ZnGeSb2: a promising thermoelectric material with tunable ultra-high conductivity

Quasiparticle effects on the linear and nonlinear susceptibility of ZnGeP2

The semiconductor zinc germanium diphosphide (ZnGeP₂) has wide applications in the infrared nonlinear optics (NLO) due to its high nonlinear optical coefficient, wide infrared transparency range and high thermal conductivity. Absorptions near the pump or generation wavelength limit the effectiveness of this materials, with their complicated microscopic origins remaining largely elusive. Most research on the absorption mechanism of ZnGeP₂ focused on the defect effect, while the quasi-particle effect and exciton effect are significant as well. We herein carried out the ab initio studies of the electronic band structure and optical properties of ZnGeP₂ crystal. The quasiparticle and excitonic effects were examined by comparing the results of PBE, GW approximation and Bethe–Salpeter equation. Quasiparticle effect was found to widen the quasi-direct band gap and increases the valence and conduction band dispersions, which mainly blue-shifts the imaginary part of the dielectric function. The increased band gap also leads to a broadened lineshape in the second order susceptibility. The excitonic effects significantly enhance the peak intensity in the long wave regime of the dielectric function and red-shift the peaks in the high energy regime, leading to the greatly improved agreement with experiment. Our results provided a microscopic guidance for improving ZnGeP₂'s optical performance.

The semiconductor zinc germanium diphosphide (ZnGeP₂) has wide applications in the infrared nonlinear optics (NLO) due to its high nonlinear optical coefficient, wide infrared transparency range and high thermal conductivity.

Intrinsic defects and their effects on the optical properties in the nonlinear optical crystal CdSiP2: a first-principles study

In view of their high nonlinear optical coefficients and good phase-matching properties, CdSiP₂ (CSP) crystals are considered as one of the most promising materials in the field of nonlinear optical applications. However, the slight absorption losses around 1.34 μm and 1.78 μm under e-polarized light have been affecting its performance. In this study, first-principles calculations were performed to identify the effects of various charge defects on the absorption properties. Different intrinsic defects in the CSP crystal were calculated using the HSE method and compared according to the specific chemical environments in the experiments. The results show that the point defects of V, Si, and V, which can be spontaneously formed, are dominant in the Cd-poor environment. The combination of Si and V defects is the most favorable cluster in the Cd-poor case because of its relatively low formation energy. Furthermore, the antisite defect Si_Cd was found to be responsible for the main absorption peaks at 1.34 and 1.78 μm in the experimental spectra, whereas other defects and clusters, such as the defects Si and V, also contribute to these red shifted absorptions. Our results intend to provide a guideline for adjusting the optical absorption in CSP by modifying its defects.