Electrical properties of α-nickel phthalocyanine/aluminium interfaces: Effects of oxygen doping and thermal annealing

Sandwich structures devices consisting of gold/nickel phthalocyanine/aluminium (Au/NiPc/Al) were thermally evaporated on borosilicate glass substrates maintained at room temperature under high vacuum. Electrical characterisation was performed under; (i) in situ, (ii) after exposure to dry air and (iii) after annealing at 395K. In all cases a rectifying junction between NiPc/Al was evident. Under forward bias condition, in situ device exhibit two different space charge limited conduction regions, whose density of traps decreases exponentially as a function of increasing energy. Upon exposure to dry air, and within the high voltage range, a transition from exponentially distributed traps to a single dominant trapping level is observed. The effect is attributed to oxygen adsorption close to NiPc/Al interface. Under reverse bias, oxygen is found to enhance Schottky type conduction. A transition to exponential trap distribution mode, in the higher voltage range, is observed upon annealing of the sample at 395K.