Vertical Organic Phototransistors With Metal/Insulator Strips as the Source Electrode/Barrier Layer

Vertical organic phototransistors with embedded source electrode (Emb-VOPTs) have the advantage of low dark current due to the blockage of dark injection from the source electrode surface. Among the function layers of Emb-VOPTs, the source electrode plays an important role in providing effective modulation of the electric field in the channel by the gate voltage. By fabrication of the source electrode of EmbVOPTs, complex patterning techniques using lithography or self-assembly processes are often required which impedes future large-area production. Therefore, development for simpler and cheaper technology is of urgent need. In this letter, we report on fabrication technology for Emb-VOPTs based on vacuum deposition of metal/insulator strips with shadow mask as the source electrode/harrier layer. With this simple and reliable technology, small molecular Emb-VOPTs can be fabricated with solely vacuum thermal deposition without the need of additional pattern processes. With vacuum deposited Al strips as the source electrode, LiF strips as barrier layer and copper phthalocyanine (CuPc) as the photoactive organic channel layer, reasonable good performance was achievable, a photoresponsivity of 293 mA/W, an external quantum efficiency (EQE) of 56%, and a specific detectivity of 1.15 x 10(11) Jones were obtained. By replacing CuPc with C-60 (50 nm)/CuPc(50 nm) heterojunction bilayer, a much higher improved performance at V-g = -100 V and P-i(nt) = 0.4 mW/cm(2), R of 5078 mA/W, EQE of 969%, D* of 7.78 x 10(11) Jones, are achieved. The present results demonstrate unambiguously that vacuum deposited metal/insulator strips as the source electrode/barrier layer could he the competitive candidate for low- cost production of Emb-VOPTs.