We have found that dividing the class of 20 students in groups of four brings agility to the group logistics and minimizes “defocusing” socialization. These are the teams of peer teachers. Each is responsible in carrying its own weight in the education of the team. They select their own “management” structure, as well as their agenda. The course itself starts with a month of lectures by the instructors and by visitors from other germane departments. The students organize visits to research labs on campus where research on crystalline materials is being performed, and invite researchers in the field to lecture the class. Each meeting period involves discussion of homework problems, where the groups, informally, present their findings. After this initial month, each team selects a topic among a wide gamut of possibilities and clears, with the instructors, the particular focus it wishes to develop further. The selected themes tend to group in science, technology, as well the general “lore” of crystals. So the themes range from the growth of crystals in reduced gravity, through the economic aspects of synthetic diamonds, to the folklore of crystals in healing. The particular selection of a theme is not as important as the way they research the topic, develop it and present it. The teams first present a survey of their topic to the class. We evaluate the presentation in terms of intellectual content and delivery. The students not only receive our feedback but also that of their peers. They have the chance to incorporate the comments in a second report, three weeks after the first when they are supposed to focus more on the initial theme and select a part for a more in-depth study. Final oral and written reports are due at the end of the semester.

Through the semester the classroom atmosphere has been that of inquiry, critical thinking, accepting of all points of view and the pursuit of diverse perspectives. The students seem to be able to take with them these attitudes and maintain them in their team meetings and discussions.

Ge-based photodetectors operating in the telecommunication wavelength range (1.3-1.6 μm) of silica fibers are highly desirable for the development of optical interconnections on SOI substrates. We have therefore investigated the structural and optical properties of Ge thick films grown directly onto Si(001) substrates using a production-compatible Reduced Pressure Chemical Vapor Deposition system. The thick Ge layers grown using a low-temperature / high temperature approach are in a definite tensile-strain configuration, with a threading dislocation density for as-grown layers of the order of 3×107 cm−2. The surface of those Ge thick layers is rather smooth, especially when considering the large lattice mismatch in-between Ge and Si. The root mean square roughness is indeed of the order of 2 nm only for as-grown layers. The layers produced are of high optical quality. An absorption coefficient α ≈10000 cm−1 @ 1.3μm (4500 cm−1 @ 1.55μm) has been found at room temperature for our Ge thick layers. A 30 meV bandgap shrinkage with respect to bulk Ge (0.77 eV ≎ 0.80 eV) is observed as well in those tensilestrained Ge epilayers.

Blanket pseudomorphic Si0.8Ge0.2/Si layer structures grown by Rapid thermal Chemical Vapor Deposition (RTCVD) on SOI substrates were etched to form 5μm × 5μm slabs, supported by a single pedestal at the center. Symmetric tri-layer slabs, 20nm Si/236nm Si0.8Ge0.2/20nm Si supported by a SiO2 pedestal are flat and x-ray diffraction measurements of the strain and the thickness of the layers confirmed that the strain is shared between the Si and SiGe layers according to the ratio of the thickness of the SiGe and Si layers. These tri-layer structures were then firmly attached to the substrate using a filling material. A thermal oxide layer was grown on the upper and lower surface of the free-standing structures and then polycrystalline Si was deposited to fill the space between the free-standing structure and the Si substrate, thus attaching the bottom strained Si layer to the substrate. The polycrystalline Si was subsequently removed by reactive ion etching except from under the /SiGe/Si slab. The top SiO2 and Si layers as well as the SiGe layer were then removed selectively by wet etching. Raman spectroscopy measurements show that the strain in the attached strained Si-on-insulator layer is ε = 0.0067.

The fabrication of electronic devices on semiconductor islands is becoming increasingly common because of silicon-on-insulator technology and/or because of strain engineering in compliant substrate approaches. While photoluminescence can be an accurate probe of Ge content and strain, in islands it can be affected by the presence of the island edges. Here we present data and a model showing that for high quality SiGe, edge effects are critical for sizes under ∼20 μm. These effects can be mitigated by regrowing epitaxial silicon to passivate the recombination states on the island edges.

The diffusion of B and Si in Ge is studied using implantation doping. Concentration profiles after furnace annealing in the temperature range 800–900 °C were obtained using high resolution secondary ion mass spectroscopy (SIMS). Diffusion coefficients are calculated by fitting the annealed profiles. For B, we obtain diRusivity values which are two orders of magnitude slower than previously reported in literature. An activation energy of 4.65(±0.3) eV is calculated for B diffusion in Ge. The results suggest that diffusion mechanism other than vacancy should be considered for B diffusion in Ge. For Si diffusion in Ge, the diffusivity values calculated in the temperature range 750–875 °C are in agreement with previous work. The activation energy of 3.2(±0.3) eV for Si diffusion is closer to that for Ge self-diffusion which suggests that Si diffusion in Ge occurs via the same mechanism as in Ge self-diffusion.

Tensile strained Si on SiGe Strain Relaxed Buffers (SRB) is an interesting candidate to increase both electron and hole mobility which results in improved device performance. Most of this work was/is based on thick (several μm), step-graded SRBs with or without Chemical Mechanical Polishing (CMP) planarisation. This approach bears several disadvantages such as issues with STI formation in the thick SiGe structure, and considerable self-heating effects due to the lower thermal conductivity of the SiGe material. Further, pMOS improvement requires SRBs with high Ge contents (> 30 %), which complicates device fabrication even more. To overcome these issues, we developed a new and cost efficient type of thin SRB (∼200 nm). The concept is based on the introduction of a thin carbon-containing layer during growth of a constant composition SiGe layer. The process relies on standard Chemical Vapor Deposition epitaxial technology without need for CMP. It is designed to allow both non-selective growth on blanket wafers and selective growth in the active area of structured wafers with Shallow Trench Isolation (STI). The selective epitaxial process for strained Si on thin SRBs proposed here, allows relatively simple and cost-effective fabrication of strained Si layers on existing STI structures without any process modification. Further, it offers a very flexible fabrication scheme to independently improve nMOS and pMOS devices. The SRB quality is comparable to the best reported in literature so far, with 70 % and 53 % mobility enhancements for long channel nMOSFETs on 22 % Ge SRBs grown on blanket and STI patterned wafers, respectively.

SiGe/Si n-type modulation doped field effect structures and transistors (n-MODFETs) have been fabricated on r-plane sapphire substrates. Mobilities as high as 1380 cm2/Vs were measured at room temperature. Excellent carrier confinement was shown by Shubnikov-de Haas measurements. Atomic force microscopy indicated smooth surfaces, with rms roughness less than 4 nm, similar to the quality of SiGe/Si n-MODFET structures made on Si substrates. Transistors with 2 μm gate lengths and 200 μm gate widths were fabricated and tested. An IDS of 9 mA was obtained by operating the transistor in an enhancement mode (positive VGS) and the maximum transconductance (gm) was 37 mS/mm at a VDS of 2.5 V. The transducer gain (Gt) measured with a loadpull system was 6.4 dB at 1 GHz for a VDS of 2.5 V and VGS=-0.4 V.

A new method for highlighting defects in thin Si/SiGe layers is used to investigate the densities of various types of defects present in strained Si layers grown on relaxed SiGe layers. Defect densities were measured in strained Si layers formed on graded SiGe buffer layers (bulk), as well as silicon germanium-on-insulator substrates (SGOI), from both external and internal sources. The result of this investigation indicates that in addition to threading dislocations (TDs) and dislocation pile-ups, planar defects, i.e., stacking faults, are present in all but one of the materials studied. Due to the larger crystalline area affected by these planar defects, citation of only TD density as an indication of material quality is inadequate. A better measure of crystalline quality should include the density of TDs, pile-up clusters and planar defects (stacking faults) as well as some indication of the length distribution of the pile-ups and stacking faults.

The crystalline quality of bonded Silicon-On-Insulator (SOI) wafers were examined by spectroscopic ellipsometry and Raman spectroscopy. Both techniques detect slight structural defects in the SOI layer. If a pure crystalline silicon dielectric function is assumed for the SOI layer, the spectroscopic ellipsometry data fitting yields an unacceptably large discrepancy between the experimental and modeled data. The best fits for all the samples result in a dielectric function of the SOI layer that consists of a physical mixture of crystalline silicon and about 4 % to 7 % of amorphous silicon. Using such a mixture indicates that there are still some defects in the SOI layer when compared with the high-quality bulk crystalline silicon. This observation is further supported by Raman spectroscopy measurements. The Raman spectra of all SOI samples exhibit a feature at about 495 cm−1 that is not observed in the crystalline silicon spectrum. Features similar to the 495 cm−1 feature have been reported in the literature and attributed to dislocations or faults in the silicon lattice.

Heterogeneous strain in Si/SiGe for CMOS mobility enhancement may result in device yield losses or IC performance limitations. This lateral heterogeneity in strain can be uniquely measured by Raman spectroscopy. UV Raman and Visible Raman can measure this heterogeneity respectively in the thin Si cap and in the SiGe underlayer. Both UV and Visible Raman are useful. While UV Raman is optimized for the Si channel layer, Visible Raman of the SiGe underlayer provides diagnostic information when trying to understand and reduce the heterogeneity in the Si channel. In principle Visible Raman can also measure the heterogeneity of the strain in the Si channel, but in practice this is very time consuming and not as sensitive as UV Raman. This paper focuses on the kind of heterogeneity strain information available from Visible Raman.

The effect of carbon on boron diffusion was studied in Si and strained SiGe. Several types B containing matrices were grown: (i) Si, (ii) Si containing 0.1% C peak, (iii) SiGe with 11% Ge and (iv) SiGe with 11% Ge and with a 0.1% C peak, using gas-source molecular beam epitaxy (MBE). The combination of Si, Si with C, SiGe and SiGe with C matrices allowed us to separate the effects of Ge and C on B diffusivity. To ensure non-injection surface conditions, low temperature silicon dioxide (LTO) and silicon nitride layers were deposited on top of samples in that order. These samples were then rapid thermal annealed (RTA) at 940, 1000 and 1050°C in an O2 ambient.

Diffusion coefficients of B in each type of matrix were extracted by computer simulation, using SIMS profiles obtained from samples before and after the RTA treatment. Diffusion coefficient is reduced by both Ge and C, the suppression by C being more profound. The results are compared to and found to be in reasonable agreement with limited data available in literature.

Solid phase epitaxial regrowth (SPER) has been proven to be highly advantageous for ultra shallow junction formation in advanced technologies. Application of SPER to strained Si/SiGe structures raises the concern that the Ge may out diffuse during the implantation and/or anneal steps and thus reduce the strain in the top silicon layer.

In the present studies we expose 8-30 nm strained silicon layers grown on thin relaxed SiGe-buffers, to implant conditions and anneal cycles, characteristic for formation of the junctions by solid phase epitaxial regrowth and conventional spike activation. The resulting Geredistribution is measured using SIMS. Based on the outdiffused Ge-profiles the Ge-diffusion coefficient has been determined in the temperature range of 800-1100C from which an activation energy of ∼ 3.6 eV can be deduced. Up to 1050 C, 10 min, even a 30 nm strained film remains highly stable and shows only very moderate outdiffusion.

We also have observed a far more efficient, athermal Ge-redistribution process linked to the implantation step itself. This was studied by analysing the Ge-redistribution following an Asimplant (2-15 keV, 5 1014 – 3 1015 at/cm2). It is shown that the energy of the implant species (or more specifically the position of the damage distribution function relative to the Ge-edge) plays a determining factor with respect to the Ge-migration. For implants whereby the damage distribution overlaps with the Ge-edge, a very efficient transport of the Ge is observed, even prior to any anneal cycle. The migration is entirely correlated with the collision cascade and the resulting (forward!) Ge-recoil distribution. The scaling with dose for a given energy links the observed Ge-profile with a broadening mechanism related to the number of atom displacements induced in the sample within the vicinity of the Si-SiGe-transition.

A unified diffusion model is developed, valid for all usual substitutional atoms in SiGe and strained SiGeC layers, in accordance with all published experimental data and predicting the enhancement of Arsenic diffusion in SiGe and SiGeC strained layers. Using a new SIMS methodology, the study of As intrinsic diffusion in SiGe and SiGeC layers is performed, at low concentration and under equilibrium annealing conditions. Arsenic diffusivity in fully-strained SiGe and SiGeC layers on Si substrates was successfully compared to the unified diffusion model.

Raman spectroscopy is a powerful and versatile technique for stress measurements in complex stacks of thin crystalline layers at macroscopic and microscopic scales. Using such a technique we show that thick SiGe layers epitaxially grown using graded buffer method are fully relaxed (>95%) at a macroscopic scale but exhibit a small strain modulation at a microscopic scale. For the first time we report the results of Raman micro-mapping of stress distribution in SGOI wafers produced by Smart Cut™ technology. We conclude that Smart Cut™ is a unique method to manufacture the next generation of engineered wafers that can combine strained and/or relaxed SiGe alloys, Si and Ge films, while keeping their initial strain properties at both scales. It is important to develop Raman spectroscopy tool for in-line process control in fabrication of strained Silicon On Insulator (sSOI) wafers.

Germanium is because of its intrinsically higher mobility than Si, currently under consideration as an alternative approach to improve transistor performance. Germanium oxide, however, is thermodynamically unstable, preventing formation of the gate dielectric by simple oxidation. At present, high-k dielectrics might be considered as an enabling technology as much progress has been made in the deposition of thin high-quality layers.

In this paper, we study the growth and physical properties of HfO2 deposited on Ge by MOCVD, using TDEAH and O2 as precursors, and compare the results to similar layers deposited on silicon substrates. Our results show that the physical properties of MOCVDdeposited HfO2 layers on Ge are very similar to what we have observed in the past for Si. Unfortunately, some of the negative aspects observed for Si, such as diffusion of substrate material in the high-k layer, a low density for thinner layers, or a rough top surface, are also observed for the case of Ge. However, careful surface pretreatments such as NH3 annealing the Ge substrate prior to deposition, can greatly improve the physical properties. An important observation is the very thin interfacial layer between HfO2 and Ge substrate, allowing a more aggressive scaling for Ge.

Results of intrinsic As diffusion in Si as well as in strained and relaxed Si0.9Ge0.1 layers are presented. Using Molecular Beam Epitaxy in-situ As doped epitaxial Si and compressively strained and relaxed Si-Ge layers were grown on Si substrates. The samples were annealed using Rapid Thermal Annealing (RTA) at 1000 °C. Arsenic diffusion is seen to be enhanced in SiGe than in Si. The enhancement factor is calculated to be 2.3 and 1.3 for relaxed and strained Si0.9Ge0.1, respectively. Also, using RTA in oxygen atmosphere, interstitial and vacancies were selectively injected in to the sample structures. Diffusion enhancement is also recorded in Si and Si-Ge structures with interstitial as well as vacancy injections over inert anneal. The results suggest that both interstitial and vacancy defects contribute to As diffusion in Si and Si0.9Ge0.1.

Junctions were formed in thin SiGe/strained Si substrates with a thickness of 250-350 nm to assess the effect of different buffer layer parameters (bandgap, dislocations, thickness) on the junction leakage density that can be expected in MOSFET devices. The implantations used are standard well, channel and Highly Doped Drain (HDD) implants. Both p+/n and n+/p junctions were evaluated. The total thickness of the buffer layers was varied to compare the effect of different structural layers on the diode leakage. This investigation shows that the effect of an increased defect density is dominant at room temperature for the strained Si samples, resulting in 4-5 orders of magnitude increase in leakage. However, there is a different gradation in leakage dependence for thick and thin buffer layers, especially at higher temperatures.

Boron and phosphorus were implanted into (100) Ge with energies ranging from 20-320 keV and doses of 5×1013 to 5×1016 cm−2. The as-implanted and annealed dopant profiles were examined using secondary ion mass spectrometry (SIMS) and spreading resistance profiling (SRP). The first four moments were extracted from the as-implanted profile for modeling with Pearson distributions over the entire energy range. The samples were annealed at 400, 600, or 800°C in nitrogen ambient. The dopant activation and diffusion were also examined and it was found that p-type sheet resistances immediately after boron implantation as low as 18 ohms/sq could be obtained without subsequent annealing.

Interference-enhanced Raman scattering was utilized to characterize strain in ultra-thin strained silicon-germanium (SiGe) and silicon layers on insulator. Strained SiGe and silicon films with thickness ranging from 10 to 30 nm on insulating borophosphorosilicate glass (BPSG) were formed by layer transfer techniques and/or strain manipulation via lateral expansion of strained films. The optical interference of the multiple reflections at the BPSG interfaces can substantially boost the reflectivity at the interfaces. The reflection improves Raman signal from SiGe and/or silicon films by increasing excitation intensity and Raman signal collection in the thin films. With the use of interference-enhanced Raman scattering, strain can be characterized at visible wavelengths for films as thin as 10 nm.

In this paper, we compare B diffusion in epitaxial Si, Si with 0.1%C, SiGe with 11% Ge and SiGe:C with 11%Ge and 0.1%C at 1000°C under interstitial, vacancy and non-injection annealing conditions. Diffusion coefficients of B in each material were extracted by computer simulation, using secondary ion mass spectroscopy (SIMS) profiles obtained from samples before and after annealing.

Interstitial injection enhances B diffusion considerably in all materials compared to inert annealing. In samples which experienced vacancy injection, B diffusion was suppressed. The results are consistent with the view that B diffusion in these materials occurs primarily via interstitialcy type defects.