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 (hv>E-op) decrease with increasing deposition angle, the optical energy gap E-op remains the same as for 0 degrees films, i.e., E-op=2.04 eV. A columnar structure with an inclination angle of approximately 70 degrees is formed in 80 degrees deposited films. While the value of saturated dichroism D-sat itself remains constant, independent of the intensity, it depends strongly on the deposition angle theta and the film temperature T, i.e., D-sat(theta T). For example, D-sat(80 degrees, 77 K) is more than four times D-sat(80 degrees, 300 K), and the values of D-sat(0 degrees, 300 K) and D-sat(80 degrees, 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 (similar to 3.3 h) is evaluated to be about 4.5 for 80 degrees deposited film. However, it is eliminated completely by the exposure of nonpolarized light only for about 3 min. (C) 2000 American Vacuum Society. [S0734-2101(00)08302-0].