Pulsed laser deposition of organic semiconductor rubrene thin films

Abstract

Pulsed Laser Deposition (PLD) technique is applied to produce organic semiconductor (OS) rubrene thin film for spintronics applications. The use of organic material for spintronics is motivated by the advantages such as long spin diffusion length due to low spin-orbit and hyperfine coupling^1,2, chemical tuning of electronic functionality, easy structural modifications, ability of self-assembly and mechanical flexibility³ etc. However, a major drawback of OS is its low mobility compared to inorganic semiconductors. The PLD growth of rubrene aims on fabricating OS films under more controlled environment to achieve higher crystalline order to improve its mobility and spin coherence length. Among organic materials, rubrene reveals the highest hole mobility - up to 40 cm²/(V∙s) and can be exploited in organic light-emitting diodes (OLEDs) or field-effect transistors (OFETs) ^4. In this work the rubrene thin films are produced from hardened pellets in vacuum using Nd:YAG pulsed laser operated at 1064 nm, 2 Hz and energy fluence around 0.2 J/cm². For the reference rubrene samples on SiO₂ glass the AFM data reveal continuous 5-7 nm thick films. The amorphous structures are confirmed by XRD measurements and also Raman spectra which show signatures of both tetracene and phenyl bands and a broadband at 1373 cm^-1. The obtained results indicate that continuous, defect-free rubrene films can be prepared by means of PLD for investigation of the spin polarization properties of organic-inorganic hybrids. Further studies are on the way to improve crystalline qualities of the rubrene films for less grain boundary related defects and improved mobility and spin diffusion length.