Features of the Frequency Dependence of Capacitance–Voltage Characteristics of a Semiconductor Structure of a Photoelectric Converter Based on a p–n Junction with an Antireflective Film of Porous Silicon

Technical Physics - The frequency dependence of capacitance–voltage characteristics of a semiconductor structure with an antireflective film of porous silicon, which was formed by...     

Ferroelectric characteristics of MFIS structure with P(VDF–TrFE)/BaTiO3 nanocomposite as ferroelectric layer

A metal–ferroelectric–insulator–semiconductor (MFIS) structure has been made using poly(vinylidene difluoride–trifluoroethylene)/barium titanate [P(VDF–TrFE)/BaTiO₃] nanocomposite as ferroelectric layer, on silicon/silicon dioxide (Si/SiO₂) substrate. Different concentrations of BaTiO₃ were added to P(VDF–TrFE) polymer using bath sonication method, and the films were prepared using spin coating method. The structure was annealed to 120 °C for 2 h and then the top aluminium electrode was deposited by thermal evaporation method. Capacitance–voltage shows an increase in accumulation capacitance as the BaTiO₃ nanoparticle concentrations increases. Dielectric constant was estimated from the capacitance voltage (C–V) characteristics and found to be changing as the concentration of BaTiO₃ is varied. Polarization–electric field analyses show hysteresis behaviour of the nanocomposite. A comparison of MFIS and metal–ferroelectric–semiconductor structures was done with varying ferroelectric film thicknesses. All these results suggest that this polymer nanocomposite can be a promising material which can be used in non-volatile memory devices.     

Study of density of interface states in MOS structure with ultrathin NAOS oxide

The quality of the interface region in a semiconductor device and the density of interface states (DOS) play important roles and become critical for the quality of the whole device containing ultrathin oxide films. In the present study the metal-oxide-semiconductor (MOS) structures with ultrathin SiO₂ layer were prepared on Si(100) substrates by using a low temperature nitric acid oxidation of silicon (NAOS) method. Carrier confinement in the structure produces the space quantization effect important for localization of carriers in the structure and determination of the capacitance. We determined the DOS by using the theoretical capacitance of the MOS structure computed by the quantum mechanical approach. The development of the density of SiO₂/Si interface states was analyzed by theoretical modeling of the C-V curves, based on the superposition of theoretical capacitance without interface states and additional capacitance corresponding to the charges trapped by the interface states. The development of the DOS distribution with the passivation procedures can be determined by this method.     

Fabrication of metal/quantum dot/semiconductor structure on silicon substrate

A fabrication technique and optimal growth conditions are reported to develop a Sb-based quantum dot (QD) structure as a nanostructured III–V semiconductor on a silicon substrate. By using solid-source molecular beam epitaxy, high-density (>10¹⁰ cm⁻²) InGaSb QD structures can be obtained under a low growth temperature, which is compatible for use with Si-CMOS processes. We also proposed the construction of a metal/quantum dot/semiconductor (MDS) structure by using the InGaSb QD on a Si substrate. An infrared light emission with a photon energy of 0.95 eV is successfully observed from the fabricated MDS structure under the current injection conditions. It is expected that a MDS structure using a Sb-based QD will be used as a small-sized infrared light source for silicon photonic technology.     

Passivation of defect states in Si-based and GaAs structures

Formation of defect states on semiconductor surfaces, at its interfaces with thin films and in semiconductor volumes is usually predetermined by such parameters as semiconductor growth process, surface treatment procedures, passivation, thin film growth kinetics, etc. This paper presents relation between processes leading to formation of defect states and their passivation in Si and GaAs related semiconductors and structures. Special focus is on oxidation kinetics of yttrium stabilized zirconium/SiO₂/Si and Sm/GaAs structures. Plasma anodic oxidation of yttrium stabilized zirconium based structures reduced size of polycrystalline silicon blocks localised at thin film/Si interface. Samarium deposited before oxidation on GaAs surface led to elimination of EL2 and/or ELO defects in MOS structures. Consequently, results of successful passivation of deep traps of interface region by CN⁻ atomic group using HCN solutions on oxynitride/Si and double oxide layer/Si structures are presented and discussed. By our knowledge, we are presenting for the first time the utilization of X-ray reflectivity method for determination of both density of SiO₂ based multilayer structure and corresponding roughnesses (interfaces and surfaces), respectively.     

Effect of laser irradiation of C-V characteristics of electrodeposited Ag/Tl-2223/CdSe hetero-nanostructures

One of the innovative technological directions for the high-temperature superconductors has been persued by fabricating the heteroepitaxial multilayer structures such as superconductor-semiconductor heterostructures. In the present investigation, metal/superconductor/semiconductor (Ag/Tl-2223/CdSe) hetero-nanostructures have successfully been fabricated using dc electrodeposition technique and were characterized by X-ray diffraction (XRD), full-width at half-maximum (FWHM) and scanning electron microscopy (SEM) studies. The measurement of junction capacitance as a function of biasing voltage was used for the estimation of junction built-in-potential (V _D) and to study the charge distribution in a heterojunction. The Mott-Schottky plots were measured for each junction in dark and under the photo-irradiation. The effect of laser irradiation on C-V characteristics of hetero-nanostructure has been studied.     

Studies on photoinduced effects in pulse-electrodeposited Ag/Hg-1212/CdSe hetero-nanostructures

Metal/superconductor/semiconductor (Ag/Hg-1212/CdSe) hetero-nanostructures have been fabricated using pulse-electrodeposition technique and are characterized by X-ray diffraction (XRD), full-width at half-maximum (FWHM) and scanning electron microscopy (SEM) studies. The junction capacitance of Ag/Hg-1212, Hg-1212/CdSe and Ag/Hg-1212/CdSe heterojunctions is measured in dark and under laser irradiation at room temperature. The nature of the junction formed and built-in-junction potentials were determined. The increase in carrier concentration across the junction due to photo-irradiation has been observed.     

On interface properties of ultra-thin and very-thin oxide/a-Si:H structures prepared by oxygen based plasmas and chemical oxidation

Amorphous hydrogenated silicon (a-Si:H) belongs still to most promising types of semiconductors for its utilization in fabrication of TFTs and thin film solar cell technology due to corresponding cheap a-Si:H-based device production in comparison with, e.g. crystalline silicon (c-Si) technologies. The contribution deals with both two important modes of preparation of very-thin and ultra-thin silicon dioxide films in the surface region of a-Si:H semiconductor (oxygen plasma sources and liquid chemical methods) and electrical, optical and structural properties of produced oxide/semiconductor structures, respectively. Dominant aim is focused on investigation of oxide/semiconductor interface properties and their comparison and evaluation from view of utilization of used technological modes in the nanotechnological industry. Following three basic types of oxygen plasma sources were used for the first time in our laboratories for treatments of surfaces of a-Si:H substrates: (i) inductively coupled plasma in connection with its applying at plasma anodic oxidation; (ii) rf plasma as the source of positive oxygen ions for plasma immersion ion implantation process; (iii) dielectric barrier discharge ignited at high pressures.The liquid chemical manner of formation SiO₂/a-Si:H structures uses 68 wt% nitric acid aqueous solutions (i.e., azeotropic mixture with water). Their application in crystalline Si technologies has been presented with excellent results in the formation of ultra-thin SiO₂/c-Si structures [H. Kobayashi, M. Asuha, H.I. Takahashi, J. Appl. Phys. 94 (2003) 7328].Passivation of surface and interface states by liquid cyanide treatment is additional original technique applied after (or before) formation of almost all formed thin film/a-Si:H structures. Passivation process should be used if high-quality electronical parameters of devices can be reached.     

Structural and spectroscopic analysis of hot filament decomposed ethylene deposited at low temperature on silicon surface

The deposition of decomposed ethylene on silicon wafer at lower temperature using hot filament chemical vapor deposition (HFCVD) method was applied to compose thin film of carbon and its compounds with silicon and hydrocarbon structures. The films were analyzed using Raman spectroscopy, X-ray diffraction, and scanning electron microscopy with elemental microanalysis by energy dispersive X-ray spectrometer. The structure and morphology of the early stage of the film deposition was analyzed. The obtaining of SiC as well as diamond-like structure with this method and catalytic influence of chemical admixtures on the film structure and properties are discussed.     

Study of silicon-organic interfaces by admittance spectroscopy

An admittance spectroscopy technique has been developed for the interfaces between organic monolayers and silicon. The present work involves the development of an effective equivalent circuit to represent the silicon/organic-monolayer system, and the development of a parameter extraction procedure, which yields the monolayer capacitance and the monolayer thickness, the flat-band voltage, the silicon doping density, the silicon surface potential, the interface trap density, the interface trap capture cross-section and the interface trap energy. This technique was applied to three types of silicon/organic-monolayer system.     

Growth of InSe:Mn semiconductor crystals by Bridgman–Stockbarger technique and analysis of electron irradiation effects on Sn/InSe:Mn Schottky diodes

Mn-doped p-InSe semiconductor crystals were grown by Bridgman –Stockbarger technique. The crystals were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM) and fabricated Sn/InSe:Mn Schottky diodes. The current–voltage (I–V) and capacitance–voltage (C–V) measurements of diodes were investigated to determine the response of devices to electron irradiation with 9?MeV energy and 1.2?×?10¹⁰?e^??cm^?2 dose. After irradiation, the ideality factor and barrier height of the Sn/InSe:Mn Schottky diode were determined as 1.66 and 0.85?eV, respectively. Before irradiation, they were determined as 1.37 and 0.90?eV, respectively. It has been concluded that the radiation with high energy may contribute to form defects at the interface of the Sn/InSe:Mn device.     

Electrical properties of thermally evaporated nickel-dimethylglyoxime thin films

Thin Bis-(dimethylglyoximato)nickel(II) [Ni(DMG)₂] films of amorphous and crystalline structures were prepared by vacuum deposition on Si (P) substrates. The films were characterised by X-ray fluorescence and X-ray diffraction. The constructed Al/Ni(DMG)₂/Si(P) metal-insulator-semiconductor devices were characterised by the measurement of the gate-voltage dependence of their capacitance and ac conductance, from which the surface states density D_it of insulator/semiconductor interface and the density of the fixed charges in the oxide were determined. The ac electrical conduction and dielectric properties of the Ni(DMG)₂-Silicon structure were studied at room temperature. The data of the ac measurements of the annealed films follow the correlated barrier-hopping CBH mode, from which the fundamental absorption bandgap, the minimum hopping distance, and other parameters of the model were determined.     

Influence of silicon doping density on vacuum field emission triode at high frequency range

Silicon FEA will affect the high frequency application of field emission tubes when it works at the microwave frequency range. This article shows that the electron emitting will be influenced by the majority carrier response time in semiconductor silicon. The surface capacitance and delay time of n-type and p-type silicon are calculated by using semiconductor theory. The result shows that the semiconductor conductivity will determine the maximum work frequency of device. The maximum work frequency (no considering other effects such as C_gc, g_m etc.) will be decreased from about 200 GHz to 2 GHz when the resistivity of p-type silicon is increased from 0.1 · cm to 10 cm.     

Effect of axial pressure on the capacitance of metal-tunneling-transparent oxide-semiconductor structures

The effect of axial pressure on the capacitance of molybdenum-tunneling-transparent oxide-n-type silicon is studied. The capacitance was measured in the frequency band 1 kHz–10 MHz by the bridge method. The oxide was 5·10^–9 m thick. It is shown experimentally that the effect of the pressure on the capacitance of the structures consists of a pressure-induced change in the surface charge of these structures. The largest changes in the capacitance are observed in structures based on (100) silicon at low measurement frequencies and are associated with the presence of an acceptor level, close to the Fermi level of silicon on the surface, at the silicon-oxide interface and pressure-induced recharging of the level.Deceased.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, No. 9, pp. 65–69, September, 1988.     

A comparison study between two types of nuclear detectors having (Metal–Organic thin films–Silicon) and (Metal–Silicon) structures

Nuclear detectors having metal–organic thin film–semiconductor structures have been prepared and tested. The organic thin films (50–200 nm) were thermally sublimed and deposited onto silicon slides (n-type 1000 Ω.cm). The prepared detectors show remarkable performance and their energy resolution was highly improved in comparison to metal–semiconductor (Schottky type) detectors manufactured on identical substrates and under similar conditions.     

Electrochemical impedance spectroscopy analysis of porous silicon prepared by photo-electrochemical etching: current density effect

Electrical impedance characteristics of porous silicon nanostructures (PSiNs) in frequency function were studied. PSiNs were prepared through photo-electrochemical etching method at various current densities (15–40 mA/cm²) and constant etching time. The atomic force microscope images of PSiNs show that pore diameter and roughness increase when current density increases to 35 mA/cm². The surface roughness subsequently decreases because of continuous etching of pillars, and a second etching process occurs. Photoluminescence spectra show blue and red shift with increasing applied current density that is attributed to PSiNs size. Variations of electrical resistance and capacitance values of PSiNs were measured using electrochemical impedance spectroscopy analysis. These results indicate that PSiNs prepared at 20 mA/cm² current density have uniform porous structures with a large number of pillars. Furthermore, this PSiNs structure influences large values of charge transfer resistance and double layer capacitance, indicating potential application in sensors.     

XPS analysis with pulsed voltage stimuli

We record XPS spectra while applying 0 to +10 V or 0 to −10 V square pulses to the sample rod, which normally results in twinning of all peaks at correspondingly increased (for +10 V) or decreased (for −10 V) binding energies. For poorly conducting samples, like silicon oxide layer on a silicon substrate, the twinned peaks appear at different energies due to differential charging, which also vary with respect to the frequency of the applied pulses. Moreover, the frequency dependence varies with the thickness and can be correlated with the capacitance of the oxide layer. The technique is simple and can lead to extract important information related with dielectric properties of surface structures in a totally non-contact fashion.     

分子动力学模拟研究熔态硅的局部结构

采用Tersoff势,修正试用不同的粒子间相互作用距离R,S的取值,进行了液态硅的分子动力学模拟.模拟的结果表明,修正Tersoff势下得到的径向分布函数能与X射线衍射、中子散射实验相一致.模拟得到在液态硅中,Si的配位数为6.9,键长为0.254nm.分子动力学模拟表明,液态硅中Si原子间联接成一种网络状结构,但大多数Si原子与其近邻Si原子仍保持近似于正四面体的局部构型.键角概率分布出现两个峰值~57°和~102°.通过键序参量分析,得到在液态硅近邻结构中,正四面体构型约占82%,键取向波动方差为5. 关键词：     

Local capacitance analysis using a modified deep level spectrometer

A bimorph-based xz scanner and an amplifier, increasing the capacitance and current measurement sensitivities 250-times and 1000-times, respectively, have been built into the cryostat of a deep level transient spectrometer. The setup renders point by point local capacitance-voltage (C?CV) at 1 MHz and dc currentvoltage (I?CV) measurements using a sharp tip placed into tunnelling distance from the surface of analysed semiconductor sample. The C?CV measurements revealed a strong dependence on the probe/sample separation, ranging from MOS-type at small tunnelling currents to Schottky-type at currents exceeding approximately 10 pA. Marked hysteresis was observed, indicating changes of surface state occupancy. These slow states are otherwise hardly detected, since they are absent in semiconductor/metal contacts and in MOS structures they would become mostly passivated interface states. The setup enables calibrated, fixed zero level capacitance measurement. The stray capacitance is the dominant component of the measured capacitance but it can be easily discarded.     

Synthesis,characterization and radiation damage studies of high-k dielectric (HfO2) films for MOS device applications

The current trend in miniaturization of metal oxide semiconductor devices needs high-k dielectric materials as gate dielectrics. Among all the high-k dielectric materials, HfO₂ enticed the most attention, and it has already been introduced as a new gate dielectric by the semiconductor industry. High dielectric constant (HfO₂) films (10?nm) were deposited on Si substrates using the e-beam evaporation technique. These samples were characterized by various structural and electrical characterization techniques. Rutherford backscattering spectrometry, X-ray reflectivity, and energy-dispersive X-ray analysis measurements were performed to determine the thickness and stoichiometry of these films. The results obtained from various measurements are found to be consistent with each other. These samples were further characterized by I–V (leakage current) and C–V measurements after depositing suitable metal contacts. A significant decrease in the leakage current and the corresponding increase in device capacitance are observed when these samples were annealed in oxygen atmosphere. Furthermore, we have studied the influence of gamma irradiation on the electrical properties of these films as a function of the irradiation dose. The observed increase in the leakage current accompanied by changes in various other parameters, such as accumulation capacitance, inversion capacitance, flat band voltage, mid-gap voltage, etc., indicates the presence of various types of defects in irradiated samples.