New generation of hydrotreating catalysts

Translated from Khimiya i Tekhnologiya Topliv i Masel, No. 2, pp. 2–4, February, 1991.     

Pulse trimming of thin-film resistors

Resistivity decreases can be induced in Cr-SiO films by current pulses of short duration. Precision resistance measurements between pulses permit trimming of film resistors to 0.1 percent in less than one second, provided pulse power, duration, and frequency are adjusted properly. A trimmer system that contacts several resistors through multiple probes and controls the process through a paper-tape reader is described. Pulse trimming has been applied to film resistors ranging from pure Cr up to Cr-40 mole % SiO. After annealing at 400°C, additional resistance decreases of at least 20 percent are possible with all compositions containing SiO. The interval between 15 and 30 mole % SiO is most suitable because substantial resistance changes are obtained at pulse powers well below the limits at which resistors burn out.     

Self- and mutual admittances of two identical circular loop antennas in a conducting medium and in air

The normalized self- and mutual admittances of two identical bare circular loop antennas have been evaluated when the loops are immersed in either air or an infinite homogeneous conducting medium. By decomposing the voltage and current into symmetric and antisymmetric components, the simultaneous integral equations for the distribution of current along the loop have been converted into a single integral equation similar to that for the isolated circular loop antenna which has already been studied. The computed results are presented graphically. The measured results are in good agreement with theory.     

Far infrared optical properties of amorphous semiconductors As−S systems

Far infrared reflection, Raman, and Brillouin spectra of amorphous semiconductor As?S systems are measured. From the reflection spectra, the optical constants are calculatured by the Kramers Kronig analysis. The existence of some intermediate range interaction among molecular units AsS₃ is suggested. From the analysis of the Boson peak at low frequency region in Raman scattering, the correlation length is obtained to be ca. 6 Å. From the absorption coefficient in the low frequency region about 3% fluctuation of charge is suggested for As₂S₃ by schlömann theory.     

Fully ion-implanted abrupt pn junction on semi-insulating InP

We report a fully ion-implanted pn junction using Si for n-implant and P/Be co-implant for a shallow p+ surface layer. C/V measurements indicate abrupt junction behaviour. Mesa diodes were fabricated and showed an ideality factor of two, small leakage current and avalanche breakdown at reverse bias greater than 40 V.     

Film digitization aliasing artifacts caused by grid line patterns

Sampling a radiographic film containing grid line patterns during digitization may produce aliasing artifacts (Moire pattern). The authors propose a mathematical model based on the laser spot size of the digitizer, the distance and the angle between the grid line and the sampling direction to predict the amplitudes and the frequencies of aliasing artifacts. The predicted results are compared to the experimental results. Effective ways of avoiding or reducing aliasing artifacts without sacrificing too much image quality are proposed.     

Comparison of nonlinear MESFET models for wideband circuit design

The Curtice quadratic, Materka, Statz, and Rodriguez nonlinear models are compared from DC, CV, and RF points of view, to determine which is the most suitable for nonlinear wideband circuit design. For this comparison, GaAs MESFETs of various sizes are employed. These include devices of varying gate widths, gate lengths, number of fingers, and pinch-off voltages     

InGaAs-InP P-I (MQW)-N surface-normal electroabsorption modulatorsexhibiting better than 8:1 contrast ratio for 1.55-μm applicationsgrown by gas-source MBE

We report growth of In_0.53Ga_0.47 As-InP multiple quantum well (MQW) modulators operating at 1.55 μm for fiber-to-the-home applications. By employing a 200-period InGaAs-InP MQW stack in the intrinsic region of a p-i-n structure and working in reflection, we have been able to realize surface-normal modulator devices that exhibit better than an 8:1 contrast ratio. This is the highest contrast ratio reported to date for this type of device working at this wavelength     

Losses in GaInAs(P)/InP and GaAlSb(As)/GaSb lasers--The influence of the split-off valence band

GaInAs(P)/InP and GaAlSb(As)/GaSb are interesting material systems for long wavelength optical fiber communication. However lasers fabricated from these materials exhibit a substantially higher temperature dependence of the threshold current than GaAs/ GaAlAs lasers ("T0-problem"). lntervalence band absorption and CHSH-Auger-recombination have been suggested as two possible causes for the strong temperature dependent losses in long wavelength lasers. Both mechanisms, if present, should lead to a population of the split-off valence band. In GaInAsP/InP lasers, we have studied this population by directly observing the radiative high-energy recombination of electrons with holes in the split-off valence band. In the case of the band structure of GaAlSb(As), the band gap energy E0is close or equal to the spin-orbit splitting energy Δ0, which favors hole-Auger recombination and intervalence band absorption, as confirmed by our experimental results.     

Postgrowth heat-treatment effects in high-purity liquid-phase-epitaxial In0.53Ga0.47As

Heat treatment at 670°C for 20 min has been performed on high-purity In0.53Ga0.47As/InP: Fe layers grown by different melt-baking schemes. Layers with higher purity (?77 K ? 55000 cm2/Vs) exhibit increased resistivity and the presence of a deep level after the heat treatment. It is possible that the deep level, apparently 0.56 eV above the valence band, results from Fe outdiffusion from the substrate.