ENERGY-DEPENDENCE OF LIGHT-INDUCED CHANGES IN g-As45S55 DURING RECORDING THE MICRO-RAMAN SPECTRA

Abstract

Light-induced structural changes of g-As45S55 were probed both by macro FT-Raman and energy-dependent micro-Raman spectroscopy. We suppose that new observed features in the Raman spectra of As-rich As-S glass are related to transformations of As4S4 molecules. Being initially in the structure of g-As45S55 closed and connected with glassy network only by weak Van der Vaals forces α(β)-As4S4 molecules are transformed into pararealgar pAs4S4 form during laser illumination. The effectiveness of transformations depends mainly from photon energies used for irradiation but transformation tendency observed for all used photon energies ranged from 1.65 to 2.54 eV. Observed Raman features and their structural origin are discussed. Theoretical and experimental investigations in the last years shown that chalcogenide glassy semiconductors (ChGS) continuous media are formed in a wide variety of basic short range order structural units (s. u.) than their crystal analogs [1-3]. The majorities are combined into the middlerange ordering (MRO) grouping (clusters), depending on concentration of additives and producing technology [4-6]. The ordering groups’ geometry in ChGS system' s bulk glasses and films determines physical properties [6,7]. During the few years a great importance starts to be given to structural fluctuations and separated nano-scale phases with homopolar As-As bonds for interpreting photo-induced phenomena in binary As-S glasses [8,9]. The concentration of nano-phases, n.f.~1.02.0 % in g-As2S3 is much larger than that of charged defects (Cdef~1 p.p.m.) which is foreseen by model [10,11]. The model of charged defects [10,11] in glass is known for a long time and has been the most widely spread one used to explain the photo-induced absorption in ChGS. This model is also used to explain the optical behavior in ChGS induced by the light with the energy of photons (E) lower than the Tauc band gap ( 0) in the Urbach edge region of optical absorption spectra. We have experimentally revealed that the introduction of HgS into g-As2S3 increases the absorption in the weak absorption region and is accompanied by the separation of β-As4S4 [12]. However, the