arXiv subjects

Masato Morifuji

Publications and source records attributed to Masato Morifuji.

3 recordsLinked to original sources

arXiv2015

Perturbation analysis on large band gap bowing of dilute nitride semiconductors

Contrary to the conventional empirical law, band gap of dilute nitride semiconductors decreases with nitrogen concentration. In spite of a number of investigations, origin of this "large band gap bowing", is still under debate. In order to elucidate this phenomenon, we investigate change of band edge energies of GaN$_x$As$_{1-x}$ due to nitrogen by using the perturbation theory. It is found that energy shift of conduction band edge is arising from mixing between $Γ$- and L-states and/or $Γ$- and X-states induced by displacement of Ga atoms around N. We also found that the valence band edge state shows upward shift in spite of negative potential of nitrogen. These results are well understood from character of the wavefunctions and symmetry of the perturbation potential.

cond-mat.mtrl-sci↗

arXiv2014

Reduced Hamiltonian for Electronic States of Dilute Nitride Semiconductors

We present a novel model to describe conduction band of GaN_xAs_{1-x} (GaNAs). As well known, GaNAs shows exotic behavior such as large band gap bowing. Although there are various models to describe the conduction band of GaNAs, origin of the band gap bowing is still under debate. On the basis of perturbation theory, we show that the behavior of conduction band is mainly arising from intervalley mixing between Gamma and L or X. By using renormalization technique and group theoretical treatment, we derive a reduced Hamiltonian which describes well the band gap shrinkage of GaNAs.

cond-mat.mtrl-sci↗

arXiv2006

Coherent Spin Dynamics into Space Quantization

We propose a mechanism to describe how a physical quantity, which initially can take continuous values, is restricted within some discrete values after a measurement. As an example of the present theory, in which interplay between coherence of motion and fluctuation from disturbance plays an important role, we investigate motion of a spin state in a magnetic field. First, we point out that discrete eigenstates are formed from continuous states as a result of coherence of precession motion of a spin. Next, by assuming disturbance from environmental electromagnetic fields, we investigate temporal change of direction of a spin state by applying the first order perturbation theory and the Monte Carlo technique. Results of simulations show that the spins, whose directions are randomly distributed at the initial time, are reoriented toward only two directions due to fluctuation guided by coherence.

quant-ph↗