Semiconductor Transition Research Articles

Optical Orientation of Carriers in Interband Transitions in Semiconductors

Optical orientation, meaning the preferred orientation of the electron spin upon absorption of polarized light, is one of the most fruitful methods of spectroscopy and is extensively used for the investigation of atoms and ions [1]. Observation of optical orientation in a semiconducting crystal would make it possible to use the methods developed in atomic spectroscopy to investigate semiconductors and particularly to perform accurate measurements of the lifetime, the spin-relaxation time, the carrier g-factors, etc. So far, however, only one communication was published reporting such investigations in semiconducting crystals [2].

Drift–Diffusion Simulation of Intermediate Band Solar Cell: Effect of Intermediate Band Continuity Constraint

Self-consistent drift–diffusion model has been widely employed to simulate the device performance of intermediate band solar cell (IBSC) under practical device configuration. However, one of the remained issues in the drift–diffusion modeled-based works is the difficulty to reach the IB carrier continuity through the self-consistent manner. In most of the previous reports the constraints were relaxed or just partially satisfied; which render the unreliable performance results and misguide the device design strategy. In this work, in order to solve this issue and to validate our results, we performed extensive simulations to fully disclose the significant effect of the IB continuity constraints by taking InAs/GaAs quantum dot-based IBSC as a model device using the semiconductor modules in COMSOL Multiphysics combined with the Fortran codes. We found that under rigorous satisfaction of IB continuity constraint, the band potential profiles for the IBSC with either doped or nondoped IB under various light illumination conditions are nearly identical to those under the dark conditions. Moreover, from the simulated current–voltage curve dependence on the light concentration ratio, we found the device performance based on drift–diffusion under rigorous IB continuity constraint showed similar tendency to the features simulated based on detailed balance principle except the much-lowered power conversion efficiency. Our work demonstrated here, serves as an accurate and reliable IBSC device design approach toward better IB material screening, efficiency improvement, optical management, and extended application in the emerging field such as the perovskite material-based IBSC.

Charge-Density-Wave Order And Electronic Phase Transitions in a Dilute D-Band Semiconductor.

As one of the most fundamental physical phenomena, charge density wave (CDW) order predominantly occurs in metallic systems such as quasi-one-dimensional (quasi-1D) metals, doped cuprates, and transition metal dichalcogenides, where it is well understood in terms of Fermi surface nesting and electron-phonon coupling mechanisms. On the other hand, CDW phenomena in semiconducting systems, particularly at the low carrier concentration limit, are less common and feature intricate characteristics, which often necessitate the exploration of novel mechanisms, such as electron-hole coupling or Mott physics, to explain. In this study, we combined electrical transport, synchrotron X-ray diffraction and density-functional theory (DFT) calculations to investigate CDW order and a series of hysteretic phase transitions in a dilute d-band semiconductor, BaTiS3 . Our experimental and theoretical findings suggest that the observed CDW order and phase transitions in BaTiS3 may be attributed to both electron-phonon coupling and non-negligible electron-electron interactions in the system. Our work highlights BaTiS3 as a unique platform to explore CDW physics and novel electronic phases in the dilute filling limit and could open new opportunities for developing novel electronic devices. This article is protected by copyright. All rights reserved.

Sustained Feedback-Induced Oscillations in a Hybrid Single Mode Semiconductor Plasmonic Laser

Sustained Feedback-Induced Oscillations in a Hybrid Single Mode Semiconductor Plasmonic Laser

Colossal magnetoresistance in the multiple wave vector charge density wave regime of an antiferromagnetic Dirac semimetal.

Colossal negative magnetoresistance is a well-known phenomenon, notably observed in hole-doped ferromagnetic manganites. It remains a major research topic due to its potential in technological applications. In contrast, topological semimetals show large but positive magnetoresistance, originated from the high-mobility charge carriers. Here, we show that in the highly electron-doped region, the Dirac semimetal CeSbTe demonstrates similar properties as the manganites. CeSb0.11Te1.90 hosts multiple charge density wave modulation vectors and has a complex magnetic phase diagram. We confirm that this compound is an antiferromagnetic Dirac semimetal. Despite having a metallic Fermi surface, the electronic transport properties are semiconductor-like and deviate from known theoretical models. An external magnetic field induces a semiconductor metal-like transition, which results in a colossal negative magnetoresistance. Moreover, signatures of the coupling between the charge density wave and a spin modulation are observed in resistivity. This spin modulation also produces a giant anomalous Hall response.

Life-cycle energy demand comparison of medium voltage Silicon IGBT and Silicon Carbide MOSFET power semiconductor modules in railway traction applications

Power semiconductors process roughly 70 % of global energy, with a higher percentage expected as worldwide transport electrification, renewables and wide-band-gap (WBG) semiconductors are implemented, significantly affecting global energy savings. This manuscript evaluates the cumulative energy demand (CED) encompassing the manufacture and use-phase in a railway traction application of silicon (Si) and silicon carbide (SiC) power semiconductor modules. Realistic manufacturing data from a power semiconductor fab has been considered for 3.3 kV/450 A state-of-the-art Si and SiC LinPak modules. SiC devices presented around 2.6 – 3.8× higher CED per area than Si devices in the manufacturing phase. However, due to the considerably smaller SiC chip area per ampere required, a 1.1 – 1.6× lower grey energy than Si technology is estimated. For the first time, such analysis is based on specialized power semiconductor fab data for both technologies and provides a baseline for the life cycle energy assessment of power electronics systems. Besides, the use-phase energy losses were evaluated for a realistic railway application, considering an operational lifetime of 30 years. The module manufacturing energy is negligible compared to the use-phase stage. Furthermore, the SiC technology presented an estimated energy-saving potential of 24 MWh/lifetime per module compared to the Si device.

Data-driven and physics-based reliability tests to failure of a power electronics converter

This paper presents an overview on design and execution of reliability tests for a power converter, with an outlook on in-field health management. The topics include physics-based and data-driven accelerated tests to failure, each adapted for the constituent elements of a converter: power semiconductor modules, DC link capacitors, and control electronics. The methods describe the outline of how the different role and nature of the components require a tailored reliability investigation approach to be most cost-effective for increasing system reliability. Testing examples for electronics are given in this article, as they are often neglected in the reliability discussion of power converters.

Colloidal Quantum Dots as an Emerging Vast Platform and Versatile Sensitizer for Singlet Molecular Oxygen Generation.

Singlet molecular oxygen (1O2) has been reported in wide arrays of applications ranging from optoelectronic to photooxygenation reactions and therapy in biomedical proposals. It is also considered a major determinant of photodynamic therapy (PDT) efficacy. Since the direct excitation from the triplet ground state (3O2) of oxygen to the singlet excited state 1O2 is spin forbidden; therefore, a rational design and development of heterogeneous sensitizers is remarkably important for the efficient production of 1O2. For this purpose, quantum dots (QDs) have emerged as versatile candidates either by acting individually as sensitizers for 1O2 generation or by working in conjunction with other inorganic materials or organic sensitizers by providing them a vast platform. Thus, conjoining the photophysical properties of QDs with other materials, e.g., coupling/combining with other inorganic materials, doping with the transition metal ions or lanthanide ions, and conjugation with a molecular sensitizer provide the opportunity to achieve high-efficiency quantum yields of 1O2 which is not possible with either component separately. Hence, the current review has been focused on the recent advances made in the semiconductor QDs, perovskite QDs, and transition metal dichalcogenide QD-sensitized 1O2 generation in the context of ongoing and previously published research work (over the past eight years, from 2015 to 2023).

Numerical analysis of negative chirp operation in hybrid modulation semiconductor lasers

Numerical analysis of negative chirp operation in hybrid modulation semiconductor lasers

Controlled Synthesis and Accurate Doping of Wafer-Scale Two-Dimensional Semiconducting Transition Metal Dichalcogenides.

Two-dimensional (2D) semiconducting transition metal dichalcogenide (TMDCs) possess atomically thin thickness, dangling-bond free surface, flexible band structure, and silicon-compatible feature, making them one of the most promising channels for constructing state-of-the-art field-effect transistors in the post-Moore's era. However, the existing 2D semiconducting TMDCs fall short of meeting the industry criteria for practical applications in electronics due to their small domain size and the lack of effective approach to modulate intrinsic physical properties. Therefore, it is crucial to prepare and doping of 2D semiconducting TMDCs single crystals with wafer size. In this review, wesystematically summary the up-to-date progresses regarding the wafer-scale growth of 2D semiconducting TMDCs polycrystalline and single-crystal films. The domain orientation control of 2D TMDCs and the seamless stitching of unidirectionally aligned 2D islands by means of substrate design are proposed. In addition, the accurate and uniform doping of 2D semiconducting TMDCs and the effect on electronic device performances are also discussed. Finally, the dominating challenges pertaining to enhance electronic device performances of TMDCs are emphasized, and the further development directions are put forward. This review provides a systematically and in-depth summary for high-performance device applications of 2D semiconducting TMDCs. This article is protected by copyright. All rights reserved.

Health Monitoring of Power Semiconductor Module Using Temperature Sensitive Electrical Parameter

Power semiconductor modules (PSMs) are critical components in power electronics applications such as motor drives, renewable energy systems, and electric vehicles. The reliable operation of these modules is crucial for the safe and efficient operation of these systems. One of the most common failure mechanisms in PSMs is due to overheating or repeated heating and cooling, which can result in thermal stress and component degradation. Therefore, monitoring the temperature of PSMs is essential for ensuring their health and preventing catastrophic failures. By monitoring temperature-sensitive electrical parameters (TSEPs), such as the on-state voltage drop, it is possible to detect changes in the temperature of the PSM in real-time. The change in voltage drop can be used as an early warning sign of a potential failure or degradation of the PSM. The advantage of this method is that it provides a non-invasive and real-time monitoring solution that can detect changes in the PSM's temperature distribution.

Low Ohmic contact resistance and high on/off ratio in transition metal dichalcogenides field-effect transistors via residue-free transfer.

Beyond-silicon technology demands ultrahigh performance field-effect transistors. Transition metal dichalcogenides provide an ideal material platform, but the device performances such as the contact resistance, on/off ratio and mobility are often limited by the presence of interfacial residues caused by transfer procedures. Here, we show an ideal residue-free transfer approach using polypropylene carbonate with a negligible residue coverage of ~0.08% for monolayer MoS2 at the centimetre scale. By incorporating a bismuth semimetal contact with an atomically clean monolayer MoS2 field-effect transistor on hexagonal boron nitride substrate, we obtain an ultralow Ohmic contact resistance of ~78 Ω µm, approaching the quantum limit, and a record-high on/off ratio of ~1011 at 15 K. Such an ultra-clean fabrication approach could be the ideal platform for high-performance electrical devices using large-area semiconducting transition metal dichalcogenides.

Micro-heater embedded ISFET pH sensor with high-k gate dielectrics for enhanced sensitivity

The measurement of pH is an important routine practice in many chemical and biomedical applications. This work reports the design of a pH sensor based on the Ion Sensitive Field Effect Transistor (ISFET). The COMSOL Multiphysics® platform has been used to model and simulate the pH sensor in three dimensions (3D) while combining heat transport, electrostatic, and semiconductor modules. The binding of ions in gate dielectrics results in induced charge carriers in the conducting channel of 3D ISFET, which is controlled by the applied gate voltage for determining ion concentration. Here, the pH of water as the bulk electrolyte is measured by attaining the required gate voltage to achieve a certain drain current in 3D ISFET. The pH sensitivity of 3D ISFET with different high-k gate dielectrics such as Ta2O5, Al2O3, HfO2, ZrO2, and SiO2 is measured and compared. The 3D ISFET with Ta2O5 exhibited excellent sensitivity of 59.0 mV pH−1 with a wide linear detection range of pH from 1 to 13 at room temperature compared to other high-k gate dielectrics. Furthermore, the sensitivity was further enhanced to 66.0 mV pH−1 at 60 °C due to the incorporation of a micro-heater into the ISFET. The excellent sensitivity and wide linear detection range can be attributed to the high concentration of surface sites in the Ta2O5 sensing film and improved disassociation constants in the presence of the gate dielectric in contact with the electrolyte. Finally, this sensor demonstrates its potential for real applications.

Fabrication and Characterization of Self-Aligned WSe2 p-Type Field-Effect Transistor

Semiconducting transition metal dichalcogenides (TMDCs) have been growing interests as channel materials in field effect transistors (FET) for next generation low power digital electronics. [1]. Since a complementary metal oxide-semiconductor (CMOS) inverter constructed from pairs of n-type and p-type FETs is a fundamental building blocks in modern digital electronics [2], implementation of both n-type and p-type FETs with semiconducting TMDCs is of particular importance [3]. Among various semiconducting TMDCs, tungsten diselenide (WSe2) is a promising candidate for constructing a CMOS inverter because of its high mobility, symmetric electron and hole effective mass and ambipolar transport [4]. These prominent features of WSe2 is suitable for an application to CMOS inverter.One of the significant challenges is to develop a top gate and top contact FET structure with WSe2 for CMOS device integration on the same wafer. In addition, it is desirable to minimize the access region between channel and S/D contact because this access region served as a series resistance to channel resistance, resulting in the lower drain current in FET. This study reports a self-aligned process to fabricate top gate and top contact WSe2 p-type FET. In this self-aligned structure, the gate electrode and source/drain contact edges are automatically positioned and hence there are no overlap or access region between the gate and source/drain. The feature of this proposed method is that the gate stacks was utilized as a mask for self-aligned formation of WOx, which is source/drain contact for efficient hole injection [5]. The focus on this study is the impact of self-aligned structure of p-type WSe2 FET on the electrical characteristics. The effectiveness of proposed process was experimentally demonstrated by the fabrication and characterization of device.Figures 1 shows the self-aligned fabrication process of p-type WSe2 FET. 20 nm-thick SiO2 was formed by dry oxidation of p+-Si substrate. The mechanically exfoliated multi-layer WSe2 was transferred by PDMS stamp. Next, 15 nm-thick Al2O3 was prepared by ALD at 200 oC with H2O. Then, Nickel (Ni) metal was deposited by RF sputtering on Al2O3. Ni metal was patterned for gate electrode with conventional lithography process. After that, A2O3 layer was removed by wet etching. Subsequently, substrate was exposed to oxygen radicals to form WOx used as source/drain contact at surface of WSe2. Second layer of Al2O3 was deposited as an encapsulating passivation layer. After the contact hole opening, the electrical contact pad was fabricated. Finally, forming gas (N2 : H2 = 97 % : 3 %) annealing was performed at 200 oC for 30 min. The top gate length was 5 μm. The gate width was estimated to be 40 μm by optical microscope. The electrical characteristics were measured with a manual probe station in an atmospheric pressure without inert gas purge at room temperature using a precision semiconductor parameter analyzer (Agilent 4156 C).Figures 2 shows the Id–Vg characteristics of fabricated FETs for (a) back gate operation and (b) top gate operation. Representative Id–Vg characteristics of p-type FETs were observed irrespective of back gate and top gate operation. The on/off ratio of about 106 ~ 107 order were obtained for both back gate and top gate operation. Furthermore, the threshold voltage and sub-threshold slope were modulated by varying the substrate bias during gate sweep.This study opens up interesting directions for the research and development of TMDC-based devices.AcknowledgmentsThis study was supported by a JSPS Grant-in-Aid for Scientific Research (C) (Grant No. 20K04616), a research grant for Tokyo Tech Challenging Research Award, the Samco Foundation and a research grant for Suematsu Award.

Theoretical investigation of the optical and electronic properties of surface engineered V 2 N MXene

In this work, density functional theory is utilized to explore the impact of surface adsorption of (O, S, Se and Te) on the structural, electronic and optical properties of two-dimensional vanadium nitride (V 2 N) MXene and the results are compared with pristine V 2 N MXene. Our calculations show that V 2 NSe 2 MXene has the most stable structure among all the studied structures. Adsorption energy computations reveal that all terminal groups on the surface of the pristine V 2 N tightly attach to the V atoms. A metallic to semiconductor transition is observed in all the considered V 2 NT 2 (T=O, S, Se and Te) MXene structures. Among them, oxygen, selenium and tellurium adsorbed V 2 N shows a direct bandgap of 0.45, 0.86 and 0.53 eV, respectively. However, in case of sulphur adsorbed V 2 N MXene, an indirect bandgap of 1.19 eV is observed. This study also reports the effect of surface adsorption on the optical properties and dielectric constant of V 2 NT 2 (T=O, S, Se and Te). The results reveal a larger absorption in visible region as well as in ultraviolet region for all the computed structures except oxygen adsorbed V 2 N MXene as compared to pristine V 2 N MXene monolayer, which indicates the significance of surface adsorption on the optical properties of the studied MXene. Additionally, a very low reflectivity has been seen in all the V 2 NT 2 MXene structures as compared to pristine V 2 N. Our findings demonstrate the potential of these surface adsorbed V 2 N MXene materials in novel light-electron conversion devices.

Enhancement of Optical, Electrical, Magnetic, and Thermopower Properties of LaMnO3 by Potassium‐Doping

Optical, magnetoresistance, and thermoelectric properties of La1−xKxMnO3 (x = 0.05, 0.15, and 0.25) compounds have been investigated. The crystallography demonstrates that the samples x = 0.05 and 0.15 are a single‐phase rhombohedral () structure, while x = 0.25 is near to a single rhombohedral phase with a minor amount of Mn3O4 (with a ratio of ≈2%). The optical properties manifest that the reflectivity decreases slightly with increasing x‐doping, where the sample of x = 0.05 has the lowest reflection value, making it a promising material for photovoltaic applications. Electrical resistivity measurements show that the samples have a metal–semiconductor transition, and the transition temperature Tms decreases with the K content. The thermoelectric data show a remarkable coincidence behavior of the ρ–T relationship, which has a peak at a transition temperature (TS). Magnetic susceptibility data show that the samples undergo ferro‐paramagnetic transition at a certain temperature (Curie temperature).

Terahertz optoelectronic properties of synthetic single crystal diamond

A systematic investigation is undertaken for studying the optoelectronic properties of single crystal diamond (SCD) grown by microwave plasma chemical vapor deposition (MPCVD). It is indicated that, without intentional doping and surface treatment during the sample growth, the terahertz (THz) optical conduction in SCD is mainly affected by surface H-terminations, -OH-, O- and N-based functional groups. By using THz time-domain spectroscopy (TDS), we measure the transmittance, the complex dielectric constant and optical conductivity σ(ω) of SCD. We find that SCD does not show typical semiconductor characteristics in THz regime, where σ(ω) cannot be described rightly by the conventional Drude formula. Via fitting the real and imaginary parts of σ(ω) to the Drude-Smith formula, the ratio of the average carrier density to the effective electron mass γ = ne/m*, the electronic relaxation time τ and the electronic backscattering or localization factor can be determined optically. The temperature dependence of these parameters is examined. From the temperature dependence of γ, a metallic to semiconductor transition is observed at about T = 10 K. The temperature dependence of τ is mainly induced by electron coupling with acoustic-phonons and there is a significant effect of photon-induced electron backscattering or localization in SCD. This work demonstrates that THz TDS is a powerful technique in studying SCD which contains H-, N- and O-based bonds and has low electron density and high dc resistivity. The results obtained from this study can benefit us to gain an in-depth understanding of SCD and may provide new guidance for the application of SCD as electronic, optical and optoelectronic materials.

In-Plane Electric-Field-Induced Orbital Hybridization of Excitonic States in Monolayer WSe_{2}.

The giant exciton binding energy and the richness of degrees of freedom make monolayer transition metal dichalcogenide an unprecedented playground for exploring exciton physics in 2D systems. Thanks to the well-energetically separated excitonic states, the response of the discrete excitonic states to the electric field could be precisely examined. Here we utilize the photocurrent spectroscopy to probe excitonic states under a static in-plane electric field. We demonstrate that the in-plane electric field leads to a significant orbital hybridization of Rydberg excitonic states with different angular momentum (especially orbital hybridization of 2s and 2p) and, consequently, optically actives 2p-state exciton. Besides, the electric-field controlled mixing of the high lying exciton state and continuum band enhances the oscillator strength of the discrete excited exciton states. This electric field modulation of the excitonic states in monolayer TMDs provides a paradigm of the manipulation of 2D excitons for potential applications of the electro-optical modulation in 2D semiconductors.

Influence of a Thin V2O3 Spacer on Interlayer Interactions in Fe-Ni/V2O3/FeNi Film Structures

In this paper, we explore the suggestions of the results of experimental studies on low-dimensional layered systems in FeNi/V2O3/FeNi film structures. The multifunctional material V2O3 is used as an interlayer between the magnetically active FeNi layers. The films were obtained by ultrahigh vacuum magnetron sputtering on a glass substrate with a base size of 10−10 Torr. It has been found that for V2O3 films, the decrease in the metal–semiconductor transition temperature increases significantly. Magnetic characteristics were studied on the MPMS-XL SQUID magnetometer. The exchange effect occurs both in the region where the oxide has a magnetic order and in the paramagnetic region. The latter is due to the effect of the magnetic panel in the oxide package. The phenomenon of oscillation of the exchange field occurs depending on the phenomenon of intermediate observation observed experimentally.

Out-of-Band Fibre-Optic Time and Frequency Transfer Using Asymmetric and Symmetric Opto-Electronic Repeaters.

Signal repeaters for fibre-optic communication can be realized with back-to-back connected transceivers. This configuration can provide high gain (≈30 dB) at low cost, and the needed semiconductor lasers and modulators can be realized for practically any relevant wavelength. Unfortunately, for time and frequency transfer the uncorrelated wavelength drifts in the transceiver lasers can compromise transfer stability, and device replacement due to failure may result in large time offsets that have to be measured via global navigation satellite services. This work demonstrates that good results can nevertheless be obtained with standard telecom DWDM tranceivers over long time periods (years). More importantly, a simple wavelength-symmetric repeater is proposed that can be used to cancel the detrimental effects of wavelength drifts and which lessens the need for link re-calibrations after transceiver replacements. In a proof-of-concept test setup, timing drift due to wavelength drift of a repeater laser is reduced by approximately two orders of magnitude.