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Admittance of Organic LED Structures with an Emission YAK-203 Layer
摘要： The current-voltage characteristics and admittance of multilayer structures for organic LEDs based on the PEDOT:PSS/NPD/YAK-203/BCP system have been experimentally investigated in a wide range of the measurement conditions. It is shown that at voltages corresponding to the effective radiative recombination of charge carriers, a significant decrease in the differential capacitance of the structures is observed. The frequency dependences of the normalized conductance of LED structures are in good agreement with the results of numerical simulation in the framework of the equivalent circuit method. Changes in the frequency dependences of the admittance with a change in temperature are most pronounced in the temperature range of 200–300 K and less noticeable in the temperature range of 8–200 K. From the frequency dependences of the imaginary part of impedance, the charge carrier mobilities are found at various voltages and temperatures. The mobility values obtained by this method are somewhat lower than those determined by the transient electroluminescence method. The dependence of the mobility on the electric field is well approximated by a linear function. As the temperature decreases from 300 to 220 K, the mobility decreases several times.
关键词： frequency dependence of imaginary part of impedance,LED structure,current-voltage characteristic,transient electroluminescence,organic semiconductor,charge carrier mobility,method of equivalent circuits,admittance
更新于2025-11-14 17:28:48
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Determination of physical mechanism responsible for the capacitance-voltage weak inversion “hump” phenomenon in n-InGaAs based metal-oxide-semiconductor gate stacks
摘要： Weak inversion capacitance-voltage (C-V) “hump” is a widely observed phenomenon at n-InGaAs based metal oxide semiconductor (MOS) structures. The mechanism responsible for this phenomenon is still under discussion. The C-V hump can be explained as an interaction of interface states with either one or both semiconductor energy bands. Each of the proposed mechanisms leads to a different interpretation of C-V hump. Simulating the mechanisms by relevant equivalent circuits, the capacitance and conductance characteristics of the MOS structure were calculated and compared with experimental results. The mechanism responsible for the C-V hump was determined.
关键词： interface states,equivalent circuits,n-InGaAs,metal-oxide-semiconductor,capacitance-voltage hump
更新于2025-11-14 17:28:48
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Physical properties of RF magnetron sputtered GaN/n-Si thin film: impacts of RF power
摘要： GaN thin film was successfully produced on n-Si(100) substrate by RF magnetron sputter under different RF power. Experimental measurement techniques such as UV/Vis spectroscopy, field emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), atomic force microscopy (AFM), and Micro-Raman Spectroscopy were used to research effects of Radio Frequency power on physical properties of produced thin film. It has been found that produced thin film was polycrystalline structure with (100) and (110) planes of hexagonal GaN from X-ray diffraction measurement result. It also proved that increasing RF power gives rise to deterioration in crystal quality of GaN thin film. Reason of this deterioration was discussed. It has been achieved that increasing RF power has resulted in decreasing optical band gap energy of GaN thin film. Reasons for these changes in optical band gap energy were explained. It was seen that some thin films were grown as layer-plus-island mode (Stranski–Krastanov growth mode) and others were grown as layer-by-layer growth mode (Frank van der Merwe mode) from AFM analysis. It has been found that increasing RF power has resulted in improvement of surface morphology of thin film from field emission scanning electron microscopy analysis. However, reaching RF power to 125 W leads to start to deteriorate of surface of GaN thin film. The reasons for this have been discussed. E1(TO) transverse optical phonon mode of hexagonal GaN with different intensity was detected from Micro-Raman Spectroscopy measurement. The reasons for this difference have been discussed. It was concluded that RF power has played a significant role in growing high quality GaN thin film. Morphological, structural, and optical properties of GaN thin film were enhanced by controlling RF power, making them a potential candidate for LED, solar cell, diode application.
关键词： Thin film,III-nitride,RF magnetron sputter,Semiconductor,GaN
更新于2025-11-14 15:25:21
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Influence of pulse frequency on physicochemical properties of InSb films obtained via electrodeposition
摘要： Presented work focuses on the tremendous and often skipped role of pulse frequency on the structural, optical and electrical properties of electrodeposited InSb films. Tailoring the pulse frequency during electrodeposition allows to obtain stoichiometric, nanocrystalline, smooth films with relatively high electrical conductivity or Sb-rich, almost insulating, ultra smooth ones. It was observed that a double coherent domain size reduction (via decrease of pulse frequency) leads to a six fold increase in resistivity of the film. Further increasing pulse on time results in increasing resistivity of the material up to ca. 540 U cm. Based on the FTIR and SPV measurements it was confirmed that obtained materials are characterized by small band gap and p-type conductivity. Moreover, stoichiometric, ultra smooth InSb films obtained with 10 ms pulse on time have high photovoltage amplitude and charging time constant with relatively high conductivity, which makes them a good, low-cost candidate for optoelectronic devices.
关键词： Pulse frequency,Electrodeposition,InSb,p-type semiconductor
更新于2025-11-14 15:19:41
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Density functional theory for investigation of optical and spectroscopic properties of zinc-quinonoid complexes as semiconductor materials
摘要： Three Zn(II) complexes of a new organic compound [(E)-4-methyl-N1-((E)-4-methyl-6-(p-tolylimino) cyclohex-3-en-1-ylidene)-N2-(p-tolyl) benzene-1, 2-diamine] (HMBD) were prepared and characterized by various techniques, including Fourier transform infrared (FTIR), UV–visible measurements, 1H-NMR, X-ray diffraction (XRD), and scanning electron microscopy (SEM). The data revealed that the HMBD ligand has an ONS tridentate-forming structure, while the complex of HMBD with zinc metal has a distorted octahedral structure, providing sp3d2 hybridization type. The geometry, HOMO, LUMO, polarizability, and other energetic parameters were evaluated by density functional theory (DFT) on Materials Studio package. Optical band gap (Eg) was estimated by DFT theory and optical properties for [Zn(MBD)(Cl)(H2O)2].2H2O (1), [Zn(MBD)](NO3)2H2O].2H2O (2), and [Zn(MBD)(CH3COO)(H2O)].3H2O (3) thin films as well, revealing that [Zn(MBD)(CH3COO)(H2O)].3H2O (3) thin film has the smallest energy gap and can be considered a highly efficient photovoltaic material. The resulting band gap energy values from both methods were found to be close to each other. Thin films of the ligand and zinc complexes were successfully fabricated by spin coating method. The optical constants, refractive index (n), and the absorption index (k) over the spectral range of the thin films were determined.
关键词： Optical properties,Semiconductor materials,Density functional theory,Thin film,Zinc-quinonoid complexes
更新于2025-11-14 15:19:41
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Tin( <scp>ii</scp> ) thiocyanate Sn(NCS) <sub/>2</sub> – a wide band gap coordination polymer semiconductor with a 2D structure
摘要： Semiconductors based on tin(II) show promising hole-transport characteristics due to the 5s electrons that form the valence band. In this paper, we report the synthesis and comprehensive characterization of tin(II) thiocyanate [Sn(NCS)2] and identify it as a novel transparent coordination polymer semiconductor. The single crystal X-ray analysis reveals covalently-bonded 1D polymeric chains that form a 2D structure through Sn–S tetrel bonds. Density functional theory calculations also confirm the importance of the van der Waals interactions between the 2D sheets. Furthermore, we show that the s character of Sn(II) is maintained at the top of the valence band, resulting in dispersed states with a small hole effective mass. The coordination with NCS ligands also leads to a conduction band which is high in energy, giving rise to a wide band gap and excellent transparency in the visible spectrum. This is the first report on the electronic properties of Sn(NCS)2 which highlights the potential of developing new transparent semiconductors based on thiocyanate coordination polymers.
关键词： hole transport,band gap,tin(II) thiocyanate,transparent,semiconductor,coordination polymer
更新于2025-10-22 19:40:53
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Investigation of Fe-doped room temperature dilute magnetic ZnO semiconductors
摘要： Different ceramics sample of Zn1-xFexO (ZFO) series have been sintered by solid state reaction method. Single phase polycrystalline Fe-doped ZnO sample with hexagonal wurtzite structure has been obtained with x < 0.03 mol. Segregation of Fe and/or its oxides have not been found in the XRD patterns. A weak secondary phase of ZnFe2O4 has been detected with x ≥ 0.03 mol. Presence of Ohmic conductivity has been detected in the dielectric property analysis and the reasons for this Maxwell-Wagner-Sillars (MWS) relaxation has been explained by the grain boundary barrier defect (GBBD) process. The obtained shift of diamagnetic behavior of pure ZnO samples to para-magnetic for ZFO samples has been established with the defect and impurity structure. The band gap energy for ZFO samples has been calculated between 2.85 eV to 3.15 eV. The results indicate the potential use of Fe doped ZnO ceramics in high frequency device applications.
关键词： Spintronics,XRD,Hysteresis loops,Dilute magnetic semiconductor,Dielectric constant,Optical property
更新于2025-10-22 19:40:53
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Normally-off AlGaN/GaN Heterojunction Metal-Insulator-Semiconductor Field-Effect Transistors with Gate-First Process
摘要： In this study, AlGaN/GaN heterojunction metal-insulator-semiconductor field-effect transistors with gate-first process were developed for normally-off operation with p-GaN cap layers and SiNx dielectrics. To avoid the effect of the annealing process on the gate, a low-temperature ohmic contact technique was developed at an annealing temperature of about 500 oC for 20 min in N2 ambient. With the assistance of inductively coupled plasma dry etching, a contact resistance of 1.45 Ω·mm and sheet resistance of 1080.1 Ω/□ were obtained in the recessed region. Owing to the inset of the SiNx layer, the threshold voltage of fabricated device was enhanced to approximately 2 V, and good pinch-off was observed with the gate voltage up to 16 V. Compared with the conventional high-temperature ohmic annealing process, the gate leakage current was suppressed significantly in both reverse and forward directions. Good device performance was confirmed with a maximum channel electron field-effect mobility of 1500 cm2V-1s-1.
关键词： low-temperature ohmic contact,normally-off,gate-first,metal-insulator-semiconductor,AlGaN/GaN HFET
更新于2025-09-23 15:23:52
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Projector-based renormalization approach to electron-hole-photon systems in their nonequilibrium steady state
摘要： We present an extended version of the projector-based renormalization method that can be used to address not only equilibrium but also nonequilibrium situations in coupled fermion-boson systems. The theory is applied to interacting electrons, holes, and photons in a semiconductor microcavity, where the loss of cavity photons into vacuum is of particular importance. The method incorporates correlation and fluctuation processes beyond mean-field theory in a wide parameter range of detuning, Coulomb interaction, light-matter coupling, and damping, even in the case when the number of quasiparticle excitations is large. This enables the description of exciton and polariton formation and their possible condensation through spontaneous phase symmetry breaking by analyzing the ground-state, steady-state, and spectral properties of a rather generic electron-hole-photon Hamiltonian, which also includes the coupling to two fermionic baths and a free-space photon reservoir. Thereby, the steady-state behavior of the system is obtained by evaluating expectation values in the long-time limit by means of the Mori-Zwanzig projection technique. Tracking and tracing different order parameters, the fully renormalized single-particle spectra and the steady-state luminescence, we demonstrate the Bose-Einstein condensation of excitons and polaritons and its smooth transition when the excitation density is increased.
关键词： exciton condensation,nonequilibrium steady state,semiconductor microcavity,projector-based renormalization method,electron-hole-photon systems,Bose-Einstein condensation,polariton condensation
更新于2025-09-23 15:23:52
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Challenges in semiconductor single entity photoelectrochemistry
摘要： It is challenging to study the single semiconductor (SC) nanocrystal electrochemistry and photoelectrochemistry. The photocatalytic process that results from the electron-hole pair formed within a nanoparticle (NP) like the oxidation of methanol and iodide allow the detection of discrete current transient events assigned to single entities. Photocatalytic current amplification allows detection of collisions between the semiconductor NPs and the ultramicroelectrode (UME) that produce current transient. Staircase responses and blips in the i vs. t response indicate that irreversible and reversible NP/electrode interactions result depending on the experimental conditions. Dye sensitization increases the photocurrent magnitude of ZnO and TiO2 with respect to bare TiO2 NPs. The microelectrodes used are Pt, TiO2/Pt, TiO2/Au and F-doped SnO2 (FTO).
关键词： semiconductor,photoelectrochemistry,ultramicroelectrode,nanoparticle,dye sensitization,single entity
更新于2025-09-23 15:23:52