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A fully three-dimensional (3-D) atomistic quantum mechanical simulation is presented for examining the random dopant-induced effects in nanometer metal-oxide-semiconductor field-effect transistors (MOSFETs). Results suggest an increase in the threshold fluctuation and a decline in threshold lowering due to quantum mechanical effects.

The equilibrium and nonequilibrium electronic transports through a double quantum dot coupled to leads in a symmetrical parallel configurations was studied in the presence of both the inter- and the intradot Coulomb interactions. A zero-bias maximum of the differential conductance induced by the interdot interaction was found and due to the presence of the interdot interaction, the local density of states peaks around the dot levels are split.

The valence energy subbands and optical transitions of the InAs/GaAs quantum ring are calculated by using a four-band valence band model that can also be used to calculate the hole states of quantum wells, quantum wires, and quantum dots. The calculations show that the effect of the difference between effective masses of holes in different materials on the valence subband structures is significant.

The transmission of electrons through a hierarchical self-assembly of GaAs/AlxGa1-xAs quantum dots is calculated using the coupled-channel recursion method. The results reveal that the number of conductance peaks does not change when the barrier widths change, but the intensities decrease as the barrier widths increase.

The phenomenological band coupling model is employed to explain the origin of magnetism, as observed in the transition metal doped CuI systems. The electronic structures of the doped CuI compound are also discussed.

The atomistic pseudopotential quantum mechanical calculations are used for analyzing the transport in million atom nanosized metal-oxide-semiconductor field-effect transistors. A partition method and a quasi-Fermi level method are the two methods to occupy the electron eigenstates to yield the charge density in a nonequilibrium condition that are tested and compared.

The electronic structure and magnetic coupling properties of rare-earth metals (Gd, Nd) doped ZnO are examined by using first-principles methods. For ZnO:Nd system, the ferromagnetism between Nd ions is enhanced by appropriate holes doping into the sample and the room-temperature ferromagnetism is achieved in the n-conducting ZnO:Nd sample.

The effective-mass theory is used for examining the electronic structure and exciton states of cylindrical ZnO nanorods. The exciton binding energies are increased by the dielectric mismatch and the optical transition rule is obtained when the small spin-orbit splitting of ZnO is neglected.

The electron-hole pair confined in a simplified infinite potential is considered and the low-lying excition states in a ZnO cylindrical nanodisk are calculated by using effective-mass theory. It is shown that the exciton radiative lifetime in a cylindrical nanodisk is of the order of tens of picoseconds, which is small when compared to the lifetime of bulk ZnO material.

First-principles methods are used for studying the mechanism of defect formation and electronic structures for 3d transition-metal impurities doped in silicon nanowires. The results have shown that the defect formation energies of Mn and Fe impurities are lower than those of V, Cr, and Co impurities in silicon nanowires.

The couplings between different energy band valleys in a metal-oxide-semiconductor field-effect transistor (MOSFET) device are examined by using self-consistent calculations of million-atom Schrodinger-Poisson equations. The system eigenstates derived from different bulk valleys is calculated separately and this has reduced the simulation time because the diagonalization of the Hamiltonian matrix scales as the third power of the total number of basis functions.

First-principles study is used for examining the ferroelectricity of rhombohedral PbTi[O.sub.3] under uniaxial compression. The results have shown that the Pb, Ti and O atoms have different contributions to the total polarization with increasing the magnitude of uniaxial compressive stress and that the Ti atoms no long have contributions to the polarization, leading to the changes of ferroelectricity and piezoelectricity.

The binding energy of a hydrogenic donor impurity in a rectangular parallelepiped-shaped quantum dot (QD) is examined in the framework of effective-ass envelope-function theory by using the plane wave basis. The results are very useful for the application of QDs in photoelectric and electronic devices.

The electron transport through an Aharonov-Bohm (AB) interferometer with a noninteracting quantum dot in each of its arms is analyzed. The results have shown that the conductance and the local density of states can become spin polarized by tuning the magnetic flux and the Rashba interaction strength, indicating that the electron spin can be manipulated by adjusting the Rashba spin-orbit strength and the structure parameters.

The electronic structure and binding energy of a hydrogenic impurity in a hierarchically self-assembled GaAs/[Al.sub.x][Ga.sub.1-x]As quantum dot (QD) in the framework of effective-mass envelope-function theory is calculated. Results reveal that all the impurity energy levels depend strongly on the GaAs QW width, a donor impurity in the QD has only one binding energy level except when the GaAs QW is large, and an acceptor impurity in the QD has two binding energy levels.

The Stark effects of an in-plane electric field on the excitonic energy in a bilayer system are investigated theoretically within the framework of the effective-mass approximation. The radiative lifetime of heavy-hole excitons in a bilayer system could be increased by two orders by an in-plane electric field of 2 kV/cm when distance d is twice the excitonic Rydberg.

A study is conducted to investigate the current-voltage properties of a double quantum dot (DQD) connected by leads in arrangements that vary from series to symmetrical parallel configurations, in the presence of strong intradot Coulomb interaction. It is found that the total current flowing through the parallel-connected DQD is much larger than that of the series one.

The single-electron and two-electron vertically assembled quantum disks are studied in an axial magnetic field using the effective mass approximation. The findings show that the variation of the energy difference between the lowest S=0 and S=1 states in the strong-B S=0 state is fairly linear.

The transmission through coupled quantum dots (CQDs) is calculated using the coupled-channel recursion method. The results show that the conductance peaks move to high energy as the CQDs radius decreases or the period increases.

The dephasing rate, time evolution of the quantum state of the electron in an InAs/GaAs quantum dot (QD), and the interaction of the two electrons located in different QDs is studied. The time evolution of the quantum mechanical state of an electron is calculated.