Conductivity of layers of a chalcogenide glassy semiconductor Ge<Subscript>2</Subscript>Sb<Subscript>2</Subscript>Te<Subscript>5</Subscript> in high electric fields

Effect of high electric fields on the conductivity of 0.5-1-μm-thick layers of a chalcogenide glassy semiconductor with a composition Ge₂Sb₂Te₅, used in phase memory cells, has been studied. It was found that two dependences are observed in high fields: dependence of the current I on the voltage U, of the type I ∝ U ⁿ , with the exponent (n ≈ 2) related to space-charge-limited currents, and a dependence of the conductivity σ on the field strength F of the type σ = σ₀exp(F/F ₀) (where F ₀ = 6 × 10⁴ V cm⁻¹), caused by ionization of localized states. A mobility of 10⁻³–10⁻² cm² V⁻¹ s⁻¹ was determined from the space-charge-limited currents.     

Comparison between the noise performance of current-mode and voltage-mode amplifiers

A comparison is made between the noise performance of current mode- and voltage mode feedback amplifiers, in terms of their noise figureF _i andF _v , respectively. WhereasF _v of a well designed voltage amplifier is dominantly affected by the input stage only, all stages of a current amplifier including the feedback network may potentially contribute toF _i . This paper investigates the transferfunction to the output of the various noise sources of current mode feedback amplifiers, whose full recognition is essential in order to design CMFA's of reasonable noise performance. Also discussed is the effect the dynamic range of a postamplifier may have on its noise figure. Although the bulk of this paper deals with postamplifiers, the important subject of low noise current amplification is covered as well.A short version of this paper has been published in Proceedings ECCTD'93, pp. 1565-1568.1. Patent 5410271, USA     

Protein Adsorption on Grafted Zwitterionic Polymers Depends on Chain Density and Molecular Weight

This study demonstrates that protein adsorption on end‐grafted, zwitterionic poly(sulfobetaine) (pSBMA) thin films depends on the grafting density, molecular weight, and ionic strength. Zwitterionic polymers exhibit ultralow nonspecific fouling (protein adsorption) and excellent biocompatibility. This picture contrasts with a recent report that soluble pSBMA chains bind proteins and alter the protein folding stability. To address this apparent contradiction, the dependence of protein adsorption on the chain grafting parameters is investigated: namely, the grafting density, molecular weight, and ionic strength. Studies compared the adsorption of phosphoglycerate kinase and positively charged lysozyme versus the scaled grafting parameter s/2R_F, where s is the distance between grafting sites and R_F is the Flory radius. Plots of the adsorbed protein amount versus s/2R_F exhibit a bell‐shaped curve, with a maximum near s/2R_F ≈ 1 and an amplitude that decreases with ionic strength. This behavior is qualitatively consistent with theoretical models for colloid interactions with weakly attractive, grafted chains. The results confirm that proteins do adsorb to pSBMA thin films, and they suggest an underlying mechanism. Comparisons with polymer models further identify design rules for pSBMA films that effectively repel protein.     

Effective elastic constant theory of transverse wave interaction in a piezoelectric semiconductor

Small-signal low-frequency current gains of the npn and pnp transistor sections of high and low power thyristors were measured by a three-terminal technique. From their dependence upon current and temperature it was found that the saturation current dependence of the isolated centre junction primarily determines temperature stability. Current gain measured at a series of temperatures, and plotted para-metrically with anode current, qualitatively correctly predicts the temperature dependence of the two-terminal latching currents. Gold-doping predictably leads to a low current gain for the pnp section.     

The Effect of Gradual Fluorination on the Properties of FnZnPc Thin Films and FnZnPc/C60 Bilayer Photovoltaic Cells

Motivated by the possibility of modifying energy levels of a molecule without substantially changing its band gap, the impact of gradual fluorination on the optical and structural properties of zinc phthalocyanine (F_nZnPc) thin films and the electronic characteristics of F_nZnPc/C₆₀ (n = 0, 4, 8, 16) bilayer cells is investigated. UV–vis measurements reveal similar Q‐ and B‐band absorption of F_nZnPc thin films with n = 0, 4, 8, whereas for F₁₆ZnPc a different absorption pattern is detected. A correlation between structure and electronic transport is deduced. For F₄ZnPc/C₆₀ cells, the enhanced long range order supports fill factors of 55% and an increase of the short circuit current density by 18%, compared to ZnPc/C₆₀. As a parameter being sensitive to the organic/organic interface energetics, the open circuit voltage is analyzed. An enhancement of this quantity by 27% and 50% is detected for F₄ZnPc‐ and F₈ZnPc‐based devices, respectively, and is attributed to an increase of the quasi‐Fermi level splitting at the donor/acceptor interface. In contrast, for F₁₆ZnPc/C₆₀ a decrease of the open circuit voltage is observed. Complementary photoelectron spectroscopy, external quantum efficiency, and photoluminescence measurements reveal a different working principle, which is ascribed to the particular energy level alignment at the interface of the photoactive materials.     

Activation Energy Spectra: Insights into Transport Limitations of Organic Semiconductors and Photovoltaic Cells

Some mechanisms of charge transport in organic semiconductors and organic photovoltaic (OPV) cells can be distinguished by their predicted change in activation energy for the current, E_a, versus applied field, F. E_a versus F is measured first in pure films of commercially available regioregular poly(3‐hexylthiophene) (P3HT) and in the same P3HT treated to reduce its charged defect density. The former shows a Poole–Frenkel (PF)‐like decrease in E_a at low F, which then plateaus at higher F. The low defect material does not exhibit PF behavior and E_a remains approximately constant. Upon addition of [6,6]‐phenyl‐C₆₁‐butyric acid methyl ester (PCBM), however, both materials show a large increase in E_a and exhibit PF‐like behavior over the entire field range. These results are explained with a previously proposed model of transport that considers both the localized random disorder in the energy levels and the long‐range electrostatic fluctuations resulting from charged defects. Activation energy spectra in working OPV cells show that the current is injection‐limited over most of the voltage range but becomes transport‐limited, with a large peak in E_a, near the open circuit photovoltage. This causes a decrease in fill factor, which may be a general limitation in such solar cells.     

Gain and internal losses in InGaAsSb/InAsSbP double-heterostructure lasers

We report on a study characterizing internal losses and the gain in InGaAsSb/InAsSbP diode-heterostructure lasers emitting in the mid-infrared (3–4 μm). Numerical simulations of the current dependence of the intensity of spontaneous emission above the laser threshold and of the differential quantum efficiency allowed us to determine the intraband absorption k ₀ ≈5.6×10⁻¹⁶ cm². The cavity-length dependence of the threshold current is used to estimate the internal losses at zero injection current α ₀≈5 cm⁻¹. Calculations of the internal losses at laser threshold showed that they increase more than fourfold when the cavity length is decreased from 500 μm to 100 μm. The temperature dependence of the differential quantum efficiency is explained on the assumption that intraband absorption with hole transitions into a split-off band occurs. It is shown that the maximum operating temperature of “short-cavity” lasers is determined by the intraband absorption rather than by Auger recombination. The internal losses are shown to have a linear current dependence. The separation of the quasi-Fermi levels as a function of current demonstrates an absence of voltage saturation of the p-n junction above threshold. Fiz. Tekh. Poluprovodn. 33, 759–763 (June 1999)     

Diagnostics of the quality of MOSFETs

The excess noise behaviour of silicided p-channel MOSFETs is investigated. Due to contact problems, generation-recombination noise spectra are observed. Analysis of the current noise spectra versus the current on a single device, showed that the generation-recombination noise was due to trapping of carriers in the source and drain contacts. An analysis of an L-array is not necessary to distinguish between channel and contact contribution. The classical geometry and current dependence of the noise is no longer valid if the noise in the series resistance is dominant. Large generation-recombination noise components, with the dependence S_I ∝ I⁴, point to poor device contact quality.     

Temperature dependent IDS-VGS characteristics of an N-channel Si tunneling field-effect transistor with a germanium source on Si(110) substrate

在Si(110)衬底上制备了Ge源n型Si沟道隧穿场效应晶体管（TFET）。本文研究了温度对Ge源Si TFET器件的电学性能的影响。温度相关性研究显示器件漏电流主要由漏区的Shockley - Read - Hall (SRH) 产生于复合电流决定。器件开态电流随温度升高而增加,这是因为温度升高材料禁带宽度减小,隧穿几率增大。界面缺陷引起的隧穿电流的亚阈值摆幅随温度升高而变差,但是带间隧穿电流的亚阈值摆幅不随温度变化而变化。     

Voltage step-up filters not using transformers

A network of resistors and capacitors is to serve as a filter for an arbitrary signal voltagef(t). It consists of twin parts connected in parallel across the input terminals. One part is a low pass ladder filter; the rungs of the ladder are capacitors, and the other branches are resistors. The twin part is connected to the input terminals in theopposite direction. The output signal is the voltageg(t) measured between the end nodes of the ladders. Kirchhoff's current law gives a differential equation relatingf and (g−f). IfF is the Fourier transform off, then the transform of the differential equation is an algebraic equation relating the transformsF and (G−F). This equation shows that ⋎G/F⋎>1. Then by Parseval's theorem the norm off is greater than the norm ofg. Thus there is a stepup; the norm of the output always exceeds the norm of the input. Such a filter is here termed anRCformer. This paper is dedicated to Abraham Charnes, mathematician (1917–1992)     

MXene Electrode for the Integration of WSe2 and MoS2 Field Effect Transistors

Recently, MXenes, which are 2D early transition metal carbides and carbonitrides, have attracted wide attention because of their excellent conductivities. Here, the electrode applications of Ti₂C(OH)_xF_y, one member of the MXene family, in WSe₂ and MoS₂ field effect transistors (FETs) are assessed. Kelvin probe force microscopy analysis is performed to determine its work function, which is estimated to be ≈4.98 eV. Devices based on WSe₂/Ti₂C(OH)_xF_y and MoS₂/Ti₂C(OH)_xF_y heterostructures are fabricated with the mechanical transfer method and their electronic performances evaluated. The temperature‐dependent current–voltage transfer characteristics of the devices are determined to extract their Schottky barrier heights. The hole barrier between WSe₂ and Ti₂C(OH)_xF_y is estimated to be ≈0.23 eV and the electron barrier between the MoS₂ band and Ti₂C(OH)_xF_y is ≈0.19 eV, which indicates that the pinning effect occurs at the MoS₂/Ti₂C(OH)_xF_y interface but not at the WSe₂/Ti₂C(OH)_xF_y interface; this difference arises because of the difference between the band structures of WSe₂ and MoS₂. A complementary metal–oxide–semiconductor inverter based on these electrode properties of Ti₂C(OH)_xF_y with MoS₂ (n‐channel) and WSe₂ (p‐channel) is fabricated, which demonstrates that Ti₂C(OH)_xF_y is a promising electrode for future nanoelectronics applications.     

Electrochemically Induced Conformational Change of Di-Boronic Acid-Functionalized Ferrocene for Direct Solid-State Monitoring of Aqueous Fluoride Ions

While fluoride ions (F⁻) are abundant across environmental and biological systems, common procedures and potentiometric sensors for quantifying aqueous F⁻ are inefficient, time-consuming, and suffer from poor pH resiliency and high detection limits. Herein, this work reports a new di-boronic acid-functionalized ferrocene (FDBA) molecular receptor for noncovalent F⁻ recognition, toward the development of a solid-state miniaturized voltammetric fluoride sensor capable of direct and reversible F⁻ detection in drinking water (DW) (pH 6) and community water (pH 7.6–9.1) over the µg L⁻¹–mg L⁻¹ range. The associated sensing mechanism is enabled by the conformational change of FDBA from the open (charge-repelled) to closed (π-dimerized) conformation, which is facilitated by the unique linkage of two electron-accepting phenylboronic acid moieties with the electron-donating ferrocene moiety using rigid conjugated amide linkers. The square wave voltammetric (SWV) oxidation current response of the FDBA-based fluoride sensor is spectroscopically investigated, suggesting a combination of electrooxidation-triggered conformational change of FDBA on a nanocarbon-modified electrode, F⁻ anion–π interactions, and resulting electron transfer between F⁻ and FDBA. The performance of the voltammetric fluoride sensor is compared to that of a commercial liquid junction-based fluoride ion-selective electrode (F-ISE), and of a solid-contact (SC) F-ISE sensor chip, demonstrating significant advantages versus traditional potentiometric F-ISEs.     

Further Results on n-D Polynomial Matrix Factorizations

In this paper, some new results on zero prime factorization for a normal full rank n-D (n>2) polynomial matrix are presented. Assume that d is the greatest common divisor (g.c.d.) of the maximal order minors of a given n-D polynomial matrix F ₁. It is shown that if there exists a submatrix F of F ₁, such that the reduced minors of F have no common zeros, and the g.c.d. of the maximal order minors of F equals d, then F ₁ admits a zero right prime (ZRP) factorization if and only if F admits a ZRP factorization. A simple ZRP factorizability of a class of n-D polynomial matrices based on reduced minors is given. An advantage is that the ZRP factorizability can be tested before carrying out the actual matrix factorization. An example is illustrated.     

Emitter Current Push-Out Effect under Avalanche Multiplication in the Collector p–nJunction

An expression that describes emitter current push-out to the emitter edges with consideration for avalanche multiplication of the current in the collector p–njunction of a bipolar transistor was derived. A strong power dependence of the avalanche multiplication coefficient on the base potential is shown to weaken the push-out effect and to smooth out the current distribution in the system.     

Gain and Dark Current Characteristics of Planar HgCdTe Avalanche Photo Diodes

HgCdTe midwave infrared pin avalanche photodiodes (APDs) have been studied as a function of temperature and bias, for two types of junction profiles with different nominal junction width and the same cut-off wavelength λc = 5.0 μm at T = 77 K. A gain of 5,300 at a reverse bias of 12.5 V was demonstrated in the nominally wide junction pin-APD at T = 77 K. The nominally narrow pin-APD showed a higher gain at low bias, but the maximum gain was lower due to an earlier onset of excess currents. The gain was measured for temperatures (T) between 30 K and 150 K and was found to decrease with increasing temperatures, in correlation with the increase in band gap. However, the useful gain was reduced at lower temperatures, due to increased excess current at high reverse bias, indicating a tunnel limited origin of the sensitivity limiting excess current. The noise factor, F, showed a nearly deterministic multiplication of the carriers, with F = 1–1.5 up to gains of 5,000.     

A new empirical extrapolation method for time-dependent dielectric breakdown reliability projections of thin SiO2 and nitride–oxide dielectrics

The results of an investigation of time-dependent dielectric breakdown (TDDB) of thin gate oxide and nitride–oxide (N–O) films are presented for a wide range of fields and temperatures. It was found that TDDB of both gate oxide and N–O films followed a power-law dependence of mean value of average leakage current (I_avg). An empirical extrapolation model using average leakage current as a major parameter was proposed based on experimental results. This proposed lifetime model has been successful to predict dielectric reliability. It could continuously fit the entire breakdown data from both wafer level and module level stress. The extrapolation from wafer level data to module data was excellent. The power of current versus TDDB showed exponential dependence on oxide thickness. This proposed TDDB projection methodology also worked for N–O films with an abrupt current increase in the I–V curve at a certain voltage well below the breakdown voltage, while the conventional models clearly failed to fit all data from this region. The observation of TDDB dependence of the current may open a new window for oxide lifetime projections and provide some insights into the nature of oxide breakdown and its implications for reliability studies.     

Hydrogen transport in doped and undoped polycrystalline silicon

Hydrogen diffusion in B, P, and undoped poly-Si is investigated. The diffusion activation energy, E_A, depends significantly on the Fermi energy, E_F, and the H concentration. E_A varies between 0.1 eV and 1.69 eV, accompanied by a variation of the diffusion prefactor D₀ by 12 orders of magnitude. Using the theoretical value of D₀, the energy required to yield the measured diffusion coefficients was calculated. depends strongly on E_F and agrees well with the theoretical E_F dependence of the formation energies of H⁺ or H⁻. To account for this behavior a modified H transport model based on trap-limited diffusion is proposed.     

Electronic structure and current injection in zinc phthalocyanine doped with tetrafluorotetracyanoquinodimethane: Interface versus bulk effects

The p-type doping of zinc phthalocyanine (ZnPc) with the highly electronegative tetrafluorotetracyanoquinodimethane (F₄-TCNQ) is investigated via direct and inverse photoemission spectroscopy and in situ current–voltage (I–V) measurement. The electron affinity of F₄-TCNQ and the ionization energy of ZnPc are found to be energetically compatible with an electron transfer between the highest occupied molecular orbital (HOMO) of the host and the lowest unoccupied molecular orbital of the dopant. The Fermi level is near mid-gap in undoped ZnPc, and drops to 0.42 and 0.18 eV above the HOMO in the 0.3% and 3% doped films, respectively, consistent with efficient p-doping. The dependence of the Au/ZnPc:0.3%F₄-TCNQ/Au I–V characteristics on the thickness of the organic film is analyzed in terms of injection-limited versus space-charge-limited current. The analysis demonstrates that the large doping-induced increase in hole current is primarily due to improved carrier injection via tunneling through the narrow interface space charge layer.     

Diode and MOSFET Properties of Trench‐Gate‐Type Super‐Barrier Rectifier with P‐Body Implantation Condition for Power System Application

In this paper, we investigate the electrical characteristics of two trench‐gate‐type super‐barrier rectifiers (TSBRs) under different p‐body implantation conditions (low and high). Also, design considerations for the TSBRs are discussed in this paper. The TSBRs’ electrical properties depend strongly on their respective p‐body implantation conditions. In the case of the TSBR with a low p‐body implantation condition, it exhibits MOSFET‐like properties, such as a low forward voltage (V_F) drop, high reverse leakage current, and a low peak reverse recovery current owing to a majority carrier operation. However, in the case of the TSBR with a high p‐body implantation condition, it exhibits pn junction diode–like properties, such as a high V_F, low reverse leakage current, and high peak reverse recovery current owing to a minority carrier operation. As a result, the TSBR with a low p‐body implantation condition is capable of operating as a MOSFET, and the TSBR with a high p‐body implantation condition is capable of operating as either a pn junction diode or a MOSFET, but not both at the same time.