Masaki Narushima

Vacancy-Type Defects Introduced by Gas Cluster Ion-Implantation on Si Studied by Monoenergetic Positron Beams

Vacancy-type defects in Ar and B gas cluster ion-implanted Si were probed by monoenergetic positron beams. The acceleration energy of the clusters ranged between 20–60 keV, and the mean cluster size was 2×103 atoms. Doppler broadening spectra of the annihilation radiation were measured, and the vacancy-rich region was found to localize at a depth of 0–13 nm. Measurements of the lifetime spectra of positrons revealed that two different defect species coexisted in the damaged region introduced by Ar gas cluster implantation, and these were identified as divacancy-type defects and large vacancy clusters filled with Ar. The formation of the vacancy clusters was attributed to extremely high temperature and its rapid transients in impact regions of Ar cluster ions. For B gas cluster ion implanted Si, the detected momentum distribution of electrons in the damaged region was broader than that in the defect free Si, suggesting that the trapping of positrons by open spaces adjacent of B clusters.

Magnetic Quantum Oscillations in In 0.53Ga 0.47As/In 0.52Al 0.48As Multiquantum Well Observed by Millimeter Wave Response

We report on millimeter wave measurements of an In0.53Ga0.47As/In0.52Al0.48As multiquantum well fabricated by gas source molecular beam epitaxy. Transmission experiments with the millimeter waves (16–110 GHz) were carried out as a function of the magnetic field up to 10 T at temperatures down to 0.6 K. The quantum oscillations corresponding to the Shubnikov-de Haas effect are observed in the amplitude and phase of the transmitting waves. The effective mass can be estimated as 0.058m0 for the 1st-subband electron. In spite of a small Fermi energy of 27 meV for the 1st subband, the enhancement of an effective mass is 30% over the bulk band-edge mass of 0.041m0. The large difference originates from the resonant polaron coupling due to a fundamental GaAs-like LO-phonon in addition to the band nonparabolicity of the In0.53Ga0.47As well.

Transport Properties in InP/InAlAs Type II Single Heterostructure

A type II interface is formed in an undoped InP/InAlAs single heterostructure grown by gas source molecular beam epitaxy. From measurements of the electrical resistivity, magnetoresistance and Hall effect, it is confirmed that a two-dimensional electron gas system containing a sheet carrier concentration of 1.8 × 1011 cm-2 is formed in the single hetero interface. In this study, the effective mass is estimated to be 0.074m0, corresponding to the 1st subband by the Shubnikov-de Haas effect at different temperatures. It can be clarified experimentally that the effective mass of the 1st subband is almost equal to the electron-mass in bulk InP. The energy difference between the Fermi level and the 1st subband is obtained as 5.8 meV, which is lower than the energy separation between the 1st and 2nd subbands.