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.     

Offset frequency stabilization of RF excited waveguide CO2 laser arrays

A close-packed array of waveguide lasers provides an offset frequency which is inherently more stable than that from independent devices, and permits difference frequency tuning based on the tilting of a common resonator mirror. Examples are given for two- and three-channel arrays. Passive stability of the beat frequencies between channels generated by this tuning method is shown to be good, and for two channel arrays was further enhanced by using an electronic stabilization loop. A simple model of the control loop is formulated to express the relationship between the loop parameters and resultant improvement in frequency stability. The model parameters are compared to experimental results through Allan variance measurements. An Allan variance minimum of 20 Hz has been achieved for the two-channel system and areas for further improvements are considered     

Scaling the Si MOSFET: from bulk to SOI to bulk

Scaling the Si MOSFET is reconsidered. Requirements on subthreshold leakage control force conventional scaling to use high doping as the device dimension penetrates into the deep-submicrometer regime, leading to an undesirably large junction capacitance and degraded mobility. By studying the scaling of fully depleted SOI devices, the important concept of controlling horizontal leakage through vertical structures is highlighted. Several structural variations of conventional SOI structures are discussed in terms of a natural length scale to guide the design. The concept of vertical doping engineering can also be realized in bulk Si to obtain good subthreshold characteristics without large junction capacitance or heavy channel doping     

Photogeneration of High Pretilt Angles of Nematic Liquid Crystals by Non‐Polarized Light Irradiation of Azobenzene‐Containing Polymer Films

A vertical‐alignment (VA) cell of nematic liquid crystals (LCs) was prepared using photoirradiated thin films of a poly(methacrylate) with mesogenic moieties of 4‐trifluoromethoxyazobenzene as the side chains. Optical anisotropy was generated by oblique irradiation of the azobenzene‐containing polymer films with non‐polarized UV light, followed by annealing treatment to enhance the photodichroism, which displayed thermal stability. The combination of oblique exposure to non‐polarized UV light and subsequent annealing treatment brought about high pretilt angles of nematic LCs so that a photoaligned VA LC cell was fabricated. The photopatterned LC cell exhibited electro‐optical properties with excellent optical quality when a voltage was applied even after heating at 100 °C for several hours.     

Optical properties of undoped n-AlGaN/GaN superlattices as affected by built-in and external-electric field and by ar-implantation-induced partial disordering

High-resolution x-ray diffraction patterns and 90 K microcathodoluminescence (MCL) spectra were taken for undoped, symmetric AlGaN/GaN superlattices (SLs) with GaN quantum-well (QW) widths of 35 Å and 80 Å. The short-period SL spectra were blue shifted by about 60 meV compared to the GaN substrate, and the magnitude of the blue shift was increased by about 20 meV by application of a reverse bias of ?3 V (electric field of about 4 · 10⁵ V/cm) to a Schottky diode prepared on this SL. A small red shift of about 40 meV compared to GaN was observed for the long-period SL. The two latter observations were interpreted as manifestations of the presence of a strong built-in piezoelectric field, giving rise to the quantum-confined Stark effect (QCSE). Partial disordering of the short-period SL was observed after Ar ion implantation (energy 150 keV, dose 8·10¹³ cm^?2 and 80 keV, 2·10¹³ cm^?2) and subsequent annealing at 1000°C for 3 h under the protective layer of Si₃N₄. However, it was observed that this partial disordering was accompanied by strain relaxation via formation of misfit dislocations or cracks.