Vertical organic light-emitting transistors with an evaporated Al gate inserted between hole-transporting layers

Similar to the configuration of static induction transistor (SIT), vertical organic light-emitting transistors (VOLETs) with an evaporated Al gate inserted between hole-transporting layers were fabricated and their static characteristics were characterized. By using Alq(3) as the emissive layer. the basic transistor characteristics of the VOLETs were compared with two organic hole-transporting layers, N,N'-diphenyl-N.N'-bis(3-methylphenyl)-(1,1'-biphenyl)-4,4'-diamine (TPD) and N,N'-bis-(1-naphthyl)-N,N'-diphenyl-1,1'-biphenyl-4,4'-diamine (NPB) Our experimental data show that the intensity of emission from VOLETs can be tuned by adjusting gate voltages. The emission intensity of device ITO/TPD/Al/TPD/Alq(3)/Al decreases by increasing the applied gate voltages, showing an operation in depletion mode, however, it shows the operation in enhancement mode for VOLET device ITO/NPB/Al/NPB/Alq(3)/Al Further, the reasons for these two different phenomena were discussed in terms of the dielectric constant of materials. carrier mobility and energy barriers at electrode/organic interface. (C) 2009 Elsevier B V All rights reserved