An investigation of molecular beam epitaxy “in-situ” grown Ag/GaAs schottky diodes

Electrical properties of molecular beam epitaxy “in-situ” grown Ag on (001) GaAs Schottky diodes were investigated. X-ray rocking curves show a (111) main peak for “in-situ” Ag grown at low temperature. During annealing, the main peak of Ag rotates from (111) to (200) to closely match that of the underlying GaAs lattice. The barrier height, 0.991 eV (determined by C-V measurement), decreases whereas doping concentration increases with increasing annealing temperature. Interdiffusion and the formation of some compound phases were also observed during annealing. A simple model, in which Ga dissociates from GaAs resulting in an increase in uncompensated ions at the metal-semiconductor interface, is proposed to explain the observation that carrier concentrations increase after annealing.     

Design of an Optimal Unknown Input Observer for Load Compensation in Motion Systems

Recently, several model‐based control designs have been proposed for motion systems and computerized numerical control (CNC) machines to improve motion accuracy. However, in real applications, their performance is seriously degraded when significant disturbances or cutting forces are applied. In this paper, we derive straightforward design procedures for a general‐structured unknown input observer (UIO) which perfectly decouples the effect of the external disturbance from the state estimation. Furthermore, we derive the optimal UIO by minimizing the estimation errors for both the state and the disturbance via the Riccati equation. Experimental results show that the performance of alladvanced motion controllers suffers when external loads are applied. By compensating for the disturbance of a servo motor using the proposed optimal‐UIO, the original contouring accuracy, which is degraded by the external loading, can be successfully recovered.     

Improved Extraction Efficiency of Light-Emitting Diodes by Modifying Surface Roughness With Anodic Aluminum Oxide Film

An anodic alumina oxide (AAO) film with nano-roughening is added on the top window layer of AlGaInP light-emitting diodes (LEDs) to improve the light extraction of the device. The AAO film has a natural porosity to provide light scattering centers at the surface, allowing an increase of light emission intensity with no loss of or damage to the semiconductor material. Further, the fabricated AAO film with a refractive index is about which is intermediate between those of air and the window layer of GaP. By inserting this layer between the ambient and GaP, it broadens the critical angle for light emission and reduces internal reflection. Experiments with laboratory-fabricated AlGaInP devices of conventional design demonstrated a 32% improvement in the luminous intensity at 20 mA for the device with the AAO layer. This letter shows by theory and experiment that AAO films can be used as a low-cost, easily implemented surface nano-roughening for improving extraction efficiency of AlGaInP LEDs.     

Direct bonding of recessed-structure SAW filter on silicon substrate

A procedure for fabricating a recessed surface acoustic wave (SAW) device coupled with silicon substrate is reported. The recessed structure is stable and rugged enough against the bonding process, and it can be applied to integrate a semiconductor device into one chip by a direct bonding technique. In this paper, the tensile strength of silicon (Si)-to-recessed-SAW filter is measured, and the performance of the device is discussed.     

Notch filters with novel microstrip, triangle-type resonators

A novel notch filter is designed and fabricated using novel microstrip, triangle-type resonators. The main advantage of the new notch filter is superior microwave characteristics in increasing the frequency of the third harmonic response, as demonstrated in simulations using fullwave electromagnetic (EM) simulators. The novel notch filter is demonstrated using the following frequency characteristics: central frequency f/sub 0/ = 1.975 GHz, a 3 dB bandwidth of 39.5%, and an insertion loss S/sub 21/ of -54.273 dB. The experimental and simulation results closely correspond to each other. The superior features of the proposed filter make it suitable for use in microwave communication systems and other applications.     

A novel cross-shape DGS applied to design ultra-wide stopband low-pass filters

This letter presents a novel low-pass filter with an ultra-wide stopband. The proposed filter is comprised of a new cross-shape defected ground structure (CSDGS). By using this structure, the filter not only supports conventional DGS performances with a sharp rejection, but also exhibits an ultra-wide stopband. For the deigned low-pass filter, an insertion loss of less than 2dB from dc to 3.5GHz and the rejection is better than 20dB from 4.3 to 15.8GHz. Predicted performances show widened and deepened stopband beyond the low passband. Furthermore, it is confirmed by measurement.     

A PCB-compatible 3-dB coupler using microstrip-to-CPW via-hole transitions

A 3-dB coupler by implementing microstrip-to-coplanar waveguide (CPW) via-hole transitions is proposed. The proposed coupler, with the advantages of wider coupled line widths and spacing without using any bonding wires, can eliminate the uncertain factors of conventional Lange couplers caused by the printed circuit board (PCB) manufacturing processes. The proposed coupler can be easily fabricated on a single-layer PCB substrate instead of using multilayer substrates. Good agreements between the simulation and the measurement in the frequency range from 0.45 to 5 GHz can be achieved. The measured results at the center frequency of 2.4 GHz have the return loss better than -15dB; the insertion loss of coupled and direct ports is about 3/spl plusmn/ 0.2dB and the relative phase difference of 89/spl plusmn/0.3/spl deg/. The dimension of the coupler is 3.1cm /spl times/ 1.8cm.     

N-shaped negative differential resistance in a transistor structurewith a resistive gate

Voltage-controlled negative differential resistance (NDR) characteristics in a N-AlGaAs/p⁺-GaAs/n-GaAs transistor structure are proposed and demonstrated. The gate, made using self-aligned p-type diffusion, is placed in the n-GaAs collector layer instead of the p⁺-GaAs base layer, resulting in a so-called resistive gate. For a fixed gate voltage, the device current is modulated by the applied anode voltage. Under appropriate gate voltage with respect to the anode, the device shows good voltage-controllable NDR characteristics, including large peak-to-valley current ratios (PTV's) and a voltage extension in the N-shaped curve which is equivalent to the common-emitter breakdown voltage in a transistor. A numerical model based on the transistor model for the carrier transport in this device, taking account of the influence of the applied anode voltage on the gate, is proposed. The experimental results show large room temperature PTV's (e.g., 140 at a gate bias of 1.5 V) and large voltage extension in N-shaped curves (about 9 V). Reasonable agreement between theoretical and experimental results is observed