RESUMO
This paper presents a comprehensive study of the performance of Sezawa surface acoustic wave (SAW) devices in SweGaN QuanFINE® ultrathin GaN/SiC platform, reaching frequencies above 14 GHz for the first time. Sezawa mode frequency scaling is achieved due to the elimination of the thick buffer layer typically present in epitaxial GaN technology. Finite element analysis (FEA) is first performed to find the range of frequencies over which the Sezawa mode is supported in the grown structure. Transmission lines and resonance cavities driven with Interdigital Transducers (IDTs) are designed, fabricated, and characterized. Modified Mason circuit models are developed for each class of devices to extract critical performance metrics. We observe a strong correlation between measured and simulated dispersion of the phase velocity (vp) and piezoelectric coupling coefficient (k2). Maximum k2 of 0.61% and frequency-quality factor product (f.Qm) of 6×1012 s-1 are achieved for Sezawa resonators at 11 GHz, with a minimum propagation loss of 0.26 dB/λ for the two-port devices. Sezawa modes are observed at frequencies spanning up to 14.3 GHz, achieving a record high in GaN microelectromechanical systems (MEMS) to the best of the authors' knowledge.
RESUMO
Photoluminescence (PL) behaviour in InN nanocolumns reveal decreasing, increasing and near invariant peak energies (E(PL)) as a function of temperature. Samples, having E(PL)~0.730 eV at 20 K, showed temperature invariance of E(PL). Samples possessing E(PL) on the lower and higher energy side of 0.730 eV demonstrate a normal redshift and anomalous blueshift, respectively, with increasing temperature. This temperature evolution can be effectively explained on the basis of a competition between a conventional red shift from lattice dilation, dominant for low carrier density sample, on one hand, and a blue shift of the electron and hole quasi Fermi-level separation, dominant for high carrier density samples, on the other.
