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The use of omnidirectional mirrors (an special case of distributed Bragg reflectors) as cladding for planar waveguides is proposed and analyzed. The proposed structure is an all-porous silicon multilayer consisting of a core layer inserted between two omnidirectional mirrors. The transfer matrix method is applied for the modal analysis. The influence of the parameters of the waveguide structure on the guided modes is analyzed. These parameters are the layer thickness and number of periods of the omnidirectional mirror, and the refractive index and thickness of the core layer. Finally, the confinement of the omnidirectional mirror cladding is analyzed with respect to two other different distributed Bragg reflector claddings. [ABSTRACT FROM AUTHOR]

This paper presents a compact electrical equivalent circuit which describes the dark current-voltage characteristics of nonideal p-n junction solar cells in a wide range of temperatures. The model clearly separates the voltage drop in the junction and bulk regions. It is based on the combination of two exponential mechanisms, shunt and series resistances and space-charge limited current. In order to increase the accuracy of the parameter extraction process, both ln(I-V) and its derivative plots are fitted simultaneously. From the temperature dependence of the extracted parameters, the conduction mechanisms governing the I-V characteristics can be obtained without assuming dominating terms. In addition, the extracted parameters can be related to other electrical magnitudes obtained from such independent measurements as capacitance-voltage measurements (diffusion potential) and illuminated current-voltage characteristics (series resistance and open-circuit voltage). To exemplify the application, a p+ a-SiC:H/n c-Si solar cell is studied and a number of major physical aspects derived from the analysis of the fitting values are discussed. [ABSTRACT FROM AUTHOR]

We have fabricated, electrically characterized and simulated n-type hydrogenated amorphous silicon germanium alloys on p-type crystalline-silicon heterojunction diodes with three different a-SiGe:H layer thicknesses: 37, 86, and 200 nm. The capacitance–voltage results confirm the existence of abrupt heterojunctions. The conduction and valence-band discontinuities of the heterojunctions and the electron affinity of the n-type a-SiGe:H films were obtained. The conduction mechanisms were determined by analyzing the temperature dependence of the current–voltage characteristics. The results show that at low forward bias (V<0.45 V) the diodes with thinner amorphous layers (37 and 86 nm) are dominated by recombination in the a-SiGe:H depletion region, whereas the thicker diode (200 nm) is dominated by multistep tunneling through depletion region. In addition, at high forward bias (V>0.45 V) the space-charge limited effect becomes the main transport mechanism in all the measured devices. The increase in the amorphous layer thickness also causes an increase in the leakage reverse current. Numerical simulations support the proposed transport mechanisms. [ABSTRACT FROM AUTHOR]

Multilayers consisting of the periodic repetition of two layers with different refractive indices (nH and nL) may have an omnidirectional band gap, the width of which depends on the incidence medium and on the refractive index ratio nH/nL. In porous silicon, this ratio is limited by the material and fabrication characteristics. This article makes a theoretical study of two multilayer structures in order to enlarge the omnidirectional band gap with the same refractive index ratio by varying only the thickness of the period. These structures are named balanced and unbalanced mirrors and consist of a few periodic multilayers stacked together. Porous silicon balanced and unbalanced mirrors with enlarged omnidirectional band gap for 1.55-μm applications are proposed. The results obtained with these mirror structures are compared with the results obtained with a chirped structure with the same characteristics. [ABSTRACT FROM AUTHOR]

The performance of the standard hydrogenated amorphous silicon carbon–crystalline silicon solar cell is extensively compared with the performance of a hybrid structure subjected to a high-temperature annealing processing. Our analysis indicates that high-temperature-annealed heterojunctions show more robustness in the presence of energy offsets and defective amorphous-crystalline interfaces. Annealed hybrid cells are also less vulnerable to the negative impact of amorphous silicon carbon doped layers with poor electrical properties. Furthermore, annealed structures have the potential to generate higher efficiencies than conventional heterojunctions regardless of the wafer quality. The presence of boron at the amorphous-crystalline interface and in the wafer front region plays an important role in annealed hybrid structures that are made with low-quality wafers or where there is a highly defective amorphous-crystalline interface. In this scenario, a linear boron profile in the wafer front region is more appropriate, for which there is an optimum thickness. For low defect amorphous-crystalline interfaces and high-quality wafers, a boron exponential profile is more appropriate when boron creates additional defects in the front region of the wafer. The shape of the boron profile becomes less relevant when the boron does not add additional defects to the front region of high-quality wafers and when the amorphous-crystalline interface is low defect or defect-free. [ABSTRACT FROM AUTHOR]

P[SUP+]-type hydrogenated amorphous silicon-carbon (a-Si[SUB1-x]C[SUBx] :H) on n-type crystalline silicon (c-Si) heterojunction diodes were fabricated and characterized electrically. The effects of thermal annealing on the electrical transport properties of a-Si[SUB0.8]C[SUB0.2]:H/c-Si diodes were investigated by measuring their current-voltage characteristics. From the dark current-voltage characteristics measured at different temperatures (298-373 K), transport mechanisms were analyzed in detail. Two carrier transport mechanisms were found to be the origin of forward current. At low bias voltage and temperatures above 320 K as-deposited diodes are dominated by recombination currents on the amorphous side of the space charge region whereas annealed diodes are mainly dominated by diffusion mechanisms. In contrast, at temperatures below 320 K, both types of diodes are mainly dominated by multitunneling capture emission. At higher voltages, the current becomes space charge limited for both diodes throughout the temperature range studied. [ABSTRACT FROM AUTHOR]

We present a compact model based on the Landauer transmission theory for the silicon quantum wire and quantum well metal-oxide-semiconductor field effect transistor (MOSFET) working in the ballistic limit. This model captures the static current-voltage characteristics in all the operation regimes, below and above threshold voltage. The model provides a basic framework to account for the electronic transport in MOSFETs, being easily adaptable to gate structures such as the double-gate or gate-all-around. Numerical simulations based on the proposed model have been compared with experiments and quantum mechanical self-consistent simulations, with good agreement. [ABSTRACT FROM AUTHOR]

Presents information on a study which characterized and fabricated annealed amorphous silicon-type crystalline silicon heterojunction diodes for different doping concentrations. Fabrication; Experimental results and discussion; Conclusions.

Provides information on a study that fabricated and electrically characterized n-type amorphous silicon on p-type crystalline silicon heterojunction diodes. Description on the fabrication technology; Results and discussion on the study.

Presents a study which proposed to determine the conduction band offset in single quantum well (SQW) structures. Overview of the conduction band diagram of a SQW structure with a Schottky contact; Details on the computer curves of the capacitance and conductance over frequency; List of the values of the conduction band offset.