J.A. López Villanueva

Effects of oxygen related defects on the electrical and thermal behavior of a n+-p junction

This study examines the electrical and temperature behavior of two of the levels in Czochralski-grown silicon that are most detected by different authors. A comparison between an analytical expression of the generation recombination noise in p−n junctions with experimental data taken from other authors was used as a tool for determining capture cross sections and densities of oxygen related traps in silicon. The parameters found in the literature for a deep level located at EC−0.43 eV are verified in this work. Parameters for a shallower level, a Coulomb trap with an activation energy of 0.17 eV, are also obtained. To correlate our theoretical results, obtained by noise analysis, with those of other authors, obtained with different techniques, thermally activated and field enhanced transitions between the latter center and the conduction band are considered. A thorough theoretical study of a silicon p−n junction with these levels shows a mutable electrical operation of the shallower center, acting as an e...

Generation-recombination noise in highly asymmetrical p–n junctions

A previous theory for the current noise associated with carrier generation and recombination in the space-charge region of p–n junctions is recalculated for the case of a highly asymmetrical distribution of dopant impurities. We propose a model based on the true concentrations of electrons and holes and electric field in the space-charge layer. Carriers coming from the highly doped region create a layer of mobile charge in the depletion region of the less-doped zone. This charge, usually studied under forward-bias conditions, is neglected under reverse voltages. We have demonstrated that this mobile-charge layer, although located in a very tiny region compared to the width of the space-charge layer, is crucial in the study of charge fluctuations stimulated by generation-recombination centers. Experimental results have been successfully reproduced with our theory for reverse-biased p+–n diodes with deep centers located close to the metallurgical junction.

Energy dependence of the effective mass in the envelope-function approximation

Results of a study on the tunneling electron effective mass as a function of energy and barrier width are reported. A system with a highly selective transmission factor, a double barrier, has been chosen in order to be able to define a particular energy. As the energies of the resonant transmission peaks are mostly determined by the effective mass of the material forming the well, while the transmission-peak width mostly depends on the barrier effective mass, both masses are obtained separately by fitting results for transmission using layers of periodic lattices and using the simplification allowed by the effective-mass approximation. The central well width has been varied and several transmission maxima have been considered, thus covering a wide energy range. The effective-mass in the relatively large barrier is shown to be much lower than the bulk-conduction-band value. For very thin barriers, when the decay length of tunneling electrons becomes of the same order as the barrier width, an anomalous increase in the effective mass is observed for high energies. Finally, we obtain the behavior of the effective mass as a function of energy in a one-dimensional triangular potential profile.

LOCAL LARMOR CLOCK APPROACH TO THE ESCAPE TIME

The escape of an electron from a localized state in a quantum well with one or several surrounding barriers is analyzed using the local Larmor clock approach. We show that two time scales can be involved in the escape time problem, such as in the case of a scattering configuration. The particular example of a potential well with a hard wall condition on one side, i.e. escaping through only one open channel, is investigated, and the two time components are calculated analytically. One of the time components is shown to coincide with the lifetime expression obtained with a different approach, in the case of an opaque barrier, at an energy close to the bound level in the well. q 1999 Published by Elsevier Science B.V. All rights reserved.

Compact modeling of the contact effects in organic thin film transistors

The performance of modern organic semiconductor devices is limited by non-ideal effects which are not characterized by traditional models of transport. In this work, we use experimental data from organic thin-film transistors (OTFT) based on Zinc Phthalocyanine that showed a significant influence of contact effects to illustrate how this nonideal effect can be modeled. Using the output current voltage (ID—VD) curves of these OTFTs, and different transistor models available in the literature, we illustrate the advantages and disadvantages of each model. We then demonstrate that only a combination of different approaches can accurately describe the experiments in both linear and saturation regions of operation of these OTFTs. The modified procedure has been tested with output characteristics of an ideal transistor with added contact effects with known parameters for the complete transistor.

Effect of traps in the performance of Four Gate Transistors

In this work, a study of traps located in the bulk and the Si-SiO2 interfaces of four gate transistors (G4-FETs), and their effect in the performance of these transistors, is presented. Different kinds of low frequency noise spectra measured at different voltages applied to the gates show that traps in the bulk and traps at the interfaces are the origin of such different spectra. We propose a model to evaluate low frequency noise produced in the bulk and surfaces of the device. This model is incorporated in a 2D simulator that confirms the experimental trends. It also allows us to separate the contribution of both sources and study the effects of different kinds of bulk traps on the low frequency noise.

Effect of doping in the current voltage characteristics of organic diodes

We analyze the effects of doping, traps and other defects on the electronic properties of organic/polymeric diodes. We detect the presence of dopant atoms and traps in the semiconductor in experimental current density-voltage (j-V) curves by the comparison with numerical j-V curves. The transport equations are solved by means of the Lambert-W-function. The key parameter in the procedure is the boundary value for the free carrier density at the metal-organic interface.

DC and low-frequency noise optimization of four-gate transistors

The effects of different parameters on the DC and low-frequency noise performance of four gate field effect transistors (G4-FET) are studied. Experimental data of the drain current and the current noise power spectral density (PSD) are compared with simulation results. The comparisons show that the drain current and its associated noise are very sensitive to the doping profile of the pn junctions that constitute the lateral gates of the device. The presence of recombination centers also modifies the performance of the device. These centers can degrade the excellent subthreshold slope that the G4-FET transistor exhibits. At the same time, the generation-recombination (g-r) noise produced by deep traps in the depletion regions of the device can be reduced by the presence of these recombination centers. In this work, we propose a procedure to determine an optimal dopant profile of the lateral pn junctions of the device that minimizes the subthreshold slope and the low frequency noise and maximizes the transconductance.

Optoelectronic properties in InAs/GaAs quantum dots arrays systems

A study of the physics of electronic states in cubic InAs quantum dot periodic nanostructures embedded in GaAs is presented. The miniband structure of electron states in the conduction band is related to the size and density of the quantum dots. The effect of strain is also taken into account in the simulations. The photon-electron absorption coefficient is obtained for different quantum dot configurations and different light polarization as well.

Influence of Dopant Profiles and Traps on the Low Frequency Noise of Four Gate Transistors

This work presents a study that correlates technological parameters of SOI four‐gate field‐effect‐transistors (G4‐FET) with their output characteristics and low frequency noise in order to optimize their performance. This structure can control the position and size of the conduction channel by the application of adequate voltages to its four gates (front and back MOS gates and two lateral JFET gates). Due to this reason, many parameters can affect its behavior. We have studied the dependence of I–V characteristics and low frequency noise with parameters such as the doping profile in the channel, drain and source regions, impurities in the volume of the semiconductor, and traps in the Si‐SiO2 interfaces.