Showing papers on "Schottky barrier published in 1991"

Barrier inhomogeneities at Schottky contacts

Abstract: We present a new analytical potential fluctuations model for the interpretation of current/voltage and capacitance/voltage measurements on spatially inhomogeneous Schottky contacts. A new evaluation schema of current and capacitance barriers permits a quantitative analysis of spatially distributed Schottky barriers. In addition, our analysis shows also that the ideality coefficient n of abrupt Schottky contacts reflects the deformation of the barrier distribution under applied bias; a general temperature dependence for the ideality n is predicted. Our model offers a solution for the so‐called T0 problem. Not only our own measurements on PtSi/Si diodes, but also previously published ideality data for Schottky diodes on Si, GaAs, and InP agree with our theory.

Electron transport of inhomogeneous Schottky barriers: A numerical study

Abstract: Numerical simulations are presented of the potential distribution and current transport associated with metal‐semiconductor (MS) contacts in which the Schottky barrier height (SBH) varies spatially. It is shown that the current across the MS contact may be greatly influenced by the existence of SBH inhomogeneity. Numerical simulations indicate that regions of low SBH are often pinched‐off when the size of these regions is less than the average depletion width. Saddle points in the potential contours in close proximity to the low‐SBH regions, which are shown to vary with the dimension and magnitude of the inhomogeneity as well as with bias, essentially determine the electron transport across the low‐SBH regions. It is these dependences of the saddle point which give rise to various abnormal behaviors frequently observed from SBH experiments, such as ideality factors greater than unity, various temperature dependences of the ideality factor, including the T 0 anomaly, and reverse characteristics which are strongly bias‐dependent. The results of these numerical simulations are shown to support the predictions of a recently developed analytic theory of SBH inhomogeneity.

Electrochemical Solar Cells are Schottky Barrier Devices. A Citation-Classic Commentary on Electrochemical photo and solar cells: Principles and some experiments

Abstract: Summary It is shown how the well-known photoeffects observed at semiconductor electrodes can be used to construct an electrochemical photocell. The photovoltaic effects in such cells are based on the formation of a Schottky barrier at the interface between a semiconductor and a suitable redox electrolyte. A cell design is developed and some results with CdS, CdSe or GaP electrodes are presented. The characteristics of such photocells and the problems involved in their application as solar cells are discussed.

InGaAs metal-semiconductor-metal photodetectors for long wavelength optical communications

Abstract: A review is presented of the properties of interdigitated metal-semiconductor-metal (MSM) Schottky barrier photodetectors based on the InGaAs-InP material system, and the performance achieved by experimental devices is discussed. The experimental work concentrates on the barrier-enhanced lattice-matched InAlAs-InGaAs device grown by low pressure organometallic chemical vapor deposition (OMCVD), which has to date yielded detectors with the highest performance characteristics. Current research on their integration with FETs to form monolithic receivers and with waveguides for on-chip optical signal processing is also included. >

Electron transport of inhomogeneous schottky barriers

Abstract: A novel approach is presented which leads to analytic solutions to the potential and the electron transport through inhomogeneous Schottky barriers The existence of barrier height nonuniformities is shown to provide a simple explanation of the following abnormal experimental results, routinely observed from various Schottky barriers: greater‐than‐unity ideality factors, the T0 effect, the ‘‘soft’’ reverse characteristics, and the dependence of barrier height on the technique of measurement

Applications of Quantum Semiconductor Structures

Abstract: This chapter discusses the applications of quantum semiconductor structures A new heterostructure type of FET has been developed that includes the two-dimensional electron gas field effect transistor also called high electron mobility transistor, modulation doped field effect transistor, or selectively doped heterojunction transistor depending on manufacturer It has features in common with both MESFETs and metal-oxide-silicon field effect transistors The structure is based on the heterojunction between AlGaAs and GaAs Its essential structure consists of a semi-insulating substrate on which is first grown a buffer layer of nonintentionally doped GaAs and on top of this is grown a thin layer of Al x Ga 1− x As, part of which is rather heavily n-type doped The gate metal forms a Schottky barrier to the AlGaAs and by making the ternary layer thin enough, the gate can completely deplete the AlGaAs layer of electrons Then the density of electrons on the GaAs side of the heterojunction is controlled by the voltage applied to the gate, so that the current between the source and the drain contacts can be controlled by the gate voltage

Universal passivation effect of (NH4)2Sx treatment on the surface of III-V compound semiconductors

Abstract: The effectiveness of (NH4)2Sx treatment on the (100) surface of GaP, (Al, Ga)As, InP and InAs was studied in comparison to that on GaAs by means of Auger electron spectroscopy (AES) and reflection high-energy electron diffraction (RHEED). It was concluded that the existence of sulfur atoms bonded to semiconductors prevents the adsorption of oxygen. This phenomenon brings about the metal-dependent Schottky barrier fabricated on the (NH4)2Sx-treated surfaces, implying the reduction in the interface state density. The structure and effect of the (NH4)2Sx-treated surface of III-V compounds are qualitatively the same.

Schottky-barrier and conductivity gas sensors based upon Pd/SnO2 and Pt/TiO2

Abstract: Electronic conductivity, mixed conductivity and Schottky-barrier sensors based upon the oxides SnO2 and TiO2 which are modified or contacted by the metals Pd and Pt can be used to detect gases like CO, CH4, H2 and O2. The response signals of these different types of sensors result from changes in surface and bulk conductivities or in Schottky-barrier heights, which are measured using different geometric arrangements of metal (Pd or Pt) contacts. The atomistic understanding of sensing mechanisms and corresponding sensor structures is deduced from comparative spectroscopic and electrical measurements. Our studies show that reliable sensor properties can only be achieved either by forming stable metal/oxide interfaces or by adjusting a stable dopant distribution.

Analysis of I-V measurements on PtSi-Si Schottky structures in a wide temperature range

Abstract: I–V Measurements on PtSi-Si Schottky structures in a wide temperature range from 90 to 350 K were carried out. The contributions of thermionic-emission current and various other current-transport mechanisms were assumed when evaluating the Schottky barrier height Φ0. Thus the generation-recombination, tunneling and leak currents caused by inhomogeneities and defects at the metal-semiconductor interface were taken into account. Taking the above-mentioned mechanisms and their temperature dependence into consideration in the Schottky diode model, an outstanding agreement between theory and experiment was achieved in a wide temperature range. Excluding the secondary current-transport mechanisms from the total current, a more exact value of the thermionic-emission saturation current Ite and thus a more accurate value ofΦb was reached. The barrier height Φb and the modified Richardson constant A∗∗ were calculated from the plot of thermionic-emission saturation current Ite as a function of temperature too. The proposed method of finding Φb is independent of the exact values of the metal-semiconductor contact area A and of the modified Richardson constant A∗∗. This fact can be used for determination of Φb in new Schottky structures based on multicomponent semiconductor materials. Using the experimentally evaluated value A∗∗ = 1.796 × 106Am−2K−2 for the barrier height determination from I–V characteristics the value of Φb = 0.881 ± 0.002 eV was reached independent of temperature. The more exact value of barrier height Φb is a relevant input parameter for Schottky diode computer-aided modeling and simulation, which provided a closer correlation between the experimental and theoretical characteristics.

Electron-transfer kinetics of redox reactions at the semiconductor/electrolyte contact. A new approach

Abstract: The model used for electron-transfer kinetics between the electronic charge carriers of a semiconductor and the species of a redox couple in an electrolyte has been refined by taking into account the statistics of forming a reaction pair at the interface. Electron transfer within such a reaction pair is described by the semiclassical theory. A comparison is made between the electron transfer in the forward direction over a semiconductor-metal and a semiconductor-redox electrolyte Schottky barrier of equal height

Metal/semiconductive polymer Schottky device

Abstract: Development of a metal/organic‐semiconductor Schottky junction as an alternative to the metal/inorganic‐semiconductor junction is reported. Metal/polypyrrole (PP) junctions have been prepared with electrochemically deposited doped PP films of different thickness and various metals (In, Sn, Ti, and Al) as electrodes. The electrical characteristics of the junction depend upon the work functions of PP and the metal. It has been possible to prepare Schottky barriers on the PP films with a metal electrode having a work function lower than that of the polymer. Various physical characteristics of the polymer, work function, Fermi level, and carrier concentration have been estimated.

Ion beam synthesis of buried α-FeSi2 and β-FeSi2 layers

Abstract: Using high dose implantation of Fe+ into (111)Si, followed by rapid thermal annealing (RTA) at 1150 °C for 10 s, we fabricated continuous buried layers of the metallic α‐FeSi2 phase. Rutherford backscattering experiments indicate that these layers contain a large number of Fe vacancies, up to 18%. By implanting through a SiO2 mask, we produced Schottky diodes with idealty factors of 1.4±0.1 and a Schottky barrier height of ΦB=0.84±0.03 eV on (111) n‐Si. In this letter we report for the first time the formation of the semiconducting stoichiometric FeSi2 (β‐FeSi2) phase by annealing the buried α‐FeSi2 layers below the phase transition temperature of 937 °C; specifically at 750 °C for 20 h.

A new method to fabricate Au/n-type InP Schottky contacts with an interfacial layer

Abstract: A method to fabricate Au- n -type InP Schottky contacts with an interfacial layer has been developed. The interfacial layer is formed by deposition of a P x O y layer and reaction of this layer with the InP substrate. The current-voltage and capacitance-voltage characteristics are measured at various temperatures. Excellent rectification is found in the fabricated contacts. The observed reverse currents are very low. The ideality factors are around 1.15. Apparent barrier heights qφ B are evaluated from the extrapolated forward saturation current I s . They are found to be sufficiently high. The typical value of qφ B at room temperature is obtained as 0.88 eV. The Richardson plot ln( I s / T 2 ) vs 1/ T is well fitted in a straight line, where T is the temperature. From the Richardson plot, the true barrier height is estimated to be 0.41 eV. The effects of the interfacial layer are also discussed.

Amorphous Ge bipolar blocking contacts on Ge detectors

Abstract: The authors report on the performance of high-purity Ge radiation detectors with amorphous Ge (a-Ge) contacts fabricated using RF sputtering techniques. Electrical contacts formed using sputtered a-Ge films on high-purity Ge crystals, both n- and p-type, were found to exhibit good blocking behavior with low leakage currents, with the contact biased under either voltage polarity. The a-Ge contacts have thin dead layers associated with them, and can be used in place of lithium-diffused, ion-implanted, or Schottky barrier contacts on Ge radiation detectors. The use of such contacts allows fabrication of multi-electrode detectors by means of simple processing steps. >

Temperature dependence of the Schottky-barrier height of tungsten on n-type and p-type silicon

Abstract: The Schottky-barrier heights of W and its silicide WSi2 on both n-type and p-type Si(100) have been measured in the temperature range 77–295 K with the use of current-voltage and capacitance-voltage techniques. Auger-electron and X-ray photoemission spectroscopies were used to characterize the Si(100) surfaces prior to metal deposition, and to monitor the reaction between W and Si. Silicide formation has very little or no effect on both the barrier height and its temperature dependence. The n-type barrier height for both the metal and the reacted silicide phase decreases with increasing temperature with a coefficient almost equal to the temperature coefficient of the indirect band gap in Si. The p-type barrier height does not exhibit a temperature dependence. These results suggest that the Fermi level at the interface is pinned relative to the valence-band edge. These results deviate from the predictions of models of Schottky-barrier formation based on the suggestion of Fermi-level pinning in the center of the semiconductor indirect band gap. Along with results previously reported for metal(silicide)-Si systems with a wide range in metal electronegativity, the present results show that both the silicon barrier height and its temperature dependence are affected by the metal.

1.3- mu m P-i-N photodetector using GaAs with As precipitates (GaAs:As)

Abstract: The fabrication of a GaAs detector which operates in the 1.3- to 1.5- mu m optical range is reported. The detector is a P-i-N photodiode with an intrinsic layer composed of undoped GaAs which was grown at 225 degrees C and subsequently annealed at 600 degrees C. This growth process has been demonstrated to produce a high density of As precipitates in the low-temperature grown region, which the authors show to exhibit absorption through internal photoemission. The internal Schottky barrier height of the As precipitates is found to be 0.7 eV, leading to reasonable room-temperature responsivity out to around 1.7 mu m. >

Transport Properties of Inhomogeneous Schottky Contacts

Abstract: We review an analytical model for the interpretation of transport measurements on spatially inhomogeneous Schottky contacts. The comparison of barriers from current/voltage- as well as from capacitance/voltage-curves permits a quantitative analysis of spatially distributed Schottky barriers. We reveal that the ideality coefficient n of abrupt Schottky contacts reflects the deformation of the barrier distribution under applied bias; a general temperature dependence for the ideality n is predicted and observed. An extension of our model includes the so-called flat band barrier of current/voltage curves. Here we demonstrate the interdependence of flat band Schottky barrier, ideality n and the homogenization of the barrier distribution under the application of a bias voltage. Effective photoresponse barriers and electrical noise at inhomogeneous Schottky diodes are also discussed.

BiCMOS device with low bandgap CMOS contact regions and low bandgap bipolar base region

Abstract: According to the present invention, a control gate is formed on an n-type Si substrate, and a p-type source-drain region is formed in the surface of the substrate on both the sides of the control gate. A p-type Six Ge1-x (0≦x<1) layer and an Al electrode are sequentially formed in the source-drain region. The energy difference between the valence band of the SiGe layer and a vacuum level is smaller than the energy difference between the valence band of an Si layer constituting the source-drain region and the vacuum level, and the energy difference of the conduction band of the SiGe layer and the vacuum level is larger than the energy difference of the conduction band of the Si layer and the vacuum level. For this reason, a Schottky barrier height is decreased, and resistances between the semiconductor layers and the Al electrode are reduced.

Barrier height change in GaAs Schottky diodes induced by piezoelectric effect

Abstract: A novel manifestation of piezoelectric effects in GaAs has been observed. The change of barrier height, φB, of Schottky diodes induced by uniaxial stresses, S, along 〈100〉, 〈011〉, 〈011〉, and 〈111〉 has been measured. Shifts in φB due to the appearance of piezoelectric polarization charges at the semiconductor‐metal interface for directions other than 〈100〉 are observed.

Schottky barrier heights of n-type and p-type Al/sub 0.48/In/sub 0.52/As

Abstract: The authors report electrical measurements on four different metal contacts which formed Schottky barriers to lightly doped complementary n- and p-type Al/sub 0.48/In/sub 0.52/As epitaxial material grown by molecular beam epitaxy on semi-insulating InP substrates. The Schottky contact metals studied were Au, Al, Pt, and tri-layer Ti/Pt/Au. The Schottky barrier heights varied from 0.560 eV for Al on n-type AlInAs to 0.905 eV for Al on p-type AlInAs, with intermediate values for the other metals studied. The sum of n- and p-type Schottky barrier heights for each metal contact ranged from 1.440 to 1.465 eV, in good agreement with the accepted Al/sub 0.48/In/sub 0.52/As bandgap value of 1.45 eV. >

On the Richardson constant for aluminum/gallium arsenide Schottky diodes

Abstract: Measurements have been made of the Richardson constant (A**) for Al/GaAs Schottky diodes in which the aluminum is deposited epitaxially by molecular beam epitaxy. These diodes are the nearest to ideal that have yet been reported. The value of (A**) for n‐type GaAs, after allowing for the temperature variation of the barrier height and for the effect of tunnelling, was found to be (0.41±0.15)×104 A m −2 K−2. This is much lower than the previously accepted value, and confirms the low value reported by Srivastava, Arora, and Guha. Since there is no possibility of an interfacial layer in our diodes, we believe the low value of A** to be an intrinsic property of the Al/GaAs interface. The value of A** for Al/p‐GaAs was found to be (7.0±1.5)×104 A m−2 K−2, which is lower than the theoretical value, though the discrepancy is not so large as for n‐type GaAs. Because of the uncertainty in A**, values of barrier hights obtained from C−2 vs V plots are likely to be more reliable than those deduced from I/V character...

Electrical Characterization of the Silicon‐Electrolyte Interface in the Conditions of Porous Silicon Formation

Abstract: A detailed experimental investigation of the electrical behavior of the silicon-electrolyte interface is presented, which leads to the conclusion that electrochemical dissolution of p-type silicon (doping range 10 15 cm −3 -3×10 19 cm −3 ) during porous silicon formation is mainly determined by the charge exchange at the silicon surface over the Schottky barrier formed at the interface through a thermoionic emission process. Impedance characterization of the interface allows the determination of the potential barrier formed between p-silicon and hydrofluoric acid solutions, and analysis of I(V) characteristics shows that the silicon-electrolyte junction behaves like a Schottky diode, with a particular dependence of the anodization potential vs. silicon doping which results from the voltage drop in the Helmholtz layer

Principles and technology of MODFETs

Abstract: Part 6 Measurements of transport properties of modulation doped heterostructures: Hall effect measurements interpretation of Hall measurements experimental Hall mobilities in (AI, Ga) As/GaAs MDHs - single interface structures, multiple interface structures experimental 2DEG density in AI,Ga) As/GaAs MDHs influences of substrate temperature on transport properties - ternary on top of binary - normal structures, binary on top of ternary - inverted structures the Dx centre effects in (AI, Ga) As/GaAs MDHs (AI,Ga) As/(In,Ga) As and (In,AI) As/(in,Ga)As MDHs high field electron mobility in MDHs high field electron volocity in MDHs - theoretical determination, experimental measurements. Part 7 Non-equilibrium characteristics of modulation loped fets: charge - voltage characteristics current - voltage (I-V) characteristics - normal regime, parallel conduction in the barier layer comparison with experimental I-V characteristics capacitance - voltage characteristics quasi-fermi level bending and its effect on Fet characteristics charge - voltage characteristics for invected modfets anomalies at low temperature (In,Ga) As/ (AI,Ga) as Modfet performance optimization enhanced Schottky barrier for Modfets. Part 8 Microwave characteristics of Modfets: device performance microwave modeling - small-signal model, large-signal model wave equation model - derivation of the wave-equation, solution of the wave equation, Y-parameter calculations, extraction of parameters needed for the AC model, comparison of the measured and calculated data, limitations of the microwave model noise modelling - the DC Fet model, Fet noise modeling, optimization of device parameters, evaluation of noise figures versus frequency, noise temperature. Part 9 Digital integrated circuits: basic inverters GaAs circuits - direct-coupled Fet logic (DCFL), buffered Fet logic (BFC), Schottky diode Fet logic (SDFL), source-coupled Fet logic (SCFL) modfet digital integrated circuits design and simulation of Modfet ICs - precursor logic circuits, comparator circuits, static-random access memory (SRAM) circuits, gate arrays short-channel effects radiation effects - radiation hardness of Modfest, radiation hardness of Modfet inverters and ring oscillators comparison with other technologies - ring oscillators, frequency divider, static random access memory (SRAM), projections.

Barrier height variation in Al/GaAs Schottky diodes with a thin silicon interfacial layer

Abstract: Al/n‐GaAs and Al/Si/n‐GaAs structures with thin silicon interfacial layers were grown in situ by molecular beam epitaxy and their electrical characteristics were measured. Effective barrier heights between 0.30 and 1.04 eV were determined through I‐V and C‐V measurements in the Al/Si/n‐GaAs structures under varying conditions of deposition of the silicon layer, in contrast to a barrier height of 0.78 eV without the silicon layer. The conduction‐band offset between Si and GaAs is estimated to be of the order of 0.3±0.05 eV. The results indicate that the Fermi level at the interface of GaAs on Si in the Al/Si/n‐GaAs structure is unpinned from its midgap value.

Optical determination of carrier density in pseudomorphic AlGaAs/InGaAs/GaAs hetero‐field‐effect transistor structures by photoluminescence

Abstract: A photoluminescence (PL) analysis of a highly degenerate two‐dimensional electron gas (2DEG) in pseudomorphic modulation‐doped AlGaAs/InGaAs/GaAs transistor structures is reported. The PL response from samples with one or two populated electron subbands is dominated by one or two spectral bands, respectively, with a high‐energy intensity cutoff. The spectral width varies linearly with the measured 2DEG sheet density ns or with a Schottky barrier depletion voltage, which directly reflects the two‐dimensional density of states (2DDOS) below the Fermi level. We used the effective electron mass from cyclotron resonance experiments to evaluate the 2DDOS and can thus directly determine ns from the spectral width via the 2DDOS. Independent ns values were obtained from Shubnikov–de Haas measurements and agree excellently with ns values from PL.

A simple high-speed Si Schottky photodiode

Abstract: Design, fabrication, and UV-heterodyne characterization of Ni-Si-Ni metal-semiconductor-metal (MSM) Schottky barrier photodetectors is reported. Planar detectors were fabricated, with a simple 3-level lithography process on bulk Si, in both simple-gap and interdigitated geometries with gap dimensions from 1 to 5 mu m. Frequency response of these devices was characterized using a CW-laser heterodyne system at 334.5 nm. For a 4.5- mu m interdigitated device, a 3-dB response of 16 GHz is measured, giving 22 GHz when deconvolved from the package/connector. A detailed theoretical model of the photodiode response incorporating effects of carrier transport and device geometry is in excellent agreement with the measurement. This model predicts a 86-GHz 3-dB response for the 1- mu m gap geometry devices. >

Pt-based gate enhancement-mode InAlAs/InGaAs HEMTs for large-scale integration

Abstract: The barrier heights of several n-InAlAs/metal Schottky contacts are discussed. A thin-Pt/Ti/Pt Au multilayer gate is proposed for InP-based InAlAs/InGaAs HEMTs. Its Schottky barrier height was measured as 0.83 eV, and it shows good threshold voltage stability. Performance measurements of an enhancement-mode HEMT fabricated using a 1.1- mu m-long multilayer gate indicate a threshold voltage of 0.05 V and a transconductance of 540 mS/mm. >

Pd-on-GaAs Schottky Contact: Its Barrier Height and Response to Hydrogen

Abstract: A Pd-on-GaAs Schottky contact was prepared by depositing palladium using a tungsten heater, rather than electron-beam heating, onto a GaAs surface. The interface composition was investigated by sputter Auger electron spectroscopy. An intermediate layer resulting from the reaction of Pd and GaAs was observed under certain conditions. The Schottky barrier height estimated from the measurements of forward current-voltage (I-V) or reverse capacitance-voltage (C-V) characteristics was found to depend on the interface structure. The response of the Schottky contact to hydrogen was found to be correlated with the barrier height. We pointed out that hydrogen can be used as a probe to the interface structure, whether metallic Pd or an intermediate material of Pd-Ga-As is in contact with GaAs. The observation was consistent with both p- and n-type GaAs.

Hydrogen sensor based on a Pt/GaAs Schottky diode

Abstract: A new sensitive hydrogen detector based on a Pt/GaAs Schottky barrier diode has been fabricated. When the device is implemented with an organic layer (polyetherimide), the diode sensitivity increases. The effects of temperature, hydrogen concentration and ambient atmosphere on the device responses are examined.