Energy Band Profile Research Articles

Ultralong Compositional Gradient Perovskite Nanowires Fabricated by Source-Limiting Anion Exchange.

Anion exchange in halide perovskites offers prospective approaches to band gap engineering for miniaturized and integrated optoelectronic devices. However, the band engineering at the nanoscale is uncontrollable due to the rapid and random exchange nature in the liquid or gas phase. Here, we report a source-limiting mechanism in solid-state anion exchange between low-dimensional perovskites, which readily gives access to ultralong compositional gradient nanowires (NWs) with lengths of up to 100 μm. The exchanged NWs remain single-crystalline with intact morphology, while the halogen content exhibits an apparent gradient distribution, leading to a tapered energy band profile along a NW. In the dynamic study of anion behavior, it is shown that the spatial stoichiometric composition can be precisely tuned following Fick's law of diffusion. In addition, self-powered, spectrally resolved photodetectors incorporating multiple detection units within a single gradient NW are demonstrated. This work provides a feasible strategy for the realization of perovskite-based ultracompact optoelectronics, imaging sensors, and other miniaturized semiconductor devices.

Impact of source/drain lateral straggle on GIDL current of low SS NC-FinFET

ABSTRACT In this paper, the gate-induced drain leakage (GIDL) issue in negative capacitance (NC-FinFET) has been comprehensively addressed using Sentaurus 3-D TCAD simulations. Incorporation of ferroelectric (FE) materials in the gate stack of NC-FinFET increases with current by 12% compared to that of baseline FinFET. A steeper sub-threshold swing (SS) of 8 mV/dec is achieved at a FE-thickness of 5 nm at a lateral straggle; (σ) = 0 nm. GIDL behaviour with respect to the variation of source/drain σ and gate oxide thicknesses of NC-FinFET with and without the presence of the GateTunneling model is thoroughly investigated. Investigations demonstrate that in NC-FinFET, there are steeper energy band profiles near source/drain owing to coupling of fringing fields to the ferroelectric layer, which exhibits a larger and prior commencement of the longitudinal band to band tunnelling current compared to conventional FinFET. Moreover, the effect of variation of σ on various parameters viz. SS, capacitance and transconductance has also been investigated, which shows better results for lower σ values. At σ = 0 nm, drain-induced barrier lowering is −187.23 mV/V as compared to that of σ = 5 nm, which is −355.3 mV/V. Furthermore, we have also investigated drain current noise spectral density (SID) and gate voltage noise spectral density (SVG) with respect to fin width (WFIN) at the optimised σ value.

Growth and performance of n++ GaN cap layer for HEMTs applications

Apart from providing high-quality ohmic contacts to III-N devices, n++ GaN cap layers can eliminate surface-related current collapse effects in high-electron-mobility transistors (HEMTs). Various metal-organic chemical vapor deposition conditions and n-type doping are tested in GaN growth on sapphire by using triethylgallium as a Ga precursor, replacing more conventional trimethylgallium. Consequently, despite relatively low temperature of the growth at 800 °C to facilitate InAlN barrier capping, optimized growth conditions and SiH4 flow provided free electron concentration of 7.2 × 1019 cm−3 and mobility of 103 cm2/Vs. Moreover, electron concentration in the range of 1020 cm−3 is demonstrated by using flow modulation epitaxy. On the other hand, as calibration growths indicated, excessive SiH4 flow alone can lead to high density of edge dislocations and surface undulations without enhancing free electron concentration. 6 nm (Si: 4.2 × 1019 cm−3) and 8 nm thick (Si: 7.2 × 1019 cm−3) n++ GaN cap is implemented in normally-off n++ GaN/InAlN/AlN/GaN HEMTs grown on Si, with a collapse-free performance for the latter case. By calculating energy band and free carrier concentration profiles of the heterostructures it is shown, that free electrons of a sufficiently thick and doped n++ GaN cap can shield the channel from the unstable surface potential.

ZnIn2S4-based heterostructured photocatalysts for CO2 reduction: A mini review

Abstract ZnIn2S4 (ZIS)’s superior photocatalytic CO2 reduction efficacy, coupled with its distinct layered architecture and narrow energy band profile, makes it an intriguing target for CO2 conversion studies. This article evaluates the photogenerated charge transfer mechanism and photocatalytic CO2 reduction (PCR) efficacy of varied ZIS-based heterostructure catalysts. ZIS-based heterojunctions are initially classified, ensuing discourse on advanced engineering techniques enhancing heterojunction phot catalysts’ PCR functionality like co-catalyst incorporation and morphologic manipulation. The concluding section provides an overview of the present study state and future progression in regard to ZIS-based heterostructured photocatalysts for PCR.

Structural, electronic, and optical properties of Zn-doped V2O5 thin films

V2O5 shows a diverse range of applications due to its remarkable electronic and optical properties. This research is designed to tune the electronic and optical properties of V2O5 through modification in the energy band profile by varying Zn doping concentration. Density functional theory (DFT) calculations were used to investigate the Density of States (DOS) spectra for pure V2O5, exhibiting the prominent contribution of V-d and O-p orbitals, representing the p-d hybridized orbitals along with additional Zn-d orbital contribution in Zn-doped compositions. The effects of doping on the structural, morphological, elemental, and optical properties of the developed thin films were investigated employing x-ray diffraction (XRD), scanning electron microscope (SEM), x-ray dispersive spectroscopy (EDX), and spectroscopic ellipsometry (SE), respectively. x-ray diffraction analysis revealed the orthorhombic crystal structure in thin films. Surface morphology depicts the uniformly distributed compact rod-like features. The experimentally calculated band gap was found to decrease with Zn doping from 2.77 eV for pure V2O5 to 2.45 eV for maximum doping content. A significant variation is recorded in optical parameters like the increase in absorption coefficient and optical conductivity, which makes these more favorable for optoelectronic devices, particularly focusing on photovoltaics.

Lead‐free perovskite Cs2NaGaBr6 n‐i‐p solar cell for higher power conversion efficiency to improved energy storage performance

AbstractIt is important to enhance the efficiency of perovskite solar cells (PSCs) to improve the energy storage performance within a time frame. In this study, a lead‐free perovskite Cs2NaGaBr6 n‐i‐p solar cell is presented for higher PCE to improve energy storage performance. Keeping the toxicity of lead‐based perovskite in mind we have made attempts to study the characteristics of n‐i‐p solar cells based on lead‐free double halide perovskite Cs2NaGaBr6 novel material. In the proposed photovoltaic framework, M21+N2+N3+X61− as a double perovskite material is used, where N2+ = Na, M21+ = Cs, N3+ = Ga, and X61− = Br. The Cs2NaGaBr6 is an organic‐inorganic perovskite material because of its direct band gap structure with a band gap of 1.762 eV. The solar cell proposed in the present framework has achieved a higher efficiency of 26.09% with optimized parameters specific to device design in terms of different absorber layer thicknesses (0.6–1.2 μm), and absorber layer doping concentrations (1 × 1018 cm−3 to 1 × 1022 cm−3). In the present study, improved results are obtained such as electric field, current density, energy band profile, generation and recombination factor, quantum efficiency, and generation/ recombination factor by suitably varying the absorber layer thicknesses and absorber layer doping concentrations. Additionally, many parameters related to the photovoltaic performance of solar cells such as Jsc (19.535 mA/cm2), Voc (1.775 V), FF (91.35%), and PCE (η) (27.81%) have been evaluated in the present study. Therefore, the device, that is, solar cell based on lead‐free double halide perovskite Cs2NaGaBr6 novel material, proposed in the present study may be used to manufacture much more efficient lead‐free perovskites for photovoltaic applications and also improve the energy storage performance within a time frame.

CO adsorption on two-dimensional 2H-ZrO2 and its effect on the interfacial electronic properties: implications for sensing

Environmental pollution is commonly caused by direct and indirect greenhouse gasses and various traces of toxic gasses. CO is a tasteless, colourless and highly hazardous greenhouse gas that can bind with the hemoglobin much easier than oxygen. Materials with effective CO sensing capability are highly desirable. In this work, we have studied the repercussions of the molecular adsorption of toxic carbon monoxide (CO) on the structural, electronic, interfacial electronic and gas sensing properties of the two-dimensional (2D) 2H phase of zirconium dioxide (2H-ZrO2) using density functional theory (DFT) calculations. The most suitable adsorbent structure is screened out and interaction strengths between adsorbate molecule and adsorbent layer are provided in terms of binding energies. As a result of CO adsorption, the energy band gap (Eg) is altered and the resulting change in the conductivity of 2H-ZrO2 monolayer has implications for sensing. Energy band profiles relating to CO adsorbed 2H-ZrO2 reveal that fermi level shifts towards conduction bands exhibiting a development of n-type semiconducting character. Eg values relating to pristine and CO adsorbed 2H-ZrO2 sites such as TM, H, CB and B are 1.58, 1.98, 2.05, 2.06 and 2.03 eV, respectively. Further insights into the adsorption reveal that charge is accumulated near 2H-ZrO2 in the case of H and B adsorption sites, whereas for the case of TM and CB sites, depletion is noted. Essential gas sensing properties such as conductivity sensitivity (S), and recovery time (τ) are also reported. Notably, TM, CB, and B absorption sites depicted 17%, 2%, and 6% lower S values than H site. Furthermore, the H site achieved a shorter (32 ps) than the other adsorption sites. Response of pristine and CO adsorbed 2H-ZrO2 to that of incident photons is investigated with the help of real and imaginary parts [ and ] of complex dielectric function, electron energy loss function [] and joint density of states [] for a broader range of 0 to 10 eV. Major differences in dielectric function exist along in-plan and out-of-plan directions. After a detailed comparison, it is reported that more number of optical transitions exist between the linked states for the case of CO adsorbed 2H-ZrO2.

InN TFET with extended gate for high sensitivity label‐free biosensor

AbstractAn extended gate tunneling field effect transistor (EG‐TFET) with narrow bandgap material InN as a label‐free dielectric modulated biosensor is proposed and investigated. An optimum structure of the proposed InN TFET is given by comparing on‐state and ambipolar current. The on‐state current is improved by increasing the length of source overlap, for the rate of forward tunneling increases. Further, the ambipolar current is suppressed by increasing the length of drain offset, for the rate of backward tunneling decreases. A cavity under the gate electrode is formed for sensing biomolecules by dielectric modulation. The performance of EG‐TFET biosensor corresponding to varied dielectric constants of biomolecule is analyzed. In addition, the impacts of charge density and partial filled cavity on the drain current sensitivity are investigated. The electric field, surface potential and energy band profiles are used to explain the working principle of the EG‐TFET biosensor. The simulations reveal that the drain current sensitivity is 3.72 × 107 when neutral biomolecule with κ = 12 is immobilized in the cavity. A linearity fit verification is given, and the results of current sensitivity reveal a good linearity of the EG‐TFET biosensor with fitness coefficient γ2 > 0.99.

Junctionless-accumulation-mode stacked gate GAA FinFET with dual-k spacer for reliable RFIC design

This study investigates how incorporating a dual-k spacer (SiO2 + HfO2) affects the RFIC design feasibility of a junctionless-accumulation-mode (JAM) stacked-gate (GS) gate-all-around (GAA) FinFET in the sub-10 nm range. The proposed device is compared with a conventional FinFET and those without a spacer, air, and a single-k spacer (SiO2). At a low voltage power supply, fringing field effects raise the proposed device's on-current by 35.34% and reduce the off-current by more than 76 times compared to conventional FinFET, thereby improving electron velocity, energy band profiles, transconductance, device efficiency, etc. Thus, the proposed device is well-suited for high-performance CMOS circuits. Further investigation shows that integrating a dual-k spacer reduces the output conductance, which boosts the intrinsic gain and early voltage by five times the value recorded for conventional FinFET. Although the cut-off frequency drops by 15.98%, the GTFP and GFP soar by 475.67% and 352.25%, respectively. Consequently, JAM-GS-GAA FinFET with dual-k spacer is an encouraging device for low-power RFIC circuits.

Operation-induced degradation mechanisms of 275-nm-band AlGaN-based deep-ultraviolet light-emitting diodes fabricated on a sapphire substrate

Degradation mechanisms of 275-nm-band AlxGa1-xN multiple quantum well deep-ultraviolet light-emitting diodes fabricated on a (0001) sapphire substrate were investigated under hard operation conditions with the current of 350 mA and the junction temperature of 105 °C. The optical output power (Po) initially decreased by about 20% within the operating time less than 102 h and then gradually decreased to about 60% by 484 h. For elucidating the causes for the initial and subsequent degradations, complementary electrical, time-resolved photoluminescence (TRPL), and impurity characterizations were carried out making a connection with the energy band profiles. Because the degradation of the wells was less significant than the Po reduction, the initial degradation is attributed essentially to the decrease in carrier injection efficiency (ηinjection), not in internal quantum efficiency of the wells, most likely due to depassivation of initially H-passivated preexisting nonradiative recombination centers (NRCs) in a Mg-doped p-type Al0.85Ga0.15N electron blocking layer. The principal cause for the subsequent Po reduction until 484 h is attributed to further decrease in ηinjection due to the appearance of certain current bypasses in addition to continuous depassivation of the NRCs in p-type AlxGa1-xN layers. According to our database on the species of vacancy-type defects acting as NRCs in GaN and AlN, which have been identified using the combination of positron annihilation and TRPL measurements, vacancy clusters comprised of a cation vacancy (VIII) and nitrogen vacancies (VN), such as VIIIVN2∼4, are the most suspicious origins of the NRCs in Mg-doped p-type AlxGa1-xN layers.

Design and analysis of high-performance double-gate ZnO nano-structured thin-film ISFET for pH sensing applications

This paper reports a high-performance double-gate zinc-oxide thin-film ion-sensitive field-effect transistor (DG-ZnO-ISFET) for pH sensing applications. The sensing mechanism of DG-ZnO-ISFET and a simulation model for pH sensing analysis are demonstrated herein. Various aspects of the device are elucidated through the study of channel conductance, electron density, energy band, and surface-potential profiles. The DG-ZnO-ISFETs enhance minor surface potential variations by capacitive coupling across the dielectrics of the top and bottom gates. Further, it operates by altering the bottom-gate voltage (VBG), obviating the need for a reference electrode system. The device depicts enhanced voltage sensitivity of 205.57 mV/pH, which is substantially 3.48 × greater than the Nernst limit sensitivity. In addition, the DG-ZnO-ISFET renders a maximum current sensitivity of 10.82 mA/mm.pH at VBG=5V. Furthermore, it exhibits high linearity in both voltage and current sensitivity, with the coefficient of determination (R2) values of 0.984 and 0.964, respectively. With their increased sensitivity and linearity, DG-ZnO-ISFETs have the potential device for next-generation biosensors.

Investigation of palladium gated polarity controllable FET as a highly sensitive and robust hydrogen gas sensor

AbstractThe paper investigates the design and performance of a novel palladium gated‐polarity controllable Field Effect Transistor (FET) (PC‐FET) for hydrogen gas sensing applications. In the present work, catalytic sensing metal gate (palladium) is chosen as control gate (CG) and hydrogen gas molecules are exposed on the region controlled by CG. A compact analytical model has been derived for PC‐FET based sensor and the performance of the proposed gas sensor has been examined in terms of energy band profile, surface potential, electric field, transfer characteristics and transconductance and the derived analytical results are verified using TCAD simulated results. Furthermore, the sensitivity metrics such as threshold voltage sensitivity, drain current sensitivity, transconductance sensitivity and ION/OFF sensitivity have also been extensively investigated for both modes of proposed sensor for a wide range of pressure that is, 10−14–10−8 Torr.

Sensitivity assessment of dielectric modulated GaN material based SOI-FinFET for label-free biosensing applications

Abstract This work presents the sensitivity assessment of gallium nitride (GaN) material-based silicon-on-insulator fin field effect transistor by dielectric modulation in the nanocavity gap for label-free biosensing applications. The significant deflection is observed on the electrical characteristics such as drain current, transconductance, surface potential, energy band profile, electric field, sub-threshold slope, and threshold voltage in the presence of biomolecules owing to GaN material. Further, the device sensitivity is evaluated to identify the effectiveness of the proposed biosensor and its capability to detect the biomolecules with high precision or accuracy. The higher sensitivity is observed for Gelatin (k = 12) in terms of on-current, threshold voltage, and switching ratio by 104.88%, 82.12%, and 119.73%, respectively. This work is performed using a powerful tool, three-dimensional (3D) Sentaurus Technology computer-aided design using a well-calibrated structure. The results pave the way for GaN-SOI-FinFET to be a viable candidate for label-free dielectric modulated biosensor applications.

Numerical simulation of Transparent Gate Thin-Film Transistor (TG-TFT) with varied gate materials for high-performance applications

This work presents the performance evaluation of Transparent Gate Thin-Film Transistor (TG-TFT) with the relative analysis of numerous materials such as Aluminum (Al), Gold (Au), Indium Tin Oxide (ITO), Zinc Oxide (ZnO), and Titanium Nitride (TiN). This work also aims to find the best suitable gate material on the TFT for high-performance applications through a solid thin film. It is observed from the outcomes that TG-TFT performance improves significantly with TiN gate in terms of mobility (∼4 times), switching ratio (ION/IOFF) by 46.42 %, and electric field by ∼ 29 % as compared to conventional gate material (Au). Further, surface potential and energy band profile have been shown. Therefore, the examination shows the perspective of TiN as gate materials that can be reused for requests in nanoelectronics tools and designing of IC boards owing to the better conductivity, robustness, and cheap nature of TiN along with proven results it can be used as a gate material.

Optical FOMs of extended-source DG–TFET photodetector in the visible range of the spectrum

In this paper, the optical characteristics of an extended-source double-gate tunnel field-effect transistor (ESDG–TFET)–based photodetector in the visible range of the spectrum at wavelength λ = (300–700) nm are investigated. The optical characteristics are examined at three specific wavelengths λ= 300, 500, and 700 nm at an intensity of 0.7 W cm−2. The optical characteristics of photosensors, such as absorption rate, generation rate, energy band profiles, transfer characteristics, sensitivity (S n), quantum efficiency (η), signal-to-noise ratio (SNR), and detectivity, are extracted according to the incident wavelength of light. The results reveal that the ESDG–TFET-based photosensor exhibits better optical characteristics at λ = 300 nm compared to at λ = 500 and 700 nm. Moreover, the proposed photosensor provides sensitivity, SNR, and responsivity in the order of 91.2, 79 (dB), and 0.74 (A Watt−1), respectively, at λ = 300 nm. Due to the high incident optical energy (E g) at 300 nm, the absorption and emission rates of this photosensor are significantly larger; consequently, it reports better optical characteristics. Finally, a comparative study of the proposed TFET-based photosensor with photosensors cited in the literature is summarized in tabular form. A comparison study in terms of spectral sensitivity between single-gate and double-gate ESDG–TFET is also reported. Moreover, an inverter circuit based on ESDG–TFET is designed, and the corresponding transient analysis is highlighted under both dark and light states.

Performance analysis of dielectrically modulated InSb/Si TFET based label free biosensor

This work reports a novel structure of gate dielectric modulated SOI TFET for biological sensing applications. The device uses InSb/Si heterojunction with N+ pocket at drain channel junction. The nanocavity is caved between gate electrode and channel region towards drain side. InSb is used as a source material to enhance ON current. ATLAS TCAD is used to investigate electrical characteristics such as ambipolarity, energy band profile and sensitivity for better understanding of biosensing mechanism. The major advantage of the proposed structure is that it offers very low power consumption, high flexibility, portability, and sensitivity that can bring out new possibilities of developing very highly sensitive biosensors. The device exhibits excellent controllability over the channel and reduces the leakage current. The sensing of the biomolecules is based on ambipolar current which is dependent on the dielectric constant of nanocavity. Higher dielectric constant results in enhanced sensitivity of the device. Further, the device performance with 1/3 filled, 2/3 filled and fully filled cavity has also been investigated systematically.

Study of the structural, electronic, mechanical, electro-thermal and optical properties of double perovskite structures Cs2SbAgX6, (X = I, Br, or Cl)

In the double perovskites structures, Cs2SbAgX6, X is I, Br, or Cl, the structural, electronic, thermodynamic, thermoelectric and optical, properties have been investigated by using the density functional theory (DFT) correction method. The XRD structural study exhibits that the double perovskite structures are stable in the cubic phase structures. Elastic parameters reveal all structures to be very hard and ductile in nature. The energy band profiles display indirect band-gap of semiconductor behavior for the structures Cs2SbAgX6; X is Cl or Br, while exhibiting metallic behavior of the structure Cs2SbAgI6. The thermoelectric transport properties were verified in the temperature range (5–1000) K, which includes electrical conductivity, thermal conductivity, Seebeck coefficients, and the figure of merit, ZT, for Cs2SbAgX6 structures. These structures exhibit high thermal conductivity with good Seebeck coefficients at room temperature. The semiconducting structure, Cs2SbAgBr6, has appropriate band gaps and best Seebeck coefficients; therefore, it has the best values of ZT reached 0.000 16 at 1000 K, which means the suitable structure for employment in thermoelectric and spintronic devices applications. The optical properties of these structures exhibit that the absorption effective region at the Visible-Ultraviolet region, therefore these materials are suitable in the applications of solar cells and optoelectronic devices.

Rational Design of WSe2 /WS2 /WSe2 Dual Junction Phototransistor Incorporating High Responsivity and Detectivity.

The excellent semiconducting properties and ultrathin morphological characteristics allow van der Waals (vdW) heterostructures based on 2D materials to be promising channel materials for the next-generation optoelectronic devices, especially in photodetectors. Although various 2D heterostructure-based photodetectors have been developed, the unavoidable trade-off between responsivity and detectivity remains a critical issue for these devices. Here, an ingenious phototransistor based on WSe2 /WS2 /WSe2 dual-vdW heterostructures is constructed, performing both high responsivity and detectivity. In the charge neutrality point (gate voltage of -15V and bias voltage of 1V), this device demonstrates a pronounced photosensitivity, accompanying with high detectivity of 1.9×1014 Jones, high responsivity of 35.4AW-1 , and fast rise/fall time of 3.2/2.5ms at 405nm with power density of 60µWcm-2 . Density functional theory calculations, energy band profiles, and optoelectronic characteristics jointly verify that the high performance is ascribed to the distinctive device design, which not only facilitates the separation of photogenerated carriers but also produces a strong photogating effect. As a feasible application, an automotive radar system is demonstrated, proving that the device has considerable potential for application in vehicle intelligent assisted driving.

Cross-sectional low-temperature scanning tunneling spectroscopy of an InAs p–n junction

Scanning tunneling spectroscopy was used to examine the cross-sectional surface of an InAs p–n junction at low temperature. The depletion layer only in the p-type region was studied by employing a substrate that was doped with large amounts of donor and acceptor impurities as the n-type region. The energy band profile for the p–n junction reveals that the width of the depletion layer in the n-type region is negligibly small. Compared with the expected width of the depletion layer in the p-type region on the basis of the doped acceptors, the observed width is much wider, indicating the low ionization ratio of the acceptors at low temperature. Owing to the small amount of tip-induced band bending (TIBB) for the conduction band in the p-type region, the observed conduction band edge is fitted well with a simple calculation. In contrast, the observed valence band edge is modified by the TIBB.

An analytical drain current model of Germanium source vertical tunnel field effect transistor

This paper presents an analytical modeling of the drain current for a Germanium source vertical tunnel field effect transistor. Both one dimensional (1D) and two dimensional (2D) Poisson's equation are used for solving the potential distribution as the device structure possess both vertical and lateral band-to-band tunneling components. The 2D band-to-band tunneling model is employed for solving the lateral tunneling while the 1D band-to-band tunneling model is implemented on solving the vertical tunneling which consist of the source region and the overlap channel region. The length of the maximum and minimum tunneling widths are calculated by measuring the distance from the edge of the valence band to conduction band of the energy band profile. Kane's band-to-band tunneling generation rate is used to model the drain current by superimposing two current components. In addition, the impact of bandgap narrowing as well as quantum correction on the drain current are also factored into the model. The analytical models are checked and matched against the results obtained from the TCAD simulations to ensure its accuracy.