Influence of deposition distance and substrate temperature on the CdSe thin films deposited by electron beam evaporation technique

Abstract

Cadmium Selenide (CdSe) thin films were deposited on the microslide glass substrates by electron beam evaporation technique at source to substrate distance (Dd) of 10cm and 15cm and at different substrate temperatures (room temperature to 450°C). The influence of Dd and substrate temperature on the structural, optical and morphological properties of CdSe thin films was studied. X-ray diffraction studies revealed that CdSe films deposited at 10cm and 15cm and at different substrate temperatures possess hexagonal crystal system with preferential growth along (002) plane. Further the effect of Dd and substrate temperature on the microstructural parameters such as crystallite size, strain, dislocation density and lattice constants was studied. CdSe films deposited at Dd 10cm and 15cm and at 150°C acquired low strain and dislocation density with respect to that of the other films. The optical transmittance of the film deposited at Dd 10cm and at 350°C showed maximum transmittance of about 98% at 875nm whereas the film deposited at Dd 15cm and at room temperature showed maximum transmittance of about 84% at 747nm. Direct optical band gap energy of the films deposited at Dd 10cm is decreased with increase in substrate temperature. Scanning electron microscope studies revealed that the surface of the CdSe film deposited at Dd 10cm and at room temperature contains spherical shaped grains distributed on the surface and the surface becomes smooth with increase in substrate temperature. Surface of the film deposited at Dd 15cm and at room temperature showed fine grains with a few pinholes whereas the surface of the film deposited at 250°C and 350°C become rough with pinholes. Elemental analysis showed the presence of cadmium and selenium in the deposited thin films. Photoluminescence spectrum showed red emission band at ~740nm for the films deposited at Dd 10cm and 15cm and at room temperature, 150°C and 450°C.