Photoconductivity and optical properties of amorphous GeTe

Unlike crystalline GeTe, amorphous GeTe has a relatively wide energy gap of 0.7 eV at 295°K, and 0.77 eV at 77°K. Its resistivity is about 103 ohm-cm at room temperature, and increases exponentially with T-1, giving an activation energy of 0.35 eV. The crystallization temperature for the amorphous GeTe films is about 390°K. The measured absorption coefficient is used to calculate a density of states which behaves very much as one would expect on the basis of the Mott model. The photocurrent for low photon energies has a long lifetime of tens of milliseconds, however, at higher photon energies, above 1 eV, the lifetime is less than 30 nsec. At low temperatures the fast lifetime is slowed to a few μsec. Near room temperatures where the thermally generated carrier density is approximately 3 × 1016 cm-3, obtained from our density of states, the dependence of the photocurrent on the light intensity is linear; below 150°K, the intensity dependence is a square root law, indicating bimolecular recombination. © 1970.