The performance of strained silicon (Si) as the channel material for today’s metal-oxide-semiconductor field-effect transistors may be reaching a plateau. New channel materials with high carrier mobility are being investigated as alternatives and have the potential to unlock an era of ultra-low-power and high-speed microelectronic devices. Chief among these new materials is germanium (Ge). This work reviews the two major remaining challenges that Ge based devices must overcome if they are to replace Si as the channel material, namely, heterogeneous integration of Ge on Si substrates, and developing a suitable gate stack. Next, Ge is compared to compound III-V materials in terms of p-channel device performance to review how it became the first choice for PMOS devices. Different Ge device architectures, including surface channel and quantum well configurations, are reviewed. Finally, state-of-the-art Ge device results and future prospects are also discussed.

Reducing supply voltage is a promising way to address the power dissipation in nano-electronic circuits. However, the fundamental lower limit of subthreshold slope (SS) within metal oxide semiconductor field effect transistors (MOSFETs) is a major obstacle to further scaling the operation voltage without degrading ON/OFF ratio in current integrated circuits. Tunnel field-effect transistors (TFETs) benefit from steep switching characteristics due to the quantum-mechanical tunneling injection of carriers from source to channel, rather than by conventional thermionic emission in MOSFETs. TFETs based on group III-V compound semiconductor materials further improve the ON-state current and reduce SS due to the low band gap energies and smaller carrier tunneling mass. The mixed arsenide/antimonide (As/Sb) In_xGa_1-xAs/GaAs_ySb_1-y heterostructures allow a wide range of band gap energies and various staggered band alignments depending on the alloy compositions in the source and channel materials. Band alignments at source/channel heterointerface can be well modulated by carefully controlling the compositions of the mixed As/Sb material system. In particular, this review introduces and summarizes the progress in the development and optimization of low-power TFETs using mixed As/Sb based heterostructures including basic working principles, design considerations, material growth, interface engineering, material characterization, device fabrication, device performance investigation, band alignment determination, and high temperature reliability. A review of TFETs using mixed As/Sb based heterostructures shows superior structural properties and distinguished device performance, both of which indicate the mixed As/Sb staggered gap TFET as a promising option for high-performance, low-standby power, and energy-efficient logic circuit application.

In this paper, we benchmark the read/write performance and standby power of several static random access memory (SRAM) cell architectures utilizing 45-nm Si CMOS MOSFET and/or tensile-strained Ge/InGaAs tunnel FET (TFET) devices under low-voltage operation (0.2 V ≤ |V _DD | ≤ 0.6 V). We then introduce a novel tensile-strained Ge/InGaAs TFET-based SRAM circuit using several access schemes and investigate the impact of cell access design on static and dynamic performance. SRAM cells utilizing outward access transistors exhibit wide read and write static noise margins, but suffer from increased read delay times. A 7T SRAM cell architecture is proposed in order to resolve the degraded read delay time. Cell standby energy was found to exhibit a strong dependence on operational voltage and Ge strain state. Variation of the Ge strain state from 1.5% to 3% resulted in an up to 98% reduction in cell standby energy (|V _DD | = 0.6 V) as compared with similar CMOS-based SRAM cells. These results demonstrate the superior performance of the proposed 7T TFET SRAM design for operation in the low- and ultralow-voltage regime.

Germanium-based materials and device architectures have recently appeared as exciting material systems for future low-power nanoscale transistors and photonic devices. Heterogeneous integration of germanium (Ge)-based materials on silicon (Si) using large bandgap buffer architectures could enable the monolithic integration of electronics and photonics. In this paper, we report on the heterogeneous integration of device-quality epitaxial Ge on Si using composite AlAs/GaAs large bandgap buffer, grown by molecular beam epitaxy that is suitable for fabricating low-power fin field-effect transistors required for continuing transistor miniaturization. The superior structural quality of the integrated Ge on Si using AlAs/GaAs was demonstrated using high-resolution x-ray diffraction analysis. High-resolution transmission electron microscopy confirmed relaxed Ge with high crystalline quality and a sharp Ge/AlAs heterointerface. X-ray photoelectron spectroscopy demonstrated a large valence band offset at the Ge/AlAs interface, as compared to Ge/GaAs heterostructure, which is a prerequisite for superior carrier confinement. The temperature-dependent electrical transport properties of the n-type Ge layer demonstrated a Hall mobility of 370[emsp14]cm2/Vs at 290[emsp14]K and 457[emsp14]cm2/Vs at 90[emsp14]K, which suggests epitaxial Ge grown on Si using an AlAs/GaAs buffer architecture would be a promising candidate for next-generation high-performance and energy-efficient fin field-effect transistor applications.

This paper introduces a new synthesis procedure to form erbium-doped ceria nanoparticles (EDC NPs) that can act as an optical medium for both up-conversion and down-conversion in the same time. This synthesis process results qualitatively in a high concentration of Ce3+ ions required to obtain high fluorescence efficiency in the down-conversion process. Simultaneously, the synthesized nanoparticles contain the molecular energy levels of erbium that are required for up-conversion. Therefore, the synthesized EDC NPs can emit visible light when excited with either UV or IR photons. This opens new opportunities for applications where emission of light via both up- and down-conversions from a single nanomaterial is desired such as solar cells and bio-imaging.

To develop low-moment, low-damping metallic ferromagnets for power-efficient spintronic devices, it is crucial to understand how magnetic relaxation is impacted by the addition of nonmagnetic elements. Here, we compare magnetic relaxation in epitaxial $\mathrm{Fe}$ films alloyed with light, nonmagnetic elements of $\mathrm{V}$ and $\mathrm{Al}$. $\mathrm{Fe}\text{−}\mathrm{V}$ alloys exhibit lower intrinsic damping compared with that of pure $\mathrm{Fe}$, reduced by nearly a factor of 2, whereas damping in $\mathrm{Fe}\text{−}\mathrm{Al}$ alloys increases with $\mathrm{Al}$ content. Our experimental and computational results indicate that reducing the density of states at the Fermi level, rather than the average atomic number, has a more significant impact on lowering damping in $\mathrm{Fe}$ alloyed with light elements. Moreover, $\mathrm{Fe}\text{−}\mathrm{V}$ is confirmed to exhibit an intrinsic Gilbert damping parameter of about 0.001, which is among the lowest ever reported for ferromagnetic metals.