Photoinduced dichroism and its low-temperature characteristics in obliquely deposited amorphous As–Ge–Se–S thin films

Abstract

The photoinduced dichroism and its low-temperature characteristics in obliquely deposited amorphous As–Ge–Se–S thin films have been studied using a linearly polarized 632.8 nm He–Ne laser light and a control system capable of increasing the film temperature from 77 K. Our experimental results have been discussed on the basis of native valence-alternation pairs depended on the film fabrication. Although the absorption slopes in the extended region (hν>Eop) decrease with increasing deposition angle, the optical energy gap Eop remains the same as for 0° films, i.e., Eop=2.04 eV. A columnar structure with an inclination angle of approximately 70° is formed in 80° deposited films. While the value of saturated dichroism Dsat itself remains constant, independent of the intensity, it depends strongly on the deposition angle θ and the film temperature T, i.e., Dsat(θ,T). For example, Dsat(80°,77 K) is more than four times Dsat(80°,300 K), and the values of Dsat(0°,300 K) and Dsat(80°,300 K) are about 4.2% and 6.0%, respectively. We believe that an enhanced D in a columnar film is attributed to the increase of disorder (boids and dangling bonds). The photoinduced dichroism relaxes during a dark relaxation after its saturation and eventually sustains any value of nonzero, which depends on the inducing light energy and especially the value obtained after a prolonged exposure (∼3.3 h) is evaluated to be about 4.5 for 80° deposited film. However, it is eliminated completely by the exposure of nonpolarized light only for about 3 min.

Influence of Hydrogenation on the Amorphous-to-Crystalline Phase Transition Characteristics of Ge2Sb2Te5 and Ge8Sb2Te11 Thin Films

“…4) The structural changes in achalcogenides have been explained on the basis of behaviors of intrinsically charged defects, called valence-alternation pairs (VAPs). [5][6][7][8][9] VAPs either originate from the neutral defects on the process of film deposition via an exothermic reaction with an overall negative effective correlation energy (native VAPs) or are created from regular atoms by illumination of over-band-gap light (photo-created VAPs).…”