W.A. Anderson

Highly sensitive photodetector using porous silicon

A highly sensitive photodetector was made with a metal‐porous silicon junction. The spectral response was measured for the wavelength range from 400 nm to 1.075 μm. It was demonstrated that close to unity quantum efficiency could be obtained in the wavelength range of 630–900 nm without any antireflective coating. The detector response time was about 2 ns with a 9 V reverse bias. The possible mechanisms are discussed.

Temperature dependence of the electrical characteristics of Yb/p‐InP tunnel metal‐insulator‐semiconductor junctions

High barrier Yb/p‐InP metal‐insulator‐semiconductor (MIS) and metal‐semiconductor (MS) junctions were fabricated by evaporation of Yb on InP:Zn substrates. The capacitance‐voltage (C‐V) and current‐voltage (I‐V) characteristics of these devices were measured over a wide range of temperatures. From the room‐temperature forward I‐V data, the values of 1.06 and 1.30 for the ideality factor (n) were obtained for the MIS and MS diodes, respectively. The higher value of n was attributed to an order of magnitude higher density of interface states in the MS junction than in the MIS diodes. The I‐V/T data over the temperature range 190–400 K, indicated that the forward current transport in the Yb/p‐InP MIS junction was controlled by the thermionic‐field emission (TFE) mechanism. The analysis of the reverse saturation current I0 in terms of the TFE model provided a value of 1.07±0.03 V for the zero bias, zero temperature barrier height (φ0) which was in close agreement with the value of φ0=1.03±0.04 V, provided by ...

High-barrier height Schottky diodes on N-InP by deposition on cooled substrates

Ultrahigh barrier height (φB=0.96 eV) Schottky contacts to n‐InP, without an intentionally grown interficial oxide, were formed using metal deposition on a substrate cooled to as low as 77 K [low temperature (LT)]. φB = 0.46–0.52 eV for diodes deposited at room temperature (RT=300 K) agree well with previously published results, and give an ideality factor near unity. For the diodes deposited at LT=77 K, the leakage current density (J0) was reduced by more than 6–7 orders of magnitude with respect to the RT diodes. The φB for the LT diodes was increased from 0.48 to 0.96 eV for Pd metal and from 0.51 to 0.85 eV for Au metal, respectively. An alteration of the metal‐induced interface states, inhibition of surface segregation of the released In and P atoms, and very uniform metal coverage may be responsible for the distinct differences between the RT and LT diodes.

Reactively sputtered RuO2 thin film resistor with near zero temperature coefficient of resistance

Ruthenium oxide thin film resistors were reactively sputtered onto SiO2/Si substrates using d.c. magnetron sputtering. Resistors with near zero temperature coefficient of resistance (TCR) were realized by optimizing the sputtering conditions. Experimental results demonstrated that the TCR was a strong function of substrate temperature during sputtering. A critical temperature around 80°C during sputtering was found at which the TCR changed signs, i.e. a temperature dependence of semiconductor-like behavior of the resistors compared with metal-like behavior. The dependence of the TCR on the material properties of the films was analyzed using scanning electron microscopy, X-ray diffraction, and energy dispersive X-ray analysis. Films with amorphous structure usually gave a negative TCR but a positive TCR for the films with a polycrystalline structure. The resistors with near zero TCR were believed to have a microcrystalline structure.

Stability of tantalum nitride thin film resistors

Post-deposition rapid vacuum annealing of tantalum nitride (Ta 2 N) thin film resistors (TFR) was successful in improving the temperature coefficient of resistance (TCR) to ±5 ppm/°C with starting TCR at about −140 ppm/°C. A subsequent aging study revealed degradation of the nichrome (NiCr) contact interlayer. Two improved contact layers, TiW and Tamelox (Ta/NiCr), were compared. The structural grain growth induced by the annealing effect resulted in Ta 2 N films having 100–1000 A polycrystals in an amorphous matrix. The corresponding current conduction mechanisms were identified with a substrate-assisted tunneling model. The frequency response predicted potential applications to 100 GHz.

Sputter deposition of YBa2Cu3O7-x films on Si at 500 °C with conducting metallic oxide as a buffer layer

Superconducting YBa{sub 2}Cu{sub 3}O{sub 7{minus}{ital x}} thin films were deposited on Si substrates at 500 {degree}C by rf magnetron sputtering from a stoichiometric oxide target. Metallic oxide RuO{sub 2}, sputtered by reactive dc magnetron, was used as a buffer layer to nucleate the superconducting film and minimize the reactions between Si and superconductor. The as-deposited thin films, without further post high-temperature annealing, were completely superconductive at 79 K. Very smooth surface morphology was demonstrated by scanning electron microscopy. X-ray diffraction data indicated that the films had a randomly oriented polycrystalline structure. Auger electron spectroscopy did not reveal interdiffusion of elements in the three layers.

Low leakage current BaTiO3 thin film capacitors using a multilayer construction

Abstract Innovative device designs were used to fabricate low leakage ferroelectric BaTiO3 (BTO) thin film capacitors. BTO thin films with thicknesses ranging from 220 nm to 265 nm were deposited using reactive r.f. magnetron sputtering. A highly stable and conductive metallic oxide, RuO2, was used as the bottom electrode of the capacitors on SiO 2 Si substrates. Layers of BTO deposited at low temperature were amorphous and those deposited at high temperature above 600 °C were polycrystalline. Microcrystallization of amorphous BTO took place at a thermal treatment temperature of above 600 °C. Capacitors with a bilayer configuration of polycrystalline layers on microcrystalline layers showed a capacitance per unit area of around 2.4 × 105pF cm−2 and a leakage current density of (8.5 ± 0.5) × 10 −8 A cm −2 at a field intensity of 2 × 10 5 V cm −1 . A capacitance per unit area of around 1.4 × 10 5 pF cm −2 and a leakage current density of around 10−10A cm−2at a field intensity of 2 × 10 5 V cm −1 were achieved on the capacitors with a nanolayer configuration of amorphous layers on a number of stacked cycles of polycrystalline layers on microcrystalline layers.

High‐barrier height metal‐insulator‐semiconductor diodes on n‐InP

Metal‐insulator‐semiconductor diodes were fabricated using Pd, Ni, and Au contacts on n‐InP covered by a 40‐A chemically grown oxide. The oxide had a refractive index of 1.4–1.6 with a composition of mainly In2O3+some InPO3 near the surface and mixed oxide+InP near the interface. Pd devices gave the highest‐barrier height of 0.80 eV and the lowest reverse saturation current density of 3×10−8 A/cm2. Current‐voltage‐temperature and capacitance‐voltage‐temperature data gave temperature dependence of barrier height and revealed an interface state recombination current mechanism with surface states 0.4 eV above the valence‐band level. Richardson plots gave good straight lines when empirically corrected using barrier height divided by ideality factor.

BaTiO3 thin film capacitors deposited by r.f. magnetron sputtering

Abstract Barium titanate, BaTiO3, thin film capacitors were deposited by r.f. magnetron sputtering using a perpendicular arrangement of the substrate with respect to the target. Capacitors with a single-layer amorphous or polycrystal structure, a bilayer structure of amorphous/polycrystal, and a trilayer structure of amorphous/graded polycrystal/polycrystal were extensively investigated. Comparatively, the single-layer amorphous BaTiO3 capacitor demonstrated the highest breakdown voltage (as high as 2.5 × 106Vcm-1) but lowest dielectric constant of around 16. The single-layer polycrystal BaTiO3 capacitor displayed a much higher dielectric constant of above 300 but also revealed high leakage current which in turn reduced the breakdown voltage. By combining the advantages of the amorphous and polycrystal BaTiO3 films, bilayer and trilayer capacitors were produced, yielding superior electrical properties. An optimum thickness for the amorphous layer minimizes the reduction in effective dielectric constant while providing a low d.c. conductivity of 7.0 × 10 -11 Ω -1 cm -1 at a bias of 4 V and a high breakdown voltage of 1.9 x 106Vcm-1.

Study of Dynamics and Mechanism of Metal- Induced Silicon Growth

The present study addresses the mechanism of metal-induced growth of device-quality silicon thin films. Si deposition was performed by magnetron sputtering on a 25-nm-thick Ni prelayer at 525–625 °C and yielded a continuous, highly crystalline film with a columnar structure. A Ni disilicide intermediate layer formed as a result of the Ni reaction with Si deposit provides a sufficient site for the Si epitaxial growth because lattice mismatch is small between the two materials. The reaction between Ni and Si was observed to progress in several stages. The NixSiy phase evolution in a Ni:Si layer was studied by x-ray photoelectron spectroscopy, Auger electron spectroscopy, Rutherford backscattering spectrometry, transmission electron microscopy, and x-ray diffraction and found to be controlled by the Ni-to-Si concentration ratio at the growing front. After Ni is completely consumed in the silicide, continued Si deposition leads to the nucleation and growth of Si crystals on the surface of the NiSi2 grains. Th...