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ABSTRACT: In this work we calculate the electron band structure of a silicon periodic nanostructure embedded into SiO<sub>2</sub> and describe the computational implementation we used for this purpose. Further, we discuss the influence of nonparabolicity of electron silicon band structure in the dispersion relation of the periodic nanostructure.
Nanotechnology, 2009. IEEE-NANO 2009. 9th IEEE Conference on; 08/2009
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ABSTRACT: In this work, we propose a correction to the effective mass approach (EMA) to be used in Si quantum dot simulations. This correction tries to connect the different ways of modeling quantum dots within tight binding (considering the actual positions of the atoms and using additional atoms to passivate the surfaces) with those within the EMA, adapting the size of the simulated quantum dots to take the difference into account. With this aim, we implemented a 6×6 k ∙ p calculation for the valence band and used a nonparabolic and anisotropic model for the conduction band to study hole and electron confinement, respectively. We then tested and used a very fast computational algorithm to obtain the electron and hole spectra in both cubic- and spherical-shaped quantum dots.
Journal of Applied Physics 12/2008; · 2.17 Impact Factor
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ABSTRACT: In this work we propose a correction to the effective mass approach (EMA), to be used in Si quantum dot simulations. With this technique we obtained results comparable to those calculated by the tight-binding method (TB). We used this new approach to obtain the hole spectra in spherical quantum dots by means of a fast algorithm, thus improving the accuracy of the EMA.
Computational Science and Engineering Workshops, 2008. CSEWORKSHOPS '08. 11th IEEE International Conference on; 08/2008
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ABSTRACT: In this work we formulate the nonparabolic Schrödinger equation for a quantum dot in order to explore the main features of the carriers in these systems. In addition, we present a fast iterative numerical algorithm to solve it, obtaining the energy levels and envelope functions. We also model the electrostatic potential profile in a manner that makes it possible to discuss the effects of stronger confinements on the results. To demonstrate a practical implementation of this algorithm, we carry out an investigation into the effects of nonparabolicity of the valence band on the eigenstates of a Si quantum dot. Finally, we fit our results, using power expressions to relate the energy levels to the size of the cubic quantum dots, thus demonstrating the relevance of nonparabolicity.
Journal of Applied Physics 06/2007; · 2.17 Impact Factor
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ABSTRACT: In this paper we develop a suitable method for solving the effective-mass Schrödinger equation for two-dimensional electron and hole gases in semiconductor structures such as quantum wells using a general nonparabolic band structure. We present two different ways to treat barriers, the first being the exact solution and the second a suitable option when the band structure is not determined inside the gap. As a first application, this procedure was implemented to solve the effective-mass Schrödinger equation for holes in Si and Ge using an analytical valence-band model. Analyzing the results obtained enabled us to demonstrate the importance of nonparabolicity in energy quantization in these systems and to discuss the suitability of each of these two procedures for dealing with barriers.
Journal of Applied Physics 09/2005; · 2.17 Impact Factor
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ABSTRACT: We present a study of the main features of a two-dimensional hole gas confined near a Si–SiO <sub> 2 </sub> heterointerface. Starting from the framework of the effective mass theory, we were able to separate the Luttinger Hamiltonian into two 3×3 matrices using a semiaxial approximation and still retaining the warped shape of the isoenergetic surfaces in the k<sub>x</sub>-k<sub>y</sub> plane and the coupling of heavy, light, and split-off holes. This allows us to solve iteratively and simultaneously the Schrödinger and Poisson equations in the case of an inversion layer of holes in a P-channel metal–oxide–semiconductor structure for different applied gate biases. We have obtained the energy subbands and the main characteristics of the inversion layer. The form of the energy subbands suggests that the use of parabolic bands should be seriously questioned, and that even the use of a unique effective mass in each subband is not a realistic assumption. Furthermore, our results show that the character of the subbands becomes mixed as k <sub>||</sub> separates from zero, and that the complete dispersion characteristics must be considered in hole studies. © 1999 American Institute of Physics.
Journal of Applied Physics 08/1999; · 2.17 Impact Factor
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ABSTRACT: We have studied the electron‐transport properties of strained‐Si on relaxed Si 1-x Ge x channel MOSFETs using a Monte Carlo simulator adapted to account for this new heterostructure. The low‐longitudinal field as well as the steady‐ and nonsteady‐state high‐longitudinal field transport regimes have been described in depth to better understand the basic transport mechanisms that give rise to the performance enhancement experimentally observed. The different contributions of the conductivity‐effective mass and the intervalley scattering rate reduction to the mobility enhancement as the Ge mole fraction rises have been discussed for several temperature, effective, and longitudinal‐electric field conditions. Electron‐velocity overshoot effects are also studied in deep‐submicron strained‐Si MOSFETs, where they show an improvement over the performance of their normal silicon counterparts. © 1996 American Institute of Physics.
Journal of Applied Physics 12/1996; · 2.17 Impact Factor
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ABSTRACT: Results of electron mobility calculations at room temperature in quantized cubic silicon carbide (β‐SiC) inversion layers are reported. A comparison with silicon mobility curves is provided. Drift velocities both at room and higher temperatures are calculated by Monte Carlo simulations including electron quantization and Coulomb scattering, in addition to phonon and surface roughness scattering. We have also observed that steady‐state drift velocity curves show a maximum that decreases as the transverse electric field increases, due to the greater importance of intervalley scattering with respect to polar phonon scattering. © 1996 American Institute of Physics.
Applied Physics Letters 11/1996; · 3.84 Impact Factor
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ABSTRACT: The main nonradiative capture mechanisms, cascade and multiphonon emission, have been numerically simulated by the Monte Carlo method. To do so, both mechanisms were included in the frame of a previous numerical procedure to which the nonacoustic‐phonon contribution was also added. Different centers were studied. Capture by shallow donors (P, As, and Sb) in n‐type silicon were interpreted considering only the cascade process. Capture by acceptors levels of platinum, gold, and titanium in silicon, and one level of Cr, EL2, and EL3 in gallium arsenide, were analyzed considering only multiphonon emission, and calculating the values of Huang–Rhys factor when it is not available. In the study of capture by attractive deep centers, such as single ionized donor centers of sulfur and selenium in silicon, both cascade and multiphonon mechanisms must be combined. In this case the importance of the nonacoustic phonon has been shown in the cascade process. © 1995 American Institute of Physics.
Journal of Applied Physics 04/1995; · 2.17 Impact Factor
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ABSTRACT: A new method for the direct determination of majority thermal-capture cross sections and concentration of deep levels in p-n junctions is proposed. The combined use of a capacitance technique and a numerical simulation (which reproduces the experimental details) provides accurate results through the fitting of experimental and numerical capture transients. The sensitivity of the method to these electrical magnitudes is also shown. This procedure is applicable not only to abrupt p<sup>+</sup>-n junctions, which have been quite thoroughly analyzed, but also to samples where a nonabrupt shallow-dopant profile together with a high concentration of deep levels makes them respond to a capture pulse in ways not reported until now. This method was used to analyze the two levels of platinum in silicon in nonabrupt p<sup>+</sup>-n junctions with a platinum concentration comparable to that of the shallow dopant.
Journal of Applied Physics 09/1993; · 2.17 Impact Factor
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ABSTRACT: A real (nonabrupt) p‐n junction has been theoretically analyzed. It consists of a graded profile of shallow dopant atoms and a uniform profile of deep impurities, their relative concentrations varying along the structure (i.e., there are regions where deep impurity concentration is highest and others where dopant concentration dominates). This type of structure was excited by majority‐carrier pulses, which allowed us to describe and explain new components in the charge distribution through the junction. The change in the interpretation of results from the application of capacitance techniques to these samples is quite remarkable. The validity of the theory is verified by comparison with experimental results obtained for silicon p‐n junctions highly doped with platinum. The detailed analysis of the electrical model of a gradual junction with two deep levels, located in both halves of the band gap has allowed us to explain the following: (a) the disappearance of peaks in deep level transient spectroscopy (DLTS), (b) the existence of both positive and negative signals in a majority‐DLTS spectrum, and (c) decreasing capacitance and voltage transients due to the emission of majority carriers or transients in which rising and falling sections are combined. The last two points cannot be explained by using the extended model of p<sup>+</sup>‐n or n<sup>+</sup>‐p junctions even if the deep‐level concentration N T is assumed to be of the same order as the free carrier concentration.
Journal of Applied Physics 12/1992; · 2.17 Impact Factor
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ABSTRACT: The energy levels introduced by Pt in silicon have been measured in a non-abruptp
+-n junction using constant-capacitance thermal-emission rate measurements and a numerical simulation of high frequency-capacitance.
Two levels have been detected with activation energies of:E
c -E
T = 0.22 eV with acceptor character andE
T -E
v = 0.34 eV with donor character. The sample preparation and diffusion of Pt is similar to previous works in which an acceptor
levelE
c -E
T = 0.34 eV was found instead of or besides a donorlike levelE
T -E
v = 0.34 eV. Our numerical calculation of the shallow-impurity profile points to the existence of a gradual transition near
the metallurgical junction for these samples. We have demonstrated that the well-known model of an abrupt junction is not
appropriate for these types of junctions, and could lead to errors in the location attributed to the detected levels. Simulation
of the electrical behavior leads to the non-existence of the acceptor levelE
c −E
T = 0.34 eV located in then-side of the junction.
Journal of Electronic Materials 08/1992; 21(9):883-886. · 1.47 Impact Factor
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ABSTRACT: Charge trapping and the generation of interface traps in thermally grown SiO 2 and its interface with silicon, produced by Fowler–Nordheim tunneling injection at low temperatures from highly doped Si substrates, have been investigated. The results that can be obtained with the constant‐current‐injection method, when a moderate amount of charge is trapped inside the potential barrier, have been analyzed. This has afforded information about the position of the charge trapped in the oxide. No increase in the interface‐trap density has been produced immediately after injection at 77 K, but, as the temperature is raised after injection, the growing of a peak of interface states has been observed. This phenomenon had been reported to be produced as a consequence of a previous hole trapping but, in this case, this intermediate stage of positive‐charge building has not been observed. This effect is discussed, taking into account published models.
Journal of Applied Physics 11/1991; 70(7):3712 - 3720. · 2.17 Impact Factor
