Temperature-dependent photoconductive properties of Ge-Sb-Te thin films

The present paper reports the study of photoconductive properties viz. steady state photoconductivity, dark conductivity , dark activation energy , transient photoconductivity on vacuum evaporated thin films of Ge20Te80-xSbx (x = 0, 2, 4, 6, 10 at. %). At higher concentration of antimony, dark activation energy is found to decrease. A similar trend in the optical band gap is also observed. Optical band gap also decreases with the addition of antimony in the system. This drop in activation energy points towards an increase in the density of defect states in the system. Dark conductivity values are found to increase, and this rise is due to an increase in polarizability of antimony and partial ionic behaviour of the system. Photosensitivity decreases with an increase in the antimony content in the matrix. Photocurrent versus light intensity follows the power law and predominance of bimolecular recombination is found. During transient measurements, the decay rate is found to be non-exponential. A differential lifetime is found to increase with the addition of antimony as a dopant. The study of the decay of photocurrent reveals relaxation processes in the present chalcogenide glassy matrix. This behaviour indicates a slow decay process due to the increase in the density of defect state in the mobility gap. Similar results are also confirmed with an increase in the carrier concentration.