Single crystals of the amino acid glycine (Gly) C2H5NO2 doped with croconic acid (CA) C5H2O5 were synthesized by evaporation from an aqueous solution. The crystals grow in the form of hexagonal pyramids or thin plates. Analysis of polarized Raman scattering spectra (excitation wavelength of 532 nm) measured at room temperatures showed that crystals in the form of pyramids corresponded to γ-polymorph (γ-Gly), and crystals in the form of plates to α-polymorph of glycine (α - Gly). The presence of croconic acid molecules in the crystals is confirmed by the change in their color from white in pure Gly crystals to light or dark yellow, characteristic of CA crystals, as well as the presence of weak lines corresponding to CA in the Raman spectra. In single crystals of both Gly:CA polymorphs, strong green luminescence significantly exceeding the intensity of Raman scattering is observed in the range 400 - 700 nm with a maximum at 510 nm (2.44 eV) upon excitation at λ= 325 nm.

The results of joint theoretical and experimental studies aimed at revealing features in the Raman spectra, which can be used for evaluation of the interface quality between GaN and AlN layers in short-period GaN/AlN superlattices (SLs) are presented. The Raman spectra for SLs with sharp interface and with different degree of interface diffusion are simulated by ab initio calculations and within the framework of random-element isodisplacement model, respectively. The comparison of the results of theoretical calculations and experimental data obtained on PA MBE and MOVPE grown SLs, leads to conclusion that the spectral region of the A1(LO) confined phonons is very sensitive to the degree of interface sharpness. As a result of comprehensive studies, the correlations between the parameters of the A1(LO) confined phonons and the structure of SLs are obtained. The results of the complex studies can be used to optimize the parameters of the growth process in order to form structurally perfect short-period GaN/AlN SLs.