Search Results (72)

The development of an integrated circuit faces the challenge of the physical limit of Moore’s Law. One of the most important “Beyond Moore” challenges is the scaling down of Metal-Oxide-Semiconductor Field-Effect Transistors (MOSFETs) versus their increasing static power consumption. This is because, at room temperature, the thermal emission transportation mechanism will cause a physical limitation on subthreshold swing (SS), which is fundamentally limited to a minimum value of 60 mV/decade for MOSFETs, and accompanied by an increase in off-state leakage current with the process of scaling down. Moreover, the impacts of short-channel effects on device performance also become an increasingly severe problem with channel length scaling down. Due to the band-to-band tunneling mechanism, Tunnel Field-Effect Transistors (TFETs) can reach a far lower SS than MOSFETs. Recent research works indicated that TFETs are already becoming some of the promising candidates of conventional MOSFETs for ultra-low-power applications. This paper provides a review of some advances in materials and structures along the evolutionary process of TFETs. An in-depth discussion of both experimental works and simulation works is conducted. Furthermore, the performance of TFETs with different structures and materials is explored in detail as well, covering Si, Ge, III-V compounds and 2D materials, alongside different innovative device structures. Additionally, this work provides an outlook on the prospects of TFETs in future ultra-low-power electronics and biosensor applications. Full article

The monolithic integration of III-V semiconductors with silicon (Si) is a critical step toward advancing optoelectronic and photonic devices. In this work, we present GaAs nanoheteroepitaxy (NHE) on Si nanotips using gas-source molecular beam epitaxy (GS-MBE). We discuss the selective growth of fully relaxed GaAs nanoislands on complementary metal oxide semiconductor (CMOS)-compatible Si(001) nanotip wafers. Nanotip wafers were fabricated using a state-of-the-art 0.13 μm SiGe Bipolar CMOS pilot line on 200 mm wafers. Our investigation focuses on understanding the influence of the growth conditions on the morphology, crystalline structure, and defect formation of the GaAs islands. The morphological, structural, and optical properties of the GaAs islands were characterized using scanning electron microscopy, high-resolution X-ray diffraction, and photoluminescence spectroscopy. For samples with less deposition, the GaAs islands exhibit a monomodal size distribution, with an average effective diameter ranging between 100 and 280 nm. These islands display four distinct facet orientations corresponding to the {001} planes. As the deposition increases, larger islands with multiple crystallographic facets emerge, accompanied by a transition from a monomodal to a bimodal growth mode. Single twinning is observed in all samples. However, with increasing deposition, not only a bimodal size distribution occurs, but also the volume fraction of the twinned material increases significantly. These findings shed light on the growth dynamics of nanoheteroepitaxial GaAs and contribute to ongoing efforts toward CMOS-compatible Si-based nanophotonic technologies. Full article

In the context of increasing digitalization and the emergence of applications such as smart cities, embedded devices are becoming ever more pervasive, mobile, and ubiquitous. Due to increasing concerns around energy efficiency, gate density, and scalability in the semiconductor industry, there has been much interest recently in the fabrication of viable low-power energy-efficient devices. The Hetero-Dielectric Gate-All-Around (HD-GAA) MOSFET represents a cutting-edge transistor architecture designed for superior sustainability and energy efficiency, improving the overall efficiency of the system by reducing leakage and enhancing gate control; therefore, as part of the transition to a sustainable future, several semiconductor industries, including Intel, Samsung, Texas Instruments, and IBM, are using this technology. In this study, Hetero-Dielectric Single-Metal Gate-All-Around MOSFET (HD-SM-GAA MOSFET) devices and circuits were designed using Schottky source/drain contacts and tunable high-k dielectric Hf_xTi_1−xO₂ in the TCAD simulator using the following specifications: N-Channel HD-SM-GAA MOSFET (‘Device-I’) with a 5 nm radius and a 21 nm channel length alongside two P-Channel HD-SM-GAA MOSFETs (‘Device-II’ and ‘Device-III’) with radii of 5 nm and 8 nm, respectively, maintaining the same channel length. Thereafter, the inverters were implemented using these devices in the COGENDA TCAD simulator. The results demonstrated significant reductions in short-channel effects: subthreshold swing (SS) (‘Device-I’ = 61.5 mV/dec, ‘Device-II’ = 61.8 mV/dec) and drain-induced barrier lowering (DIBL) (‘Device-I’ = 8.2 mV/V, ‘Device-II’ = 8.0 mV/V) in comparison to the existing literature. Furthermore, the optimized inverters demonstrated significant improvements in noise margin values such as Noise Margin High (NM_H) and Noise Margin Low (NM_L), with Inverter-1 showing 38% and 44% enhancements and Inverter-2 showing 40% and 37% enhancements, respectively, compared to the existing literature. The results achieved illustrate the potential of using this technology (e.g., for power inverters) in embedded power control applications where energy efficiency and scalability are important, such as sustainable smart cities. Full article

The third-generation semiconductors have the characteristics of a large bandgap, a high breakdown electric field, a fast electron saturation rate, high-temperature resistance, corrosion resistance, and radiation resistance, making them the preferred core materials and devices for cutting-edge high-tech fields, such as mobile communication, new energy vehicles, and smart grids in the future. The III–V compound semiconductors are a typical representative of them. In order to discover and explore new III–V semiconductor materials more efficiently and accurately, this paper adopts a machine-learning method optimized by the beetle algorithm and combined with first-principle calculation verification to efficiently and accurately predict the performance of III–V nitride materials and study their physicochemical properties. This study improved the prediction efficiency of nitrogen-rich III–V semiconductor materials through the combination of machine learning and first principles, providing a new approach for the efficient and accurate prediction of semiconductor materials. Full article

Indium Arsenide is a III–V semiconductor with low electron effective mass, a small band gap, strong spin–orbit coupling, and a large g-factor. These properties and its surface Fermi level pinned in the conduction band make InAs a good candidate for developing superconducting solid-state quantum devices. Here, we report the epitaxial growth of very thin InAs layers with thicknesses ranging from 12.5 nm to 500 nm grown by Molecular Beam Epitaxy on In_xAl_1−xAs metamorphic buffers. Differently than InAs substrates, these buffers have the advantage of being insulating at cryogenic temperatures, which allows for multiple device operations on the same wafer and thus making the approach scalable. The structural properties of the InAs layers were investigated by high-resolution X-ray diffraction, demonstrating the high crystal quality of the InAs layers. Furthermore, their transport properties, such as total and sheet carrier concentration, sheet resistance, and carrier mobility, were measured in the van der Pauw configuration at room temperature. A simple conduction model was employed to quantify the surface, bulk, and interface contributions to the overall carrier concentration and mobility. Full article

Due to the excellent quantum conversion and spectral response characteristics of the AlGaN photocathode, it has become the most promising III-V group semiconductor photocathode in solar-blind signal photoconversion devices in the ultraviolet band. Herein, the influence factors of the time-resolved characteristics of the AlGaN photocathode are researched by solving the photoelectron continuity equation and photoelectron flow density equation, such as the AlN/AlGaN interface recombination rate, AlGaN electron diffusion coefficient, and AlGaN activation layer thickness. The results show that the response time of the AlGaN photocathode decreases gradually with the increase in AlGaN photoelectron diffusion coefficient and AlN/AlGaN interface recombination rate, but the response time of the AlGaN photocathode gradually becomes saturated with the further increase in AlN/AlGaN interface recombination rate. When the thickness of the AlGaN photocathode is reduced from 250 nm to 50 nm, the response time of the AlGaN photocathode decreases from 63.28 ps to 9.91 ps, and the response time of AlGaN photocathode greatly improves. This study provides theoretical guidance for the development of a fast response UV detector. Full article

A gallium nitride (GaN) semiconductor is one of the most promising materials integrated into biomedical devices to play the roles of connecting, monitoring, and manipulating the activity of biological components, due to its excellent photoelectric properties, chemical stability, and biocompatibility. In this work, it was found that the photogenerated free charge carriers of the GaN substrate, as an exogenous stimulus, served to promote neural stem cells (NSCs) to differentiate into neurons. This was observed through the systematic investigation of the effect of the persistent photoconductivity (PPC) of GaN on the differentiation of primary NSCs from the embryonic rat cerebral cortex. NSCs were directly cultured on the GaN surface with and without ultraviolet (UV) irradiation, with a control sample consisting of tissue culture polystyrene (TCPS) in the presence of fetal bovine serum (FBS) medium. Through optical microscopy, the morphology showed a greater number of neurons with the branching structures of axons and dendrites on GaN with UV irradiation. The immunocytochemical results demonstrated that GaN with UV irradiation could promote the NSCs to differentiate into neurons. Western blot analysis showed that GaN with UV irradiation significantly upregulated the expression of two neuron-related markers, βIII-tubulin (Tuj-1) and microtubule-associated protein 2 (MAP-2), suggesting that neurite formation and the proliferation of NSCs during differentiation were enhanced by GaN with UV irradiation. Finally, the results of the Kelvin probe force microscope (KPFM) experiments showed that the NSCs cultured on GaN with UV irradiation displayed about 50 mV higher potential than those cultured on GaN without irradiation. The increase in cell membrane potential may have been due to the larger number of photogenerated free charges on the GaN surface with UV irradiation. These results could benefit topical research and the application of GaN as a biomedical material integrated into neural interface systems or other bioelectronic devices. Full article

Gallium nitride (GaN) semiconductors and their broadband InGaN alloys in their hexagonal phase have been extensively studied over the past 30 years and have allowed the development of blue-ray lasers, which are essential disruptive developments. In addition to high-efficiency white light-emitting diodes, which have revolutionized lighting technologies and generated a great industry around these semiconductors, several transistors have been developed that take advantage of the characteristics of these semiconductors. These include power transistors for high-frequency applications and high-power transistors for power electronics, among other devices, which have far superior achievements. However, less effort has been devoted to studying GaN and InGaN alloys grown in the cubic phase. The metastable or cubic phase of III-N alloys has superior characteristics compared to the hexagonal phase, mainly because of the excellent symmetry. It can be used to improve lighting technologies and develop other devices. Indium gallium nitride, In_xGa_1−xN alloy, has a variable band interval of 0.7 to 3.4 eV that covers almost the entire solar spectrum, making it a suitable material for increasing the efficiencies of photovoltaic devices. In this study, we successfully synthesized high-quality cubic InGaN films on MgO (100) substrates using plasma-assisted molecular beam epitaxy (PAMBE), demonstrating tunable emissions across the visible spectrum by varying the indium concentration. We significantly reduced the defect density and enhanced the crystalline quality by using an intermediate cubic GaN buffer layer. We not only developed a heterostructure with four GaN/InGaN/GaN quantum wells, achieving violet, blue, yellow, and red emissions, but also highlighted the immense potential of cubic InGaN films for high-efficiency light-emitting diodes and photovoltaic devices. Achieving better p-type doping levels is crucial for realizing diodes with excellent performance, and our findings will pave the way for this advancement. Full article

Using the example of III–V nitrides crystallizing in a wurtzite structure (GaN, AlN, and InN), this review presents the special role of hydrostatic pressure in studying semiconductor properties. Starting with a brief description of high-pressure techniques for growing bulk crystals of nitride compounds, we focus on the use of hydrostatic pressure techniques in both experimental and theoretical investigations of the special properties of nitride compounds, their alloys, and quantum structures. The bandgap pressure coefficient is one of the most important parameters in semiconductor physics. Trends in its behavior in nitride structures, together with trends in pressure-induced phase transitions, are discussed in the context of the behavior of other typical semiconductors. Using InN as an example, the pressure-dependent effects typical of very narrow bandgap materials, such as conduction band filling or effective mass behavior, are described. Interesting aspects of bandgap bowing in In-containing nitride alloys, including pressure and clustering effects, are discussed. Hydrostatic pressure also plays an important role in the study of native defects and impurities, as illustrated by the example of nitride compounds and their quantum structures. Experiments and theoretical studies on this topic are reviewed. Special attention is given to hydrostatic pressure and strain effects in short periods of nitride superlattices. The explanation of the discrepancies between theory and experiment in optical emission and its pressure dependence from InN/GaN superlattices led to the well-documented conclusion that InN growth on the GaN substrate is not possible. The built-in electric field present in InGaN/GaN and AlGaN/GaN heterostructures crystallizing in a wurtzite lattice can reach several MV/cm, leading to drastic changes in the physical properties of these structures and related devices. It is shown how hydrostatic pressure modifies these effects and helps to understand their origin. Full article

Au nanoparticles (NPs) were designed to be embedded into III-V semiconductors to form Au/GaAs Schottky heterostructures, which were used as top-modified cover layers for quantum dot semiconductor saturable absorption mirrors (QD-SESAMs). By harnessing the distinctive localized surface plasmon resonance (LSPR) effect exhibited by Au NPs, a remarkable enhancement in photogenerated carrier concentration is achieved at the heterojunction interface. Consequently, this leads to a significant improvement in the nonlinear optical characteristics of the device. The modulation depth (MD) and saturation fluence of the device are optimized from the initial 2.2% and 16.1 MW/cm² to 2.8% and 8.3 MW/cm², respectively. Based on the optimized device, a Q-switched laser has been developed with an impressive output power of 17.61 mW and a single pulse energy of 274.9 nJ. These results unequivocally showcase the exceptional advantages offered by utilizing Au NPs to optimize the nonlinear optical characteristics of III-V semiconductor devices, thereby highlighting its immense potential for practical applications in various fields. Full article

With the growing trend in the information industry, silicon photonics technology has been explored in both academia and industry and utilized for high-bandwidth data transmission. Thanks to the benefits of silicon, such as high refractive index contrast with its oxides, low loss, substantial thermal–optical effect, and compatibility with CMOS, a range of passive and active photonic devices have been demonstrated, including waveguides, modulators, photodetectors, and lasers. The most challenging aspect remains to be the on-chip laser source, whose performance is constrained by the indirect bandgap of silicon. This review paper highlights the advancements made in the field of integrated laser sources on the silicon photonics platform. These on-chip lasers are classified according to their gain media, including V semiconductors, III–V semiconductors, two-dimensional materials, and colloidal quantum dots. The methods of integrating these lasers onto silicon are also detailed in this review. Full article

Recent developments in long wavelength and cryogenic laser power converters have unlocked record performances in both areas. Here, devices for an optical input at ~1470 nm are studied for cryogenic applications, combining these cryogenic and long-wavelength attributes. Multijunction laser power converters are demonstrated to have a high-efficiency operation at 77 K. The photovoltaic-power-converting III-V semiconductor devices are designed with InGaAs-absorbing layers, here with 10 thin subcells (PT10), connected by transparent tunnel junctions. Unprecedented conversion efficiencies of up to 67.5% are measured at liquid nitrogen temperatures with an output power of P_mpp = 1.35 W at an average optical input intensity of ~62 W/cm². A remarkably low bandgap voltage offset value of W_oc~50 mV is obtained at an average optical input intensity of ~31 W/cm². Full article

The combination of the unique physical properties of molybdenum disulfide (MoS₂) with those of gallium nitride (GaN) and related group-III nitride semiconductors have recently attracted increasing scientific interest for the realization of innovative electronic and optoelectronic devices. A deep understanding of MoS₂/GaN interface properties represents the key to properly tailor the electronic and optical behavior of devices based on this heterostructure. In this study, monolayer (1L) MoS₂ was grown on GaN-on-sapphire substrates by chemical vapor deposition (CVD) at 700 °C. The structural, chemical, vibrational, and light emission properties of the MoS₂/GaN heterostructure were investigated in detail by the combination of microscopic/spectroscopic techniques and ab initio calculations. XPS analyses on as-grown samples showed the formation of stoichiometric MoS₂. According to micro-Raman spectroscopy, monolayer MoS₂ domains on GaN exhibit an average n-type doping of (0.11 ± 0.12) × 10¹³ cm⁻² and a small tensile strain (ε ≈ 0.25%), whereas an intense light emission at 1.87 eV was revealed by PL analyses. Furthermore, a gap at the interface was shown by cross-sectional TEM analysis, confirming the van der Waals (vdW) bond between MoS₂ and GaN. Finally, density functional theory (DFT) calculations of the heterostructure were carried out, considering three different configurations of the interface, i.e., (i) an ideal Ga-terminated GaN surface, (ii) the passivation of Ga surface by a monolayer of oxygen (O), and (iii) the presence of an ultrathin Ga₂O₃ layer. This latter model predicts the formation of a vdW interface and a strong n-type doping of MoS₂, in closer agreement with the experimental observations. Full article

Photovoltaic multijunction power-converting III–V semiconductor devices generate electrical power from the optical energy of laser beams. They exhibit conversion efficiencies reaching values greater than 60% and 50% for the GaAs and the InP material systems, respectively. The applications of optical wireless power transmission and power-over-fiber greatly benefit from employing such laser power converters constructed with multiple subcells; each is designed with either thin GaAs or InGaAs absorber regions. This study elucidates how the application of electric fields on thin heterostructures can create specific current–voltage characteristics due to modifications of the absorption characteristics from Franz–Keldysh perturbations and the onset of quantum-confined Stark effects. Negative differential photocurrent behavior can be observed as the reverse bias voltage is increased, until the corresponding current-clamping subcell reaches its reverse breakdown condition. The reverse voltage breakdown characteristics of the subcells were also measured to depend on the thickness of the subcell and on the optical intensity. The onset of the reverse breakdown was found to be at ~2.0–2.5 V under illumination and the thinner subcells exhibited higher levels of reverse bias currents. These effects can produce distinctive current–voltage behavior under spectrally detuned operations affecting the thinner subcells’ biases, but have no significant impact on the performance and maximum power point of multijunction power converters. Full article

Improving the performances and reducing costs of III-V multijunction solar cells are crucial in aerospatial energy systems and in terrestrial concentrator modules. We attempted to achieve both objectives by implementing non-ohmic metal/semiconductor interface contacts on the front surface of III-V/Ge triple-junction solar cells. We demonstrate the feasibility of this concept for this type of solar cell by a simple evaporation of Al only either on the GaAs contact layer or the AlInP window. The best results were obtained when sulfur passivation by (NH₄)2S_x was conducted on the GaAs contact layer. This allowed for a reduction in reverse saturation dark current density by one order of magnitude and a slight increase in V${}_{oc}$ of almost 20 mV under 1 sun illumination relative to a reference device with Pd/Ge/Ti/Pd ohmic contacts. However, poor performances were observed at first under concentrated sunlight. Further annealing the solar cells with Al front metallization resulted in the reduction of V${}_{oc}$ to the same level as the reference solar cell but allowed for good performances under high illumination. Indeed, an efficiency over 34% was observed at 500 suns light intensity both for Al and Pd/Ge/Ti/Pd contacted solar cells. Full article