GB-EBIC) and cathodoluminescence (CL). It was found two deep level traps and one shallow trap existed at the interface of the bonded interface; these supply the recombination centers for carriers. The total recombination probability based on GB-EBIC data increased with the excitation level monotonically; however, the radiative recombination based on D1-D2 CL data exhibited a maximum at a certain excitation level. By applying an external bias across the bonded interface, the CL signal of D-lines was enhanced dramatically. These results are consistent with our models about two channels of recombination via the trap levels.

Uniaxial strain on wafer-level was realised by mechanically bending and direct wafer bonding of Si wafers in the bent state followed by thinning one of the Si wafers by the smart-cut process. This approach is flexible and allows to obtain different strain values at wafer-level in both tension and compression. UV micro-Raman spectroscopy was used to determine the strain in the thin transferred Si layers. Numerical modelling by 3D finite elements of the strain provided a good description of the experimental results.

Direct wafer bonding between high-density-plasma chemical vapour deposited (HDP-CVD) oxide and thermal oxide (TO) has been investigated. HDP-CVD oxides, about 230 nm in thickness, were deposited on Si(0 0 1) control wafers and the wafers of interest that contain a thin strained silicon (sSi) layer on a so-called virtual substrate that is composed of relaxed SiGe (∼4 μm thick) on Si(0 0 1) wafers. The surfaces of the as-deposited HDP-CVD oxides on the Si control wafers were smooth with a root-mean-square (RMS) roughness of 2 nm. After HDP-CVD oxide deposition on the sSi/SiGe/Si substrates, the RMS roughness of the oxide surfaces was also found to be the same, i.e., >2 nm. To use these wafers for direct bonding the RMS roughness had to be reduced below 1 nm, which was carried out using a chemo-mechanical polishing (CMP) step. After bonding the HDP-CVD oxides to thermally oxidized handle wafers, the bonded interfaces were mostly bubble- and void-free for the silicon control and the sSi/SiGe/Si(0 0 1) wafers. The bonded wafer pairs were then annealed at higher temperatures up to 800 °C and the bonded interfaces were still found to be almost bubble- and void-free. Thus, HDP-CVD oxide is quite suitable for direct wafer bonding and layer transfer of ultrathin sSi layers on oxidized Si wafers for the fabrication of novel sSOI substrates.

Fabrication of strained silicon on insulator (sSOI) substrates by wafer bonding and layer splitting is described in this paper. The sSi layer of 20 nm thickness is obtained on an 8 in. virtual substrate that consists of a plastically relaxed SiGe layer grown epitaxially on Si(0 0 1) by chemical vapor deposition (CVD). The plastic relaxation of the initially pseudomorphic SiGe layer is mediated by helium implantation into the Si wafer below the SiGe/Si(0 0 1) interface and subsequent annealing. A SiO 2 layer is grown by plasma enhanced (PE) CVD on the sSi/virtual substrate prior to wafer bonding. The PECVD oxide layer is used to compensate the thermal stress existing at the bonding interface during annealing. The SiO 2 /sSi/virtual substrate wafers are then implanted with hydrogen at a high dose (3.5 × 10 16 H 2 + cm −2 ) and subsequently bonded to Si(0 0 1) handle wafers. Subsequent annealing of the bonded wafer pair leads to the transfer of the implanted layer (containing the sSi layer) from the virtual substrate to the Si handle wafer. The final sSOI structure is realized by subsequent chemo-mechanical polishing followed by selective wet chemical etching. The sSOI substrate shows good thickness uniformity (∼20 nm) of the sSi layer over the entire 8 in. area and the strain measurements indicate a value of ∼0.66%.

Tensile strained Si (sSi) layers were epitaxially deposited onto fully relaxed Si0.78Ge0.22 (SiGe) epitaxial layers (4 μm) on silicon substrates. Periodic arrays of 150 nm × 150 nm and 150 nm × 750 nm pillars with a height of 100 nm were fabricated into the sSi and SiGe layers by electron-beam lithography and subsequent reactive ion etching. The strain in the patterned and unpatterned samples was analyzed using high-resolution UV micro-Raman spectroscopy. The 325 nm excitation line used probes strain in Si close to the surface (penetration depth of ∼9 nm). The Raman measurements revealed that the nano-patterning yields a relaxation of strain of ∼33% in the large pillars and ∼53% in the small pillars of the ∼0.95% initial strain in the unpatterned sSi layer.

Hydrophobic wafer bonding causes the formation of dislocation networks in the bonded interface. The structure of the dislocation network depends on the misorientation between both wafers during the bonding. The characterization of the dislocation networks proved that the luminescence depends only on the structure of the dislocation network. Different degrees of misorientation cause that different lines in the PL- and CL- spectra appear. This makes it possible to construct monochromatic light sources.

On-chip optical interconnects require a CMOS-compatible electrically pumped Si-based light emitter at about 1.5 μm. Dislocations in silicon offer a recombination centre for light emission at the desired energy. Here we report on the radiative properties of dislocation networks, created in a well controllable manner at a certain depth of silicon wafers. Dislocation networks, created by ion implantation and annealing, misfit dislocation in SiGe buffers and a novel concept of dislocations created by misoriented direct bonded Si wafers are discussed. We demonstrate that under a specific misorientation a dislocation network with efficient room temperature D1 (1.55 μm) emission might be generated.

Defined placement of biomolecules at Si surfaces is a precondition for a successful combination of Si electronics with biological applications. We aim to realize this by Coulomb interaction of biomolecules with dislocations in Si. The dislocations form charged lines and they will be surrounded with a space charge region being connected with an electric field. The electric stray field in a solution of biomolecules, caused by dislocations located close to the Si surface, was estimated to yield values up to few kVcm � 1 . A regular dislocation network can be formed by wafer direct bonding at the interface between the bonded wafers in case of misorientation. The adjustment of misorientation allows the variation of the distance between dislocations in a range from 10 nm to a few Am. This is appropriate for nanobiotechnology dealing with protein or DNA molecules with sizes in the nm and lower Am range. Actually, we achieved a distance between the dislocations of 10–20 nm. Also the existence of a distinct electric field formed by the dislocation network was demonstrated by the technique of the electron-beam-induced current (EBIC). Because of the relatively short range of the field, the dislocations have to be placed close to the surface. We positioned the dislocation network in an interface being 200 nm parallel to the Si surface by layer transfer techniques using hydrogen implantation and bonding. Based on EBIC and luminescence data we postulate a barrier of the dislocations at the as bonded interface

Ambient pressure plasma processes were applied for surface activation of semiconductor (Si, Ge and GaAs) and other wafers (glass) before direct wafer bonding for MEMS and engineered substrates. Surface properties of activated wafers were analysed. Caused by activation high bond energies were obtained for homogeneous (e.g. Si/Si) as well as for heterogeneous material combinations (for instance Si/Ge) after a subsequent low temperature annealing process at 200°C. The resulting bond energies are analogous or higher as obtained for low-pressure plasma activation processes. The advantages of the ambient pressure plasma processes are described; a technical solution is discussed demonstrating the low risk for contamination and radiation damage.

When mirror-polished, flat, and clean wafers are brought into contact, they are locally attracted to each other and adhere or bond. This phenomenon is known as semiconductor wafer bonding. Different adhesion forces (van der Waals forces, hydrogen bonding) are the reason for the bonding effect at room temperature. The different bonding mechanisms acting in dependence on the surface conditions (hydrophilic, hydrophobic) are reviewed. Variations of the properties of bonded interfaces (structural, mechanical, electrical) during annealing are discussed. The focus is on low-temperature bonding techniques. Reasons for the formation of interface defects are presented. Applications of semiconductor wafer bonding for future developments are briefly summarized.

A new concept for a Si light emitting diode (LED) capable of emitting efficiently at 1.55 μm or at 1.3 pm, respectively, is proposed. It utilizes radiation from a well-defined dislocation network created in a reproducible manner by direct Si wafer bonding. The wavelength of the light emitted from the network can be tailored by adjusting the misorientation between the Si wafers. That way dominance of radiation at 1.55 μm (D1 line) or at 1.3 μm (D3 line) was achieved. There are hints that decoration of the dislocations by oxygen enhances the intensity of the D1 radiation. A critical analysis of the light emitter proposed by W. L. Ng et al. [Nature 410, 192 (2001)] using band-to-band emission is given. Its application at the above wavelengths would require a few microns thick SiGe layer on top of the Si substrate.

Reproducible formation of well-controlled dislocation structures is a prerequisite to use dislocations as an active part of devices. Regular dislocation networks have been formed at the interface by Si wafer direct bonding. The barriers of interface were generally smaller than 100 meV. The temperature dependence of the electron-beam-induced current (EBIC) contrast of the interface indicates a deep state density of a few 10E5 per cm along the dislocation lines in the network. It is also found that the dislocation networks in Si can act as effective channel for carrier transport. Photoluminescence (PL) reveals that the D line spectrum related to the dislocation networks can be tailored by the bonding misorientation. So, the D1 line can be made the dominating feature in the PL spectrum. It is suggested that regular dislocation networks represent an interesting new nanosystem for future applications, such as accommodation biomolecules onto silicon, dislocation-based LED or buried nanowires.

A systematic investigation of the hydrogen implantation-induced blister formation on the surface of Si 0.78 Ge 0.22 when annealed in the temperature range of 300–700 °C was carried out. The strain-relaxed Si 0.78 Ge 0.22 layers were grown epitaxially on 8-inch Si(1 0 0) substrates by reduced pressure chemical vapour deposition (RPCVD). These wafers were implanted with hydrogen, H 2 + , ions at 240 keV with a dose of 5 × 10 16 cm −2 . The formation of optically detectable blisters on the surface was observed using an optical microscope in Nomarski contrast mode. The width and depth of the blisters was determined with a profilometer. The characterization of the hydrogen implantation-induced damage and defects inside the Si 0.78 Ge 0.22 layer was performed using cross-sectional transmission electron microscopy (XTEM). The Arrhenius plot of blistering time versus annealing temperature revealed two different activation energies for the formation of blisters. In the low temperature regime (300–400 °C) an activation energy of 1.2 eV was obtained, while in the high temperature regime (400–700 °C) the activation energy was 0.38 eV. In analogy to the case in Si, the lower activation energy can be associated with the free atomic diffusion of hydrogen in Si 0.78 Ge 0.22 and the higher activation energy can be related to the hydrogen diffusion limited by trapping-detrapping phenomena. The depth of the broken blisters and the depth of the hydrogen-induced microcracks inside Si 0.78 Ge 0.22 came out to be around 1.05 μm, which matches quite well with the calculated (by Stopping and Ranges of Ions in Matter, SRIM code) concentration peak of the hydrogen distribution inside Si 0.78 Ge 0.22 for the case of 240 keV H 2 + implantation.

Electroluminescence of B and P implanted samples has been studied. P implantation is found to have a similar effect on light emission as B implant. The band-to-band (BB) luminescence of P implanted diodes is observed to increase by more than one order of magnitude upon rising the temperature and an internal efficiency of 2 % has been reached at 300 K. An efficiency larger than 5% seems to be reachable. The strong BB line emission at 1.1 &m is attributed to high bulk SRH lifetime. The BB line escapes from the substrate below the p-n junction. It is not due to the implantation-related defects/dislocations. The luminescence spectrum can be tailored to achieve dominance of the dislocation-related D1 line at about 1.5 &m. It is observed that a regular periodic dislocation network, formed by Si wafer direct bonding with a specific misorientation, exhibits even at 300 K only D1 photoluminescence. Such a dislocation network is believed to be a serious candidate to gain an efficient Si-based light emitter.

Wafer bonding of strained silicon (sSi) layer to oxidized Si (0 0 1) handle wafers is described in this paper. The sSi resides on two types of relaxed SiGe layers, a thick one (2 μm in thickness) grown on top of a compositionally graded buffer and a thin one (∼180 nm) for which He implantation and annealing are used to induce plastic strain relaxation by misfit dislocations. The thick SiGe layer shows a pronounced cross-hatch pattern resulting in a high surface micro-roughness (>1 nm). For direct bonding this roughness is reduced to Spontaneous and void-free bonded interfaces were obtained when both types of substrates were brought in contact with the oxidized handle wafers at room temperature. The bonding energies obtained after annealing at moderate temperatures (e.g. 500 °C) are sufficiently high to withstand further processing involved in layer transfer.

RIE-plasma etching of sub-micron structures in 150-200-nm thick Cr layers deposited on 4-inch SiO"2/Si/SiO"2 wafers was investigated as a function of the gas composition, RF power, and resist type. An optimal recipe is obtained yielding a Cr etching rate of about 7 nm/min and a ratio of the resist to the Cr etching rates of about 2 in case of etching the sub-micron structures in Cr with a ZEP 520 resist mask. SEM investigations show nearly vertical sidewalls of features etched in Cr layers with a lateral size ranging from 0.3 to 0.5 @mm.

Strained silicon devices provide for an enhanced carrier mobility compared to that of unstrained silicon devices of identical dimensions. The device performance gets even better when using strained silicon on insulator material. We report experimental procedures based on wafer bonding, smart cutting and selective chemical etching to obtain thin strained silicon (∼15 nm) on insulator wafers. The starting material is an 8″ wafer with pseudomorphically grown strained silicon on a so-called virtual substrate as realized by epitaxial chemical vapor deposition of relaxed SiGe (grown with a grading rate of 10% Ge in the SiGe-alloy per 1 μm layer deposition) on a Si(0 0 1) substrate. The starting and bonded wafers are characterized: (i) structurally using transmission electron microscopy, (ii) topographically, using atomic force microscopy and (iii) the strain is quantified using UV-Raman spectroscopy.

Electroluminescence (EL) of light-emitting diodes (LED) with different active regions and photoluminescence (PL) of Ge layers embedded in Si barriers on Si substrates has been studied. Increasing the tensile strain in the active region of Ge LEDs by using GeSn virtual substrate technology leads to an enhancement of the direct band luminescence. An intensity increase by a factor of four is achieved due to n-type doping with an antimony concentration of 3 × 1019 cm−3. The EL of LEDs with a GeSn/Ge multi quantum well structure as active region show an increased direct band luminescence of GeSn by a factor of 16 compared to an intrinsic Ge LED, revealing the advantage of carrier confinement. A high density of threading dislocations, due to the lattice mismatch of Ge and Si, causes a huge drop of PL intensity in the range of one to two orders of magnitude in the temperature range from 80 to 350 K. Thin and pseudomorphically grown Ge layers between Si barrier layers exhibit a huge PL intensity due to the absence of threading dislocations. Taking into account the thickness of the active region the direct band luminescence intensity is increased by two orders of magnitude.

Strain engineering is ubiquitous in the design and fabrication of innovative, high-performance electronic, optoelectronic, and photovoltaic devices. The increasing importance of strain-engineered nanoscale materials has raised significant challenges at both fabrication and characterization levels. Raman scattering spectroscopy (RSS) is one of the most straightforward techniques that have been broadly utilized to estimate the strain in semiconductors. However, this technique is incapable of measuring the individual components of stress, thus only providing the average values of the in-plane strain. This inherit limitation severely diminishes the importance of RSS analysis and makes it ineffective in the predominant case of nanostructures and devices with a nonuniform distribution of strain. Herein, we circumvent this major limitation and demonstrate for the first time the application of RSS to simultaneously probe the two local stress in-plane components in individual ultrathin silicon nanowires based on the imaging of the splitting of the two forbidden transverse optical phonons.

The influence of dislocations in the channel of MOS-FETs is analyzed. The drain current at room temperature increases about 50 times for nFETs and about 10 times for pFETs, as compared to reference devices. The observations might be interpreted as a strong increase of the mobility of charge carriers. Moreover, the observed stepwise changes of the drain current at 5 K may point to Coulomb blockades.

A significant increase of the drain current appears if defined arrangements of dislocations are present in the channel of MOSFETs. Furthermore, analyses of the electronic properties of individual defects refer to a supermetallic behavior of dislocations. The reason is the extremely high strain in the dislocation core exceeding values of ϵ ≅ 0.1. Such high strain causes substantial changes of the band structure and means that dislocations represent quantum wires. Quantum mechanical device simulations based on this conclusion demonstrated the transport of carriers on dislocations. The effect of gate voltage and strain in the dislocation core was analyzed in detail.

Studies dealing with the bonding behavior of silicon wafers coated with thermal oxide, plasma-enhanced chemical vapor deposition (PE-CVD) oxide, PE-CVD oxynitride, PE-CVD nitride and low-pressure (LP) CVD nitride are presented. The PE-CVD layers require a chemo-mechanical polishing (CMP) before bonding to reduce the surface roughness. The bonding energies of the wafer pairs with different interface layers are similar to those of bonded hydrophilic silicon wafers. Infrared microscopy of patterned wafer pairs reveals interfaces which are almost free of bubbles. Presumably, the gas, which usually generates such interface bubbles, diffuses into the interface cavities. The tensile strengths of patterned wafer pairs including a PE-CVD oxide or a PE-CVD oxynitride interface layer are about twice as high as for patterned hydrophilic silicon wafer pairs.