On the Current-Voltage Characteristic of an Ideal Metal-Semiconductor Schottky-Barrier Contact

The model of an ideal (without an intermediate layer and electron surface states) metal-semiconductor Schottky-barrier contact is numerically analyzed with allowance for the effect of image-force barrier-height lowering. It is shown that the nonlinear dependence of barrier height on the bias voltage inherent in this contact causes not only the deviation of the current-voltage (I-V) characteristic from an ideal one but also the so-called “low-temperature anomaly” — an increase in the I-V-characteristic ideality factor n and a decrease in the barrier height ϕ_bm measured from the saturation current as the temperature is decreased. A more exact equation for the I-V characteristic of the ideal contact is theoretically substantiated using parameters n and ϕ_bm in a wide temperature range.__________Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 81–88, March, 2005.     

Simultaneous formation of contacts and diffusion barriers for VLSI by rapid thermal silicidation of TiW

The formation of (Ti_xW_1–x)Si₂/(Ti_xW_1–x)N, by rapid thermal processing of Ti_xW_1–x on Si in an N₂ ambient is investigated. An activation energy of 1.7 eV is obtained for silicide formation. A distinct snow-ploughing of As atoms is observed during silicide formation whereas the interfacial B concentration decreases with increasing silicide formation temperature. The diffusion barrier properties of the (Ti_xW_1–x)Si₂/(Ti_xWi_1–x)N stack in contact with Al is investigated upon post-metal annealing. No interaction between the layers is found for temperatures as high as 475°C after 60 min. The improved thermal stability of the (Ti_xW_1–x)N layer in contact with Al is attributed to nitrogen blocking of the grain boundaries.     

Pt interlayer effects on Ni germanosilicide formation and contact properties

Ni and Ni(Pt) germanosilicide formation and their contact properties on n-type epitaxial Si_0.84Ge_0.16 have been studied in this work. It is revealed that compared to NiSi, NiSiGe has enhanced phase stability but worse morphology stability. It is also found that Pt incorporation in germanosilicidation improves the morphology of the germanosilicide film. The Schottky contact characteristics of NiSiGe and Ni(Pt)SiGe on n-SiGe were evaluated by current–voltage (I–V) technique at room temperature. NiSiGe/n-SiGe contact shows a Schottky barrier height (SBH) of 0.65 eV with little difference from that of NiSi/n-Si contact. However, the contact shows a reduced SBH with a markedly increased ideality factor and leakage current when annealing temperature increases to 650 °C, indicating thermal degradation of the contact quality. Pt incorporation increases the SBH to 0.73 eV. In addition, its diode parameters such as SBH, ideality factor, and reverse leakage show better conformity during the whole annealing temperature range (from 450 to 650 °C). Therefore, it is concluded that Pt interlayer between Ni and SiGe can modulate the barrier height of Ni germanosilicide and improve its contact properties.     

Effect of oxidation on the magnetic properties of Ni3Cr alloy

The effect of oxidation on magnetic susceptibility and electrical resistance was studied in samples of Ni₃Cr alloy which had been prehardened from 1066, 1190, and 1250°C. X-radio-graphic analysis of the samples was carried out. It was shown that the observed increase of the magnetic susceptibility of the alloy after oxidation in the temperature range 750–1050°C is related to the formation on the surface of the sample of a layer with a variable nickel content in the range Ni₃Cr to pure nickel.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 38–41, May, 1972.     

A new structure of In-based ohmic contacts ton-type GaAs

Electrical, structural and reaction characteristics of In-based ohmic contacts ton-GaAs were studied. Attempts were made to form a low-band-gap interfacial phase of InGaAs to reduce the barrier height at the metal/semiconductor junction, thus yielding low-resistance, highly reliable contacts. The contacts were fabricated bye-beam sputtering Ni, NiIn and Ge targets on VPE-grownn ⁺-GaAs film (1 m, 2 × 10¹⁸ cm^–3) in ultrahigh vacuum as the structure of Ni(200 Å)/ NiIn(100 Å)/Ge(40 Å)/n ⁺-GaAs/SI-GaAs, followed by rapid thermal annealing at various temperatures (500–900°C). In this structure, a very thin layer of Ge was employed to play the role of heavily doping donors and diffusion limiters between In and the GaAs substrate. Indium was deposited by sputtering NiIn alloy instead of pure In in order to ensure In atoms to be distributed uniformly in the substrate; nickel was chosen to consume the excess indium and form a high-temperature alloy of Ni₃ln. The lowest specific contact resistivity ( _c) of (1.5 ± 0.5) × 10^–6 cm² measured by the Transmission Line Method (TLM) was obtained after annealing at 700°C for 10 s. Auger sputtering depth profile and Transmission Electron Microscopy (TEM) were used to analyze the interfacial microstructure. By correlating the interfacial microstructure to the electronical properties, In _x Ga_{1– x}As phases with a large fractional area grown epitaxially on GaAs were found to be essential for reduction of the contact resistance.This work was supported by the National Natural Sciences Foundation of China (NSFC)     

Interfacial roughnes and alloy scattering in the InGaAs/InAlAs/InP system grown by ALE and LAMBE

Molecular beam epitaxial growth of In_xGa_1−xAs and In_yAl_1−yAs on Inp has been carried out by atomic layer epitaxy (ALE) and laser assisted molecular beam epitaxy (LAMBE). It is shown that these growth techniques have minimized both alloy clustering and interface roughness in the InGaAs/InAlAs system. Splitting of the PLE spectra indicates a roughness of 2–3 monolayers while transport measurements have placed an upper limit to the roughness at 4 monolayers.     

Approaches to diffusion barrier creation and trench filling for copper interconnection formation

The technique of copper filling of trenches which is based on the effect of the melting temperature decrease, depending on film thickness reduction, has been proved and demonstrated experimentally. An approach to diffusion barrier creation is proposed. Ta-W-N amorphous alloy has been selected as the barrier material for copper. This barrier layer keeps its properties in the Cu/Ta-W-N/TiSi₂/Si structure up to 800 °C, and in the Cu/Ta-W-N/SiO₂ structure up to 850 °C. The temperature for copper filling of the trenches is shown to be significantly lower than the temperature of bulk copper melting, and to depend on the thickness of the film. It is determined that this effect is caused not only by the lowering of the phase changing temperature as a result of the thinning of the film, but also by the system tendency to optimize its form by the change in the ratio of the surface and volume energies. When the thickness is 50 nm the temperature of filling is 750 °C, when it is 100 nm – 850 °C. However, this temperature reduction is not enough for use of the presented approach in UVLI technology, and further development of this approach is required, including possible combination with other filling methods. PACS 66.30.Ny; 68.35.Rh; 68.60.Dv     

Characteristics of SrBi2Ta2O9 ferroelectric films on Si using LaAlO3 thin film as an insulator

Metal–ferroelectric–insulator–semiconductor structures using LaAlO₃ (LAO) layers as an insulating barrier have been investigated. LAO films were deposited on n-Si substrates by low-pressure metalorganic chemical vapor deposition (MOCVD). SrBi₂Ta₂O₉ (SBT) films were prepared as ferroelectric layers at a low processing temperature of 650 °C by a metalorganic decomposition method. The MOCVD-derived LAO buffer layer shows an amorphous structure, relatively high dielectric constant, and good electrical properties. Au/SBT/LAO/n-Si exhibits a larger counterclockwise C–V memory window of 3.7 V and a lower leakage-current density of 2.5×10^-8 A/cm² at an applied voltage of 10 V. It has been confirmed that the hysteresis loop is caused by ferroelectricity. The Auger electron spectrometry depth profile indicates that the introduction of the LAO buffer layer prevents the interfacial diffusion between SBT and the Si substrate effectively and improves the interface quality. PACS 77.84.Dy; 81.15.Fg     

Calculation of current–voltage characteristics of a Cu (II) complex/n-Si/AuSb Schottky diode

In this study, Cu (II) complex/n-Si structure has been fabricated by forming a thin organic Cu (II) complex film on n-Si wafer. It has been seen that the structure has clearly shown the rectifying behaviour and can be evaluated as a Schottky diode. The contact parameters of the diode such as the barrier height and the ideality factor have been calculated using several methods proposed by different authors from current–voltage (I–V) characteristics of the device. The calculated barrier height and ideality factor values from different methods have shown the consistency of the approaches. The obtained ideality factor which is greater than unity refers the deviation from ideal diode characteristics. This deviation can be attributed to the native interfacial layer in the organic/inorganic interface and the high series resistance of the diode. In addition, the energy distribution of the interface state density (N_ss) in the semiconductor band gap at Cu (II) complex/n-Si interface obtained from I–V characteristics range from 2.15 × 10¹³ cm⁻² eV⁻¹ at (E_c − 0.66) eV to 5.56 × 10¹² cm⁻² eV⁻¹ at (E_c − 0.84) eV.     

The effect of carrier concentration in the semiconductor on the voltage-current characteristics of Schottky barrier diodes at low temperatures

We report the results of a study of voltage-current characteristics of gallium arsenide metal-semiconductor Schottky barrier structures, in which palladium and W-Ni alloy were electrochemically deposited in SiO₂ windows to form the barrier. It is demonstrated that the voltage-current characteristics are significantly distorted at low temperatures. The observed behavior of the voltage-current characteristics at low temperatures —the appearance of excess current and the increase in the ideality factor with carrier concentration in the excess current regime —is explained by a model in which peripheral mechanical stresses in the contacts lower the potential barrier height on the periphery of the contacts.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No, 10, pp. 87–93, October, 1986.     

Investigation of the total conductivity of heterolasers with a strip contact with reverse bias

The electrical properties of DGS lasers with a strip contact on the basis of Al_xGa_1–xAs with reverse bias, including the breakdown domain, are investigated experimentally. It is shown that the dependence of the barrier capacitance on the voltage is described well by the relationship C_b = C_o/(1– V/V_k)^1/m, where C_o = (50–110) pF and m = 2.0–2.7. The capacitance for zero bias C_o depends weakly on the frequency in the range 660 kHz–60 MHz. The active conductivity for V = 0 increases by approximately an order as the frequency changes from 15–60 MHz. The dependence of the active and reactive components of the total laser conductivity on the current is investigated at fixed frequencies in the range mentioned. The weak dependence of the reactive component on the current is noted in the breakdown regime associated with stabilization of the reverse voltage on the laser. Possible physical mechanisms responsible for the kind of characteristics obtained are discussed.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 52–56, November, 1983.     

Effect of hydrostatic pressure on characteristics of GaAs-Ge1−x(GaAs)x heterojunctions

The conditions of obtention of nGaAs-pGe_1–x(GaAs)_x alloy heterojunctions and the behavior of the electrical and photoelectric characteristics of these structures under hydrostatic compression were investigated. It is shown that the mechanism of current transport in this structure is of the tunneling-recombination type. The pressure coefficients of the forbidden gap width in the solid solution, the effective electron mass in gallium arsenide, and the height of the potential barrier were experimentally determined.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 90–93, February, 1979.     

About some optical properties of AlxGa1−xN /GaN quantum wells grown by molecular beam epitaxy

Wurtzitic nitride quantum wells grown along the (0001) axis experience a large Stark effect induced by the differences of spontaneous and piezoelectric polarizations between the well and barrier materials. In Al_xGa_1−xN/GaN quantum wells, due to the adverse actions of quantum confinement, that blue-shifts transition energies, and of the Stark field, that red-shifts them, the transition energies are nearly independent of barrier compositions at a particular well thickness (L₀2.6 nm), at least for x≤0.3. The effect of alloy fluctuations is then minimal, as reflected by a minimum in the quantum well luminescence linewidth when LL₀ for wells grown by molecular beam epitaxy on silicon or sapphire substrates. We use this effect to estimate the average variances of well widths and alloy composition fluctuations. Both results are in good agreement with, respectively, a scanning tunneling microscopy study of GaN (0001) surfaces, and estimates based on the lateral extent of the quantum well excitons.We then discuss the optical properties of the Al_xGa_1−xN barrier material, with particular emphasis on the symmetry of the valence band maximum (Γ₉ or Γ₇). We show that it may play an important role in the apparent barrier luminescence efficiency. We analyse the possible consequences of the barrier Γ₉–Γ₇ crossover on the Al_xGa_1−xN/GaN quantum well properties.     

Analysis of the actual Schottky-barrier contact model in a wide temperature and bias-voltage range

We numerically study the model of an actual metal-semiconductor Schottky-barrier contact with an interfacial layer and surface states (the Bardeen model). Our study is based on the previously developed view that the anomalies of the characteristics of such a contact is a consequence of the nonlinear dependence of the barrier height on the bias voltage. It is shown that on this basis it is possible to explain in a natural way the so-called low-temperature anomaly in metal-semiconductor Schottky-barrier contacts (an increase in the ideality factor of the current-voltage characteristic and a decrease in the measured barrier height with decreasing temperature), as well as the relationship between different barrier heights characterizing a contact, namely, among the actual barrier height, which is measured from a saturation current, the flat-band barrier height, and the barrier height measured from a C — V characteristic.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 47, No. 9, pp. 769–783, September, 2004.     

Electrical behavior of size-controlled Si nanocrystals arranged as single layers

A metal–oxide–semiconductor structure containing a single layer of size-controlled silicon nanocrystals embedded into gate oxide was fabricated. Size control for the silicon nanocrystals was realized by using a SiO₂/SiO/SiO₂ layer structure with the embedded SiO layer having the thickness of the desired Si nanocrystals and using a high-temperature annealing for forming the silicon nanocrystals. Current–voltage, capacitance–voltage, and conductance–voltage characteristics were measured for a sample containing 4-nm-sized crystals. From the Fowler–Nordheim plot an effective barrier height of 1.6 eV is estimated for our silicon nanocrystals. Electron trapping, storing, and de-trapping in silicon nanocrystals were observed by capacitance–voltage and conductance–voltage measurements. The charge density was measured to be 1.6×10¹² /cm², which is nearly identical to the silicon-nanocrystal density measured approximately via a transmission electron microscopy image. Conductance measurements reveal a very low interface charge of our structure. PACS 72.80.Sk; 73.63.Bd; 73.40.Qv     

On the Phase Transformations in Cr–FeB and Fe–CrB Systems at High Temperature

The solid state interactions occurring at high temperature in the Cr–FeB and Fe–CrB systems were studied by transmission Mössbauer and X-ray diffraction techniques on samples prepared by powders carefully mixed, cold-compacted and then treated at 1000°C for times up to 16 h. In the Cr–FeB system, iron atoms liberated by the substitutional diffusion of Cr into FeB lattice preferentially destabilize the iron monoboride with formation of Cr-containing Fe₂B. In the Fe–CrB system, chromium atoms liberated by the substitutional diffusion of Fe into CrB lattice interacts with iron forming an Fe–Cr metal alloy. Moreover, zones of Cr-containing FeB and Fe₂B form at the contact between metal iron and chromium monoboride, and tend to disappear as iron is consumed by the alloying process.     

Barrier layers as resonators on deep centers

A response is given to the paper of L. S. Barman and A. A. Lebedev (Izv. Vyssh. Uchebn. Zaved. SSSR, Fiz., No. 12, 88–90 (1989)), and it is shown that the arguments given there are not satisfactory. New experimental data have been obtained for n⁺-p junctions in Si, where square reverse-bias pulses U < U_res are observed to shift the DLTS peaks. Here U_res is the magnitude of the pulse for which all activation-drift processes become activation-transit processes and the barrier layer operates as a freshly prepared resonator on deep centers (see the paper by P. T. Oreshkin, Elektronnaya Tekhnika, Ser. 3, Mikroelektronika, No. 4 (128), 12–20 (1988).Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 21–25, November, 1990.     

Transition temperature to crystal phase of Al86Mn14 quasicrystal ultrafine particles determined by direct observation and characterization of surface oxide layer

Al–Mn quasicrystal ultrafine particles can be produced by the advanced gas evaporation method (AGEM), which is a method of preparing ultrafine alloy particles by coalescence growth among the particles near the evaporation sources. We investigated the phase transition temperature from a quasicrystal to a stable crystal, by examining successive electron diffraction patterns of an ultrafine particle in an in situ experiment using a transmission electron microscope. In spite of the report that the Al₈₆Mn₁₄ quasicrystal transforms into the crystal phase at around 400–670 °C on thin film specimens, the quasicrystal ultrafine particle transformed at 800 °C, i.e., the quasicrystal ultrafine particle is more stable. Since the cross-sectional view of the surface oxide layer of the quasicrystal ultrafine particles can be easily observed, the surface oxides of η-Al₂O₃ and MnO were characterized as a result of the oxidation of residual atoms on the surface of the produced alloy particles including the quasicrystals. The conditions required for Al–Mn quasicrystal ultrafine particle formation by the AGEM can be estimated under the cooling rate of 10⁵ K/s.     

Free Surface and Interface Thermodynamics of Liquid Nickel in Contact with Alumina

Sessile drop experiments of Ni and Ni(2at.%Al) were conducted under controlled working conditions, at 1500°C, P(O₂) 10^–9 Torr. It is shown that Al and oxygen atoms engaged in the capillary driven mass transport at the interface have a significant impact on the surface/interface thermodynamics. The surface energy of liquid Ni determined from experiments in which Ni comes into contact with Al₂O₃ is significantly lower than that of high purity Ni, due to the segregation of Al. The free energy of segregation of Al to the free surface of Ni ( G _S) was found to range from –164 to –152 kJ/mol, indicating a relatively strong tendency for segregation of Al to the free surface of Ni(Al). It is proposed that an Al(O)-rich liquid layer forms adjacent to the Ni-Al₂O₃ interface, which improves interfacial adhesion. In the Ni(Al)-Al₂O₃ system, an increase in the Al content of the alloy leads to the improvement of both wetting and adhesion of the alloy on the ceramic, correlating with the improvement in the interface strength after solidification.     

High-temperature operation of AlGaInAs/InP lasers1994

We discuss the design of uncooled lasers which minimizes the change in both threshold current and slope efficiency over the temperature range from–40 to +85°C [1]. To prevent carrier overflow under high-temperature operation, the electron confinement energy is increased by using the Al _x Ga _y In_1–x–y As/InP material system [1] instead of the conventional Ga _x In_1–x As _y P_1–y /InP material system. Experimentally, we have investigated strained quantum well lasers with three different barrier layers and confirmed that the static and dynamical performance of the lasers with insufficient carrier confinement degrades severely under high-temperature operation [2]. With an optimized barrier layer, the Al _x Ga _y In_1–x–y As/InP strained quantum well lasers show superior hightemperature performance, such as a small drop of 0.3 dB in slope efficiency when the heat sink temperature changes from 25 to 100°C [3], a maximum CW operation temperature of 185°C [4], a thermally-limited 3-dB bandwidth of 13.9 GHz at 85°C [2], and a mean-time-to-failure of 33 years at 100°C and 10 mW output power [5].