Hisaomi Iwata

Cubic polytype inclusions in 4H–SiC

Multiple stacking faults in 4H–SiC, leading to narrow 3C polytype inclusions along the hexagonal c direction, have been studied using an ab initio supercell approach with 96 atoms per supercell. The number of neighboring stacking faults considered is two, three, and four. The wave functions and the two-dimensional energy bands, located in the band gap and associated with the narrow inclusions, can be reconciled with a planar quantum-well model with quantum-well depth equal to the conduction band offset between 3C– and 4H–SiC. We show that the existence of the electronic dipole moment due to the spontaneous polarization leads to a clear asymmetry of the bound wave functions inside the quantum well, and that the perturbation associated with the change in the dipole moment caused by the 3C–like inclusion accounts for the appearance of very shallow localized states at the valence band edge. We have also calculated the stacking fault energies for successive stacking faults. It is found that the stacking fault ...

Donor and acceptor concentration dependence of the electron Hall mobility and the Hall scattering factor in n-type 4H– and 6H–SiC

Theoretical calculation of the electron Hall mobility and the Hall scattering factor in 4H– and 6H–SiC is performed based on the low-field transport model. Our mobility calculation as a function of temperature, net-doping concentration ([ND]-[NA]), and compensation ratio ([NA]/[ND]), where ND and NA are the donor (nitrogen) and acceptor concentrations, respectively, provides the theoretical values of the electron Hall mobility expected for the high quality SiC crystal. The results can be used for the evaluation of the crystalline quality of a given SiC sample. We also present the ratio of the Hall and drift mobility, i.e., the Hall scattering factor, which is needed to make a bridge between the experimentally measured Hall mobility and the theoretically calculated drift mobility using, for example, Monte Carlo simulation. Our calculations of both the electron Hall mobility and the Hall scattering factor are in very good agreement with the experimental results.

Theoretical study of planar defects in silicon carbide

We report on a theoretical investigation of extended planar defects in 3C-, 4H-, 6H-, and 15R-SiC which can be formed without breaking any bonds, covering a wide range of planar defects: twin boundaries, stacking faults, and polytype inclusions. Their electronic structures have been intensively studied using an ab initio supercell approach based on the density functional theory. Stacking fault energies are also calculated using both the supercell method and the axial next-nearest-neighbour Ising model. We discuss the electronic properties and energies of these defects in terms of the geometrical differences of stacking patterns.

Ab initio study of 3C inclusions and stacking fault–stacking fault interactions in 6H-SiC

Ab initio supercell calculations of cubic inclusions in 6H-SiC are performed. The cubic inclusions can be created in perfect 6H-SiC by the propagation of successive partial dislocations having the same Burgers vector in neighboring basal planes, i.e., multiple stacking faults. We have studied the electronic structures and the total energies of 6H-SiC single crystals that contain one, two, three, and four stacking faults, based on density functional theory in local density approximation. Our total energy calculations have revealed that the second stacking fault energy in 6H-SiC is about six to seven times larger than that of an isolated stacking fault, which is actually opposite the trend recently obtained for 4H-SiC [J. Appl. Phys. 93, 1577 (2003)]. The effects of spontaneous polarization on the electronic properties of stacking disorders are examined in detail. The calculated positions of the quantum-well-like localized bands and stacking fault energies of 3C inclusions in 6H-SiC are compared with those ...

Stacking Fault – Stacking Fault Interactions and Cubic Inclusions in 6H-SiC: an Ab Initio Study

We report on a first-principles supercell calculation of cubic inclusions in 6H-SiC. Motions of successive partial dislocations having the same Burgers vector in the basal planes can lead to a 3C-l ...

Electronic Properties of Stacking Faults and Thin Cubic Inclusions in SiC Polytypes

The ability of SiC to crystallize in many different polytypes still remains a mystery. The distance over which an often complicated stacking order repeats ranges from around 10 A in 4H-SiC to several hundred A in the largest polytypes. The mechanism behind such a long-range correlation is difficult to imagine, and intuitively deviations from perfect stacking order, i.e., the occurrence of stacking faults (SF), should be quite common.

Effective mass of electrons in quantum-well-like stacking-fault gap states in silicon carbide

A first-principles calculation of the effective mass of electrons in quantum-well-like gap states induced by stacking faults and cubic inclusions in 4H- and 6H-SiC is performed, based on the densit ...

Electronic Structure of Twin Boundaries in 3C-SiC, Si and Diamond

We report on a first-principles band structure calculation of twin boundaries in 3C-SiC, Si, and diamond, based on the density functional theory in the local density approximation. It is found that ...

Insight into the Degradation Phenomenon in SiC Devices from Ab Initio Calculations of the Electronic Structure of Single and Multiple Stacking Faults

Soon after the discovery of the problem with electrical degradation of bipolar SiC devices, we started to perform ab initio calculations in order to evaluate the hypothesis that the degradation is ...

An ab initio study of intrinsic stacking faults in GaN

A first-principles study of intrinsic stacking faults in GaN is reported. Our calculations are based on density functional theory in local density approximation. We have found that the electron wav ...