Crystallinity of PTCDA films on silicon derived via optical spectroscopic measurements

Optical spectroscopies: Raman, infrared (IR) and photoluminescence (PL) wer e used to investigate the influence of the substrate temperature on the him formation of the organic molecule 3,4,9,10-perylenetetracarboxyl dianhydri de (PTCDA) on hydrogen-passivated silicon(1 0 0) substrates. Raman spectra exhibit four phonon bands below 125 cm(-1), indicating the crystalline natu re of the films. The spectral changes of both Raman- and infrared-active mo des reflect that the size of the individual crystals increases with the sub strate temperature during growth. Moreover, they support an increase in the content of the alpha -phase at the expense of the beta -phase. The rising background in the high frequency range of the Raman spectra is related to a n enhancement of the PL efficiency connected to a reduced number of non-rad iative centres of recombination. Time-resolved PL measurements reveal that the PL decay time increases with the substrate temperature, approaching the value characteristic for a PTCDA single crystal. (C) 2001 Elsevier Science B.V. All rights reserved.