Investigation of electrical properties of organic Schottky diodes using MgPc—the effect of oxygen absorption and post deposition annealing

Abstract

Sandwich structures of magnesium phthalocyanine (MgPc) thin films using aluminium (Al) and gold (Au) electrodes were prepared by thermal evaporation. Device characteristics of Al/MgPc/Au were found to show rectification properties. The electrical conductivity had been measured for the oxygen-doped, as-deposited and annealed samples. Current density–voltage characteristics under forward bias (aluminium electrode negative) were found to be due to the ohmic conduction at lower voltage regions with a hole concentration p0 = 3.92 × 1018 m−3 and mobility μp = 1.81 × 10−6 m2 V−1 s−1 for the as-deposited films. At higher voltage regions space charge limited conductivity (SCLC) controlled by a discrete trapping level of 4.51 × 1021 m−3 was obtained at about 0.73 eV above the valance band edge. The electrical parameters of oxygen-doped, as-deposited and annealed samples in the ohmic and SCLC regions were determined. The reverse bias curves were interpreted in terms of a transition from the electrode-limited Schottky emission to the bulk-limited Poole–Frenkel effect. The Schottky barrier parameters of oxygen-doped and annealed structures along with the as-deposited samples were determined from the C2–V characteristics. The space charge density N = 2.54 × 1022 m−3, built-in potential Vbi = 0.80 eV, depletion width W = 135 nm and barrier height φ = 1.09 eV were obtained for the as-deposited films.