ICMCTF2003 Session C7: Optical Thin Films for Active Devices

Recently, there has been an increased interest in organic light emitting diodes (OLEDs) due to their potential applications to color flat panel displays and in new optoelectronic components. These devices are assembled using three organic molecular materials: an electron injection layer, the emitting one and finally the hole injection layer. However, in most cases the electron injection is more difficult to achieve than hole injection. In this work two different amorphous carbon nitride thin films cathode were used to decrease the electron injection barrier. The first kind were a-C:N thin films deposited by Plasma Enhanced Chemical Vapor Deposition (PECVD) onto the MTCD/Alq3 layer structure thermally deposited. Amorphous carbon films were obtained with 100% N₂ partial pressures (total pressure P=8 Pa). Next, amorphous silicon carbon nitride thin films (a-SiC:N) have been deposited using a rf Magnetron Sputtering (13.56 MHz) system onto the same organic structure. In this case the films were deposited in reactive nitrogen-argon atmospheres. Also in this case, the deposition pressures was P = 8 Pa. In both cases a thick (150 nm) aluminum electrode were deposited onto the whole structure. The deposition process for the organic compounds is performed in high vacuum environment(6x10^-6 Torr)on glass substrates coated with an hole injecting ITO transparent layer. A preliminary investigation was conducted on the properties of the OLED device with the two a-C intermediate layers. The relationship between the properties of the amorphous carbon deposited films on the electroluminescent characteristics of the different devices are investigated. The refractive index of the a-C film deposited, their conductivity and optical absorption, the OLED I-V curves, a preliminary photoluminescent and electroluminescent OLED results are presented and discussed.

This work is supported by CNPq (RENAMI), FAPERJ and FAPESP.

High-transparency, low-electrical-resisitivity indium-tin-oxide (ITO) films (7.2 times 10^-5 ohm-cm) and Al-doped ZnO (AZO) films (9.27 times 10^-5 ohm-cm) were prepared by pulsed laser deposition (PLD) using an ArF excimer laser (wavelength : 193 nm).

First, a remarkable feature of the method used in this study to fabricate the ITO films is to deposit films in magnetic field (1.24 T), which is caused by rare earth permanent magnet of NdFeB, applied perpendicular to plume. As a reason to explain these results, it is thought that electrons in the plume accelerated by Lorentz force play a role to ionize species such as atoms, molecules and clusters, to promote plasma densities and to increase carrier concentrations. Next, in order to improve a reproducibility of the method, the distances between the target and the substrate were varied from 80 mm to 10 mm. A purpose of this trial is to make full use of a thermal energy of the plume and to increase Hall mobilities through an improvement in crystallinity caused by exposing the substrate to instantaneously high-temperatures. As a result, the films with 10^-5 ohm-cm were obtained in the probability of about 75 %.

Secondly, a similar method such as applying magnetic field to plume and shortening the distance between the target and the substrate was adopted to fabricate AZO films. As a result, we were preferentially able to fabricate the AZO films with the lowest-electrical-resistivity (9.27 times 10^-5 ohm-cm) by optimizing various preparation conditions.