Micro and Nanostructures最新文献

In this work, we investigated the effects of Si doping on the oxygen vacancy defects in SnO₂ nanoparticles for detecting changes in humidity levels. XRD measurements showed that all samples exhibit tetragonal rutile phase and the crystallite structure of SnO₂ was tuned with Si content increasing. XPS analysis revealed more oxygen vacancies defects (the percentage of O_V increases from 11.52 % to 19.02 %) were confirmed to be produced, accelerating chemisorption of water molecules on Si doped SnO₂ surface. Additionally, we discussed the various situations involving the utilization of electrons and holes corresponding to the different states of oxygen vacancies via photoluminescence spectroscopy. The humidity sensing results exhibited that the 5 mol% Si doped SnO₂ humidity sensor shows high sensitivity, low hysteresis (5.7 %) and fast response/recovery times (7 s/10 s) range from 11 % to 95 % relative humidity. The chemical mechanisms for enhancement in humidity performance induced by oxygen vacancy defects formed on SnO₂ surface is proposed.

A quantitative numerical exploration is conducted to scrutinize the combined effects of size and dielectric confinement consequences on the electronic and optical characteristics of spherical multilayered quantum dot CdSe/ZnS/CdSe/ZnS (SMLQD) and its inverted configuration ZnS/CdSe/ZnS/CdSe (ISMLQD) buried into two oxides: HfO₂ and SiO₂. By employing the effective mass approximation (EMA) and the density matrix approach (DMA), the derived quantized electron energy states and their associated wave functions were obtained by solving the Schrödinger equation in a spherical coordinates. The dipole transition element, both real and imaginary parts of the effective complex dielectric function (ECDF) as well as its linear, nonlinear and total counterparts are brought out for various values of inner core radii, number density of QDs and incident photon intensity. In addition, a specific analysis of electron probability distributions is provided to gain a clearer understanding of the underlying physical factors. Our findings point to a notable influence of these mentionned factors on the computed coefficients. The study unveils that the dielectric mismatch occurring at the system/oxide interfaces plays a crucial role in modifying the electronic structure and a substantial impact on both linear and third-order nonlinear components is witnessed.

Enhancing the photosensitivity and response speed of transition metal dichalcogenides (TMDs)-based photodetectors through the construction of semiconductor heterostructures poses an ongoing challenge in optoelectronic devices field. In this study, we conducted a systematic investigation using first-principles calculations to explore the characteristics of MXene/TMDs heterostructures, specifically focusing on the Zr₂CO₂/WS₂ heterostructure. Computational analysis verifies that the Zr₂CO₂/WS₂ heterostructure displays a type II band alignment, which facilitates efficient carrier separate transportation within the heterostructure. In both the zigzag and armchair directions, the heterostructure formation enhances the carrier mobilities. Furthermore, modulation of the heterostructure is accomplished by applying external electric fields and axial stress. Notably, the light absorption ability of the Zr₂CO₂/WS₂ heterostructure is more sensitive to external electric fields rather than interlayer distance. Overall, Zr₂CO₂/WS₂ van der Waals heterostructures offer inherent advantages for the development of high-performance photodetectors.

All-inorganic Cs₂TiI_xBr_(6-x)-based perovskite solar cells (PSCs) are recently attracting a lot of attention for their tunable bandgaps, earth abundance, non-toxicity, and ultra-stability. Among the Cs₂TiI_xBr_(6-x) family of materials, Cs₂TiI₂Br₄ with a bandgap of ∼1.38 eV has the potential to be an excellent single junction solar cell material with a theoretically higher Shockley-Queisser limit of power conversion efficiency (PCE). Its excellent optoelectronic properties make it a potential candidate for being the highest-performing PSC from the Cs₂TiI_xBr_(6-x) family. In our study, a total of eight hole transport materials (P3HT, PTAA, Spiro-OMeTAD, PEDOT:Pss, CuSCN, CuI, NiO, and MoO₃) and six electron transport materials (PCBM, TiO₂, CdS, SnO₂, ZnO, and IGZO) were investigated to select suitable charge transport materials. The defect densities of interface and absorber, different absorber layer thicknesses, several metal work functions, series-shunt resistance, and temperature were investigated to derive the conditions for optimum performance. After thorough investigation, we derived four novel devices with the combination of all the organic and inorganic charge transport materials to provide optimum performance. Among them, the combination of inorganic SnO₂ and CuSCN as electron and hole transport layer respectively achieved the highest PCE of 23.41 %.

A novel double deck gate field plate structure on a normally-off AlGaN/GaN HEMT is proposed and compared with the conventional no field plate structure. Several passivation materials with relative permittivity (ε_r) ranging from 3.9 to 22 is taken into consideration to study the breakdown and DC characteristics. The implementation of field plate along with a higher ε_r material helps in improving breakdown voltage (V_Br) as they both decrease the electric field at the gate's drain edge. Aiming device optimization several field plate configurations are studied including tri field plate structure, dual field plate structures and single gate FP structure. Extensive analysis in these structures are done with different lengths of the field plates and distance between source and drain. Distance between source and drain (L_SD) is varied from 8.4 to 13.4 μm, source FP lengths (L_{S_FP}) varies from 1 to 7 μm, gate FP lengths (L_{G_FP}) varies from 0.9 to 2.3 μm and drain FP lengths (L_{D_FP}) varies from 0.2 to 4.9 μm. In all scenarios with varying L_SD, V_Br rises with increasing L_SD. For source, gate and drain FP lengths variation, V_Br decreases as it gets longer because the electric field becomes very high. As the distance between the FP edge and the drain becomes narrower with increase in FP lengths, the breakdown occurs at lower voltage. At L_SD 13.4 μm, this novel double deck gate FP structure with conventional drain field plate structure gives highest V_Br of 1660 V and a small R_on of 2.39 Ω mm as compared to other structures. It also outperforms the other three structures in F_T (9.84 GHz) at this particular L_SD. Analysis of the simulated structures shows that the union of gate-drain field plate boosts the V_Br while decreasing the R_on, resulting in improved electrical performance and a wider application range.

In this paper, a metal strip loaded doping less TFET (MS-DLTFET) biomarker with four cavities is proposed for SARs-CoV-2 detection virus. The results demonstrate that the proposed device offers an improved biomarker performance by introducing the charged plasma concept and the metal strips. The electrical parameters such as electron tunneling rate, drain current (I_ds), current ratio (I_ON/I_OFF), threshold voltage (V_th) are evaluated through simulations by immobilized dielectric constant (k) and charge density (ρ) of the bioelements in the nano-gap cavities. In addition, their sensitivity is also calculated with respect to air. The results depict that the proposed device tenders better performance in terms of I_ds, I_ON/I_OFF and V_th sensitivity as compared to existing devices. The device's response time under varying k and ρ values are investigated. The non-uniform cavity configurations formed due to steric hindrance effect are studied. It is found that concave configuration offers the best performance compared to other. Furthermore, the cavity size analysis is also performed to optimize the device performance.

van der Waals heterostructures can enable adjustment of graphene's electronic properties, which is important for the application of graphene-based electronic devices. The structural, electronic and optical properties of heterostructures composed of graphene and β-Si₃N₄ under different strain conditions are studied in this paper using first-principle calculation. The result shows that the heterojunction constituted with β-Si₃N₄ opens a small bandgap at the Brillouin zone Γ, which is about 0.099 eV, and the bandgap is highly sensitive to the direction and magnitude of strain. Under uniaxial compressive (tensile) strain, the heterojunction bandgap increases linearly, reaching 1.901 eV and 1.614 eV at −11 % and 11 %, respectively; under biaxial strain, the heterojunction bandgap decreases linearly with the compressive strain, decreasing to 0.087 eV at −11 %, and increases linearly with the tensile strain, reaching 0.113 eV at 11 %. And the rate of the bandgap under uniaxial strain is larger than that under biaxial strain, which suggests that the uniaxial strain regulation is more effective. Optical property study shows that uniaxial (biaxial) compressive strain improves the light absorption of the heterojunction in the blue-ultraviolet region band, especially when the uniaxial compressive strain reaches 9 %, the light absorption of the heterojunction increases significantly in the whole spectral interval. These research results will provide a theoretical basis for the practical applications of graphene and β-Si₃N₄ heterostructures in the fields of pressure sensors and optical modulators.

In the present work, impact of various mechanical strains on the optoelectronic properties of monolayer ReS₂ (m-ReS₂) are investigated by using density functional theory. The bandgap of monolayer is determined to be 1.44 eV and 1.31 eV when computed using PBE and PBE + SOC methods. The monolayer displays outstanding electronic and optical tunability under biaxial compressive and shear strains. Under strain variations of 0 %–8 %, the bandgap for biaxial compression varies from 1.44 eV (1.31 eV) to 0.54 eV (0 eV), whereas for shear xx-yy strains, it varies from 1.44 eV (1.31 eV) to 0.34 eV (0.28 eV) when calculated using PBE (PBE + SOC) methods. A semiconductor-to-metal transition is observed for higher values of biaxial compressive strain. A pronounced impact of strain on the optical characteristics is likewise observed. We noticed that the absorption edge of monolayer ReS₂ shifts from 1.32 eV to 0.50 eV with a 0 %–8 % increase in biaxial compression, leading to an 11 % red shift in wavelength per 1 % strain change. Moreover, high optical absorption (5 × 10⁵ cm⁻¹), lying from infrared to UV region is observed. The present study points out that strain engineering can be an efficient tool for modifying both the electronic and optical properties of m-ReS₂ and may open new avenues for using this material in future optoelectronic applications.

The single-event-transient (SET) effect due to heavy ions and alpha particles irradiation on n-type gate-all-around tunnel field effect transistor (GAA TFET) and n-type gate-all-around MOSFET (GAA MOSFET) has been carried out. Due to differences in carrier injection mechanisms, the generated electron-hole pairs (EHPs) due to high-energy particles (HEPs) act differently on the device. In addition, the impact of HEPs (i.e., heavy ions and alpha particles) on several locations along the channel are analyzed followed by the analysis of different energies of heavy ions and alpha particles irradiation on the device. Further, the impact of varying striking angles of HEPs on the device is also analyzed to get a close match as practically exposed device characteristic. Finally, the bipolar gain of the device has been analyzed which shows GAA TFET device has more immunity toward heavy ions strike and weak immunity toward alpha particle strikes when compared to the GAA MOSFET counterpart.

P-AlGaN EBLs are usually used to control the overflow of electrons from the multiple quantum wells (MQWs) in AlGaN-based deep ultraviolet (DUV) edge-emitting laser diodes (EELDs). They're specially designed to prevent the excess flow of electrons from the MQW. This control is essential for maintaining the laser's efficiency and performance. Using optimized parameters of Al composition through theoretical calculations using Crosslight software helps certify the electrically driven EELD functions effectively within the desired operational range. In this study, the traditional p-AlGaN EBL within the electrically driven EELD is substituted with an undoped AlGaN EBL. This modification aims to raise the effective barrier height of the conduction band, and thus effectively stopping the electron leakage while improving the injection of holes. By optimizing the aluminum composition in the current research, efforts are made to lower the threshold current (I_th) and elevate the overall enactment of the graded undoped AlGaN EBL EELD. Various structural designs, including both conventional and undoped configurations, have been successfully created and analyzed in this study. Particular attention was given to investigating the impact of grading techniques applied to the electron-blocking layer. The graded undoped AlGaN EBL EELD performed better than the highly doped AlGaN EBL EELD due to the minimized free carrier absorption loss. Specifically, it shows higher slope efficiency (S.E) of 1.45 W/A and a significantly lower I_th of 790 mA. A new AlGaN EBL EELD design was tested with different layers. The ones with a graded undoped EBLs performed better than traditional AlGaN EBL EELD, improving power efficiency. The graded undoped EBLs setup also reduced the threshold current compared to traditional AlGaN EBL EELD.