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.

Photo-crystallization in a-Se imaging targets: Raman studies of competing effects

“…Raman scattering has been utilized effectively by a number of researchers to study photo-induced crystallization in a-Se and other chalcogenide-based glasses [12,[22][23][24][25][26]. The Raman spectrum of a-Se is dominated by a broad band with maximum near 250 cm À1 ($20 cm À1 FWHM), due to the A 1 -symmetry bondstretching vibrations of the chain fragments and ring-like units that comprise the amorphous Se structure [22,27,28].…”

Enthalpic structural relaxation in Te-Se glassy system

“…the GeSe 4 tetrahedra in Ge-Se glasses), that would cause the structure to become heavily crosslinked or interconnected, are being formed, the consequence of which is that no initial rapid increase of activation energies with increasing Te content had to be expected. The factual decrease of Δh ⁎ is probably related to the lower energy of Te-Se bonds [17,18]. Process of structural relaxation involves many different subprocesses (as e.g.…”

Compositional dependence of the optical properties of amorphous Se100-xTex thin films

“…Also, amorphous chalcogenides, based on Se and Te, have been well studied [1][2][3] and compounds of selenium and tellurium have potential applications in semiconductor devices, transistors and detectors [4]. This underlines the importance of the characterization of these amorphous materials through the determination of their optical constants, such as refractive index and extinction coefficient, as well as their optical band gaps In recent decades, optical properties of thin dielectric films have been the subject of intense study and significant efforts have been made to develop the mathematical formulation describing the transmittance and reflectance of different optical systems [5][6][7][8].…”