Takeshi Nishimatsu

Codoping method for the fabrication of low-resistivity wide band-gap semiconductors in p-type GaN, p-type AlN and n-type diamond: prediction versus experiment

We review our new valence control method of a co-doping for the fabrication of low-resistivity p-type GaN, p-type AlN and n-type diamond. The co-doping method is proposed based upon ab initio electronic structure calculation in order to solve the uni-polarity and the compensation problems in the wide band-gap semiconductors. In the co-doping method, we dope both the acceptors and donors at the same time by forming the meta-stable acceptor-donor-acceptor complexes for the p-type or donor-acceptor-donor complexes for the n-type under thermal non-equilibrium crystal growth conditions. We propose the following co-doping method to fabricate the low-resistivity wide band-gap semiconductors; p-type GaN: [Si + 2 Mg (or Be)], [H + 2 Mg (or Be)], [O + 2 Mg (or Be)], p-type AlN: [O + 2 C] and n-type diamond: [B + 2 N], [H + S], [H + 2 P]. We compare our prediction of the co-doping method with the recent successful experiments to fabricate the low-resistivity p-type GaN, p-type AlN and n-type diamond. We show that the co-doping method is the efficient and universal doping method by which to avoid carrier compensation with an increase of the solubility of the dopant, to increase the activation rate by decreasing the ionization energy of acceptors and donors, and to increase the mobility of the carrier.

Band Structures of Perovskite-Like Fluorides for Vacuum-Ultraviolet-Transparent Lens Materials

In the semiconductor industry, perovskite-like fluorides that have wide band gaps are potential candidates for vacuum-ultraviolet-transparent lens materials in optical lithography steppers. KMgF3 and BaLiF3 single crystals have already been grown, but materials with wider band gaps are desired. To find compositions more effective than KMgF3 and BaLiF3, we performed local density approximation (LDA) based ab initio band calculations for perovskite-like fluorides ABF3, where A and B include an exhaustive list of alkali metals, alkaline-earth metals, and other selected elements. We found that LiBeF3, NaBeF3, KBeF3, and RbMgF3 may have wider indirect band gaps than KMgF3 does. We also found that SrLiF3 may have a wider direct band gap than BaLiF3 does.

Fast molecular-dynamics simulation for ferroelectric thin-film capacitors using a first-principles effective Hamiltonian

A newly developed fast molecular dynamics method is applied to

First-principles accurate total energy surfaces for polar structural distortions of BaTiO 3 , PbTiO 3 , and SrTiO 3 : consequences for structural transition temperatures

{\text{BaTiO}}_{3}

Ferroelectric phase transitions in ultrathin films of BaTiO3.

ferroelectric thin-film capacitors with short-circuited electrodes or under applied voltage. The molecular dynamics simulations based on a first-principles effective Hamiltonian clarify that dead layers (or passive layers) between ferroelectrics and electrodes markedly affect the properties of capacitors, and predict that the system is unable to hop between a uniformly polarized ferroelectric structure and a striped ferroelectric domain structure at low temperatures. Simulations of hysteresis loops of thin-film capacitors are also performed, and their dependence on film thickness, epitaxial constraints, and electrodes are discussed.

Ab initio study of donor-hydrogen complexes for low-resistivity n-type diamond semiconductor

Specific forms of the exchange-correlation energy functionals in first-principles density-functional-theory-based calculations, such as the local-density approximation (LDA) and generalized-gradient approximations (GGA), give rise to structural lattice parameters with typical errors of

First-principles-based calculation of the electrocaloric effect in BaTiO3: A comparison of direct and indirect methods

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Direct Molecular Dynamics Simulation of Electrocaloric Effect in BaTiO3

and 2%. Due to a strong coupling between structure and polarization, the order parameter of ferroelectric transitions, they result in large errors in estimation of temperature-dependent ferroelectric structural transition properties. Here, we employ a recently developed GGA functional of Wu and Cohen [Phys. Rev. B 73, 235116 (2006)] and determine total energy surfaces for zone-center distortions of

Theoretical study of hydrogen-related complexes in diamond for low-resistive n-type diamond semiconductor

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The structural, dielectric, elastic, and piezoelectric properties of KNbO3 from first-principles methods

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