This paper presents a new approach for the design of film bulk acoustic resonators (FBARs) with high-quality factor Q _a at antiresonant frequency f _a . Lamb waves are among the main contributors to the loss of energy at f _a and the deterioration of Q _a . The targeted approach is an optimization process of a dual-step frame structure to alleviate the problem with Lamb waves at f _a . Such a frame is a combination of two neighboring steps that have different acoustic impedances reflecting the two Lamb modes that carry the largest amount of energy. The dimensions of these steps are computed using the diffraction grating method. To do so, the dispersion curves of Lamb waves and their associated power flows are calculated using a global matrix method and the acoustic Poynting's Theorem. This results in an enhancement in Q _a of nearly 82% for an FBAR with a dual-step frame in comparison with an FBAR with no frame, as well as a smoother electrical response, at frequencies above fa but below the resonant frequency f _r spurious resonances are moderately increased.

In this paper, the Q-factor enhancement of the Thin Film Bulk Acoustic Wave Resonator (FBAR) with Type-II dispersion is investigated. Our purpose is to improve the Q-factors of the resonator, especially the one at anti-resonance frequency (f _a ), by the application of a frame structure on its periphery. The frame performs as a lateral acoustic Bragg reflector, which is able to reflect two Lamb modes S ₁ and S ₀ upon the FBAR border region. These two modes are presumed to contribute the most to lateral acoustic leakage. The results of one of the modified FBARs exhibit a superior improvement of the Q factor at f _a (Q _a ) of about 1000 over the one without optimization.

Experimental results examining the photoluminescence spectra of selectively Si-doped $\text{GaAs}/{\text{Al}}_x{\text{Ga}}_{1-x}\text{As}$ heterostructures is presented. Possible mechanisms of carrier recombination are discussed with a special emphasis on the peculiarities of excitonic photoluminescence. Strong intensity lines in photoluminescence spectra are associated with the formation and enhancement of free exciton and exciton-polariton emission in the flat band region of an active $i$ -GaAs layer. The excitonic PL intensity is sensitive to the excitation intensity indicating high nonlinear behavior of spectral-integrated photoluminescence intensity and exciton line narrowing. These observed phenomena may be related to the collective interaction of excitons and the interaction of excitons with emitted electromagnetic waves. The gain of the amplification of the excitonic photoluminescence intensity in the heterostructure was found to be more than 1000 times larger than the intensity of $i$ -GaAs active layer. The quality factor of the exciton line emission and the exciton-polariton line was found to be 3800 and 7600, respectively.

The optical transitions in 20 nm wide silicon and beryllium $\delta$ -doped GaAs/AlAs multiple quantum wells with various doping levels were investigated at different excitation intensities. A fractional dimensionality model was used to describe the free hole-donor and free electron-acceptor transitions in the quantum wells. The measured photoluminescence spectra from samples of different doping level related to donor-impurity or acceptor-impurity induced effects in the photoluminescence lineshape, were compared within the framework of these model calculations. Both experimentally and theoretically it was shown that acceptor and donor related optical transitions and photoluminescence line shapes were related to the difference in the effective masses of holes and electrons. This effect also leads to a difference in the photoluminescence spectra in which the luminescence band for the donor related spectrum is narrower in comparison to the acceptor related spectrum.

The competition between various carbohydrates in the binding to Concanavalin A (Con A) can be exploited in gravimetric microsensors that detect changes in mass or viscoelasticity as a function of glucose concentration. Such sensors are based on the immobilisation of Con A as the ligand specific element, and a successful application requires that the binding property of Con A is retained. This paper presents a simplified immobilisation procedure of Con A on a quartz surface, a common material for gravimetric microsensors. Structural assessment with atomic force microscopy confirmed that the surface was covered with a layer of macromolecules. This layer shows the presence of entities of various sizes, presumably monomers, dimers and tetramers among which dimers of the Con A are the most dominant structure. Functional assessment using fluorescent labelled dextran (FITC and Alexa 488) suggests a surface coverage ranging from 1.8 × 10¹¹ to 2.1 × 10¹² immobilised fluorescent molecules per cm². The assay was responsive to glucose over a concentration range from 0–40 mM, but became gradually saturated above 20 mM. Hence, the immobilised Con A is able to bind dextran, which is displaced by glucose in a concentration dependent manner, thus triggering a mass change proportional to the M_W of dextran.