Strong influence of the Pd-Si ratio on the valence transition in EuPd2_2Si2_2 single crystals

Single crystals of intermediate valent EuPd$_2$Si$_2$ were grown from an Eu-rich melt by the Bridgman as well as the Czochralski technique. The chemical and structural characterization of an extracted single crystalline Czochralski-grown specimen yielded a slight variation of the Si-Pd ratio along the growth direction and confirms the existence of a finite Eu(Pd$_{1-m}$Si$_m$)$_2$ homogeneity range. The thorough physical characterization carried out on the same crystal showed that this tiny variation in the composition strongly affects the temperature T$_v$ at which the valence transition occurs. These experiments demonstrate a strong coupling between structural and physical properties in the prototypical valence-fluctuating system EuPd$_2$Si$_2$ and explain the different reported values of T$_v$

Axial Inhomogeneity of Mg-Doped GaN Rods: A Strong Correlation among Componential, Electrical, and Optical Analyses

We systematically characterized the inhomogeneous doping properties along the <i>c</i>-axis of Mg-doped <i>p</i>-GaN microrods. Axial variation of doping concentration and electrical resistance on the <i>p</i>-GaN rod were measured by time-of-flight secondary-ion-mass-spectrometry and four-point probe measurements, respectively. Defects-related optical information was obtained from photoluminescence spectra together with Raman experiments revealing the change of crystal quality and strain along the rod. On the basis of a correlation of these analyses, we confirmed that Mg concentration decreased along the axial direction of the rod, leading to increasing electrical resistance. This axial Mg concentration change was revealed by green luminescence because the intensity of green luminescence sensitively varied with the doping density in both high-doping and low-doping rods. Interestingly, all the resistances at the highly doped rods were higher than the lowly doped rods due to overall mobility degradation at the high-doping rods caused by a scattering effect of increased Mg impurities and strain. All analyses provided complementary information on the <i>p</i>-type doping process and contribute to understanding the <i>p</i>-doping properties of GaN rod based photonic devices. Furthermore, our axially resolved optical spectroscopic (photoluminescence and Raman) methods can provide a facile, fast, and nondestructive way to estimate the axial doping and conductivity inhomogeneity of a Mg-doped <i>p</i>-GaN rod without having complex, time-consuming, and destructive structural and electrical measurements