Mechanism of Reversible Optical Storage in Evaporated Amorphous AsSe and Ge10As40Se50
The holographic response (Keneman, 1971; Ohmachi and Igo, 1972) of evaporated AS2S3 at 4880Å has been ascribed to photo-polymerization of a hard-sphere As4S6 glass (deNeufville et al., 1973). The effect of illumination is to shift the location of the optical absorption edge (ΔE=-0.06eV), and to increase the refractive index (An=0.08). A comparable increase in refractive index occurs during annealing of evaporated As2S3 at 189 C, near its glass transition temperature, accompanied by a smaller edge shift (Δn=-0.03eV). While the optical absorption edge can be reversibly cycled by exposure at 25°C and annealing at 180°C (ΔE=-0.03eV), the accompanying index changes are relatively small (ΔE=**0.01). Furthermore, the X-ray diffraction pattern is unaffected by cycling, suggesting that the optical effects arise from the creation (exposure) and elimination (annealing) of a nonequilibrium concentration of trapped charge carriers rather than from an innate structural change.
KeywordsOptical Absorption Edge Trap Charge Carrier Innate Structural Change Interband Optical Transition Optical Transition Energy
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