Device characteristics of polymeric Light Emitting Diodes (pLED) with controlled oxidation of the calcium cathode during growth

The presence of oxygen during the deposition of the calcium electrode of po lymeric light-emitting diodes is investigated. The devices are fabricated i n an ultraclean setup. We used ITO as anode, OC1C10 PPV as electroluminesce nt polymer, calcium as cathode and aluminium as protecting layer. The influ ence of the presence of dry oxygen during deposition is investigated and th e exposure of the calcium layer to dry oxygen subsequently to the depositio n on the polymer. The change of the structure due to the exposure to oxygen is determined with elastic recoil detection analysis (ERDA) and correlated to the I-V-light characteristics of the devices. Exposure of the devices t o oxygen during deposition leads to a decrease in brightness and current wi th increasing oxygen pressure. The exposure of the calcium to oxygen subseq uently to the deposition does not affect the performance of the devices exc ept at calcium layer thicknesses less than 10 nm.