Electrical properties, optical and structural studies and Schottky device fabrication in thin films of the organic semiconductors – CdPc, InPcCl and AlPcCl

Abstract

Thin films of Cadmium phthalocyanine (CdPc), Indium phthalocyanine chloride (InPcCl) and Aluminium phthalocyanine chloride (AlPcCl) are prepared by thermal evaporation under high vacuum. Dependence of activation energy on film thicknesses and substrate temperatures is studied. Post deposition annealing of the films is done, both in air and in vacuum, at different temperatures. Annealed films are also investigated for the dependence of activation energy on annealing temperature. Films annealed in air and films deposited at various substrate temperatures are subjected to optical studies for finding the fundamental as well as excitonic band gaps. Variation of refractive index (n), extinction coefficient (k) and optical dielectric constants (and#949;1 and and#949;2) with photon energy is also studied. Films deposited at various substrate temperatures are subjected to X-ray diffraction studies for finding their grain sizes and phase transformation. Sandwich structures of the type Au-CdPc-Al , Au-InPcCl-Al and Au-AlPcCl-Al are fabricated and subjected to d.c. conductivity studies. Under forward bias, a transformation from ohmic conductivity to space charge limited conductivity (SCLC) with exponential trapping distribution is observed. Electrical transport parameters of CdPc, InPcCl and AlPcCl are derived from the forward-bias conductivity studies. Under reverse-bias, Schottky emission is detected. Schottky barrier height (and#966;s) and width (and#969;) are derived. Gold and Aluminium are found to form ohmic and Schottky contacts respectively with CdPc, InPcCl and AlPcCl thin films.