Depletion region

About: Depletion region is a research topic. Over the lifetime, 9393 publications have been published within this topic receiving 145633 citations.

Physical limitations on the frequency response of a semiconductor surface inversion layer

Abstract: The physical phenomena associated with the frequency response of the surface inversion layer of an MOS capacitor are examined. It is shown that the equivalent circuit presented by Lehovec and Slobodskoy for an MOS capacitor in the depletion-inversion mode of operation may be simplified when the capacitor is biased in the heavy inversion layer mode. Further it is shown that an additional resistance, to account for generation-recombination in the depletion region, must be included. This new resistance dominates the response for silicon units, which is shown to be as low as I–5o cps at room temperature. Experimentally, there are at least two observations which cannot be explained by the first order one dimensional model on which these equivalent circuits are based. The frequency responses of complementary units, fabricated on almost identical p- and n-type silicon differ by orders of magnitude, it is typically in the range 1–100 cps for n-type units, but may be as high as 10 Mc/s for equivalent p-type units. In addition, pronounced hysteresis in the bias dependence of the capacitance of some p-type units has been observed. A second-order two dimensional model is proposed to explain these anomalies. This model includes an “external” inversion layer, surrounding the gate electrode, produced during the formation of the oxide. The gate inversion layer, in this model, is coupled to the bulk through an additional RC network, representing the external inversion layer, which is in parallel with the equivalent network of the first order model. An approximate analysis of this second order model predicts a frequency response which is in agreement with experiment. The possibility of charge migration on the surface of the oxide, which serves to decouple the gate inversion layer from the external inversion layer, can account for the hysteresis in the capacitance vs. bias characteristics observed in these units.

Nanowire Piezo-Phototronic Photodetector: Theory and Experimental Design

Abstract: one-dimensional structures of these materials are ideal for fabricating strain-controlled piezo-phototronic devices. The strain applied to cause the deformation of the nanowires is mainly through shape change of the fl exible substrate that supports the device. Such devices can be the basis for active fl exible electronics, which uses the mechanical actuation from the substrate for inducing new electronic/optoelectronic effects. As the piezopotential is controlled by externally applied mechanical deformation with different orientation and magnitude, the piezo-phototronics effect can be combined with fl exible optoelectronics to promote new device functions. Previously, we have demonstrated the enhancement of the sensitivity of UV photodetector, [ 6 ] the response of photocells, [ 7 ] and the emission effi ciency of light emitting diodes. [ 8 ] In these reports, the coupling between piezoelectric effect and photoexcitation has been investigated experimentally. Theoretical calculation of the piezopotential along ZnO nanowires under different strain has been carried out, [ 9‐11 ] and a theoretical framework has been built for the two-way coupling between the piezoelectric effect and semiconductor transport properties. [ 12 ] Theoretical study for the three-way coupling in piezophototronics remains to be investigated. Constructing such a model will not only provide an in-depth understanding about the experimental results, but also explore the core phenomena and build high performance devices. Besides piezo-phototronic effect, other factors such as piezoresistance effect and change of contact area or contact condition can also affect the device performance. It is important to distinguish the contribution made by the piezo-phototronics effect from these other factors through theoretical analysis. In this paper, we have constructed a theoretical model and fabricated corresponding experimental devices to study the piezo-phototronic photodetectors based on single-Schottky and double-Schottky contacted metal‐semiconductor‐metal (MSM) structures. We have coupled the photoexcitation and piezoelectric terms into basic current equations to study their infl uence on the fi nal device performance. Theoretically predicted results have been quantitatively verifi ed by photodetectors based on CdS nanowires for visible light and ZnO nanowires for UV light. Our experimental results show that the piezo-phototronic effect dominates the performance of the photodetector rather than other experimental factors. It is shown that the piezophototronic effect is signifi cantly pronounced at low light intensities, which is important for extending the sensitivity and application range of the photodetector. The conclusions drawn on Schottky contacts present the core properties of the effect and can easily be extrapolated to other structures like p-n junctions. Finally, based on the theoretical model and experimental results, we have proposed three criteria for describing the contribution made by the piezo-phototronic effect to the performance of the photodetectors, which are useful for distinguishing this effect from other factors in governing the performance of the photodetector. The theoretical model for two-way coupling in piezotronics has been developed in a previous report. [ 12 ] Here we adopt the same assumptions and follow similar methods, as schematically shown in Figure 1 . The depletion approximation is assumed for the Schottky contact. Piezoelectric polarization is induced in a semiconductor nanowire when it is subjects to strain, it is reasonable to assume that the piezo charges are distributed in a layer in the depletion zone, which tune the Schottky barrier height. The formation of an inner potential will drive the free charge carriers to redistribute. If there is no external bias, the inner electric fi eld and net charges should only exist in the depletion zone at static or quasi-static state. The Schottky contact current equation will be used as the basic starting point. The infl uence of photoexcitation and piezo-charges on the material band structure will be discussed, and the fi nal coupled term will be integrated into the current transport equation. To give more intuitive perspective of the piezo-phototronic effect, we have also carried out numerical simulations. A one-dimensional model and other simplifi cations are adopted for easy understanding. The core equations and conclusions are shown in the anayltical model below. Current Density for a Forward Schottky Contact : For a piezophototronic photodetector, a measurement of the photoninduced current is an indication of photon intensity. The coupling effect of piezoelectricity and photon excitation is also

Power-limiting breakdown effects in GaAs MESFET's

Abstract: State-of-the-art GaAs MESFET'S exhibit an output power saturation as the input power is increased Experiments indicated that this power saturation is due to the combined effects of forward gate conduction and reverse gate-to-drain breakdown This reverse breakdown was studied in detail by performing two-dimensional numerical simulations of planar and recessed-gate FET's These simulations demonstrated that the breakdown occurs at the drain-side edge of the gate The results of the numerical simulations suggested a model of the depletion layer configuration which could be solved analytically This model demonstrated that the breakdown voltage was inversely proportional to the product of the doping level and the active layer thickness

Properties of Au, Pt, Pd and Rh levels in silicon measured with a constant capacitance technique

Abstract: Measurements of emission rates and majority carrier capture cross-sections of Au, Pt, Pd and Rh centres in silicon are reported, and the activation energies associated with the different levels of these centres are determined. Where appropriate, our results are compared with values reported in the literature; other results have not been previously reported. The measurement depends on the emission and capture of majority carriers on the centres in the depletion layer of a p-n junction or Schottky barrier. The change in charge state of the centres is monitored by measuring the change in reverse bias applied to the junction necessary to keep the junction capacitance constant. The advantage of this technique, compared with the usual method of keeping the bias voltage constant and measuring the change in capacitance, is demonstrated.

Surface Effects on Metal-Silicon Contacts

Abstract: Surface effects on metal‐silicon contacts have been studied in detail using gate‐controlled Schottky‐barrier diode structures. The ``excess'' forward and reverse currents at small and moderate bases, respectively, and low breakdown voltages usually associated with metal‐silicon contacts are clearly shown to be due to high fields near the corner region when the surface is accumulated. These currents can be eliminated and breakdown voltage increased by depleting or inverting the surface. By studying the diode characteristics when the surface is inverted, it is shown that the generation current in the depletion region often constitutes a significant part of the total reverse current and cannot in general be neglected.