Stability of amorphous Se/Se100−xTex multilayers: A Raman study

Abstract

The Raman spectra of amorphous Se/Se100−xTex multilayers (AMLs) of various compositions and sublayer thicknesses have been measured at room and low temperature (38 K) with the aim to assess the thermal and absorption effects of laser illumination on the structural stability of the AMLs. Under thermal treatment at room temperature (mediated by increasing gradually the power of the probing laser line), the AML stability (manifested by the rate of Se crystallization) increases with decreasing Se100−xTex sublayer thickness and with decreasing Te content. However, in single layers (2 μm thickness) of Se100−xTex, we have observed the opposite effect, that is, the stability of single layers increases with increasing Te content. This apparent contradiction is explained in terms of thermodynamic energy considerations stated previously [K. Tanaka et al., Mater. Res. Soc. Symp. Proc. 118, 343 (1988)] and of a higher crystallization temperature of Se sublayers in the AMLs than that of bulk Se of the single layer. In order to eliminate (or, at least, reduce considerably) the thermal effects of laser illumination and study the photoinduced structural changes (due to absorption) in Se/Se100−xTex AMLs, low temperature (38 K) measurements were carried out using the 530.9 nm Kr+ laser line which is strongly absorbed by these AMLs. The rate of photoinduced crystallization increases with increasing Te content, which means that their stability to photoinduced changes is (again) higher, the lower the Te content. This is in agreement with previous results concerning three-dimensional Se100−xTex alloys, implying that the dimensionality change (from 3 in the alloys to 2 in the AMLs) does not affect significantly the Se–Se and Se–Te bond energies.