Physics of Organic Semiconductors, 2nd, Completely New Revised Edition

1

Organic Molecular Beam Deposition

Frank Schreiber

1.1 Introduction

Organic semiconductors exhibit a range of interesting properties, and their application potential is rather broad, as seen in many other chapters in this book. For the crystalline “small-molecule” systems, grown by organic molecular beam deposition (OMBD), the subject of this chapter, it is generally agreed that the structural definition is important for the functional properties. The following list should serve to illustrate the various aspects:

1. The definition of interfaces (degree of interdiffusion and roughness)

a. Organic–organic (e.g., in organic diodes)

b. Organic–metal (e.g., for electrical contacts)

c. Organic–insulator (e.g., in transistors, insulating layer between gate and semiconductor)

2. The crystal structure

a. Which structure is present? (Note that polymorphism is very common in organics).

b. Are different structures coexisting?

c. Orientation of the structure (epitaxy)?

d. Is the structure strained (epitaxy)?

3. Crystalline quality/defect structure

a. Mosaicity (note that in a thin film one has to distinguish between quality in the -plane and in -direction (surface normal)).

b. Homogeneity within a given film (density of domain boundaries etc.)

c. Density of defects (and their nature), which ...