Spectroscopic ellipsometric characterization of organic films obtained via organic vapor phase deposition

Thin films of Tris(8-hydroxyquinoline)-aluminum( III) (Alq(3)) and N, N'-Di-[(1-naphthyl)-N,N'-diphenyl]( 1,1'-biphenyl)- 4,4'-diamine (alpha-NPD) were deposited on large-area silicon substrates by means of the recently developed organic vapor phase deposition (OVPD) method. Variable-angle spectroscopic ellipsometry was used to measure the optical constants of OVPD Alq(3) and alpha-NPD layers in the 0.8 - 5 eV energy range. The absorption onset which defines the lower limit of the optical band gap was found to be at similar to 2.65 eV and similar to 2.9 eV for Alq(3) and alpha-NPD, respectively. Additionally, the thicknesses of the layers as well as the thickness profiles of the organic thin films were determined along the 8" diameter of the wafers. The thickness analysis revealed large-area uniform deposition of the films.