On the Performance of Single-Gated Ultrathin-Body SOI Schottky-Barrier MOSFETs

The authors study the dependence of the performance of silicon-on-insulator (SOI) Schottky-barrier (SB) MOSFETs on the SOI body thickness and show a performance improvement for decreasing SOI thickness. The inverse subthreshold slopes S extracted from the experiments are compared with simulations and an analytical approximation. Excellent agreement between experiment, simulation, and analytical approximation is found, which shows that S scales approximately as the square root of the gate oxide and the SOI thickness. In addition, the authors study the impact of the SOI thickness on the variation of the threshold voltage V-th of SOI SB-MOSFETs and find a non-monotonic behavior of V-th. The results show that to avoid large threshold voltage variations and achieve high-performance devices, the gate oxide thickness should be as small as possible, and the SOI thickness should be similar to 3 nm

Fabrication of epitaxial CoSi₂ nanowires

We have developed a method for fabricatingepitaxialCoSi₂nanowires using only conventional optical lithography and standard silicon processing steps. This method was successfully applied to ultrathin epitaxialCoSi₂ layers grown on Si(100) and silicon-on-insulator substrates. A nitride mask induces a stress field near its edges into the CoSi₂/Siheterostructure and leads to the separation of the CoSi₂ layer in this region during a rapid thermal oxidation step. A subsequent etching step and a second oxidation generate highly homogenous silicide wires with dimensions down to 50 nm

Evaluating intuitive decision-making in non-metric sex estimation from the cranium: an exploratory study

In recent years, forensic science has seen a rise in the number of multidisciplinary studies examining the effect of human cognition on the evaluation of forensic evidence. Notably, the House of Lords’ report highlighted the need for further investigation of the consequences of cognitive factors on decision-making processes involved in evidence evaluation and interpretation. Utilizing the concepts of intuitive and methodical decision-making, this pilot study investigated this dichotomy within the field of forensic anthropology, applied to sex estimation from the skull. Participants were asked to estimate the biological sex of six crania in two experiments: once ‘intuitively’ under time-pressure, and once by rationally applying the Acsádi and Nemeskéri method with no time-pressure. The potential influence of experience and its correlation with the participants’ confidence levels was also explored. The results demonstrate that intuitive and methodical evaluations can be consistent with each other, yet consistency decreases as ambiguity increases. Confidence was affected more by time availability, and less by level of experience. The insights from this exploratory study address how decision-making processes are involved in the examination of skeletal remains and offers justification for future exploration into the value of applying wider decision-making theories in the field of forensic anthropology

Nanopatterning of epitaxial CoSi₂ using oxidation in a local stress field and fabrication of nanometer metal-oxide-semiconductor field-effect transistors

A patterning method for the generation of epitaxialCoSi₂nanostructures was developed based on anisotropic diffusion of Co∕Si atoms in a stress field during rapid thermal oxidation (RTO). The stress field is generated along the edge of a mask consisting of a thin SiO₂ layer and a Si₃N₄ layer. During RTO of the masked silicide structure, a well-defined separation of the silicide layer forms along the edge of the mask. The technique was used to make 50-nm channel-length metal-oxide-semiconductor field-effect transistors(MOSFETs). These highly uniform gaps define the channel region of the fabricated device. Two types of MOSFETs have been fabricated: symmetric transistor structures, using the separated silicide layers as Schottky source and drain, and asymmetric transistors, with n+ source and Schottky drain. The asymmetric transistors were fabricated by an ion implantation into the unprotected CoSi₂ layer and a subsequent out diffusion to form the n+ source. The detailed fabrication process as well as the I–V characteristics of both the symmetric and asymmetric transistor structures will be presented

Scanning spreading resistance microscopy of two-dimensional diffusion of boron implanted in free-standing silicon nanostructures

B implants of 1keV, 1×10¹⁵at.cm⁻² into 125-nm-wide, free-standing Si nanostructures have been characterized using scanning spreading resistancemicroscopy following a 0s, 1050°Canneal in N₂. A curved diffusion front has been observed. B in the center of the ridge diffuses further than at the sides. A similar effect has been observed in SUPREM-IV simulations. It is attributed to a reduction in transient enhanced diffusion close to the vertical surfaces due to recombination of ion-implantation-induced excess Si self-interstitials

Impact of TFET unidirectionality and ambipolarity on the performance of 6T SRAM cells

We use mixed device-circuit simulations to predict the performance of 6T static RAM (SRAM) cells implemented with tunnel-FETs (TFETs). Idealized template devices are used to assess the impact of device unidirectionality, which is inherent to TFETs and identify the most promising configuration for the access transistors. The same template devices are used to investigate the $ extV- m DD range, where TFETs may be advantageous compared to conventional CMOS. The impact of device ambipolarity on SRAM operation is also analyzed. Realistic device templates extracted from experimental data of fabricated state-of-the-art silicon pTFET are then used to estimate the performance gap between the simulation of idealized TFETs and the best experimental implementations

Strained Silicon Complementary TFET SRAM: Experimental Demonstration and Simulations

A half SRAM cell with strained Si nanowire complementary tunnel-FETs (TFETs) was fabricated and characterized to explore the feasibility and functionality of 6T-SRAM based on TFETs. Outward-faced n-TFETs are used as access-transistors. Static measurements were performed to determine the SRAM butterfly curves, allowing the assessment of cell functionality and stability. The forward p-i-n leakage of the access-transistor at certain bias configurations leads to malfunctioning storage operation, even without the contribution of the ambipolar behavior. At large VDD, lowering of the bit-line bias is needed to mitigate such effect, demonstrating functional hold, read and write operations. Circuit simulations were carried out using a Verilog-A compact model calibrated on the experimental TFETs, providing a better understanding of the TFET SRAM operation at different supply voltages and for different cell sizing and giving an estimate of the dynamic performance of the cell

Optical Transitions in Direct-Bandgap Ge1-xSnx Alloys

A comprehensive study of optical transitions in direct-bandgap Ge0.875Sn0.125 group IV alloys via photoluminescence measurements as a function of temperature, compressive strain and excitation power is performed. The analysis of the integrated emission intensities reveals a strain-dependent indirect-to-direct bandgap transition, in good agreement with band structure calculations based on the 8-band k·p and deformation potential methods. We have observed and quantified Γ valley-heavy hole and Γ valley-light hole transitions at low pumping power and low temperatures in order to verify the splitting of the valence band due to strain. We will demonstrate that the intensity evolution of these transitions supports the conclusion about the fundamental direct bandgap in compressively strained GeSn alloys. The presented investigation, thus, demonstrates that direct-bandgap group IV alloys can be directly grown on Ge-buffered Si(001) substrates despite their residual compressive strain

Correlation of bandgap reduction with inversion response in (Si)GeSn/high-k/metal stacks.

The bandgap tunability of (Si)GeSn group IV semiconductors opens a new era in Si-technology. Depending on the Si/Sn contents, direct and indirect bandgaps in the range of 0.4 eV to 0.8 eV can be obtained, offering a broad spectrum of both photonic and low power electronic applications. In this work, we systematically studied capacitance-voltage characteristics of high-k/metal gate stacks formed on GeSn and SiGeSn alloys with Sn-contents ranging from 0 to 14 at.% and Si-contents from 0 to 10 at.% particularly focusing on the minority carrier inversion response. A clear correlation between the Sn-induced shrinkage of the bandgap energy and enhanced minority carrier response was confirmed using temperature and frequency dependent capacitance voltage-measurements, in good agreement with k.p theory predictions and photoluminescence measurements of the analyzed epilayers as reported earlier. The enhanced minority generation rate for higher Sn-contents can be firmly linked to the bandgap reduction in the GeSn epilayer without significant influence of substrate/interface effects. It thus offers a unique possibility to analyze intrinsic defects in (Si)GeSn epilayers. The extracted dominant defect level for minority carrier inversion lies approximately 0.4 eV above the valence band edge in the studied Sn-content range (0 to12.5 at.%). This finding is of critical importance since it shows that the presence of Sn by itself does not impair the minority carrier lifetime. Therefore, the continuous improvement of (Si)GeSn material quality should yield longer non-radiative recombination times which are required for the fabrication of efficient light detectors and to obtain room temperature lasing action

Process modules for GeSn nanoelectronics with high Sn-contents

In this paper we present a systematic study of GeSn n-FETs. First, process modules such as high-k metal gate stacks and NiGeSn-metallic contacts for use as source/drain contacts are characterized and discussed. GeSn alloys of different Sn content allow the study of the capacitance-voltage (CV) and contact characteristics of both direct and indirect bandgap semiconductors. We then present GeSn n-FET devices we have fabricated. The device characterization includes temperature dependent IV characteristics. As important step towards GeSn for tunnel-FET Ge0.87Sn0.13 tunnel-diodes with negative differential resistance at reduced temperature are shown. The present work provides a base for further optimization of GeSn FET and novel tunnel FET devices