We have studied the epitaxial growth and photoluminescent (PL) properties of Eu3+-doped ZnO layers in correlation with structural analyses. Incorporation of Eu3+ ions into a ZnO host resulted in deterioration in crystal quality and lattice distortion. The spectral structure of Eu3+ emission revealed that Eu3+ ions were located at site symmetries lower than the original C3v of the Zn2+ ion sites in a hexagonal wurtzite structure of ZnO, which allowed for efficient red luminescence based on the electric dipole transitions. Moreover, we have found an anticorrelation of PL intensity between the excitonic and Eu3+ emissions, related to energy transfer from the ZnO host to the Eu3+ ions. The excitonic structure at the band edge was obscured upon doping with Eu3+ ions due to the formation of a band tail around 3.2 eV. This correlated with a reduction in excitonic emissions, leading to enhancement of Eu3+ emission. Strong PL emission from Eu3+ ions was only observed at low temperatures, and was remarkably suppressed with increasing temperature due to two types of nonradiative energy transfer paths. For the energy transfer process to Eu3+ ions, we suggest that the recombination energy of an electron–hole pair at the band tail near the band edge is close to that of high-lying excited levels in the Eu3+ 4f shell, providing an efficient energy pathway for the excitation of Eu3+ ions in the ZnO system.

Near-infrared Er photoluminescence (PL) is markedly modified using a plasmonic In2O3: Sn nanoparticle (NP) sheet. Modeling and optical measurements reveal the presence of different electric fields (E-field) in the NP sheet. The local E-field excited at the interface between the NP sheet and Er-emitting layer of ZnO contributes significantly towards the spectral modifications of Er PL due to matching with the photon energy of Er PL. We also determine the critical temperature for Er PL modifications, which is related to the energy transfer efficiency between Er transition dipoles in ZnO and the plasmon modes on the NP sheet.

A new sensor platform is realized by surface plasmon resonance on doped oxide semiconductors of In2O3:Sn layers (oxide‐based SPR) in the near‐infrared range. The detection sensitivity of oxide‐based SPR is initially demonstrated by enhancement of the absorption band ascribed to molecular‐vibrational modes in the NIR range, which indicates that the enhancing effects occur only when coupling is achieved between excitations of surface plasmons and molecular vibrations. These results are supported by theoretical analyses of electromagnetic field amplitudes on the layer surfaces. Further studies with SPR measurements of glucose‐water solutions reveal that the precise detection sensitivity (S) of oxide‐based SPR is 7576 nm RIU−1, which is consistent with the theoretically estimated sensitivity (S = 7447 nm RIU−1). The experimentally and theoretically obtained resolution in the refractive index is on the order of 10−5, which also supports the appearance of molecular‐vibrational modes in the SPR spectra. Finally, it is found that the detection sensitivity of oxide‐based SPR is close to that of Au metal‐based SPR working in the visible range, a result that is discussed in relation to the spatial coherence and major characteristics of SP waves at the metal–water interfaces of In2O3:Sn and Au layers.

We report two types of surface plasmon (SP) modes guided by a Ga-doped ZnO (ZnO:Ga) layer bounded between air and glass. A symmetric SP (s-) mode having leaky waves was found at an air-ZnO interface by attenuated total reflection measurements and showed a cutoff thickness region from 141 to 107 nm. Consequently, only an asymmetric SP (a-) mode bound at a ZnO-glass interface remained, as confirmed by numerical analyses and finite-difference time-domain simulations. s- and a-modes of the ZnO:Ga layer exhibited a high cutoff thickness and a strongly confined SP field at air-ZnO and ZnO-glass interfaces, respectively.

An inductor-less 110GHz ring-type frequency divider (RILFD) has been proposed. Body-injection and biasing technique have been adopted to achieve high speed and divideby-three operation and fine tuning of operation frequency. The RILFD was fabricated by a 1P12M 65nm bulk CMOS process. The core size is 10.8×8.5μm2. The locking range is 9.1%, from 100.8 to 110.4GHz, under varying of body-bias voltage from -0.2V to 0.4V. The RILFD consumes 4.5mW at the supply voltage of 1V excluding an output buffer. The output phase noise is -117.6dBc/Hz at 1MHz offset. This work has been achieved the smallest core size among frequency dividers reported to date operating over 100GHz.