Layer-by-layer growth of precisely controlled hetero-molecular multi-layers and superlattice structures

•Layer-by-layer growth of organic molecules by hot-wall deposition technique.•pn-junction of organic semiconductors with single-molecular scale flatness•Characterization of morphologies by atomic force microscopy and X-ray reflection.

We demonstrate a technique for growing fine molecular films on a monolayer scale. We achieve layer-by-layer growth under thermally equilibrium condition by precisely controlling the conditions of an ultra-slow deposition technique. This technique is applicable to various kinds of p-type and n-type organic semiconductors and makes it possible to form a hetero-molecular interface (p-n junction) with molecular level flatness. The technique was used to produce a molecular superlattice, which enables the well-controlled design of energy level alignments in organic semiconductors.