Tellurium suboxide($TeO_x$) thin films prepared by deoxidization evaporation method are found to have the property of showing a large change in optical transmittance on thermal or optical heating due to the amorphous-crystalline phase transition.
To observe the temperature dependence of the optical transmittance, the thin films with various compositions are heated in the temperature range 30 ∼ 300℃ and at the same time transmittance is measured at 0.6328 μm.
Abrupt change in transmittance occurs near the phase transition temperature (80 ∼ 170℃) depending on x value of $TeO_x$.
To find the mechanism of transmittance change, X-ray diffraction patterns are examined. The results show that the structure of the deposited sample is amorphous but by heat treatment, the sample changes to a slightly ordered polycrystalline structure.
The spectral transmittance of the thin films are measured in the 0.45 ∼ 0.95 μm wavelength range.
And from the measured transmittance data, the changes of optical constants before and after the heat treatment are calculated. The refractive indices of $TeO_{1.0}$ sample at 0.6328 μm are 3.32(before) and 3.60(after), extinction coefficients are 0.88(before) and 1.26(after), respectively.
Laser annealing by He-Ne laser beam is performed and the changes of transmittance with time as a function of intensity are measured. CW laser annealing causes nearly the same effect in transmittance change as the thermal heating. Writing, erasing with YAG(Nd$^{3+}$) laser and reading with He-Ne laser are performed.
Writing with long annealing pulse (40 μ$\sec$, not Q-switched), erasing with passively Q-switched short pulse (20n$\sec$) and direct readout during writing and erasing are performed. The threshold energies for the writing and erasing are found 210nJ and 16nJ, respectively.
