Si-based Devices Research Articles

First-principles study of oxygen vacancy defects in β-quartz SiO2/Si interfaces

Abstract Understanding the electronic structures of gate oxides in Si-based devices is significant for improving device performance. We investigate the electronic properties of the oxygen vacancy defects in β-quartz SiO2/Si interface structure using first-principles calculations. The results indicate that the constructed (SiO2)4/(Si)4 structure is an indirect-gap semiconductor, with its band edges contributed by Si side and a large band-edge energy difference ( > 1.780 eV). Our study reveals that the presence of oxygen vacancy defects reduces the band gap, and V O 1 is transformed from indirect into direct band gap. The Si dangling bonds in V O 1 cause charge localization around the O vacancy, while the formation of Si–Si bonds in V O 2 and V O 3 lead to electron delocalization. In the calculation of defect formation energies, we find that V O 1 maintains the lowest formation energy across different states, making it more likely to form and structurally stable. Compared to O-rich environments, the formation energy in O-poor environments is overall reduced by approximately 4.5 eV, indicating that oxygen vacancy defects are more likely to form and be controlled under O-poor conditions. Our study emphasizes the importance of interface structure and defect characteristics in semiconductor research, providing insights for the development of Si-based devices.

Flexible Soft X-Ray Image Sensors based on Metal Halide Perovskites With High Quantum Efficiency.

Soft X-ray imaging is a powerful tool to explore the structure of cells, probe material with nanometer resolution, and investigate the energetic phenomena in the universe. Conventional soft X-ray image sensors are by and large Si-based charge coupled devices that suffer from low frame rates, complex fabrication processes, mechanical inflexibility, and required cooling below -60°C. Here, a soft X-ray photodiode is reported based on low-cost metal halide perovskite with comparable performance to commercial Si-based device. Nanothrough network electrodeminimized the optical loss due to the shadowing of insensitive layers, while a multidimensional perovskite heterojunctionis generated to reduce the photo-generated carrier loss. This strategy promoted a record quantum efficiency of 8×103% without cooling, several orders of magnitude greater than the previously achieved. Flexible and curved soft X-ray imaging arrays are fabricated based on this high-performance device structure, demonstrating stable soft X-ray response and sharp imaging capabilities. This work highlights the low-cost and efficient perovskite photodiode as a strong candidate for the next-generation soft X-ray image sensors.

Performance enhancement of silicon photodiodes through the integration of green synthesized reduced graphene oxide variants

This study examines the potential of enhancing the optoelectronic properties of silicon photodiodes by producing and analyzing heterostructures that incorporate reduced graphene oxide (rGO) synthesized with silicon using different reduction methods. Graphene oxide (GO) was manufactured utilizing an enhanced Hummers’ method. Subsequently, reduced graphene oxides (rGOs) were made by chemical and thermal reduction processes, which are considered ecologically friendly. The use of ascorbic acid to produce ascorbic acid-reduced graphene oxide (ArGO) and thermal processing to produce thermally reduced graphene oxide (TrGO) have significantly contributed to the development of high-performance photodiode technology. The electrical properties were carefully assessed under different levels of light, revealing the substantial impact of integrating reduced graphene oxides (rGOs) on the performance of the diodes. Comparing ArGO/Si, TrGO/Si, and GO/Si heterostructures shows that customized rGO has the potential to greatly influence the responsivity and efficiency of Si-based optoelectronic devices, making a significant contribution to photodiode technology.

Construction of micro-nano structured Si/C anode armed with rGO hollow spheres for high-performance lithium-ion hybrid capacitors

Because of the unique ability to combine high energy density with high power density, lithium-ion hybrid capacitors (LICs) have generated significant interest. Among the various anodes being explored for LICs, silicon (Si) stands out as a particularly promising anode material due to its high theoretical capacity. Nevertheless, the formidable challenge lies in the rapid capacity fade resulting from substantial volume expansion. Herein, a simple and efficient spray drying technique was used to fabricate a Si@rGO@NC composite with micro-nano structure. In this composite, Si nanoparticles are encapsulated between reduced graphene oxides (rGO) hollow spheres and a layer of carbon is coated on the surface of both the Si and the micron-sized composite particles, forming a rigid and mechanically stable structure. The composite combines the high activity of nano-Si with the industrially easy handling of micron-scale particles. Moreover, the rGO hollow spheres not only enhance the electrical conductivity but also buffer the volume expansion of the electrode and provide channels for the rapid transport of electrolyte/ions. Thanks to its advantageous structural features, the constructed LICs with activated carbon as cathode can achieve a Max. energy/power density of 253.1 Wh kg−1/10,824.1 W kg−1 and maintain 84.3 % of its initial capacitance after 8000 cycles. The micro-nano structured design concept of Si-based materials developed in our work could offer new insights and directions for the future development of Si-based energy storage devices.

Al nanowire-embedded silicon for broadband optical modulation: Forming mechanism and optical performance

In recent decades, silicon has been widely used in light regulation devices, owing to its wideband high refractive index and low dispersion. To meet the increasing demands for various applications, optical modulation techniques appear of great potential to enhance the optical performance of Si-based devices. However, challenges still remain in achieving precise control over the band structure and resonance modes without introducing complex artificial structures. In this study, a composite film composed of silicon embedded with high fraction aluminum nanowires was developed by magnetron sputtering. It was revealed that the formation of aluminum nanowires was attributed to the spontaneous phase separation between silicon and aluminum, which was strongly dependent on the filling fraction and surface diffusion length of the aluminum during the co-sputtering process. The composite microstructure was precisely regulated by manipulating adatom diffusion and reevaporation through ion bombardment, thereby modifying its broadband optical properties. Moreover, exceptional electromagnetic properties were achieved by incorporating aluminum nanowires into silicon, as evidenced by the metallic behaviors in the short-wavelength regime and dielectric properties in the infrared spectrum range.

High-efficiency electroluminescence devices containing Si nanocrystals/SiC multilayers via improved carrier injection and recombination process

Realizing high efficiency of all Si-based light-emitting devices is currently one of interesting issues in order to develop monolithic opto-electronic integration on chips. Here, we report an electroluminescence device based on phosphorus (P)-doped silicon nanocrystals (Si NCs)/silicon carbide (SiC) multilayers by modulating carrier injection and recombination process. The p+-Si substrate is used instead of p-Si substrate for facilitating the hole injection into Si NCs. Additionally, the influences of annealing temperature on the device performance have been studied, and the optimized annealing temperature is achieved by balancing the crystallinity, defect state density, and recombination process.

Impact of MoS2 Monolayers on the Thermoelastic Response of Silicon Heterostructures.

Understanding the thermoelastic response of a nanostructure is crucial for the choice of materials and interfaces in electronic devices with improved and tailored transport properties at the nanoscale. Here, we show how the deposition of a MoS2 monolayer can strongly modify the nanoscale thermoelastic dynamics of silicon substrates close to their interface. We demonstrate this by creating a transient grating with extreme ultraviolet light, using ultrashort free-electron laser pulses, whose ≈84 nm period is comparable to the size of elements typically used in nanodevices, such as electric contacts and nanowires. The thermoelastic response, featuring coherent acoustic waves and incoherent relaxation, is tangibly modified by the presence of monolayer MoS2. Namely, we observed a major reduction of the amplitude of the surface mode, which is almost suppressed, while the longitudinal mode is basically unperturbed, aside from a faster decay of the acoustic modulations. We interpret this behavior as a selective modification of the surface elasticity, and we discuss the conditions to observe such effect, which may be of immediate relevance for the design of Si-based nanoscale devices.

N-doped β-Ga2O3/Si-doped β-Ga2O3 linearly-graded p-n junction by a one-step integrated approach

The p-n junction is the foundation building structure for manufacturing various electronic and optoelectronic devices. Ultrawide bandgap semiconductors are expected to overcome the limited power capability of Si-based electronic device, however, it is very difficult to achieve efficient bipolar doping due to the asymmetric doping effect, thereby impeding the development of p-n homojunction and related bipolar devices, especially for the Ga2O3-based materials and devices. Here, we demonstrate a unique one-step integrated growth of p-type N-doped (2¯01) β-Ga2O3/n-type Si-doped (2¯01) β-Ga2O3 films by phase transition and in-situ pre-doping of dopants, and fabrication of full β-Ga2O3 linearly-graded p-n homojunction diode from them. The full β-Ga2O3 p-n homojunction diode possesses a large built-in potential of 4.52 eV, a high operation electric field > 2.90 MV/cm in the reverse-bias regime, good longtime-stable rectifying behaviors with a rectification ratio of 104, and a high-speed switching and good surge robustness with a weak minority-carrier charge storage. Our work opens the way to the fabrication of Ga2O3-based p-n homojunction, lays the foundation for full β-Ga2O3-based bipolar devices, and paves the way for the novel fabrication of p-n homojunction for wide-bandgap oxides.

A Waterproof Flexible Paper-Based Thermoelectric Generator for Humidity and Underwater Environments.

A thermoelectric generator (TEG) is one of the important energy harvesting sources for wearable electronic devices, which converts waste heat into electrical energy without any external stimuli, such as light or mechanical motion. However, the poor flexibility of traditional TEGs (e.g., Si-based TE devices) causes the limitations in practical applications. Flexible paper substrates are becoming increasingly attractive in wearable electronic technology owing to their usability, environmental friendliness (disposable, biodegradable, and renewable materials), and foldability. The high water-absorbing quality of paper restricts its scope of application due to water failure. Therefore, we propose a high-performance flexible waterproof paper-based thermoelectric generator (WPTEG). A modification method that infiltrates TE materials into cellulose paper through vacuum filtration is used to prepare the TE modules. By connecting the TE-modified paper with Al tape, as well as a superhydrophobic layer encapsulation, the WPTEG is fabricated. The WPTEG with three P-N modules can generate an output voltage of up to 235 mV at a temperature difference of 50 K, which can provide power to portable electronic devices such as diodes, clocks, and calculators in hot water. With the waterproof property, the WPTEG paves the way for achieving multi-scenario applications in humid environments on human skin.

Observation of Omnidirectional Exchange Bias at All-Antiferromagnetic Polycrystalline Heterointerface.

Due to promising functionalities that may dramatically enhance spintronics performance, antiferromagnets are the subject of intensive research for developing the next-generation active elements to replace ferromagnets. In particular, the recent experimental demonstration of tunneling magnetoresistance and electrical switching using chiral antiferromagnets has sparked expectations for the practical integration of antiferromagnetic materials into device architectures. To further develop the technology to manipulate the magnetic anisotropies in all-antiferromagnetic devices, it is essential to realize exchange bias through the interface between antiferromagnetic multilayers. Here, the first observation on the omnidirectional exchange bias at an all-antiferromagnetic polycrystalline heterointerface is reported. This experiment demonstrates that the interfacial energy causing the exchange bias between the chiral-antiferromagnet Mn3Sn/collinear-antiferromagnet MnN layers is comparable to those found at the conventional ferromagnet/antiferromagnet interface at room temperature. In sharp contrast with previous reports using ferromagnets, the magnetic field control of the unidirectional anisotropy is found to be omnidirectional due to the absence of the shape anisotropy in the antiferromagnetic multilayer. The realization of the omnidirectional exchange bias at the interface between polycrystalline antiferromagnets on amorphous templates, highly compatible with existing Si-based devices, paves the way for developing ultra-low power and ultra-high speed memory devices based on antiferromagnets.

Tunable zero-field magnetoresistance responses in Si transistors: Origins and applications

The near-zero-field magnetoresistance (NZFMR) response has proven to be a useful tool for studying atomic-scale, paramagnetic defects that are relevant to the reliability of semiconductor devices. The measurement is simple to make and, in some cases, simple to interpret. In other cases, more sophisticated modeling based on the stochastic Liouville equation (SLE) is needed to access valuable information from NZFMR results. It has been shown that hyperfine and dipolar coupling interactions at atomic-scale defects affect the NZFMR line shape, but experimental parameters related to the detection method of NZFMR can also affect the nature of the response. Here, we demonstrate four distinct NZFMR detection methods in Si MOSFETs, which all access identical Si/SiO2 interface defects. In all four cases, we show that the line shape of the response is tunable based on experimental parameters alone. Using SLE-based modeling, we verify that time constants connected to physical carrier capture rates at the defect sites lead to these NZFMR line shape changes. The results demonstrate a method to extract some atomic-scale information for the purpose of defect identification. They also have broader applications to the continued development of ultra-sensitive magnetometers based on NZFMR in semiconductors. Additionally, the NZFMR effect in common Si-based devices may provide an inexpensive and accessible platform that mimics similar radical pair mechanisms that have become increasingly important in various biology fields.

Separation of wafer bonding interface from heterogenous mismatched interface achieved high quality bonded Ge-Si heterojunction

In the realm of optoelectronic integration, silicon-based Ge bonding has attracted great attention due to its advantages in short-wave infrared response and low cost. However, owing to the inherent lattice mismatch and thermal mismatch between Ge and Si, the bonded Ge-Si heterogenous interfaces encountered problems of thermal instability and high interface states. Herein, an approach of separating the bonding interface from the heterogenous interface is proposed through inserting a Ge epitaxial layer (GeEL) between the Si substrate and Ge film. This separation modifies the bonding interface to a homogenous one, alleviating the massive mismatch stress and achieving film relaxation, enhancing bonding stability in all aspects. Moreover, during 850 °C annealing, GeEL is doped via diffusion hence realizes electric filed modulation, inhibiting the carrier recombination leakage current and trap assisted tunneling in this defect-rich layer. A Ge-Si heterogenous PIN diode prepared by this bonding method has achieved a remarkable low dark current density (1.33 mA/cm2), a low ideality factor (1.11), and a high on–off ratio (106), confirming the outstanding quality of the bonded heterojunction. This work provides great prospects for higher performance, larger scale and multi-functional Si-based heterogenous material device applications.

Effects of phosphorous and antimony doping on thin Ge layers grown on Si

Suppression of threading dislocations (TDs) in thin germanium (Ge) layers grown on silicon (Si) substrates has been critical for realizing high-performance Si-based optoelectronic and electronic devices. An advanced growth strategy is desired to minimize the TD density within a thin Ge buffer layer in Ge-on-Si systems. In this work, we investigate the impact of P dopants in 500-nm thin Ge layers, with doping concentrations from 1 to 50 × 1018 cm−3. The introduction of P dopants has efficiently promoted TD reduction, whose potential mechanism has been explored by comparing it to the well-established Sb-doped Ge-on-Si system. P and Sb dopants reveal different defect-suppression mechanisms in Ge-on-Si samples, inspiring a novel co-doping technique by exploiting the advantages of both dopants. The surface TDD of the Ge buffer has been further reduced by the co-doping technique to the order of 107 cm−2 with a thin Ge layer (of only 500 nm), which could provide a high-quality platform for high-performance Si-based semiconductor devices.

Highly Robust Room-Temperature Interfacial Ferromagnetism in Ultrathin Co2Si Nanoplates.

The reduced dimensionality and interfacial effects in magnetic nanostructures open the feasibility to tailor magnetic ordering. Here, we report the synthesis of ultrathin metallic Co2Si nanoplates with a total thickness that is tunable to 2.2 nm. The interfacial magnetism coupled with the highly anisotropic nanoplate geometry leads to strong perpendicular magnetic anisotropy and robust hard ferromagnetism at room temperature, with a Curie temperature (TC) exceeding 950 K and a coercive field (HC) > 4.0 T at 3 K and 8750 Oe at 300 K. Theoretical calculations suggest that ferromagnetism originates from symmetry breaking and undercoordinated Co atoms at the Co2Si and SiO2 interface. With protection by the self-limiting intrinsic oxide, the interfacial ferromagnetism of the Co2Si nanoplates exhibits excellent environmental stability. The controllable growth of ambient stable Co2Si nanoplates as 2D hard ferromagnets could open exciting opportunities for fundamental studies and applications in Si-based spintronic devices.

Interface Modulation for the Heterointegration of Diamond on Si.

Along with the increasing integration density and decreased feature size of current semiconductor technology, heterointegration of the Si-based devices with diamond has acted as a promising strategy to relieve the existing heat dissipation problem. As one of the heterointegration methods, the microwave plasma chemical vapor deposition (MPCVD) method is utilized to synthesize large-scale diamond films on a Si substrate, while distinct structures appear at the Si-diamond interface. Investigation of the formation mechanisms and modulation strategies of the interface is crucial to optimize the heat dissipation behaviors. By taking advantage of electron microscopy, the formation of the epitaxial β-SiC interlayer is found to be caused by the interaction between the anisotropically sputtered Si and the deposited amorphous carbon. Compared with the randomly oriented β-SiC interlayer, larger diamond grain sizes can be obtained on the epitaxial β-SiC interlayer under the same synthesis condition. Moreover, due to the competitive interfacial reactions, the epitaxial β-SiC interlayer thickness can be reduced by increasing the CH4/H2 ratio (from 3% to 10%), while further increase in the ratio (to 20%) can lead to the broken of the epitaxial relationship. The above findings are expected to provide interfacial design strategies for multiple large-scale diamond applications.

Design of Half-Bridge Switching Power Module Based on Parallel-Connected SiC MOSFETs for LLC Resonant Converter with Symmetrical Structure and Low Parasitic Inductance

SiC MOSFETs are used in many power conversion applications because of their superior characteristics, such as fast switching speed, low on-resistance, and high operating temperature. In certain high-power systems, SiC MOSFETs are connected in parallel to enhance their current capacity and power efficiency. However, compared with Si-based devices, the current imbalance caused by the parasitic inductance difference becomes more severe when driving SiC MOSFETs in parallel, owing to the fast switching speed. Furthermore, the power loop inductance imbalance that occurs when constructing a half-bridge with parallel SiC MOSFETs has rarely been addressed in previous studies. In this study, a half-bridge switching power module based on parallel-connected SiC MOSFETs is proposed to solve the current imbalance through a symmetric structure of the gate and power loops. The effects of the magnitude and imbalance of the gate and power loop inductances in the half-bridge structure based on parallel-connected devices are also explained. A detailed printed circuit board layout of the proposed switching power module is provided, and the inductance symmetry is verified through simulations. A double-pulse test is conducted to verify the current-balancing capability of the proposed switching power module. In addition, an LLC resonant converter is designed using the proposed switching power module, and the power loss between parallel SiC MOSFETs is compared. The experimental results indicate the total power loss error between the parallel-connected SiC MOSFETs of the proposed power module is only 1.94%.

Lateral GeSn p-i-n photodetectors on insulator prepared by the rapid melting growth method.

In this work, GeSn lateral p-i-n photodetectors (PDs) on insulator were fabricated with an active GeSn layer grown by the rapid melting growth (RMG) method. Taking advantages of the defect-free GeSn strips, GeSn PDs with 5.3% Sn content have low dark current and high responsivities, which are about 0.48, 0.47, and 0.24 A/W for wavelengths of 1550, 1630, and 2000 nm, respectively. The radio frequency of the lateral GeSn PDs was also studied and a 3 dB bandwidth of about 3.8 GHz was achieved. These results indicate that the GeSn grown by the rapid melting growth method is capable of fabricating high-performance Si-based optoelectronic devices.

Surface Modification of Silicon Nanowires with Siloxane Molecules for High-Performance Hydrovoltaic Devices.

Hydrovoltaic devices (HDs) based on silicon nanowires (SiNWs) have attracted significant attention due to their potential of high output power and good compatibility with Si-based photovoltaic devices for integrated power systems. However, it remains a major challenge to further improve the output performance of SiNW HDs for practical applications. Here, a new strategy to modify the surface of SiNWs with siloxane molecules is proposed to improve the output performance of the SiNW HDs. After modification, both the open-circuit voltage (Voc) and short-circuit current density (Jsc) of n-type SiNW HDs can be improved by approximately 30%, while the output power density can be greatly increased by over 200%. With siloxane modification, Si-OH groups on the surface of typical SiNWs are replaced by Si-O-Si chemical bonds that have a weaker electron-withdrawing capability. More free electrons in n-type SiNWs are liberated from surface bound states and participate in directed flow induced by water evaporation, thereby improving the output performance of HDs. The improved performance is significant for system integration applications as it reduces the number of required devices. Three siloxane-modified SiNW HDs in series are able to drive a 2 V light-emitting diode (LED), whereas four unmodified devices in series are initially needed for the same task. This work provides a simple yet effective strategy for surface modification to improve the output performance of SiNW HDs. Further research into the effect of different surface modifications on the performance of SiNW HDs will greatly promote their performance enhancement and practical applications.

Deep-tissue NIR-II bioimaging performance of Si-based and InGaAs-based imaging devices using short-wave infrared persistent luminescence

Deep-tissue NIR-II bioimaging performance of Si CCD and InGaAs FPA cameras was evaluated under identical imaging-signal-only tissue environment using 950–1100 nm SWIR persistent luminescence signals from MgGeO3:Yb3+ nanoparticles (NPs).

Modified SEPIC DC-DC Converter with Wide Step-up/Step-down Range for Fuel Cell Vehicles

The high efficient buck-boost DC-DC converter with wide step-up/step-down range is the way to solve the issue of voltage matching for commercial fuel cell vehicles with a strong hydrogen-electric hybrid. Based on the conventional SEPIC converter, the negative of one of the capacitors is connected with the negative of the power source to get more energy. A modified SEPIC buck-boost DC-DC converter with the advantages of wide voltage conversion range, continuous input current, common ground, and high conversion efficiency is proposed in this paper, meeting all the requirements of DC-DC converters for commercial fuel cell vehicles. On the basis of the steady-state analysis and comparison, the controller is designed based on the small-signal model. To verify the efficiency of the proposed converter, experimental prototypes are built using Si-based and SiC-based devices respectively. The experimental results show that the proposed buck-boost converter can effectively realize 2/3 times step-down and 5 times step-up. When disturbance and voltage dip occur, the adjust time of the control system is less than 200ms. The controller is verified to be robust and have fast responses. The maximum calculation, simulation and experimental efficiencies all exceed 96%, and the maximum efficiency of the SiC prototype under rated power is 96.1%.