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

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>E op ) decrease with increasing deposition angle, the optical energy gap E op remains the same as for 0° films, i.e., E op =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 D sat itself remains constant, independent of the intensity, it depends strongly on the deposition angle θ and the film temperature T, i.e., D sat (θ,T). For example, D sat (80°,77 K ) is more than four times D sat (80°,300 K ), and the values of D sat (0°,300 K ) and D sat (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.