Enhanced electron emission from phosphorus-doped diamond-cladsilicon field emitter arrays

Undoped and phosphorus (P)-doped diamond-clad Si field emitter arrays have been successfully fabricated using microwave plasma chemical vapor deposition (MPCVD) technology. The electron emission from the blunt diamond-clad microtips are much higher than those for the pure Si tips with sharp curvature due to a lower work function. Furthermore, the characteristics of emission current against applied voltage for the P-doped diamond-clad tips show superior emission at lower field to the undoped ones. After the examination of Auger electron spectroscopy (AES) and electrical characteristics of as-grown diamond, such a significant enhancement of the electron emission from the P-doped diamond-clad tips is attributed to a higher electron conductivity and defect densities     

WKB近似下的Fourier衍射成象方法

对于介质目标微波衍射成象，本文引入了ＷＫＢ近似来模拟目标内部总场。基于这种近似，我们导出了Ｆｏｕｒｉｅｒ衍射公式，并采用了广义滤波逆传播方法由目标空间谱实现目标特性的重建。计算机模拟结果表明采用ＷＫＢ近似重建目标特性较Ｂｏｒｎ近似有明显改善。     

Room temperature characterization of Hg1-xCdxTe P-on-n heterostructure photodiodes

Measurements of 77K R_oA and 300K reverse bias dynamic impedance (R_dA) products at one volt reverse bias has been carried out to assess the degree of correlation of this figure of merit. Planar P-on-n heterostructures were grown on near lattice-matched CdZnTe substrates with Hg_1-xCd_xTe (0.20< x <0.30) by molecular beam epitaxy. These devices were passivated with CdTe and doped with indium and arsenic as n- and p-type dopants, respectively. Current-voltage characteristic of these devices exhibit thermally generated dark currents at small and modest reverse bias. We have observed that R_oA values of these long wavelength infrared P-on-n heterostructure photodiodes at 77K correlate with room temperature R_dA values. Diode arrays with high room temperature R_dA values at one volt reverse bias also have high R_oA values at 77K. Similarly, low R_dA values at room temperature indicate poor performance at 77K where deviation from diffusion current occurs at reverse bias of 0.2 to 1 volt at room temperature. The results presented here, for a small samples of devices, demonstrate that room temperature measurements of current-voltage characteristics to evaluate Hg_1-xCd_xTe (0.22< x <0.28) diode performance and array uniformity at lower temperatures can be used. This provides an acceptable criteria for further study at lower temperatures.     

Thermal stability of Al/AlGaAs and Al/GaAs/AlGaAs (MBE) Schottky barriers

Outstanding stability has been observed in Al/Al/sub x/Ga/sub 1-x/As and Al/GaAs/Al/sub x/Ga/sub 1-x/As (x=0.25) Schottky barriers prepared by depositing Al in situ by MBE on annealing up to 400 degrees C. Conventionally evaporated barriers have been fabricated and compared with epitaxial ones. The changes in barrier height and ideality factor induced by annealing are reported.<>     

A simple and effective precoding scheme for noise whitening onintersymbol interference channels

A precoding scheme for noise whitening on intersymbol interference (ISI) channels is presented. This scheme is compatible with trellis-coded modulation and, unlike Tomlinson precoding, allows constellation shaping. It can be used with almost any shaping scheme, including the optimal SVQ shaping, as opposed to trellis precoding, which can only be used with trellis shaping. The implementation complexity of this scheme is minimal-only three times that of the noise prediction filter, hence effective noise whitening can be achieved by using a high-order predictor     

Wideband HEMT MMIC low-noise amplifier with temperaturecompensation

A wideband low-noise pseudomorphic HEMT MMIC variable-gain amplifier has been designed and fabricated. The amplifier has a nominal gain of 13 dB across the band 2-20 GHz, with gain flatness better than ±0.4 dB. The noise figure is less than 3 dB across the band 6-16 GHz. An on-chip temperature-sensing diode is used to provide a linear temperature correction which has been used to reduce the gain variation of the amplifier by a factor of 2 across the temperature range -50°C to +95°C     

A prototype 3D optically interconnected neural network

We report the implementation of a prototype three-dimensional (3D) optoelectronic neural network that combines free-space optical interconnects with silicon-VLSI-based optoelectronic circuits. The prototype system consists of a 16-node input, 4-neuron hidden, and a single-neuron output layer, where the denser input-to-hidden-layer connections are optical. The input layer uses PLZT light modulators to generate optical outputs which are distributed over an optoelectronic neural network chip through space-invariant holographic optical interconnects. Optical interconnections provide negligible fan-out delay and allow compact, purely on-chip electronic H-tree type fan-in structure. The small prototype system achieves a measured 8-bit electronic fan-in precision and a calculated maximum speed of 640 million interconnections per second. The system was tested using synaptic weights learned off system and was shown to distinguish any vertical line from any horizontal one in an image of 4×4 pixels. New, more efficient light detector and small-area analog synapse circuits and denser optoelectronic neuron layouts are proposed to scale up the system. A high-speed, feed-forward optoelectronic synapse implementation density of up to 10⁴/cm² seems feasible using new synapse design. A scaling analysis of the system shows that the optically interconnected neural network implementation can provide higher fan-in speed and lower power consumption characteristics than a purely electronic, crossbar-based neural network implementation     

On the integrability of hyperbolic systems of riccati-type equations

We consider equations of the form U_xy = U * U_x, where U(x, y) is a function taking values in an arbitrary finite-dimensional algebra T over the field ℂ. We show that every such equation can be naturally associated with two characteristic Lie algebras, L_x and L_y. We define the notion of a ℤ-graded Lie algebraB corresponding to a given equation. We prove that for every equation under consideration, the corresponding algebraB can be taken as a direct sum of the vector spaces L_x and L_y if we define the commutators of the elements from L_x and L_y by means of the zero-curvature relations. Assuming that the algebra T has no left ideals, we classify the equations of the specified type associated with the finite-dimensional characteristic Lie algebras L_x and L_y. All of these equations are Darboux-integrable. Translated from Teoreticheskaya i Matematicheskaya Fizika, Vol. 113, No. 2, pp. 261–275, November, 1997.     

The information-theoretic capacity of discrete-time queues

The information-theoretic capacity of continuous-time queues was analyzed recently by Anantharam and Verdu (see ibid. vol.42, p.4-18, 1996). Along similar lines, we analyze the information-theoretic capacity of two models of discrete-time queues. The first model has single packet arrivals and departures in a time slot and independent packet service times, and is the discrete-time analog of the continuous-time model analyzed by Anantharam and Verdu. We show that in this model, the geometric service time distribution plays a role analogous to that of the exponential distribution in continuous-time queues, in that, among all queues in this model with a given mean service time, the queue with geometric service time distribution has the least capacity. The second model allows multiple arrivals in each slot, and the queue is modeled as serving an independent random number of packets in each slot. We obtain upper and lower bounds on the capacity of queues with an arbitrary service distribution within this model, and show that the bounds coincide in the case of the queue that serves a geometrically distributed number of packets in each slot. We also discuss the extremal nature of the geometric service distribution within this model     

Inductively coupled plasma etching of InGaP, AllnP, and AlGaP in Cl2 and BCl3 chemistries

Dry etching of InGaP, AlInP, and AlGaP in inductively coupled plasmas (ICP) is reported as a function of plasma chemistry (BCl₃ or Cl₂, with additives of Ar, N₂, or H₂), source power, radio frequency chuck power, and pressure. Smooth anisotropic pattern transfer at peak etch rates of 1000–2000Å·min^?1 is obtained at low DC self-biases (?100V dc) and pressures (2 mTorr). The etch mechanism is characterized by a trade-off between supplying sufficient active chloride species to the surface to produce a strong chemical enhancement of the etch rate, and the efficient removal of the chlorinated etch products before a thick selvedge layer is formed. Cl₂ produces smooth surfaces over a wider range of conditions than does BCl₃.