Surface-wave amplifier with improved geometry

A surface-wave amplifier is proposed, in which an array of transverse conducting bars couples a narrow semiconductor strip to a broad region of piezoelectric substrate.     

Wire and strip conductors over a dielectric-coated conducting ordielectric half-space

The complex wavenumber and characteristic impedance are determined for a wire or flat strip over a dielectric-coated half-space that can be a conductor or a dielectric with large permittivity. Elevated microstrip is an example of the configuration. The properties of the wire as an antenna or transmission lines are determined from those of the insulated antenna with a two-layer eccentric insulation. The theory is extended to the strip conductor with the help of a comparison of the tubular and strip conductors over a perfectly conducting half-space     

A theoretical analysis of self-sustained pulsation phenomena innarrow-stripe semiconductor lasers

Phenomena of the self-sustained pulsation are being utilized for reduction of the excess noise in the semiconductor injection laser. The generating mechanism of the self-sustained pulsation in semiconductor lasers having a narrow strip structure was theoretically analyzed. The pulsation is generated by the existence of the active region as well as the saturable absorbing regions located outside of the active region. The width of the active region (stripe width) should be narrower than several microns in a GaAs laser to get the pulsation. The gain guiding or the antiindex guiding with narrower active region is profitable to get higher operation keeping the pulsation     

Effect of surface recombination on the transient decay of excess carriers produced by short wavelength laser pulses

Effect of surface recombination on the transient decay of excess carriers injected very near to the surface region has been analysed for a semi-infinite semiconductor sample. The one dimensional continuity equation for the excess minority carriers has been solved analytically assuming that the surface recombination is important only on the front surface from which the excess carriers are injected. The decay of total excess carrier charge as a function of time is calculated for various values of the surface recombination velocities. It is found that values of S lower than 10³ cm/sec. have little effect on the decay of total excess charge and the decay is exponential. For values of S larger than 10⁴ cm/sec. the initial decay of excess charge is much faster and is dominated by the surface recombination. However, if one waits long enough for the excess carrier to diffuse into the semiconductor the decay becomes exponential when the excess charge decays to about 5% of its initial value. This exponential decay can be used to determine the excess carrier lifetime fairly accurately. A source of error in such experiments may arise from the heating of the silicon sample by the laser pulse. This effect, however is negligible for short duration pulses of low average power.     

Optoelectronic gating of microwave signals using a silicon microstrip shunt modulator

A new silicon microstrip modulator for optoelectronic gating of microwave signals is described. Gating infrared pulses produces a small semiconductor region of high photoconductivity, which shunts the microstrip transmission line if special strip conductor structures are used. Theoretical and experimental results were found to agree fairly well.     

Depletion layer effects in the open-circuit- voltage-decay lifetime measurement

There is a renewal of interest in open circuit voltage decay as a technique for determining the base region minority carrier lifetime in semiconductor diodes. Although the existing theory of open circuit voltage decay provides a substantial foundation for interpreting the experimental data, major features of the decay curves of real silicon diodes cannot be satisfactorily explained unless depletion layer effects are taken into account. Theoretical decay curves are calculated to show the effects of depletion layer capacitance and recombination current on the otherwise ideal open circuit voltage decay. From these and from experimental decay curves, it is shown that each of these depletion layer effects is significant only below a threshold junction voltage that depends upon material parameters of the device.     

High-power transverse micro-stack weakly coupled laser diode bars

Transverse micro-stack semiconductor laser bars are put forward to improve the output optical power of semiconductor laser bars at low injection current. Micro-stack tunnel regeneration tri-active region laser structure was grown by metal organic chemical vapor deposition (MOCVD) and laser diode bars with 50% fill factors were fabricated. Experiments show that the insulated recesses strongly affect the properties of the bars. When the recess depth is less than 1.13 μm, the bars do not work well. By optimizing the insulated recess depth, threshold current can be reduced to 7.05 A, the optical power exceeds 79 W under 50 A driving current and the slope efficiency reaches 1.81 W/A.     

Transient temperature measurements and modeling of IGBT's undershort circuit

This paper discusses the estimation of possible device destruction inside power converters in order to predict failures by means of simulation. The study of insulated gate bipolar transistor (IGBT) thermal destruction under short circuits is investigated. An easy experimental method is presented to estimate the temperature decay in the device from the saturation current response at low gate-to-source voltage during the cooling phase. A comparison with other classical experimental methods is given. Three one-dimensional thermal models are also studied: the first is a thermal equivalent circuit represented by series of resistance-capacitance cells; the second treats the discretized heat-diffusion equation; and the third is an analytical model developed by building an internal approximation of the heat-diffusion problem. It is shown that the critical temperature of the device just before destruction is larger than the intrinsic temperature, which is the temperature at which the semiconductor becomes intrinsic. The estimated critical temperature is above 1050 K, so it is much higher than the intrinsic temperature (~550 K). The latter value is underestimated when multidimensional phenomena are not taken into account. The study is completed by results showing the threshold voltage and the saturation current degradation when the IGBT is submitted to a stress (repetitive short circuit)     

Theoretical model for a microsctip optoelectronic switch

A theoretical model is given to represent the active part of either an optoelectronic switch, similar to those described by Auston el al., or an optoelectronic gate such as the one we developed. These devices consist mainly of a microstrip line, with a characteristic impedance of 50 ?, which is deposited on a high-resistivity semiconductor. The centre strip has a break, creating a gap which can be illuminated by an optical laser pulse. The latter generates an electron-hole plasma of high density at the surface of the semiconductor, allowing the transmission of a signal across the gap.     

Theory of space-harmonic traveling-wave interactions in semiconductors

Strong coupling can be obtained between slow space-charge waves in thin biased semiconductors and long-wavelength microwave fields, if the semiconductor is overlaid with an insulated periodic mosaic of tiny metal stripes. Microscopic field perturbations are represented by a set of slow space-harmonic waves traveling in opposite directions, with a standing-wave interference pattern which matches the periodicity of the mosaic. When the carrier drift velocity is approximately synchronized with one of the space-harmonic waves, interaction is enhanced, space-charge waves may be induced, negative-resistance effects may appear, and power may be coupled from the semiconductor into external microwave networks. Theory indicates that the principle can be used to obtain microwave amplification or oscillation in thin biased layers of normal semiconductors such as silicon or germanium. It may also be possible to couple efficiently in this way to traveling Gunn-effect domains in extensive thin layers of gallium arsenide.     

Finite-Difference Analysis of Rectangular Dielectric Waveguide Structures

A class of dielectric waveguide structures using a rectangular dielectric strip in conjunction with one or more layered dielectrics is analyzed with a finite-difference method formulated directly in terms of the wave equation for the transverse components of the magnetic field. This leads to an eigenvalue problem where the nonphysical, spurious modes do not appear. Moreover, the analysis inclndes hybrid-mode conversion effects, such as complex waves, at frequencies where the modes are not yet completely bound to the core of the highest dielectric constant, as well as at frequencies below cutoff. Dispersion characteristic examples are calculated for structures suitable for millimeter-wave and optical integrated circuits, such as dielectric image lines, shielded dielectric waveguides, insulated image guides, ridge guides, and inverted strip, channel, strip-slab, and indiffused inverted ridge guides. The numerical examples are verified by results available from other methods.     

Characteristic impedance measurements of a coplanar waveguide

A coplanar waveguide which consists of a strip of metallic thin film on the surface of a dielectric slab with two ground electrodes running adjacent and parallel to the strip is easily accessible for shunt connections of semiconductor devices. This letter presents experimental data, and a theoretical equation including correction factors, for an effective relative permittivity concerning characteristic impedance. The measurements have been made by the t.d.r. method.     

RC-IGBT的snap-back现象及其仿真

The RC-IGBT(reverse conducting insulated gate bipolar transistor) is a new kind of power semiconductor device which has many advantages such as smaller chip size,higher power density,lower manufacturing cost,softer turn off behavior,and better reliability.However,its performance has a number of drawbacks,such as the snap-back effect.In this paper,an introduction about the snap-back effect of the RC-IGBT is given firstly. Then the physical explanations are presented with two simplified models.After that,some numerical simulations are carried out to verify the correctness of the models.     

逆导IGBT实现Snapback-Free所需最小P-emitter长度的理论计算

A physically based equation for predicting required p-emitter length of a snapback-free reverse- conducting insulated gate bipolar transistor （RC-IGBT） with field-stop structure is proposed. The n-buffer resis- tances above the p-emitter region with anode geometries of linear strip, circular and annular type are calculated, and based on this, the minimum p-emitter lengths of those three geometries are given and verified by simulation. It is found that good agreement was achieved between the numerical calculation and simulation results. Moreover, the calculation results show that the annular case needs the shortest p-emitter length for RC-IGBT to be snapback-free.     

Bias-dependent phase delay of Schottky contact microstrip line

Schottky contact lines are a form of microstrip on a semiconducting substrate, the strip of which forms a rectifying metal?semiconductor contact. Such a line has an extremely low phase velocity that is determined by the ratio of the depletion-region width to the substrate thickness, i.e. by the bias. Measurements agree well with theoretical expressions that are deduced from a parallel-plate-waveguide model.     

Thermal stress and fracture in shear-constrained semiconductor device structures

The construction of semiconductor devices, as well as other electron devices, often requires the utilization of brittle materials, such as the semiconductor itself, as part of a larger structure. Thermal stress, caused by cooling from high temperature bonding operations, can cause fracture of the brittle part, due to thermal expansivity mismatch with other parts of the structure. This paper considers a widely used type of bond, consisting of a nonpenetrating butt-joint, wherein the parts develop thermal stresses by reason of shear constraint in a solder layer. This type of joint is therefore called a shear-constrained bond. A one-dimensional, elastic analytical model is presented, which predicts the location and orientation of the principal tensile stress in a shear-constrained brittle strip. The tensile stress required for brittle fracture is shown to be induced, primarily, by shear tractions in the solder layer which are applied to one face of the strip. Extended to a real structure, the model would predict the highest tensile stress at the outer periphery of a bond, and oriented at 45° with the plane of the bond interface. This prediction is found to be in agreement with the bulk of fracture experience in shear-constrained semiconductors.     

高功率高可靠性9XX nm激光二极管

为了提高半导体激光二极管的输出功率和可靠性,通过在有源区两侧势垒层和波导层之间引入高禁带宽度的GaAsP,抑制有源区载流子的泄漏,极大地改善了器件的性能。研究结果表明:在10~40℃温度范围内器件特征温度从原来的150 K提高至197.37 K(-75.76℃),峰值波长随温度的漂移系数为0.207 nm/℃;条宽200μm、腔长2000μm的9XX nm激光二极管可靠性工作的最大输出功率高达14.4 W;器件在注入电流为7 A时取得71.8%的最大电光转换效率,斜率效率为1.21 W/A。器件在恒定电流下的加速老化测试显示激光二极管可靠性工作寿命达2000 h以上。     

Effects of Losses on the Current Spectrum of a Printed-Circuit Line

This paper studies the effects of practical conductor and dielectric losses on the high-frequency current excited on a microstrip line by a gap voltage source. The analysis shows that whereas losses cause an exponential decay in the propagating bound mode (as expected), the continuous-spectrum current is much less influenced by the presence of material losses. As a consequence, the nature of the strip current far away from the source is dramatically affected by the presence of losses, and will be dominated by the continuous spectrum. This results in unusual behavior that is observed for the strip current far away from the source.     

The effects of fixed bulk charge on the thermal noise in metal-oxide-semiconductor transistors

The theory of the thermal noise due to channel conductance fluctuation is extended for insulated gate (MOS) field effect transistors with the gate voltage induced channel structure by including the bulk charge from the ionized impurities in the semiconductor substrate. In the saturation range of the drain characteristics, the theory shows thatR_{gns} g_{ms} geq 2/3, where the equality condition corresponds to the previously obtained result for an intrinsic or chemically pure semiconductor substrate. Satisfactory correlations between theory and experimental measurements are obtained for both P-channel and N-channel silicon devices with either a thin oxide (2000A) or a thick oxide (6200 and 8400A) gate.     

Diffusion-controlled adecay of laser-excited photoconductivity in optoelectronic switches

When illuminating a semiconductor surface inhomogeneously, e.g. by a small laser spot, the photoexcited electrons and holes will partly diffuse into the dark or shaded semiconductor regions. The effect of such a carrier diffusion on measured decay of photoconductivity is studied quantitatively. The analysis yields a decay proceeding faster than linear recombination would imply. Particularly in the initial stages, the decay is quite similar to a plasma decay controlled by Auger recombination.