CdGeAs₂ is a recent developing mid-infrared nonlinear optical material. It has high non-linear optical coefficient (d₃₆ = 236 pm/V), wide transparency range (2.3 ~ 18 μm), sufficient birefringence (n_e- n_o ≈ 0.09) and high thermal conductivity (about 42 - 93 mW/cm·K). These unique properties make CdGeAs₂ crystal a good candidate material for infrared frequency conversion applications. In this work, we have investigated in detail the low-temperature polarized-Raman-scattering spectra of CdGeAs₂ single crystal grown by the modified vertical Bridgman method. Comparing with the results of first-principles calculations, we identified all vibrational modes of CdGeAs₂ predicted from group-theory arguments. Our experimental results demonstrate that all-center modes can be grouped in three energy bands. First, within a very narrow energy range centered around 260 cm^-1 are four modes (1B₁+1B₂+2E). Next, in an intermediate region extending from 215 to 158 cm^-1 are five modes (1A₁+1B₁+1B₂+2E). And, finally, at much lower energy the dispersion of the acoustic branches gives, in the range 45-72 cm^-1, another series of four modes which are associated with 1B₁+1B₂+2E symmetry. Calculated from the three B₂ and six E modes, the macroscopic effective charges of CdGeAs₂ which determine the magnitude of the LO-TO splitting (longitudinal optic-transverse optic splitting) are all quite close to the results of first-principles calculations.

• Legal notice:
  

  Copyright (c) Pielaszek Research, all rights reserved.
  The above materials, including auxiliary resources, are subject to Publisher's copyright and the Author(s) intellectual rights. Without limiting Author(s) rights under respective Copyright Transfer Agreement, no part of the above documents may be reproduced without the express written permission of Pielaszek Research, the Publisher. Express permission from the Author(s) is required to use the above materials for academic purposes, such as lectures or scientific presentations.
  In every case, proper references including Author(s) name(s) and URL of this webpage: https://science24.com/paper/29691 must be provided.