Thin organic heterostructures deposited via organic vapor phase deposition: spectroscopic ellipsometry characterization

Abstract

Thin heterostructures and mixed layers of tris(8–hydroxyquinoline)-aluminum(III) (Alq 3) and N,N′-Di-[(1-naphthyl)-N,N′-diphenyl]-(1,1′-biphenyl)-4,4′-diamine ( α-NPD) were deposited on large-area silicon substrates by means of the recently developed organic vapor phase deposition (OVPD) method. Variable angle spectroscopic ellipsometry (VASE) was employed as a non-destructive technique to measure the thickness and optical constants of the single layers deposited by OVPD. Using the determined optical constants it is demonstrated that spectroscopic ellipsometry is capable of determining the thicknesses of individual layers in Alq 3/ α-NPD heterostructures. Furthermore, the percentage of mixing in uniformly mixed Alq 3− α–NPD layers can be determined from the analysis of the ellipsometric data. A simulation of ellipsometric parameters Ψ and Δ demonstrates that ellipsometry is a very suitable tool for in situ real-time thickness monitoring during the OVPD deposition process.