Homoepitaxy and Heteroepitaxy of Organic Crystalline Semiconductors

Abstract

Organic and crystalline semiconductors are an exciting field of study with many applications for device fabrication. Highly ordered films synthesized out of these crystalline materials have shown significant improvements in charge mobility and exciton diffusion (as opposed to amorphous, organic films), which motivates further study and optimization of homoepitaxy and heteroepitaxy techniques to create uniform, pinhole free films fit for device fabrication. This project seeks to identify semiconducting organic materials suitable for smooth heteroepitaxial growth over template crystalline organic semiconductors and to optimize recipes for homoepitaxy and heteroepitaxy to create smooth, ordered crystalline films. Experiments of homoepitaxial growth with 2,2-bis(diphenylphosphino)-1,1-binaphthyl (BDP) and N,N-di(1-naphthyl)-N,Ndiphenyl-(1,1-biphenyl)-4,4-diamine (NPB) confirmed the requirement for slow flux and hot substrate temperature deposition for optimal layer-by-layer crystal growth and demonstrated remarkably smooth film root mean square roughnesses even at increasing adlayer thicknesses. Heteroepitaxy experiments with methyl (triphenylphosphoranylidene) acetate (MTTPA) over a template layer of BDP investigated the requirement lattice matching between the lowest energy planes of two materials to make heteroepitaxial growth over a crystalline template viable. Challenges with the thermal stability of MTTPA invited further investigation into recipes and materials that can ensure smooth, layer by layer growth and in-plane crystal alignment.