RESUMO
The significant inversion symmetry breaking specific to wurtzite semiconductors, and the associated spontaneous electrical polarization, lead to outstanding features such as high density of carriers at the GaN/(Al,Ga)N interface-exploited in high-power/high-frequency electronics-and piezoelectric capabilities serving for nanodrives, sensors and energy harvesting devices. Here we show that the multifunctionality of nitride semiconductors encompasses also a magnetoelectric effect allowing to control the magnetization by an electric field. We first demonstrate that doping of GaN by Mn results in a semi-insulating material apt to sustain electric fields as high as 5 MV cm-1. Having such a material we find experimentally that the inverse piezoelectric effect controls the magnitude of the single-ion magnetic anisotropy specific to Mn3+ ions in GaN. The corresponding changes in the magnetization can be quantitatively described by a theory developed here.
RESUMO
In this paper we present an extensive theoretical and numerical analysis of monolithic high-index contrast grating, facilitating simple manufacture of compact mirrors for very broad spectrum of vertical-cavity surface-emitting lasers (VCSELs) emitting from ultraviolet to mid-infrared. We provide the theoretical background explaining the phenomenon of high reflectance in monolithic subwavelength gratings. In addition, by using a three-dimensional, fully vectorial optical model, verified by comparison with the experiment, we investigate the optimal parameters of high-index contrast grating enabling more than 99.99% reflectance in the diversity of photonic materials and in the broad range of wavelengths.
RESUMO
In current work the application of modified Scanning Thermal Microscopy (SThM) technique for thermal imaging of multilayered periodic photonic structures is presented. The measurements were carried out using non-standard operation mode of the SThM. The thermal probe was driven by the sum of DC and small AC currents. The main advantages of presented approach are mechanical stability of the probe during measurements and high sensitivity of AC signal detection by the use of lock-in amplifier. The amplitude and phase components of probe response signal are used for visualization and analysis of the thermal properties of the layer interfaces. Basing on topographic and thermal signals the thermal boundaries between layers were revealed and the periodicity of the structure was analyzed. Presented experiment indicates that the proposed method provides spatial resolution at least about 30% better than 100 nm, which is considered for standard nanofabricated thermal probes. Therefore, proposed technique may be successfully used for the thermal boundaries mapping, as well as for the high-resolution nanoscale imaging of thermal properties distribution. The results prove that thermal imaging provides additional information to that obtained by standard AFM imaging.
