Organic molecular beam deposition: technology and applications in electronics and photonics Invited Lecture

Abstract

Organic semiconductors have been intensively studied over the past decades. The potential of this new class of materials for photonic and electronic device applications is demonstrated by successful fabrication of organic and organic-on-inorganic heterostructures for electroluminescent devices, photodetectors, and microwave diodes. The fabrication technology of organic semiconductor devices for both electronic and photonic applications is discussed. In contrast to spin-on or dipping techniques for fabrication of polymeric films, organic compounds with low molecular weight are sublimated under ultra high vacuum (UHV) conditions. The organic molecular beam deposition (OMBD) technology employed allows the reproducible growth of complex layer sequences with a defined thickness of various organic semiconductors in combination with dielectric films, different metallizations, and indium–tin oxide layers. Growth rates from 1–5 nm min^-1 and substrate temperatures from 77 to 350 K are used. Organic-on-inorganic heterostructure diodes based on crystalline thin PTCDA (3,4,9,10-perylenetetracarboxylic dianhydride) films on III–V semiconductors are investigated with regard to microwave applications with reduced forward voltage and high cut-off frequencies in the GHz regime. Secondly, efficient organic light emitting diodes with bright emission in the blue [1-AZM-Hex (N,N′-disalicylidene-1,6-hexanediaminate)zinc(II)], green, [Alq₃ (tris(8-hydroxyquinoline)-aluminum)], and red (Eu complexes) spectral region and with low operation voltages are presented. In general an onset voltage of 2.7 V, efficiencies up to 7 lm W^-1 and a luminance up to 2×10⁵ cd m^-2 (CW, RT) are attained for N,N′-diphenyl-quinacridone doped Alq₃ devices. An undoped device can be operated up to 5000 h without any loss in brightness and just a small increase of the driving voltage of about 2 V. Embedding emissive organic thin films with a narrow spectral characteristic into planar Fabry–Perot microcavities, a light intensity enhancement and a spatial redistribution of the emission is achieved.