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In this paper, we theoretically investigate the propagation characteristics of Lamb waves in one-dimensional radial phononic crystal plates with periodic corrugations. The dispersion relations, the power transmission spectra, and the displacement fields of the eigenmodes are calculated by using the finite element method based on two-dimensional axial symmetry models in cylindrical coordinates. The axial symmetry model is validated by three-dimensional finite element model in rectangular coordinates. The effects of the geometrical parameters on the band gaps are further explored numerically. Numerical results show that several complete band gaps with a variable bandwidth exist for Lamb waves in the proposed structures. The formation mechanism of opening the acoustic band gaps is attributed to the coupling between the Lamb modes and the corrugation mode. The band gaps are significantly dependent upon the geometrical parameters such as the corrugation height, the corrugation width, and the plate thickness. Significantly, as the increase of corrugation height, band width shifts, new band gaps appear, the bands become flat, and the corrugation mode plays a more prominent role in the opening of Lamb wave band gaps. These properties of Lamb waves in the radial phononic crystal plates can potentially be applied to optimize band gaps, generate filters, and design acoustic devices. [ABSTRACT FROM AUTHOR]

Spontaneous emission property of an asymmetrically graded 480 nm InGaN/GaN quantum well (QW) is investigated via k·p theory. Comparing to rectangular QW, band profiles of the graded QW change into parabolalike due to the variation of internal piezoelectric field along the growth direction, and the spontaneous emission rates of the graded QW are three times larger than rectangular case under various carrier densities. This can be attributed to the fact that the graded QW has much larger matrix element (Me)nmσ(kt) than rectangular QW considering that the wave function overlap of the graded QW is less affected by the quantum confined Stark effect. [ABSTRACT FROM AUTHOR]

Donor-related cathodoluminescence of p-Al0.11Ga0.89N electron blocking layer (EBL) embedded in a laser structure was investigated by low-energy e-beam scanning along the ridge of a vertical taper both at 82 and 300 K. When e-beam probed the close vicinity of multiquantum well from p-side, an emission at 3.313 eV only appeared at 82 K and represented a prominent increase in intensity with a blueshift up to 23 meV. Besides, its intensity exhibited a linear dependence on quantum well (QW) emission intensity at low QW excitation and a sublinear dependence at high QW excitation. Combined with the annealing behaviors of the emission at elevated temperatures, these results were ascribed to the EBL capture of the holes tunneling from neighboring QW under built-in junction field and the subsequent donor-acceptor pairs transition involving a donor level of 116 meV below conduction band, which was presumably related to nitrogen vacancy (VN). [ABSTRACT FROM AUTHOR]

InGaN/GaN triangular quantum wells (QWs) are investigated theoretically, and the electron-hole wave-function overlap and optical gain characteristics are analyzed. The strong internal piezoelectric field is taken into account to explain the major difference between the optical properties of triangular QWs and conventional rectangular QWs. Our calculations reveal that triangular QWs, in comparison to rectangular QWs, provide higher electron-hole wave-function overlap and are less affected by the quantum confined Stark effect. Furthermore, triangular QWs exhibit increased optical gain and higher polarization degree, which are beneficial to GaN-based light emitting devices. [ABSTRACT FROM AUTHOR]