Unique optical and electronic properties of thin film, non-polymeric compounds for device applications

Abstract

The non-polymeric organic compound: 3,4,9,10 - perylenetetracarboxylic dianhydride (PTCDA) has recently been observed to undergo a large increase in conductivity on irradiation with energetic particle beams. In this paper we discuss the unique properties of both the as-deposited and irradiated forms of PTCDA and related compounds. When the organic compounds are irradiated with 2 MeV Ar^+; beams, their resistivity can be reduced over 14 orders of magnitude from ρ (300K) =; 10¹⁰ Ω-cm (as-deposited) to ρ (300K) = 5 × 10^-4 Ω-cm using a maximum dose of 10¹⁷ ions/cm.² The temperature dependence of the resistivity for doses 10¹⁶cm⁻² follows ρ(T) ∝ exp (-const./ T^1/2) consistent with conduction due to hopping of carriers between isolated, conducting islands formed furing the irradiation process. In addition, we report on studies of structural changes induced by particle irradiation. The unirradiated PTCDA was vacuum sublimed onto (100), 10 Ω-cm p-Si substrates yielding a rectifying contact barrier with a height of ϕ_B = 0.74 eV. The diodes thus formed undergo avalanche breakdown at Vg = 230V, and exhibit current densities at V_B/2 of ≤50 μ A/cm.² In addition, the forward current-voltage (I_F-V) characteristics are strongly dependent on the contact metal used on the top PTCDA surface. The rectifying characteristics reported for the as-deposited material, coupled with the electronic and optical properties of irradiated PTCDA and related compounds suggest that these are interesting electronic materials whose potential device applications appear worthy of further study.