NANO-SCALE MEDIUM-RANGE ORDER IN SEMICONDUCTING GLASSY CHALCOGENIDES

Comprehensive X-ray diffraction studies of bulk glassy g-(As2S3)(0.95)In-0.05, g-(As2S3)(0.95)(GaSb)(0.05), and g-(As2S3)(0.56)I-0.44 samples reveal a large-scale medium-range ordering with correlation lengths up to similar to 50 Angstrom. The In- or Ga-doped glasses are considered non-homogeneous media containing a discrete hierarchy of metal enriched nanoclusters embedded in a metal-depleted g-As2S3 matrix. In this qualitative model, the observed additional optical absorption band, as well as the surprising phenomenon of stable optical anisotropy in g-As2S3:In, are explained. Large amounts of I atoms produce a more flexible medium-range order superstructure which may be easily rearranged by photoexcitation. This is the reason for the strong photoinduced metastable optical anisotropy in g-As2S3:I with a rather wide range of relaxation times.