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The environmentally friendly Cu2ZnSn(S,Se)4 (CZTSSe) compounds are promising direct bandgap materials for application in thin film solar cells, but the spontaneous surface defects disordering would lead to large open-circuit voltage deficit (Voc,deficit) and significantly limit kesterite photovoltaics performance, primarily arising from the generated more recombination centers and insufficient p to n conversion at p-n junction. Herein, we establish a surface defects ordering structure in CZTSSe system via local substitution of Cu by Ag to suppress disordered CuZn defects and generate benign n-type ZnAg donors. Taking advantage of the decreased annealing temperature of AgF post deposition treatment (PDT), the high concentration of Ag incorporated into surface absorber facilitates the formation of surface ordered defect environment similar to that of efficient CIGS PV. The manipulation of highly doped surface structure could effectively reduce recombination centers, increase depletion region width and enlarge the band bending near p-n junction. As a result, the AgF-PDT device finally achieves maximum efficiency of 12.34% with enhanced Voc of 0.496 V. These results offer a new solution route in surface defects and energy-level engineering, and open the way to build up high quality p-n junction for future development of kesterite technology.

This paper presents the characteristics of HgCdTe mid-wavelength infrared (MWIR) electron-initiated avalanche photodiodes (e-APDs) as a function of temperature under different biases. The devices show a low dark current density of the order of ${10^{ - 7}} \text{A/cm}^2$ at 80 K when the reverse bias voltage is below 4 V, with an exponential gain above 100 at − 8 V. Low excess noise factor of around 1.2 is also demonstrated for the devices at 80 K. The dark current and gain characteristics at different temperatures are analyzed, along with the device simulation results. A varied-temperature impact ionization model for MWIR e-APD devices is adopted based on the experimental results. In addition, a significant increase of the dark current in the APD device is observed at high temperature under large reverse bias, which can be associated with the local electric field redistribution due to the accumulation of holes in the depletion region at high temperatures. The analysis presented in this work paves the way to achieve a high operating temperature (HOT) of the HgCdTe APD with further optimization.

The pursuit of low power consumption, high charge collection efficiency (CCE), and high energy resolution is critical for the development of high performance GaN-based alpha-particle detectors. In this letter, we fabricated a low-voltage p-i-n GaN-based alpha-particle detector with superior energy resolution. The detector exhibits a very low leakage current of pA level even at −100 V and high CCEs of 31% and 92% at zero bias and reverse bias of 50 V, respectively. Meanwhile, the detector demonstrates a high energy resolution of 2.48% at −20 V. These excellent performances are attributed to the artificially enlarged path of alpha particles in the depletion region by employing the angular incidence measurement method and the high crystal quality of the epitaxial film grown on a single-crystal GaN substrate. In addition, the damage events caused by the alpha particles are also investigated using the Monte Carlo calculation. These results are anticipated to promote the research of radiation-hardened GaN-based detectors.

The Schottky barrier at the interface between the semiconductor phase and the metal phase has excellent rectification effect which can greatly facilitate the formation of the electron accumulation region. The interface electronic modulation can promote the formation of electron depletion layer in the gas sensing process, which is a powerful strategy to improve the sensing performance. In this work, ZnO–TiC composites were successfully prepared. XRD, TEM, BET and XPS characterizations of the ZnO–TiC composites were proformed to investigate the compositions and structures. The as-synthesized samples were applied to fabricate gas sensors to investigate their gas sensing performance. Compared to pure ZnO and TiC, the composites achieved high sensitivity (232 for 100 ppm aniline) and linear detection (R2 = 0.986) of aniline. The improvement of sensor performance is mainly attributed to the electronic modulation of Schottky barrier at the interface between ZnO and TiC. Our results indicate that the construction of ZnO-TiC Schottky barrier is a promising strategy for enhancing the performance of gas sensors.

We report GaN vertical trench MOS barrier Schottky (TMBS) diodes with embedded p-GaN shielding rings (SRs) and systematically investigate the impact of different structural parameters of the p-GaN SRs on the breakdown performance of the GaN-based vertical TMBS diodes by numerical simulation. The charge coupling effect by the embedded p-n junction at the bottom of the trench homogenize the electric field at the trench corner and alleviate the electric field crowding effect at the Schottky contact region, which can effectively avoid the premature breakdown and improve the reverse blocking capability of the TMBS diodes. The p-GaN SRs can also broaden the overlapped depletion region and shift the pinch-off point into the n−-GaN drift region, thus facilitating the 2-D depletion in the n−-GaN drift layer and boosting the breakdown performance of the conventional TMBS diodes. We found that the doping concentration, thickness, and the width of the p-GaN SRs are closely associated with the electric field distribution and the reverse breakdown characteristics of the GaN-based vertical TMBS diodes. The vertical TMBS diodes with optimal p-GaN SR parameters featured a dramatic improvement in the breakdown voltage from 907 to 1281 V, without an obvious degradation in the ON performance. The proposed TMBS diodes with a p-GaN SR structure can pave the way toward a high-performance GaN vertical power device for high-power and high-efficiency power switch applications.

A 2-D compact analytical model for the device potential of double metal double gate hetero-oxide Tunnel FET (DM DG Hetero-oxide TFET) has been developed in this work. The hetero-oxide (HfO2 + SiO2) and the double metal double gate allows improvement in current in the ON state of TFET as well as suppresses the ambipolar current in TFET curtailing both the limitations of TFET. Parabolic approximation method with required boundary conditions has been utilized to solve Poisson’s equation. Depletion region plays vital role in altering the potential of device in its proximity. Therefore, the depletion regions at drain and source are also considered for the modeling of the device. For this the effect of fringing field has been considered using the technique of conformal mapping in the depletion regions. The incorporation of the depletion region in potential modeling allows a precise modeling of the potential near channel-drain and source-channel junctions. The model results considering source and drain depletion region shows better match with simulation results. Validation of proposed model has done against simulation data using ATLAS TCAD SILVACO software. The compact analytical model developed here is found to have good agreement with the simulation framework.

Growth of 2D materials under ultrahigh-vacuum (UHV) conditions allows for an in situ characterization of samples with direct spectroscopic insight. Heteroepitaxy of transition-metal dichalcogenides (TMDs) in UHV remains a challenge for integration of several different monolayers into new functional systems. In this work, we epitaxially grow lateral WS2–MoS2 and vertical WS2/MoS2 heterostructures on graphene. By means of scanning tunneling spectroscopy (STS), we first examined the electronic structure of monolayer MoS2, WS2, and WS2/MoS2 vertical heterostructure. Moreover, we investigate a band bending in the vicinity of the narrow one-dimensional (1D) interface of the WS2–MoS2 lateral heterostructure and mirror twin boundary (MTB) in the WS2/MoS2 vertical heterostructure. Density functional theory (DFT) is used for the calculation of the band structures, as well as for the density of states (DOS) maps at the interfaces. For the WS2–MoS2 lateral heterostructure, we confirm type-II band alignment and determine the corresponding depletion regions, charge densities, and the electric field at the interface. For the MTB, we observe a symmetric upward bend bending and relate it to the dielectric screening of graphene affecting dominantly the MoS2 layer. Quasi-freestanding heterostructures with sharp interfaces, large built-in electric field, and narrow depletion region widths are proper candidates for future designing of electronic and optoelectronic devices.

Indium selenide (γ-In2Se3) films were prepared using RF magnetron sputtering. Influence of deposition time on structural, optical, morphological, and photoelectrochemical (PEC) performance was studied. Formation of γ-In2Se3 is confirmed by low angle XRD, Raman spectroscopy, and XPS analysis. Surface morphology investigated using FE-SEM shows that γ-In2Se3 films are uniform and have a dense grain structure, without cracks and holes. Optical properties show that γ-In2Se3films absorb mainly in the UV region, and the bandgap energy decreases from 2.81 to 2.27 eV as deposition duration increases. Conduction and valance band-edge potential values show that γ-In2Se3 films are suitable for photoelectrochemical hydrogen evolution. PEC activity of γ-In2Se3 photoanodes was evaluated using linear sweep voltammetry (LSV), and there was an increase in photocurrent density with deposition time. Electron impedance spectroscopy (EIS) analysis revealed that γ-In2Se3 photoanodes had high charge transfer resistance, and it decreases with deposition time, which leads to improved PEC performance. Investigation of Mott Schottky's (MS) results shows a shifting of flat band potential towards negative potential, suggesting movement of fermi level towards conduction band edge. Carrier density increases from 3.7 × 1019 cm−3 to 8.9 × 1020 cm−3 and depletion layer width of γ-In2Se3 photoanodes are found in the range of ~ 2.67–9.10 nm. The gradual increase in electron lifetime indicates a decrease in the recombination rate of photo-generated charge carriers. An increase in time-dependent photocurrent density reveals that γ-In2Se3 films have effective electron–hole separation. Our work demonstrates that γ-In2Se3 can be a probable candidate for PEC water splitting and opto-electronic applications.

For the first time, we report achieving a considerable output power density in metal-semiconductor field-effect transistors according to silicon-on-insulator technology (SOI MESFETs). Our main idea is to improve the breakdown voltage and the saturation current simultaneously and, therefore, the output power density of SOI MESFET devices by silicon dioxide engineering. Our silicon dioxide engineering consists of a step-shaped buried oxide (BOX) and an extra layer of silicon dioxide under the gate (SB-LO-SOI) in this work. A step-shaped in the channel area results in a more significant drain current due to increasing total carrier concentrations. Also, by omitting a part of the BOX and substituting it with n-doped silicon, the depletion layer changes, and the channel charges increase. Besides, the distribution of the electric field improves by the additional rectangular silicon dioxide layer under the gate as a result of extending the depletion layer. By having a premier electric field distribution, the breakdown voltage will enhance. According to the results, the breakdown voltage and the saturation current of the considered device improve by 130 % and 33 %, respectively, compared to the traditional one. As well as, the output power density of the considered device rises by 212 %. Thereupon, the SB-LO-SOI MESFET device outperforms the conventional SOI MESFET device in terms of electrical properties.

Nanoscale oxide layer protected semiconductor photoelectrodes show enhanced stability and performance for solar fuels generation, although the mechanism for the performance enhancement remains unclear due to a lack of understanding of the microscopic interfacial field and its effects. Here, we directly probe the interfacial fields at p-GaP electrodes protected by n-TiO2 and its effect on charge carriers by transient reflectance spectroscopy. Increasing the TiO2 layer thickness from 0 to 35 nm increases the field in the GaP depletion region, enhancing the rate and efficiency of interfacial electron transfer from the GaP to TiO2 on the ps time scale as well as retarding interfacial recombination on the microsecond time scale. This study demonstrates a general method for providing a microscopic view of the photogenerated charge carrier's pathway and loss mechanisms from the bulk of the electrode to the long-lived separated charge at the interface that ultimately drives the photoelectrochemical reactions.

The 4H-SiC trench metal–oxide semiconductor field-effect transistor (MOSFET) with the grounded p+ shielding region is one of the commercial devices with superior gate oxide reliability. However, the introduced JFET region seriously increases the influence of quasisaturation (QS) on device electrical performances, resulting in the poor output and transfer characteristics. In order to investigate the mechanism of QS effect, the output characteristic is physically analyzed by monitoring the variations of the electric field, the electron concentration, the electron velocity, and the depletion layer inside the cell structure. It is demonstrated that the channel electrons are injected into the JFET current path from the channel region by a forward bias to the channel and JFET junction at QS state. Moreover, based on the Lombardi CVT model, the influence of QS effect on devices with different channel electron mobilities is first studied. An improved SiC trench MOSFET with two-level doped current spreading layers is proposed to decrease the JFET resistance and suppress the QS effect. The QS current and the peak transconductance are improved by 42% and 23%, respectively. The specific ON-state resistance is decreased by 10% and the figure of merit is improved by 7%.

Boron-doped diamond (B-diamond) metal–oxide–semiconductor (MOS) capacitor and MOS field-effect transistor (MOSFET) are fabricated on a flat diamond epitaxial layer. Their electrical properties and thermal stabilities after annealing at 500 °C are investigated. Annealing makes the leakage current density of the B-diamond MOS capacitor increase slightly. There is a larger stretch-out for the capacitance-voltage curve in the depletion region after annealing than that before annealing. The drain-current maxima for the as-fabricated and 500 °C-annealed MOSFETs are obtained as −0.49 and −0.60 mA/mm, respectively. Extrinsic transconductance maxima are 18.7 and $21.4~\mu \text{S}$ /mm, respectively. These obtained values are considerably larger than those obtained by the previously reported B-diamond MOSFETs.

Herein we introduce and investigate a new architectural design strategy for planar single gate field effect transistors (SG-FETs) that delivers advantages from all fronts of design, fabrication and performance perspectives. The amalgamation of schottky buried metal layer (BML) and charge plasma (CP) mechanism of doping in planar single gate architecture yields a novel type of FET called as CP-BML FET. Owing to the schottky BML induced depletion region created on the bottom side of device layer reduces effective device layer thickness (TSi) suppressing short channel effects (SCEs) including drain induced barrier lowering (DIBL) and threshold voltage roll-off. The proposed FET has been analyzed for DC and RF performance figure of merits (FOMs) and compared to counter part state of the art technologies with reference to ITRS performance projections. The proposed FET is also investigated the performance FOMs on for criticality of physical parameters including gate length (Lg), device layer thickness (TSi), BML workfunction (ϕBML). The ION and IOFF for proposed device at Lg = 20nm read at 730μ A/μ m and 7 × 10− 2 pA/μ m respectively. RF performance analysis reveal transition frequency (ft) of 390 GHz with SS $\simeq \ \text {75mV/dec}$ coherent with ITRS performance projections. It is found that ultra scaled (7 nm) proposed device exhibits intrinsic delay τ of 0.6 ps which is superior to ITRS projections of 1.71 ps at 28 nm technology node. The proposed device yields Pdyn of 0.248 fJ/μ m at Lg= 7nm implicating it to be potential candidate for low power with high performance application requirements.

Flexible Cu2ZnSnSe4 (CZTSe) solar cells gradually attract much attention due to their low-cost, lightweight, and environmentally friendly features. However, the efficiency of flexible CZTSe solar cells obtained through the nonvacuum green electrodeposition process remains sluggish (3.82%), far away from that obtained from other methods (∼10% by magnetron sputtering). Herein, a championed 6.33% efficiency of flexible CZTSe solar cells prepared by the electrodeposition process is achieved through an in situ electrochemical treatment (ET) process. It is found that the ET process drives the formation of a thin MoOx layer, evoking a series of beneficial results, thus accounting for an enhancement in photovoltaic performance. With the ET process, the MoSe2 thickness is compressed and Cu- and Sn-related undesirable defects/secondary phases are inhibited, leading to improved film quality. Additionally, it prolongs the depletion region width and minority lifetime, accelerates the charge separation and collection, relieves the band tails, and favorably reverses the band bending from downward to upward at/near grain boundaries. With these effects, the efficiency increases from 4.21% to 6.33%, far beyond the highest reports on electrodeposited flexible CZTSe solar cells. Our findings offer a promising way to improving Mo foil-based flexible devices and mark a significant breakthrough for the development of electrodeposition-processed flexible CZTSSe-based solar cells.

This article describes an analysis of the electric-field-dependence mechanism for cosmic ray failure in power semiconductor devices. Two major modes for the failure have been reported. One is bipolar transistor activation caused by carrier generation from impact ionization at the n−/n+ boundary. The other is Joule heating generated by an avalanche current in high electric fields. We clarified that a bipolar transistor activation mode had not occurred even under high electric field conditions for the drift layer width used in lower-voltage-class insulated-gate bipolar transistors (IGBTs) by evaluating the drift layer thickness dependence of the failure in time (FIT) in 1700 V devices from punchthrough to non-punchthrough with and without a p+ collector layer. We also clarified that the electric field averaged over the depletion layer width (applied voltage divided by the depletion layer width) is the critical factor for failure, rather than the maximum electric field, for the first time by observing a universal curve of the average electric field dependence of FIT in 750–6500 V IGBTs and diodes. To improve the cosmic ray durability of power semiconductor devices, lowering the electric field averaged over the depletion layer width is effective for device design.

The electrical characteristics and photoresponse of the “carbon nanofilm on silicon” heterostructure obtained by laser-pulsed deposition have been investigated. The thickness of the carbon nanofilm is selected from the condition of the maximum antireflection effect of the substrate. It was found that the obtained junction is rectifying with a rectifying coefficient of 35 at 1 V. The direct current-voltage characteristic from 0.1 V to 0.35 V is in satisfactory agreement with the expression J = J0exp(eU/ηkT). An increase in voltage in the forward direction leads to the appearance of currents limited by the space charge (J = AU2). Linearization of the C–2–U dependence indicates the sharpness of the impurity distribution in the space charge region. The mechanism of the photoresponse of the heterostructure is similar to the photoresponse of anisotype heterostructures with the ‘window’ effect. The long-wavelength edge (1.1 μm) of the photosensitivity is determined by the silicon substrate, and absorption in the carbon nanofilm leads to an additional expansion of the photosensitivity region. The heterostructure has uniform photosensitivity at the level 0.8 in the wavelength range of 0.55–1.1 µm. The short-wavelength tail reaches up to 0.4 µm.

In this article, in addition to two commonly known noise parameters—dark count rate (DCR) and afterpulsing (AP)—we explore another interesting phenomenon–random telegraph signal (RTS) noise—during the transitional phase of the avalanching process. We present the properties of the RTS noise and their dependence on the biasing voltage and temperature. An analytical model is used to extract the dimension of the defects in the depletion region from the variation of the RTS noise current amplitude with biasing voltage. By comparing the DCR and AP of single-photon avalanche diode (SPAD) samples with different defect dimensions derived from the RTS noise properties, a trend that the SPAD with a larger defect dimension shows a higher DCR and AP is found.

Gate reliability and its degradation mechanism were studied for the normally off high-electron-mobility transistors (HEMTs) with regrown p-GaN gate and AlN/SiN x stack passivation. Through comparing the forward leakage current in two designed structures, the conduction mechanism is determined to be Fowler-Nordheim tunneling whose current is independent of temperature when the Pd/p-GaN Schottky junction is under high electric field. Even for the regrown p-GaN gates, this Schottky junction fails at first, resulting in an abrupt increase in gate current. The maximum gate operation voltage with a failure rate of 1% for 10-year lifetime is estimated to be about 6.87 and 6.07 V at room temperature by adopting power law and exponential law as extrapolation fitting, respectively. Degradation process monitoring reveals that the net acceptor concentration $N_{\mathrm {A}}$ extracted through $C$ – $V$ fitting presents an apparent decreasing trend from $3.8\times 10^{19}$ to $1.1\times 10^{19}$ cm−3 with the stress time increased from 30 to 2600 s. This is assumed to be related with the defects generation in the Schottky depletion region under high tunneling current and high electric field. These analyses show the feasibility of the normally off HEMTs with a regrown p-GaN gate and AlN/SiN x stack passivation for practical applications, giving directions for further improving the gate breakdown voltage and lifetime.

In2O3 vertical nanostructures (VNS) are fabricated using a glancing angle deposition (GLAD) technique upon an In2O3 thin film (TF) on a n-type silicon (n-Si) substrate. Analysis using high-resolution transmission electron microscopy (HRTEM) and high-resolution x-ray diffraction (HRXRD) revealed that the In2O3 VNS are amorphous in nature. An average ~4.5-fold enhancement in absorption was observed and a microscopic origin was proposed for observed bandgap changes for the n-Si/In2O3 TF/GLAD In2O3 VNS and bare n-Si/In2O3 TF samples in the visible region due to surface-related trap states or oxygen vacancies. The improvement in photodetection was attributed to the presence of a large number of surface-related trap states at the edge of metal contacts. The fabricated VNS detector possesses enhanced photosensitivity (~1.7-fold) due to an efficient photogating effect in the depletion region. A maximum detectivity of ~12.8 × 107 Jones was observed for the n-Si/In2O3 TF/GLAD In2O3 VNS device, which possesses ~15.6-fold enhanced detectivity as compared to the bare n-Si/In2O3 TF device.

International audience; Developing nanoscale electrical characterization techniques adapted to three-dimensional (3D) geometry is essential for optimization of the epitaxial structure and doping process of nano- and microwires. In this paper, we demonstrate the assessment of the depletion width as well as the doping profile at the nanoscale of individual microwire core–shell light-emitting devices by capacitance–voltage measurements. A statistical study carried out on single wires shows the consistency of the doping profile values measured for individual microwires compared to assemblies of hundreds of wires processed on the same sample. The robustness of this method is then demonstrated on four epitaxial structures with different growth and doping conditions. Finally, electron-beam-induced current and secondary electron profiles are used to validate the depletion region width and the position in the core–shell structure.

In this paper, we propose a novel Silicon on Insulator (SOI) Metal Semiconductor Field Effect Transistor (MESFET) with an embedded GaN layer (GL-SOI-MESFET) for modifying the electric field distribution. The main idea of this work is based on using a high breakdown field material (GaN), for amending the electric field and potential distribution near the drain region, and as a result, the breakdown voltage of the proposed structure will be higher than a conventional structure (C-SOI-MESFET). The breakdown voltage (VBR) of the GL-SOI-MESFET at the Ids = 55 mA/mm and Vgs = − 1 V has been achieved ~21 V whereas the VBR in the C-SOI-MESFET is 16 V. The proposed structure shows the improvement of DC and RF characteristics versus the C-SOI-MESFET. For obtaining the best results to improve the structure performance, dimensions of the GaN layer have been optimized. Also, by amending potential distribution and changing the depletion region between the gate and drain sides, the gate-drain capacitance reduces. The effects like the electric field, the potential distribution, breakdown voltage, the kink effect, the self-heating effect, power gains, and parasitic capacitances are investigated and the proposed structure results have superior DC and radio frequency (RF) performances compared with the conventional MESFET structure.

In this work, we fabricated vertical organic thin film transistors (VOTFTs) with lead phthalocyanine (PbPc) as the active layer and analyzed the operating characteristics and current transfer mechanism of VOTFTs. The results show that the quiescent output current of VOTFTs is not saturated, and the output current can be modulated by requiring different gate voltages. The switching parameters of the VOTFTs are ton = 2.5 μs, toff = 3.5μs, and the switching characteristic time reaches the microsecond level. When a sine wave dynamic signal is applied to the gate electrode, the cut-off frequency fc = 77 kHz. The experimental results demonstrate that short channel and vertical structure of VOTFTs make up for organic semiconductor material defects of low carrier mobility and realize high speed and low driving voltage of organic devices. Electric field intensity of depletion layer in the gate region is 7×107V/m, and high electric field intensity makes carriers tunneling become the major transport mode. The tunnel injection model is used to analyze the carrier transport inside the transistor. The results show that the operating current of the transistor conforms to the tunneling effect theory.

Pristine ZnO based hydrogen sensors pose low sensitivity (~ 43%) at the operating temperature of 150°. Herein, we explore the decoration of Phosphorene oxide quantum dots (POQDs) on RF sputtered grown ZnO nanostructures for hydrogen gas sensing application. A simplistic approach such as drop cast method is employed to decorate electrosynthesized POQDs (2- $8~\mu \text{L}$ ) onto interdigitated electrodes over ZnO nanostructures. The suggested hydrogen sensor based on POQDs ( $6~\mu \text{L}$ )/ZnO nanostructures exhibits an outstanding sensing response (~70.6%) as compared to all the sensors for 100 ppm at 150°C. Enhanced sensing response from the POQDs( $6~\mu \text{L}$ )/ZnO nanostructure might be due to the enormous active surface area of POQDs (provides more active sites for hydrogen gas) and modulation of depletion region at the interface of POQDs and ZnO. The proposed sensor can be operated at mild temperature and consume low power which is the need of the hour for the hydrogen sensors for industrial applications.

Silicon technology is dominant in electronics and optoelectronics. The cut-off wavelength of silicon is less than 1.1 $$\upmu$$ m due to the bandgap, limiting applications of silicon in communication, sensing, and light harvesting. A new strategy for infrared photodetection is presented by integrating silicon and PbSe colloidal quantum dots (CQDs), which combines advantages of silicon devices and PbSe-CQDs. In this study, we introduce a silicon-based photodetector that is sensitive to infrared light with spectral response from 405 nm to 1550 nm. The device can deliver a high responsivity of 648.7AW− 1 and a fast response of 32.3 $$\upmu$$ s at 1550 nm. Besides, the detectivity and the external quantum efficiency of the device reached 7.48 × 1010 Jones and 6.47 × 104%, respectively. The performance of the device originates from the photovoltage generated at the interface between the silicon and the quantum dots. This photovoltage changed the width of the depletion layer to realize detection. These results indicate that the silicon-based quantum dot infrared photodetectors prepared by this method have application prospects in the field of optoelectronics.

The micro-electro-mechanical system (MEMS)-based field effect transistor (FET) sensor for hydrogen detection was fabricated by modifying the gate electrode with boron nitride nanotubes (BNNTs) decorated Pd-ternary alloy (Pd63·2Ni34·3Co2.5) as a hydrogen sensing layer Electro-thermal properties of the micro-heater embedded under sensor membrane were analyzed by a finite element method (FEM) simulation. The structural and morphological properties of the gate electrode were studied by Raman spectroscopy, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and field emission scanning electron microscopy (FESEM). A variation in gate potential is observed due to the H2 atmosphere that leads to the variation in the depletion region, therefore, changing the current in the channel (BNNTs decorated Pd-ternary alloy). The BNNTs-decorated Pd ternary alloy displayed high sensing response, fast response and recovery time for H2 gas, low power consumption, long-term stability, and wide detection range from 1 to 5000 ppm H2. The drain current of the H2 FET sensor varied significantly at hydrogen gas exposure and increased with H2 concentration. As proposed H2 FET sensor can be utilized to the H2 leak detection system for safe applications.

2D materials and their heterojunctions have been explored for gas sensing applications due to their tremendous surface-to-volume ratio, active edges with atomic thickness, and tunable electrical properties. Heterostructures of 2D materials exhibit absolutely novel physics and versatility with accelerated device performance by integrating the atomic scale properties of individual materials. Traditional gas sensors use homogeneous materials as the sensing interface in which the surface adsorbed oxygen ion species play an important role in its performance. But the performance of the sensors suffers greatly due to their selectivity and high working temperature leading to poor stability and short-term uses; the van der Waals 2D p-n heterojunction-based gas sensors hold several advantages since both the materials and the depletion layer formed at the junction can actively tune the sensing performance. By choosing 2D materials with different band structures, charge polarity, carrier concentration, and work function, band alignment at the interface can be precisely engineered to achieve the selective gas sensing performance with low operating temperature. Herein, we have reviewed the working principles, recent developments, and future perspectives of p-n heterojunctions of 2D materials for gas sensing applications.

Perovskite solar cells (PSCs) have triggered a research trend in solar energy devices in view of their high power conversion efficiency and ease of fabrication. However, more delicate strategies are still required to suppress carrier recombination at charge transfer interfaces, which is the necessary path to high-efficiency solar cells. Here, a p-p+ homojunction was constructed on basis of NiO film to enhance hole transfer in an inverted planar perovskite solar cell. The homojunction was generated by fabricating a NiO/Cu:NiO bilayer film. The density functional theory calculation demonstrated the charge density difference in the two layers, which could generate a space charge region and a band bending at the junction, and the result was further proved by energy level structure analysis of NiO and Cu:NiO films. The designed homojunction could accelerate the hole transfer and inhibit carrier recombination at the interface between hole transfer layer and perovskite layer. Finally, the inverted planar perovskite solar cell with p-p+ homojunction showed an efficiency of 18.30 % and a high fill factor of 0.81, which were much higher than the counterpart of the PSCs individually using NiO or Cu:NiO as hole transfer layer. This work developed a new structure of hole transport layer to enhance the performance of PSCs, and also provided new ideas for design of charge transfer films.

In this article, novel sandwich-structured surface plasmon ultraviolet (UV) photodetectors based on ZnO thin films with engineered rear metal electrode were fabricated by radio-frequency magnetron sputtering. An exhaustive study about the impact of a dissimilar metallic layer (Au and Pt) on the structural, optical, and electrical properties of the device was carried out. The carrier collection property of the sandwich structure devices has the advantages of horizontal and vertical joint collection. In theory, adding a new metal semiconductor layer introduces a contact area and increases the resistance. An ultra-low dark noise current of less than 2.0 × 10–7 A and a responsivity exceeding 1.6 A/W were achieved with the prepared ZnO-based UV-PDs in the rear metallic electrode mode. The devices based on the ZnO/Pt/ZnO and MgZnO/Pt/MgZnO sandwich structures show high responsivity and fast response. This study provides a depletion layer width method for the fabrication of high-response UV photodetectors for surface plasmon-based materials by integrating metal semiconductor nanostructures. A homogeneous two-layer UV photodetector is constructed, which changes the traditional single-layer device structure and overcomes drawbacks of the single device structure.

This study investigates the charge injection barrier at the phthalocyanine (H2Pc)/Pd using accumulated charge measurement (ACM). Because the hole injection barrier is relatively small, the voltage ...

Improvement in sensing performance by metal oxide based materials has usually been achieved by doping, morphology tuning, particle size tailoring or porosity modification. The existing models of band bending and grain boundary depletion layer that explain chemiresistive sensing address the above issues in terms of qualitative electronic behaviour. However, for thick film sensors in particular, there is a clear demarcation between the surface and the bulk. Thus the concept of gross electronic distribution needs refinement in terms of variable behavior of electrons in the surface and in the bulk so that the roles of different layers in a sensor film are distinguishable. Using the case of improved 98.2% ethanol sensing response by paramagnetic aluminium doped tin oxide mesoporous nano-systems, we have demonstrated how Al doping promotes difference in electronic behavior in the surface and in the bulk of thick film sensors, complementing the existing charge depletion model. The 4-fold improvement in sensing responses by Sn0.947Al0.144O1.881 and Sn0.869Al0.242O1.888 as compared to tin oxide have been explained in terms of shortening of the unit cell by virtue of aluminium doping, and the 2.4-fold improvement in sensing response by Sn0.869Al0.242O1.888 as compared to Sn0.947Al0.144O1.881 has been explained by surface and bulk electron mobilization. Considering the conceptual inclusiveness of correlation studied, it is expected to be applicable in explaining sensing mechanisms based on electron mobilization in other metal oxide sensor systems also.

Treating kesterite layers with sodium has been proved to be an effective way to improve the photovoltaic performance of Cu2ZnSnS4 (CZTS) solar cells. However, elemental diffusion effects inside the film and heterojunction energy band matching on the performance of flexible solar cells are rarely reported. In this work, flexible CZTS solar cells were doped with various sodium sources using a simple solution spin-coating post-treatment method. The research results demonstrated that films prepared by Na2S2O3 solution doping exhibit improved crystalline quality and photoelectric properties, while also inhibiting the growth of impurity defects within the films. Further optimization of the doping concentration of post-treatment solution showed that when the doping ratio was 0.05 mmol mL−1, the grain growth of the prepared film was larger, and adhesion between the film layers was enhanced. The energy band bending of the CZTS/CdS heterojunction exhibited a “cliff” arrangement when the conduction band offset (CBO) value was −0.34 eV, facilitating carrier transport in the space charge region and enhancing the collection of photogenerated carriers. The flexible CZTS solar cell constructed on this basis exhibited excellent bending resistance and a maximum photoelectric conversion efficiency (PCE) of 5.83% with an open-circuit voltage (Voc) of 609 mV.

In this work, vertical NiO/Ga2O3 heterojunction diodes (HJDs) integrated with SiNx/Al2O3 double-layered insulating field plate (FP) structures have been demonstrated. With the additional post-annealing, the resultant diode exhibits a decreased differential specific on-resistance ( $\text{R}_{\mathrm{ on,sp}}$ ) of 5.4 $\text{m}\boldsymbol{\Omega } \cdot $ cm2 and an enhanced breakdown voltage (BV) of 1036 V. The improved performance is attributed by the combination of the FP-suppressed crowding electric field at the device edge and the reduced trap density at the NiO/Ga2O3 interface. In particular, the near-unity ideality factor has been achieved for this p-n HJD at an elevated temperature of 275 °C, indicating that the diffusion current is dominated. The high-temperature operation capability is owing to the quality improvement of NiO/Ga2O3 interface, where the Shockley-Read-Hall (SRH) recombination mediated by deep-level defects within the depletion region is thus suppressed.

In this paper, we report a method of increasing the sensitivity of a silicon near-infrared sensor. The sensor is realized by forming multiple trench-type photodiodes in a silicon chip. The trench photodiodes can be formed using conventional semiconductor fabrication equipment. The device structure allows the depletion layer to be spread over the entire sensor chip even at a bias voltage of 10 V or less. The sensor chip can thereby extend the collection area of photoelectrons to the maximum. At a chip thickness of 540 $\mu \text{m}$ , the conversion efficiency for near-infrared wavelengths between 940 and 1020 nm is more than 80% at room temperature. In addition, the electrical characteristics and response performance of the fabricated 2.4 mm $\times2.4$ mm test chips are reported. Since the proposed method can achieve a high conversion efficiency at low voltage without cooling in silicon semiconductors, it is expected to provide a low-cost and compact solution for various near-infrared receiver devices such as these for Internet of Things (IoT) applications.

We present a systematic study of how graphitic carbon nitride (g-C3N4) in combination with Al2O3 can be used as a double dielectric to control threshold and flat band voltage in capacitance-voltage (C-V) characteristics of an a-IGZO metal-insulator-semiconductor (MIS) device fabricated on ITO substrate. We study temperature dependence of C-V characteristics for Al2O3 based MIS structures with and without g-C3N4 in the oxide. The effective dielectric constants are estimated in both cases. We show that g-C3N4 in combination with Al2O3 can be used as an effective dielectric with larger relative permittivity than either of them. It also leads to positive threshold shift without affecting the active interface at the semiconductor. The carrier density in the semiconductor is measured from the depletion region showing small variation with respect to frequency and temperature.

Effect of an isolated Ge nanowire embedded in an n-doped Si on electron beam induced current is simulated by a Monte Carlo calculation algorithm. A circular nano-contact is used to collect the current generated by the use of primary energy of 5 or 10 keV in a perpendicular configuration along a line passing through the contact center. The nanowire, considered as a recombination center, is vertically positioned beneath the contact. Calculation takes into account various parameters such as a nano-scale depletion zone under the nano-contact, the depth of the nanowire, and its size. The surface recombination velocity is taken equal to zero. Competition between both carriers collected by the nano-contact and those captured by the nanowire is studied. Both processes are affected by the depth of the nanowire and by the primary energy. Moreover, the nanowire–Si contact behaves as a nano-scale hetero-junction, and hole storage in the nanowire leads to accentuation of energy band bending, especially in the longitudinal direction of the nanowire. Consequently, tunnel recombination would be present.

As the tight contact interface of the lateral PN junction enables high responsivity, specific detectivity, and fast response speed, atomic-scale two-dimensional (2D) lateral PN heterostructures are emerging as viable alternatives to silicon-based photodiodes. The optical properties of the current 2D heterostructures depend entirely on the intrinsic properties of 2D materials, which can be greatly improved by forming an ideal PN diode via the doping control of 2D heterostructures. In this study, we propose a high-performance photodiode using a doping-controlled WSe2–MoSe2 PN heterojunction. During the synthesis, the low chemical reactivity of Nb2O5 with WO3 as compared to MoO3 enables sequential growth and prevents niobium (Nb) doping during MoSe2 growth at low temperatures. Conversely, in the WSe2 growth at high temperatures, tungsten (W) to Nb is selectively substituted, resulting in the lateral heterostructure of Nb-doped WSe2–MoSe2. The Nb atoms in WSe2 change the WSe2 type from ambipolar to p-type dominant. Together with intrinsically n-type MoSe2, Nb-doped WSe2 forms a lateral PN heterostructure with a near-unity ideality factor (1.3) and a high forward/reverse current ratio of 104. Our ideal 2D PN photodiode effectively suppresses the dark current in the reverse bias region (∼100 fA at an overall VDS of 0 V to approximately −10 V) and enhances the photocurrent by the high built-in potential at the PN depletion layer (VOC = 0.52 V). Thus, our device exhibits a high Ilight/Idark ratio (105) and a corresponding ultra-high detectivity (5.78 × 1015 Jones), which are approximately 100 times higher than those of reported lateral 2D PN heterostructure photodiodes. These outstanding performances show that the doping-controlled transition metal dichalcogenide PN heterostructures are promising candidates for next-generation optoelectronics.

The predicaments of poor carrier separation and light absorption need to be overcome in order to maximize the preeminent performances of WO3 in photoelectrochemical (PEC) water splitting. Hence, we firstly prepared a 2D WO3/PANI core–shell hybrid heterojunction with high light absorption efficiency by a simple hydrothermal and photo-assisted electro-deposition method. A photocurrent density of 0.499 mA cm−2 at 1.23 V vs. RHE is achieved by the as-prepared hybrid heterojunction, which is about 2.35 folds higher than that of bare WO3 (0.212 mA cm−2). Moreover, the PEC stability is significantly enhanced to 87% from 60% with the deposition of organic PANI. PEC and optical measurements demonstrate that the significant PEC properties are attributed to improved photogenerated carrier separation efficiency (ηsep) and injection efficiency (ηinj) as well as broadened light absorption due to the synergistic action of the photosensitivity effect and extended space charge region (SCR), including a built-in electric field and depletion layer, in which the lifetime of photogenerated carriers is significantly improved with depletion layers of greater widths. This work can provide a favorable example for the development of more efficient hybrid photoanodes.

As most trivalent lanthanides are hypersensitive, surface photovoltage (SPV) that is associated with charge separation in a space charge region of a semiconductor might become a new method for harv...

In the field-effect transistors based on the wide-band-gap nitride heterostructures, the dielectric layers are in widespread use as one of the main elements in the active regions of the devices and the passivation layers. Stringent requirements are imposed on the dielectrics in terms of the high dielectric capacitance, large band-gap energy, and the coating integrity. Furthermore, the films must withstand high electric fields and have a low surface state density in the dielectric/semiconductor interface. For these purposes, the low temperature films grown by plasma-enhanced chemical vapor deposition, atomic layer deposition (ALD), and plasma-enhanced deposition are usually used as effective coatings. The ALD films of Al2О3, SiNх (Si3N4), SiON, and ALD AlN are used most often, and offer the greatest promise for the AlGaN/GaN heterostructures. The influence of the passivation of the ALD Al2O3, SiNx, and SiON coatings of various thicknesses on the change of the charge and the density of the states of the AlGaN/GaN heterostructures is investigated. The physical parameters of the structures are estimated by the C–V characteristics measured on various frequencies and the I–V characteristics. It is demonstrated, according to the examined energy band diagrams of the structures at various control voltages, and estimation of the elemental composition of the films by the method of Auger electron spectroscopy, that the reason for the generation of a high positive charge at the deposition of the ALD Al2O3 and SiNx films is the occurrence of an additional piezoelectric charge in the buffer layer of AlGaN. It is demonstrated that use of the SiON films with the oxygen concentration in them higher than 3% does not result in the generation of an additional positive charge but can initiate current fluctuations during the measurement of the I–V characteristics. A possible mechanism of carrier transport in the space charge region resulting in such fluctuations is discussed.

Zinc oxide (ZnO) lightning arresters have good protection performance and have been widely used in power systems. ZnO varistor is the core component of the arrester, and its electrical performance determines the overvoltage protection level of the arrester. ZnO varistor will produce space charge accumulation phenomenon under the action of electric field. In order to study the space charge characteristics of ZnO varistors more deeply, a bipolar carrier transport model considering the change of grain boundary structure was established, and the law of carrier migration in ZnO grain boundaries was simulated. From the three aspects of pressure time, ambient temperature, and depletion layer density, the space charge distribution inside the grain boundary, Schottky barrier height, and grain boundary leakage current are systematically studied.

Monolayer MoS2, a direct bandgap transition metal dichalcogenide (TMD), has attracted worldwide attention in electronics and optoelectronics. However, the performance of photodetectors based on monolayer MoS2 is restricted to a weak optical absorption, narrow absorption range, and persistent photoconductance. Herein, benefiting from an easy solution process, high light absorption coefficient, and wide absorption range, environment-friendly CuInSe2 quantum dots (QDs) are hybridized with monolayer MoS2 for high-performance broadband photodetectors. Owing to the favorable type-II energy band alignment of MoS2/CuInSe2-QDs, the hybrid photodetector exhibits a broadband photoresponse from the ultraviolet to near-infrared region, with an ultrahigh photoresponsivity of 74.8 A/W at 1064 nm, and compared with those of the pristine MoS2 device, the photoresponsivity and specific detectivity in the ultraviolet-visible region were enhanced by about 30 and 20 times, respectively. Furthermore, the formed depletion region at the MoS2/CuInSe2-QDs interface can significantly increase the photoresponse speed, and the accumulated holes in the QD side induce a strong photogating effect to improve the photoresponsive characteristics of the hybrid photodetector. Our work opens up opportunities for fabricating high-performance monolayer TMD-based broadband photodetectors.

In2O3 is a wide bandgap oxide semiconductor, which has the potential to be used as an active material for transparent flexible electronics and UV photodetectors. However, the high concentration of unintentional background electrons existing in In2O3 makes it hard to be modulated by the electric field or form p-n heterojunctions with a sufficient band-bending width at the interface. In this work, we report the reduction of the background electrons in In2O3 by Mg doping (Mg-In2O3) and thereby improve the device performance of p-n diodes based on the NiO/Mg-In2O3 heterojunction. In particular, Mg doping compensates the free electrons in In2O3 and reduces the electron concentration from 1.7 × 1019 cm-3 without doping to 1.8 × 1017 cm-3 with 5% Mg doping. Transparent p-n heterojunction diodes were fabricated based on p-type NiO and n-type Mg-In2O3. The device performance was considerably enhanced by Mg doping with a high rectification ratio of 3 × 104 and a remarkable high breakdown voltage of >20 V. High-resolution X-ray photoelectron spectroscopy was used to investigate the interfacial electronic structure between NiO and Mg-In2O3, revealing a type II band alignment with a valence band offset of 1.35 eV and a conduction band offset of 2.15 eV. A large built-in potential of 0.98 eV was found for the undoped In2O3 but decreased to 0.51 eV for 5% Mg doping of In2O3. The NiO/Mg-In2O3 diodes with an improved rectification ratio and wider depletion region provide the possibility of achieving photodetectors with rapid photoresponse.

Gas sensors based on metal oxides semiconductor (MOS) have attracted extensive attention from both academic and industry. ZnO, as a typical MOS, exhibits potential applications in toxic gas detection, owning to its wide band gap, n-type transport characteristic and excellent electrical performance. Meanwhile, doping is an effective way to improve the sensing performance of ZnO materials. In this review, the effects of different types of doping on morphology, crystal structure, band gap and depletion layer of ZnO materials are comprehensively discussed. Theoretical analysis on the strategies for enhancing the sensing properties of ZnO is also provided. This review puts forward the reasonable insight for designing efficient n-type ZnO-based semiconductor oxide sensing materials.

Constructing p-n heterojunction is considered as an effective approach to improve gas-sensing performance of nanomaterials, and the general focus is that the formation of a p-n junction can effectively broaden the electron-depletion layer, enhancing the amount of the adsorption oxygen, and being beneficial to the improvement of the gas-sensing performance. However the widening of the depletion layer can only contribute to the improvement of the sensitivity, the effect of p-n junction on other sensing parameters is still not well understood. Herein, the In2O3/Co3O4 core/shell hierarchical heterostructures (In2O3/Co3O4 HHS) are investigated to discern how p-n junction alters the sensing process. The construction of p-n junction can effectively adjust Fermi level, influence the oxidation ability of the adsorbed oxygen and significantly heighten the selectivity of sensing materials, resulting in superior sensing activity. Especially, In2O3/Co3O4 HHS exhibits obviously enhanced gas sensing performance toward formaldehyde at 180 °C with high response and good selectivity. Our findings promote the recognition of the important role of electronic structure on gas sensing performance and provide a new strategy to design sensing materials for gas detection.

It is shown that self-forming GeSi nanoislands built into the dielectric–semiconductor interface in the Si(001)-based metal–oxide–semiconductor (MOS) structures with the SiOx and ZrO2(Y) dielectric layers obtained by magnetron sputtering initiate bipolar resistive switching without preliminary electroforming. The I–V characteristics and electrical parameters of the MOS structures in the high- and low-resistance states have been investigated. The change in the charge incorporated in the dielectric at the dielectric–semiconductor interface during resistive switching has been established, which is related to the formation and destruction of conducting filaments. The optically stimulated switching of the MOS structures with the ZrO2(Y) dielectric layer from the high- to low-resistance state has been observed, which is caused by an increase in the conductivity of the space charge region in the Si substrate due to the interband optical absorption in Si leading to the voltage redistribution between Si and ZrO2(Y). A difference between the shapes of the low-signal photovoltage spectra of the MOS structures in the spectral region of the Si intrinsic photosensitivity in the high- and low-resistance states related to the leakage of photoexcited carriers from Si into a metal electrode through filaments has been found.

This article reports that Hetero-interfacial-thermal resistance (HITR) due to phonon scattering and weak electron–phonon coupling at hetero-interfaces, can impact stacked Si gate-all-around (GAA) nanosheet field effect transistor (NSHFET) self-heating effect (SHE) and reliability. We have investigated the HITR of Si/SiO2 and Si/metal-silicides on SHE of vertically stacked Si GAA NSHFET. Our simulation predictions reveal that a very noticeable effect of the HITR of Si/ M0 at front end of line (FEOL) and back end of line (BEOL) interface (FEOL/BEOL) is that the hot-spot location is shifted into the channel away from drain depletion region, which affects the device SHE and degrades device performance. The impact of nanosheet width ( ${W}_{NSH}$ ) and sheets stacking number ( ${N}$ ) on device SHE and drive current degradation with and without HITR effect are also studied. It is revealed that wider nanosheets with lower HITR can be a better device design choice for heat mitigation in high performance logic transistors.

Molybdenum disulfide (MoS2) as a typical two-dimensional (2D) transition-metal dichalcogenide exhibits great potential applications for the next-generation nanoelectronics such as photodetectors. However, most MoS2-based photodetectors hold obvious disadvantages including a narrow spectral response in the visible region, poor photoresponsivity, and slow response speed. Here, for the first time, we report the design of a two-dimensional MoS2/GaN van der Waals (vdWs) heterostructure photodetector consisting of few-layer p-type MoS2 and very thin n-type GaN flakes. Thanks to the good crystal quality of the 2D-GaN flake and the built-in electric field in the interface depletion region of the MoS2/GaN p-n junction, photogenerated carriers can be rapidly separated and more excitons are collected by electrodes toward the high photoresponsivity of 328 A/W and a fast response time of 400 ms under the illumination of 532 nm light, which is seven times faster than pristine MoS2 flake. Additionally, the response spectrum of the photodetector is also broadened to the UV region with a high photoresponsivity of 27.1 A/W and a fast response time of 300 ms after integrating with the 2D-GaN flake, exhibiting an advantageous synergetic effect. These excellent performances render MoS2/GaN vdWs heterostructure photodetectors as promising and competitive candidates for next-generation optoelectronic devices.

Lateral homojunctions made of two-dimensional (2D) layered materials are promising for optoelectronic and electronic applications. Here, we report the lateral WSe2-WSe2 homojunction photodiodes formed spontaneously by thickness modulation in which there are unique band structures of a unilateral depletion region. The electrically tunable junctions can be switched from n-n to p-p diodes, and the corresponding rectification ratio increases from about 1 to 1.2 × 104. In addition, an obvious photovoltaic behavior is observed at zero gate voltage, which exhibits a large open voltage of 0.49 V and a short-circuit current of 0.125 nA under visible light irradiation. In addition, due to the unilateral depletion region, the diode can achieve a high detectivity of 4.4 × 1010 Jones and a fast photoresponse speed of 0.18 ms at Vg = 0 and Vds = 0. The studies not only demonstrated the great potential of the lateral homojunction photodiodes for a self-power photodetector but also allowed for the development of other functional devices, such as a nonvolatile programmable diode for logic rectifiers.

A new type of AlGaAs/InGaAs/GaAs heterostructures with energy barriers formed in the AlGaAs transistor layers adjacent to the InGaAs channel, modulation-doped with donors and acceptors is presented. The height of the barriers associated with the potential of the space charge region in AlGaAs layers reaches 0.8 eV, which makes it possible to double the concentration of electrons in the channel, prevent the transition of hot electrons heated by the electric field into surrounding layers, and increase their saturation drift velocity by around $$1.2{-}1.3$$ times. As a result, microwave power output density of the transistor exceeded the world level by more than 50 $$\%$$ .