Lattice Strain in AgGaS2 Epitaxial Layers Grown on GaAs (100) by Multisource Evaporation

Lattice strain in AgGaS2 epitaxial layers of different thicknesses, which are grown on GaAs (100) by the multisource evaporation method, is described. Biaxial compressive mismatch strain in thin layers relaxes with increasing layer thickness, and biaxial tensile thermal strain becomes dominant in thick layers. The thin AgGaS2 epitaxial layers are completely oriented toward the c-axis, but the thick layers contain 180°-rotated { 112 } twin crystals. The generation of twin crystals is considered to cause partial relaxation of the thermal strain. The observed variation in the A1-mode frequency with thickness is fully explained by considering the layer thickness dependence of the lattice strain. Full width at half-maximum of the A1-mode Raman scattering line is affected by the spatial inhomogeneity of the strain magnitude in the depth direction. Raman scattering measurement of the A1 mode can be used as a sensitive technique to evaluate the lattice strain in AgGaS2.