DC and large-signal time-dependent electron transport in heterostructure devices: an investigation of the heterostructure barrier varactor

The DC and large-signal time-dependent electron transport properties of Heterostructure Barrier Varactors (HBVs) are investigated using a physical model which combines drift-diffusion current transport through the heterostructure bulk with thermionic and thermionic-field emission currents imposed at the abrupt heterointerfaces in a fully self-consistent manner. A fast and accurate hydrodynamic device simulator for generic unipolar InGaAs-InAlAs on InP, InGaAs-InP on InP, and GaAs-InGaAs-AlGaAs on GaAs HBVs has been developed based on this model. The experimentally observed current-voltage and capacitance-voltage characteristics of GaAs-AlGaAs and GaAs-InGaAs-AlGaAs HBVs are compared with the simulated results over a wide range of DC bias. Large-signal time-dependent simulations at a pump frequency of 100 GHz confirm the odd-harmonic operation of these devices and indicate that multiple barrier HBVs should provide efficient frequency multiplication, especially in high order frequency multipliers, broadband frequency triplers, and quasi-optical tripler arrays.<>     

Crystallographic orientation dependence of the growth rate for GaAs low pressure organometallic vapor phase epitaxy

The complete crystallographic orientation dependence of the growth rate for GaAs low pressure organometallic vapor phase epitaxy (LPOMVPE) is determined using a previously described semi-empirical model. A set of LPOMVPE growth rate polar diagrams is presented for reactor temperatures near 550°C as well as near 700°C. Also, the variation of the growth rate polar diagrams as a function of process variables is given. The experimental data utilized in the semiempirical model was attained using a typical horizontal reactor LPOMVPE system and typical LPOMVPE process parameters.     

Efficient representation of object shape for silhouetteintersection

A new shape representation-the radial intersection set (RIS)-is presented. The RIS is an object-centred model in which 2-D and 3-D boundaries are represented via their intersection with radial lines from some specific origin. The RIS representation allows efficient 3-D reconstruction using silhouette intersection from an arbitrary number of 2-D perspective views. The relationship between the visual hull (Laurentini, 1994) of the 3-D object and the silhouettes it may generate is defined as a set intersection operator. This operator allows the direct generation of 3-D RIS models from silhouettes. The RIS method is shown to compare favourably, in terms of both speed and storage, with existing octree techniques. Examples of images rendered from RIS models are presented. These show high visual fidelity     

Electronic Stabilization of Continuous-Wave and Pulsed Lasers Based on Macroscopic Rate-Equation Modelling

We present a macroscopic laser rate-equation model based on measurable laser parameters, allowing easy system identification. A numerical simulation based on the model is used in the design and testing of electronic laser feedback systems for intensity noise suppression and Q-switched pulse stabilization. A novel pulse energy control scheme is also presented, including experimental results.     

Trisneopentylgallium as a precursor for atomic layer epitaxy of GaAs

We report the use of a new precursor, trisneopentylgallium (NPG) for the growth of GaAs by atomic layer epitaxy (ALE). In contrast to most other alkyl gallium precursors such as triethylgallium, which decompose via a β-hydride elimination mechanism, this compound undergoes homolysis similar to that of trimethylgallium (TMGa), the normal choice as an ALE precursor. Clear self-limiting growth behavior similar to that of TMGa was observed over a reasonably wide range of growth conditions (430–500°C). Carbon incorporation was not significantly reduced compared with TMGa suggesting that the adsorbed neopentyl radicals undergo decomposition to result in a methyl terminated surface identical to that obtained for growth with TMGa.     

Multireference adaptive noise canceling applied to the EEG

The technique of multireference adaptive noise canceling (MRANC) is applied to enhance transient nonstationarities in the electroencephalogram (EEG), with the adaptation implemented by means of a multilayer perceptron artificial neural network (ANN). The method was applied to recorded EEG segments and the performance on documented nonstationarities recorded. The results show that the neural network (nonlinear) gives an improvement in performance (i.e., signal-to-noise ratio (SNR) of the nonstationarities) compared to a linear implementation of MRANC. In both cases an improvement in the SNR was obtained. The advantage of the spatial filtering aspect of MRANC is highlighted when the performance of MRANC is compared to that of the inverse auto-regressive filtering of the EEG, a purely temporal filter     

The properties of annealed AlN films deposited by pulsed laser deposition

AlN films deposited on SiC or sapphire substrates by pulsed laser deposition were annealed at 1200°C, 1400°C, and 1600°C for 30 min in an inert atmosphere to examine how their structure, surface morphology, and substrate-film interface are altered during high temperature thermal processing. Shifts in the x-ray rocking curve peaks suggest that annealing increases the film density or relaxes the films and reduces the c-axis Poisson compression. Scanning electron micrographs show that the AlN begins to noticeably evaporate at 1600°C, and the evaporation rate is higher for the films grown on sapphire because the as-deposited film contained more pinholes. Rutherford backscattering spectroscopy shows that the interface between the film and substrate improves with annealing temperature for SiC substrates, but the interface quality for the 1600°C anneal is poorer than it is for the 1400°C anneal when the substrate is sapphire. Transmission electron micrographs show that the as-deposited films on SiC contain many stacking faults, while those annealed at 1600°C have a columnar structure with slightly misoriented grains. The as-deposited films on sapphire have an incoherent interface, and voids are formed at the interface when the samples are annealed at 1600°C. Auger electron spectroscopy shows that virtually no intermixing occurs across the interface, and that the annealed films contain less oxygen than the as-grown films.     

Oxygen Deficiency and Hydrogen Turn ZnO Red

The effect of hydrogen on ZnO while annealing at 1370 K under oxygen-poor conditions with excess Zn vapor or Ti metal is studied. ZnO turns red only when hydrogen is present in a complex with oxygen vacancies. A practical method is described to remove hydrogen from ZnO in a sealed ampoule and to bind it to Ti metal. Hydrogen coupled to an oxygen vacancy is the simplest defect to explain the observations. The coloration is reversible at 1370 K by adding or removing hydrogen, consistent with an activation energy >1.5 eV. In red ZnO Hall data show a shallow donor level around 45 meV.     

LDMOS射频晶体管满足2.5G和3G蜂窝基站的新挑战

运行在869MHz-2.17GHz频段内的蜂窝无线基站是射频功率晶体替如今最大的市场。其中，基中硅的LDMOS器件被广泛使用于500MHz=2.5GHz之间的射频功率放大器应用当中。作为增强模式的N沟道MOSFET，LDMOS器件(LD代表侧面扩散，描述了器件的沟道结构)专门被设计成为具有高的工作电压(长沟道）和低寄生电容，从而能在高频下工作。在早     

Modelling direct sequence pseudonoise(dspn) satellite reception with directional antennas in the dense scatterer mobile environment

A geometric propagation model is developed for simulating the reception of direct sequence pseudonoise (DSPN) satellite signals by a directional or omni antenna in the dense scatterer mobile environment. The model is first validated for narrowband signals by a direct comparison of both simulated cumulative signal strength statistics and simulated diffuse Doppler spectra with classical theory. The model is then used to predict fading statistics for DSPN signaling, either with omni or directional antennas. As expected, the mitigation of fading is closely related to the ratio of DSPN chip duration to delay spread of the scatterer medium for both the omni and directional antennas.