ECR Plasma effect on the Optical Properties of Se₈₀Te_20-xPb_x thin films.

K.P.Tiwary*, Haider Abbas^b, L.S.S.Singh^c, M.Husain^c

Department of Applied Physics, Birla Institute of Technology, Patna-800014, India.

^bDepartment of Applied Physics, Manav Rachna College of Engineering,Faridabad, India

^c Department of Physics, Jamia Millia Islamia, New Delhi-110025 India

Abstract

The optical memory effects in amorphous semiconductor films have been investigated and utilized for various applications in recent years. Chalcogenide glasses are practically used as optical materials in a number of cases. Therefore, their transparence characteristics have to include both the visible and close infrared part of the spectrum, practically the wavelengths of He-Ne (0.6328 mm) and CO2 (10.6 mm) lasers. It is well known that the amorphous films are more transparent than the crystalline ones. These have distinct advantages, viz., large packing density, mass replication, fast data rate, high signal to noise ratio and high immunity to defects. Glassy alloys of Se₈₀Te_20-xPb_x with x=2,6 and 10 were prepared by quenching technique. The highly pure materials were weighed using electronic balance according to their atomic percentages and sealed in quartz ampoules in a vacuum of 10^-5 Torr. The sealed ampoules were then placed in a Microprocessor-controlled Programmable Muffle Furnace at 1123 K for 12 hours. The ampoules were rocked frequently to ensure the homogenization of the melt. After that the quenching was done in ice water to obtain the amorphous state. Thin films of glass alloys of thickness 3000? were prepared by the vacuum evaporation technique in which the glass substrate was kept at room temperature (300K) at a base pressure of 10^-6 Torr using a molybdenum boat. The optical band gap for thin films of Se₈₀Te_20-xPb_x before and after exposing to ECR plasma discharge have been studied as a function of photon energy in the wavelength region 400-900 nm. Thin films were exposed to plasma discharge at a pressure range varying between 0.015 to 0.020 mbar and exposure time 5 minutes. It was found that the optical band gap of the film increases after exposing to ECR plasma discharge. The change in optical band gap may be due to the reduction in disorderness of the system

Key words: Optical band gap, Thin films, amorphous semiconductor, ECR Plasma

^*Corresponding author:

Tel:  +91-0612-2223545

Fax: +91-0612-2223545

E-mail address:  kptiwary@rediffmail.com