III-nitride InGaN-based solar cells have gained importance because their band gap can potentially cover most of the solar spectrum, spanning 0.7 eV to 3.4 eV. However, to use these materials to harvest additional energy, other properties such as their thermoelectric properties should be exploited. In this work, the Seebeck coefficient and the electrical conductivity of three InGaN alloys with various indium concentrations and Gd-doped GaN (GaN:Gd) were measured, and the power factor was calculated. We report a Seebeck value of $209 lV/K for Gd-doped GaN.
It is shown that it is in principle possible to produce combined sources of polarization and magnetization that are not only radiationless but that have any (and sometimes several) of the four microscopic or macroscopic electromagnetic fields exactly zero. The conditions that such a "null-field radiationless source" must satisfy are derived, and examples are given for several cases. The implications for transformation optics and invisibility physics in general are discussed.
It is shown that a scatterer can be designed to be directionally invisible for an incident field composed of a given sum of plane waves. These scatterers are invisible only when all plane waves are present with the given amplitudes and directions of incidence, which suggests a new type of "switchable" invisibility. Such objects could find application in optical devices such as couplers, switches, and optical position sensors. It is also demonstrated that the designed scatterers have balanced gain-loss profiles that are more general than most PT-symmetric objects considered so far.
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