Search Results (172)

Graphene’s exceptional carrier mobility and broadband absorption make it promising for ultrafast photodetection. However, its low optical absorption limits responsivity, while the absence of a bandgap results in high dark current, constraining the signal-to-noise ratio and efficiency. Although silicon (Si) photodetectors normally offer fabrication compatibility, their performance is severely hindered by interface trap states and optical shading. To overcome these limitations, we demonstrate an epitaxial graphene/n-Si heterojunction photodiode. This device utilizes graphene epitaxially grown on germanium integrated with a transferred Si thin film, eliminating polymer residues and interface defects common in transferred graphene. As a result, the fabricated photodetector achieves an ultralow dark current of 1.2 × 10⁻⁹ A, a high responsivity of 1430 A/W, and self-powered operation at room temperature. This work provides a strategy for high-sensitivity and low-power photodetection and demonstrates the practical integration potential of graphene/Si heterostructures for advanced optoelectronics. Full article

This paper presents the first demonstration and comparison of two identical oscillator circuits employing piezoelectric zinc oxide (ZnO) microelectromechanical systems (MEMS) resonators, implemented on conventional printed-circuit-board (PCB) and three-dimensional (3D)-printed acrylonitrile butadiene styrene (ABS) substrates. Both oscillators operate simultaneously at dual frequencies (260 MHz and 437 MHz) without the need for additional circuitry. The MEMS resonators, fabricated on silicon-on-insulator (SOI) wafers, exhibit high-quality factors (Q), ensuring superior phase noise performance. Experimental results indicate that the oscillator packaged using 3D-printed chip-carrier assembly achieves a 2–3 dB improvement in phase noise compared to the PCB-based oscillator, attributed to the ABS substrate’s lower dielectric loss and reduced parasitic effects at radio frequency (RF). Specifically, phase noise values between −84 and −77 dBc/Hz at 1 kHz offset and a noise floor of −163 dBc/Hz at far-from-carrier offset were achieved. Additionally, the 3D-printed ABS-based oscillator delivers notably higher output power (4.575 dBm at 260 MHz and 0.147 dBm at 437 MHz). To facilitate modular characterization, advanced packaging techniques leveraging precise 3D-printed encapsulation with sub-100 μm lateral interconnects were employed. These ensured robust packaging integrity without compromising oscillator performance. Furthermore, a comparison between two transistor technologies—a silicon germanium (SiGe) heterojunction bipolar transistor (HBT) and an enhancement-mode pseudomorphic high-electron-mobility transistor (E-pHEMT)—demonstrated that SiGe HBT transistors provide superior phase noise characteristics at close-to-carrier offset frequencies, with a significant 11 dB improvement observed at 1 kHz offset. These results highlight the promising potential of 3D-printed chip-carrier packaging techniques in high-performance MEMS oscillator applications. Full article

This study provides new insight into the mechanisms governing solid state dewetting (SSD) in SiGe alloys and underscores the potential of this bottom-up technique for fabricating self-organized defect-free nanostructures for CMOS-compatible photonic and nanoimprint applications. In particular, we investigate the SSD of Si_1−xGe_x thin films grown by molecular beam epitaxy on silicon-on-insulator (SOI) substrates, focusing on and clarifying the interplay of dewetting dynamics, strain elastic relaxation, and SiGe/SOI interdiffusion. Samples were annealed at 820 °C, and their morphological and compositional evolution was tracked using atomic force microscopy (AFM), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), and Raman spectroscopy, considering different annealing time steps. A sequential process typical of the SiGe alloy has been identified, involving void nucleation, short finger formation, and ruptures of the fingers to form nanoislands. XRD and Raman data reveal strain relaxation and significant Si-Ge interdiffusion over time, with the Ge content decreasing from 29% to 20% due to mixing with the underlying SOI layer. EDX mapping confirms a Ge concentration gradient within the islands, with higher Ge content near the top. Full article

Germanium/tin-containing silicon oxide [SiO–(GeO/SnO)] nanoclusters have been designed with different Si/Ge/Sn particles and characterized as electrodes for magnesium-ion batteries (MIBs) due to forming MgBe [SiO–GeO], MgBe [SiO–SnO], MgCa [SiO–GeO], and MgCa [SiO–SnO] complexes. In this work, alkaline earth metals of magnesium (Mg), beryllium (Be), and calcium (Ca) have been studied in hybrid Mg-, Be-, and Ca-ion batteries. An expanded investigation on H capture by MgBe [SiO–(GeO/SnO)] or MgCa [SiO–(GeO/SnO)] complexes was probed using computational approaches due to density state analysis of charge density differences (CDD), total density of states (TDOS), and electron localization function (ELF) for hydrogenated hybrid clusters of MgBe [SiO–GeO], MgBe [SiO–SnO], MgCa [SiO–GeO], and MgCa [SiO–SnO]. Replacing Si by Ge/Sn content can increase battery capacity through MgBe [SiO–GeO], MgBe [SiO–SnO], MgCa [SiO–GeO], and MgCa [SiO–SnO] nanoclusters for hydrogen adsorption processes and could improve the rate performances by enhancing electrical conductivity. A small portion of Mg, Be, or Ca entering the Si–Ge or Si–Sn layer to replace the alkaline earth metal sites could improve the structural stability of the electrode material at high multiplicity, thereby improving the capacity retention rate. In fact, the MgBe [SiO–GeO] remarks a small enhancement in charge transfer before and after hydrogen adsorption, confirming the good structural stability. In addition, [SiO–(GeO/SnO)] anode material could augment the capacity owing to higher surface capacitive impacts. Full article

Benefiting from the progress of the germanium (Ge) epitaxy process on silicon (Si) substrates, waveguide-integrated Ge-on-Si photodetectors (PDs) have demonstrated decent performances in short-wave infrared (SWIR) detection. By lowering the operating temperature, theses PDs can meet the stringent signal-to-noise requirements for high-sensitivity detection. We systematically investigated the dark current characteristics and optical response in the 1500–1600 nm wavelength range of the waveguide-integrated Ge-on-Si PDs operated at low temperatures (200 K to 300 K). Under a −3 V bias, the PD exhibits a room-temperature dark current of 4.62 nA and a responsivity of 0.87 A/W at 1550 nm. When the temperature was reduced to 200 K, the dark current decreased to 93.69 pA, and the responsivity dropped to 0.34 A/W. Using finite-difference time-domain (FDTD) and technology computer-aided design (TCAD) simulations, we extracted the absorption coefficients of epitaxial Ge on Si at low temperatures. At room temperature, the absorption coefficient at the wavelength of 1550 nm was approximately 1100 cm⁻¹, while at 200 K, the absorption coefficient decreased to 248 cm⁻¹. The outcomes of this work pave the way for the high-performance low-temperature Si photonic systems in the future. Full article

In this work, the effects of heavy ion strike position, incident angle, linear energy transfer (LET) value, ambient temperature, bias conditions, and the synergistic effects of total dose irradiation on the single-event transient (SET) in silicon-germanium heterojunction bipolar transistors on silicon-on-insulator (SiGe-on-SOI HBTs) were investigated using TCAD simulations. It was demonstrated that, compared to the bulk SiGe HBT, the SiGe-on-SOI HBT exhibits lower transient current and less charge collection, indicating better resistance to SET. The SET response is more pronounced when heavy ions strike vertically from the emitter and base regions. Transient current and collected charge escalate with increasing incident angle, demonstrating a strong linear correlation with LET values. As the temperature decreases, the peak transient current increases, while the pulse duration decreases and the total collected charge diminishes. After total dose irradiation, the peak transient current in the SiGe-on-SOI HBT decreases, whereas the damage was more severe in the absence of irradiation. Under collector positive bias and positive bias, significant SET responses were observed, while cutoff bias and substrate bias exhibited better resistance to SET damage. These findings provide critical insights into radiation-hardened design strategies for the SiGe-on-SOI HBT. Full article

This work constitutes Part II of a comprehensive three-part study critically reviewing techniques for the indirect extraction of the thermal resistance in bipolar transistors using simple DC current/voltage measurements. While Part I focused on thermometer-based methods, this study examines techniques that rely on intersection points between electrical characteristics. The accuracy of these methods is assessed by applying them to DC curves obtained through PSPICE simulations of an in-house transistor model incorporating nonlinear thermal effects, and comparing the extracted thermal resistance data with the thermal resistance formulation embedded in the model. An InGaP/GaAs HBT and a Si/SiGe HBT for high-frequency applications are considered as case-studies. The analysis highlights key drawbacks affecting the methods, including theoretical approximations and sensitivity to the selection of intersection points. Among the techniques examined, only one adequately accounts for the nonlinear thermal behavior, though its original formulation presents practical limitations. To tackle this problem, we propose an improved and refined version of the approach that offers enhanced accuracy at the cost of increased complexity. Full article

An uncooled microbolometer is a thermal sensor consisting of a membrane suspended from the substrate to provide thermal insulation. Typically, the membrane is composed of a stack of three films integrated by a supporting film, an IR sensing film, and an IR absorbing film. However, the above increases the thickness of the device and affects its mechanical stability and thermal mass, thereby reducing its performance. One solution is to use a single film as a membrane with both IR sensing and IR absorbing properties. In this regard, this work presents the fabrication and evaluation of uncooled microbolometers using nitrogen-doped hydrogenated amorphous silicon-germanium (a-SiGe:H,N) as a single IR-absorber/IR sensing membrane. The films were deposited via low frequency Plasma Enhanced Chemical Vapor Deposition (PECVD) at 200 °C. Three microbolometer configurations were fabricated using a-SiGe:H,N films deposited from a SiH₄, GeH₄, N_2, and H₂ gas mixture with different SiH₄ and GeH₄ flow rates and, consequently, with different properties, such as temperature coefficient of resistance (TCR) and conductivity at room temperature. The microbolometer that exhibited the best performance achieved a voltage responsivity of 7.26 × 10⁵ V/W and a NETD of 22.35 mK at 140 Hz, which is comparable to state-of-the-art uncooled infrared (IR) sensors. These results confirm that the optimization of the deposition parameters of the a-SiGe:H,N films significantly affects the microbolometers final performance, enabling an optimal balance between thermal sensitivity (TCR) and conductivity. Full article

The performance of the Si MOSFET is suppressed when the channel loses its control through the gate. This paper introduces a new and novel high-channel conducting orthogonally oriented selective buried triple gate vertical power MOSFET technology to study the channel behavior compared with the conventional Si power MOSFET. Our paper investigates the performance of the proposed selective buried triple gate power MOSFET by using different channel materials (SiGe/GeSn over Si) to compare with the conventional Si MOSFET. Our 2D Silvaco simulation output significantly improves device on-current, ON-resistance, channel electron mobility, transconductance, and enhancement in various parameters governing power MOSFET. The unique design of our proposed triple gate gives very high channel mobility of 880 cm²/V·s, which we believe to be significant in the triple gate power MOSFET domain. The results show that our optimized triple-gate device achieves an ultra-low specific ON-resistance of 0.31 mΩ·cm², improving Balliga’s FOM1 by 411.61% and FOM2 by 98.704%. This makes it suitable for high-speed and switching devices, compatible with various high-mobility channel materials, and well-suited for future CMOS applications. Full article

With recent electronic devices relying on sub-nanometer features, the understanding of device performance requires a direct probe of the atomic arrangement. As an ideal tool for crystallographic analysis at the nanoscale, aberration-corrected transmission electron microscopy (ACTEM) has the ability to provide atomically resolved images and core-loss spectra. Herein, the techniques for crystallographic structure analysis based on ACTEM are reviewed and discussed, particularly ACTEM techniques for measuring strain, dislocations, phase transition, and lattice in-plane misorientation. In situ observations of crystal evolution during the application of external forces or electrical fields are also introduced, so a correlation between crystal quality and device performance can be obtained. Full article

The in situ combination of plasma-enhanced chemical vapor deposition (PECVD) and vacuum evaporation in the same vacuum chamber allowed us to integrate germanium nanocrystals (Ge NCs) into hydrogenated amorphous silicon carbide (a-SiC:H) thin films deposited from monomethyl silane diluted with hydrogen. Transmission electron microscopy (TEM) and energy-dispersive X-ray (EDX) spectroscopy were used for the microscopic characterization, while photothermal deflection spectroscopy (PDS) and near-infrared photoluminescence spectroscopy (NIR PL) were for optical characterization. The presence of Ge NCs embedded in the amorphous a-Si:C:H thin films was confirmed by TEM and EDX. The embedded Ge NCs increased optical absorption in the NIR spectral region. The quenching of a-SiC:H NIR PL due to the presence of Ge indicates that the diffusion length of free charge carriers in a-SiC:H is in the range of a few tens of nm, an order of magnitude less than in a-Si:H. The optical properties of a-SiC:H films were degraded after vacuum annealing at 550 °C. Full article

Metal–air batteries represent a category of energy storage system that leverages the reaction between metal and oxygen from the atmosphere to produce electricity. These batteries, known for their high energy density, have attracted considerable attention as potential solutions for extending the range of electric vehicles. Understanding the capabilities and limitations of metal-air batteries as range extenders is crucial for advancing electric vehicle technology, as these batteries could offer the additional energy needed to overcome current range limitations. This review paper provides a detailed overview of various metal-air battery technologies, delving into their design, functionality, and inherent challenges. By analyzing key theoretical and practical parameters, the study highlights how these factors influence overall battery performance. Additionally, the review addresses critical cost considerations, particularly the relationship between vehicle cost and driving range, uncovering the significant trade-offs involved in adopting metal-air batteries. Through an examination of nearly all the existing metal-air batteries, this paper sheds light on their potential to serve as effective range extenders, thereby facilitating the transition to a cleaner, more sustainable transportation landscape. Full article

Germanium (Ge) has long been recognized for its superior carrier mobility and narrower band gap compared to silicon, making it a promising candidate in microelectronics and optoelectronics. The recent demonstration of good biocompatibility, combined with the ability to selectively functionalize its surface, establishes the way for its use in biosensing and bioimaging. This review provides a comprehensive analysis of the most recent advancements in the wet chemical functionalization of germanium surfaces. Wet chemical methods, including Grignard reactions, hydrogermylation, self-assembled monolayers (SAMs) formation, and arylation, are discussed in terms of their stability, surface coverage, and potential for preventing reoxidation, one of the main limits for Ge practical use. Special emphasis is placed on the characterization techniques that have advanced our understanding of these functionalized surfaces, which are crucial in the immobilization of molecules/biomolecules for different technological applications. This review emphasizes the dual functionality of surface passivation techniques, demonstrating that, in addition to stabilizing and protecting the active material, surface functionalization can impart new functional properties for germanium-based biosensors and semiconductor devices. Full article

Germanium offers attractive optical properties despite being an indirect bandgap semiconductor, and new Ge-based devices are being optimized for sensing and photonics applications. In particular, considering the use of Ge as a sensor, improving its selectivity via organic grafting offers new alternatives that are still under investigation. In this work, we focus on the selective functionalization of germanium in SiGe-patterned alloys using a custom thiol-based luminescent molecule, namely 6-[2,7-bis[5-(5-hexyl-2-thienyl)-2-thienyl]-9-(6-sulfanylhexyl)fluoren-9-yl]hexane-1-thiol. The process selectively targets regions with Ge, while leaving Si-rich areas uncovered. Moreover, this study emphasizes the importance of an oxygen-free environment, as performing the functionalization in an inert atmosphere significantly improves surface coverage. Full article

The continuous scaling down of MOSFETs is one of the present trends in semiconductor devices to increase device performance. Nevertheless, with scaling down beyond 22 nm technology, the performance of even the newer nanodevices with multi-gate architecture declines with an increase in short channel effects (SCEs). Consequently, to facilitate further increases in the drain current, the use of strained silicon technology provides a better solution. Thus, the development of a novel Gate-All-Around Field-Effect Transistor (GAAFET) incorporating a strained silicon channel with a 10 nm gate length is initiated and discussed. In this device, strain is incorporated in the channel, where a strained silicon germanium layer is wedged between two strained silicon layers. The GAAFET device has four gates that surround the channel to provide improved control of the gate over the strained channel region and also reduce the short channel effects in the devices. The electrical properties, such as the on current, off current, threshold voltage (V_TH), subthreshold slope, drain-induced barrier lowering (DIBL), and I_on/I_off current ratio, of the 10 nm channel length GAAFET are compared with the 22 nm strained silicon channel GAAFET, the existing SOI FinFET device on 10 nm gate length, and IRDS 2022 specifications device. The developed 10 nm channel length GAAFET, having an ultrathin strained silicon channel, delivers enriched device performance, being augmented in contrast to the IRDS 2022 specifications device, showing improved characteristics along with amended SCEs. Full article