Injection over and through heterojunction barriers is becoming increasingly more important in modern electronic devices. We consider the properties of graded AlxGa1−xAs heterojunction barriers using a self‐consistent...
Injection over and through heterojunction barriers is becoming increasingly more important in modern electronic devices. We consider the properties of graded AlxGa1−xAs heterojunction barriers using a self‐consistent ensemble Monte Carlo method. In this paper, we consider barriers with two doping levels, 1×1015 cm−3 and 1×1017 cm−3, and two barrier heights, 100 and 265 meV. The 100‐meV barrier resulted in small rectification at room temperature whereas the higher barrier exhibited considerable rectification. In both cases the structure with the lower doped barrier has resulted in a smaller current in both forward and reverse regions due to space‐charge effects. The energy and momentum distribution functions deviate from a Maxwellian distribution inside the barrier region and in general show two peaks: one is comprised mainly of electrons near equilibrium and the second arises mainly from ballistic electrons. The higher doped structure resulted in a faster electron relaxation toward equilibrium as a function of position because the electric field decreases rapidly in the barrier region.
A new approach to modeling normal interface modulation doped field-effect transistors (MODFETs) is presented in which the 2-D electron gas density is integrated along the channel instead of the channel potential. With...
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A new approach to modeling normal interface modulation doped field-effect transistors (MODFETs) is presented in which the 2-D electron gas density is integrated along the channel instead of the channel potential. With this approach we are able to implement a highly accurate polynomial description of the Fermi potential in the channel as a function of free electron density for arbitrary acceptor densities in GaAs channel. A substantial increase in the near threshold device current results. A carrier density dependent low field mobility is also incorporated into the model. These modifications are expected to result in an improved ability to estimate device characteristics from extrinsic material and device parameters.
We introduce oriented non-radial basis function networks (ONRBF) as a generalization of Radial Basis Function networks (RBF)- wherein the Euclidean distance metric in the exponent of the Gaussian is replaced by a more...
ISBN:
(纸本)9781558601840
We introduce oriented non-radial basis function networks (ONRBF) as a generalization of Radial Basis Function networks (RBF)- wherein the Euclidean distance metric in the exponent of the Gaussian is replaced by a more general polynomial. This permits the definition of more general regions and in particular- hyper-ellipses with orientations. In the case of hyper-surface estimation this scheme requires a smaller number of hidden units and alleviates the "curse of dimensionality" associated kernel type approximators. In the case of an image, the hidden units correspond to features in the image and the parameters associated with each unit correspond to the rotation, scaling and translation properties of that particular "feature". In the context of the ONBF scheme, this means that an image can be represented by a small number of features. Since, transformation of an image by rotation, scaling and translation correspond to identical transformations of the individual features, the ONBF scheme can be used to considerable advantage for the purposes of image recognition and analysis.
This work describes the development of a multiparabolic (MP) ionospheric model and compares the results at vertical incidence with those of the equivalent Dudeney model in the absence of the geomagnetic field. The MP ...
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This work describes the development of a multiparabolic (MP) ionospheric model and compares the results at vertical incidence with those of the equivalent Dudeney model in the absence of the geomagnetic field. The MP model is extended to a multi-quasiparabolic (MQP) model in order to obtain analytical expressions for the variation of communications range as a function of elevation angle in the absence of the geomagnetic field and collisions. Results compare very favourably with those obtained using the equivalent Dudeney model and numerical ray-tracing. The MQP model can be applied in a number of HF communications problems, notably single site location HF direction finding and HF ionospheric radar.
Experimental results on InP based In0.53+xGa0.47-xAs/In0.52Al0.48As HEMT monolithic integrated amplifiers are reported demonstrating the feasibility of this technology. Strained heteroepitaxy (x≥0.0) proved to enhanc...
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Experimental results on InP based In0.53+xGa0.47-xAs/In0.52Al0.48As HEMT monolithic integrated amplifiers are reported demonstrating the feasibility of this technology. Strained heteroepitaxy (x≥0.0) proved to enhance the device performance and upper frequency limits and was used for the MMIC-realization. More than 15 dB of gain were obtained from 6 to 9.5 GHz. The maximum gain was 22 dB and the return loss better than - 10 dB. In spite of the strained heteroepitaxy which can raise material control questions for MMIC realizations the experimental results for the samples (x=0.07 and x=0.22) showed good agreement with design objectives.
A W-band monolithic mixer is designed and fabricated using InAlAs/InGaAs HEMT technology. The advantages of this material system compared with AlGaAs/GaAs are: (i) larger conduction band discontinuity (0.5 eV versus 0...
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A W-band monolithic mixer is designed and fabricated using InAlAs/InGaAs HEMT technology. The advantages of this material system compared with AlGaAs/GaAs are: (i) larger conduction band discontinuity (0.5 eV versus 0.24 eV for AlGaAs/GaAs) and therefore better carrier confinement, (ii) higher low-field mobility, and (iii) higher peak velocity. The combination of these features results in a better performance and operation capability in the submillimeter wave range. The design procedure and the circuit performance are described. A very low LO (local oscillator) power requirement is demonstrated with 13.5-dB conversion loss and only -6 dBm LO drive at 95 GHz.< >
We present a new approach for determining a time-optimal trajectory for a robot manipulator with actuator torque bounds. We find an approximation to a globally optimal trajectory which passes between two configuration...
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We present a new approach for determining a time-optimal trajectory for a robot manipulator with actuator torque bounds. We find an approximation to a globally optimal trajectory which passes between two configurations will avoiding obstacles. Our algorithm accomplishes this by by dynamically generating and searching a finite graph. Our algorithm is guaranted to produce a trajectory that performs within a user-specified factor of a time-optimal safe trajectory.
An algorithm is presented for generating near-time-optimal trajectories for an open-kinematic-chain manipulator moving in a cluttered workspace. This is the first algorithm to guarantee bounds on the closeness of an a...
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An algorithm is presented for generating near-time-optimal trajectories for an open-kinematic-chain manipulator moving in a cluttered workspace. This is the first algorithm to guarantee bounds on the closeness of an approximation to a time-optimal trajectory. The running time and space required are polynomial in the desired accuracy of the approximation. The user may also specify tolerances by which the trajectories must clear obstacles in the workspace to allow modeling of control errors.< >
Strained In/sub 0.52/Al/sub 0.48/ As/In/sub x/Ga/sub 1-x/As (x>0.53) HEMTs (high electron mobility transistors) are studied theoretically and experimentally. A device design procedure is reported that is based on b...
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Strained In/sub 0.52/Al/sub 0.48/ As/In/sub x/Ga/sub 1-x/As (x>0.53) HEMTs (high electron mobility transistors) are studied theoretically and experimentally. A device design procedure is reported that is based on band structure and charge control self-consistent calculations. It predicts the sheet carrier density and electron confinement as a function of doping and thickness of layers. The DC performance at 300 K is presented. Wafer statistics demonstrate improvement of device characteristics with excess indium in the channel (g/sub m,/ /sub intr/=500 and 700 mS/mm for x=0.60 and 0.65). Microwave characterization shows the f/sub T/ improvement (f/sub T/=40 and 45 GHz for x=0.60 and 0.65, respectively) and the R/sub ds/ limitations of the 1- mu m-long-gate HEMTs.< >
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