Effect of strain-induced anisotropy on magnetization dynamics in Y3Fe5O12 films recrystallized on a lattice-mismatched substrate

We report on the correlation of structural and magnetic properties of Y3Fe5O12 (YIG) films deposited on Y3Al5O12 substrates using pulsed laser deposition. The recrystallization process leads to an unexpected formation of interfacial tensile strain and consequently strain-induced anisotropy contributing to the perpendicular magnetic anisotropy. The ferromagnetic resonance linewidth of YIG is significantly increased in comparison to a film on a lattice-matched Gd3Ga5O12 substrate. Notably, the linewidth dependency on frequency has a negative slope. The linewidth behavior is explained with the proposed anisotropy dispersion model.

In-Situ Rheed Observation of Mocvd-Gan Film Growth

We developed the MOCVD apparatus equipped with RHEED system, which enable us to observe in-situ and real time RHEED for GaN film growth in ~100mTorr of pressure. We attempted to grow GaN film with this MOCVD chamber in 100mTorr. The in-situ RHEED was subsequently observed along the film deposition process in order to understand both the role of buffer layer and the mechanism of GaN film growth by MOCVD on highly lattice-mismatched substrate like sapphire. The results indicate that oxygen removed from the sapphire surface was observed during its cleaning in H2 flow at 1100°C. The dependence of re-crystallization and evaporation of the buffer layer on the annealing ambient was also detected. Although the nitrogen was slightly deficient, HT-GaN film with smooth surface was obtained in 100mTorr by adding H2 gas and reducing total flow rate. In preliminary deposition, the RHEED oscillation-like was observed in MOCVD-GaN growth. Thus, our developing deposition system has a potential to understand the growth mechanism with atomic level.

MASS TRANSPORT OF GaN AND REDUCTION OF THREADING DISLOCATIONS

Mass transport of patterned GaN at around 1100°C in nitrogen with an ammonia atmosphere has been discovered for the first time. The mass transport process is found to be affected by the anisotropy of surface energy of GaN. Behaviors of threading dislocations which are predominantly of the mixed type and the pure edge type are affected by the anisotropy during mass transport. Mixed type dislocations are bent keeping the geometrical relationship normal to the surfaces, while pure edge type dislocations are bent horizontally. This new-found process, the so-called "mass transport epitaxy," is one of the best methods for achieving low dislocation density GaN on the highly lattice-mismatched substrate.