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The impact of elemental boron (B) doping on the structural, optical, and magnetotransport properties of epitaxial Ge/AlAs/GaAs(001) heterostructures, grown by solid-source molecular beam epitaxy, was comprehensively investigated. Cross-sectional transmission electron microscopy analysis revealed atomically abrupt Ge:B/AlAs and AlAs/GaAs heterointerfaces and a lack of observable long-range defect formation or B segregation in the epitaxial Ge:B layer. Spectral broadening observed in the measured temperature-dependent photoluminescence spectra suggested valence band mixing during recombination, implying a splitting of the valence band heavy- and light-hole degeneracy due to residual strain resulting from substitutional B incorporation in the Ge epilayer. Temperature-dependent magnetotransport analysis of the B-doped Ge thin films exhibited the tell-tale signature of antilocalization, indicating observable spin–orbit interaction in the Ge:B system. Moreover, the temperature- and magnetic field-dependent magnetotransport results indicate the presence of single-carrier, p-type conduction in the Ge:B film, further affirming the successful incorporation and activation of B at a high concentration (∼4 × 1019 cm−3) and elimination of parallel conduction via the large-bandgap AlAs buffer. Together, these results provide insights into the effects of heavy doping (via elemental solid-source doping) on Ge-based heterostructures and their feasibility in future electronic and photonic applications. [ABSTRACT FROM AUTHOR]

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) InxGa1-xAs/GaAsySb1-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 article, we have evaluated the merits of monolithically cointegrated alternate channel complementary metal-oxide-semiconductor (CMOS) device architecture, utilizing tensile strained germanium ($\boldsymbol {\varepsilon }$ -Ge) for the p-channel FinFET and variable indium (In) compositional InxGa1-xAs ($0.10\le {x} \le0.53$) for the n- channel FinFET. The device simulation models were calibrated using the experimental results of Ge and InGaAs FinFETs and subsequently transferred to the cointegrated Ge and InxGa1-x As structure while keeping the device simulation parameters fixed. The device parameters, such as ${V}_{\text {T}}$ , ${I}_{\text {on}}$ , ${I}_{\text {off}}$ , and subthreshold-swing (SS), were determined for identical fin dimensions for n- and p-channel FinFETs as a function of In composition that alters the tensile strain in Ge. These parameters are controllable during the heteroepitaxial growth by varying In composition in InxGa1-xAs. $\boldsymbol {\varepsilon }$ -Ge p-FinFET is shown to be superior in terms of SS and ${I}_{\text {on}}/{I}_{\text {off}}$ ratio compared with other competing architectures. The cointegrated architecture of CMOS inverter exhibited an optimum performance over a range of In compositions from 20% to 40% while driving fan-out fan-out 1 (FO-1) and FO-4 load configurations. In addition, the CMOS inverter with symmetric rise and fall times as well as noise-immune functionality demonstrated 150 GHz of operating frequency with 30-nW total power dissipation at 20% In composition, and hence a superior power-delay-product comparable with International Technology Roadmap for Semiconductors (ITRS) standards. Moreover, the three-stage CMOS ring oscillator performance was evaluated with various In compositions to be stable and power efficient. Thus, the cointegrated approach has a potential to: 1) simplify large-scale CMOS integration and 2) be compatible with optoelectronic materials. [ABSTRACT FROM AUTHOR]

The structural, morphological, optical, and electrical transport characteristics of a metamorphic, broken-gap InAs/GaSb p-i-n tunnel diode structure, grown by molecular beam epitaxy on GaAs, were demonstrated. Precise shutter sequences were implemented for the strain-balanced InAs/GaSb active layer growth on GaAs, as corroborated by high-resolution X-ray analysis. Cross-sectional transmission electron microscopy and detailed micrograph analysis demonstrated strain relaxation primarily via the formation of 90° Lomer misfit dislocations (MDs) exhibiting a 5.6 nm spacing and intermittent 60° MDs at the GaSb/GaAs heterointerface, which was further supported by a minimal lattice tilt of 180 arc sec observed during X-ray analysis. Selective area diffraction and Fast Fourier Transform patterns confirmed the full relaxation of the GaSb buffer layer and quasi-ideal, strain-balanced InAs/GaSb heteroepitaxy. Temperature-dependent photoluminescence measurements demonstrated the optical band gap of the GaSb layer. Strong optical signal at room temperature from this structure supports a high-quality material synthesis. Current–voltage characteristics of fabricated InAs/GaSb p-i-n tunnel diodes measured at 77K and 290K demonstrated two bias-dependent transport mechanisms. The Shockley–Read–Hall generation-recombination mechanism at low bias and band-to-band tunneling transport at high bias confirmed the p-i-n tunnel diode operation. This elucidated the importance of defect control in metamorphic InAs/GaSb tunnel diodes for the implementation of low-voltage and high-performance tunnel field effect transistor applications. [ABSTRACT FROM AUTHOR]

The strain relaxation mechanism and defect properties of compositionally step-graded InAsyP1-y buffers grown by molecular beam epitaxy on InP have been investigated. InAsP layers having lattice misfits ranging from 1% to 1.4% with respect to InP, as well as subsequently grown lattice matched In0.69Ga0.31As overlayers on the metamorphic buffers were explored on both (100) and 2° offcut (100) InP substrates. The metamorphic graded buffers revealed very efficient relaxation coupled with low threading dislocation densities on the order of (1–2)×106 cm-2 for the range of misfit values explored here. A detailed analysis via high resolution x-ray diffraction revealed that the strain relaxed symmetrically, with equivalent numbers of α and β dislocations, and to greater than 90% for all cases, regardless of substrate offcut. Further analysis showed the relaxation to always be glide limited in these materials when grown on a graded buffer compared to a single step layer. The threading dislocation density was observed by plan-view transmission electron microscopy to be constant for the range of misfit values studied here in the top layer of the graded structures, which is attributed to the very efficient use of residual dislocations and the dominance of dislocation glide over nucleation in these graded anion metamorphic buffers, suggesting great promise for metamorphic devices with lattice constants greater than that of InP to be enabled by InAsP metamorphic structures on InP. [ABSTRACT FROM AUTHOR]

The strain relaxation mechanism and defect properties of compositionally step-graded In[As.sub.y][P.sub.1-y] buffers grown by molecular beam epitaxy on InP are examined. The threading dislocation density is seen by plan-view transmission electron microscopy to be constant for the range of misfit values in the top layer of the graded structures.