Molecular doping effect in bottom-gate, bottom-contact pentacene thin-film transistors

Abstract

A bottom-gate, bottom-contact (BGBC) organic thin-film transistor (OTFT) with carrier-doped regions over source-drain electrodes was investigated. Device simulation with our originally developed device simulator demonstrates that heavily doped layers (p+ layers) on top of the source-drain contact region can compensate the deficiency of charge carriers at the source-channel interface during transistor operation, leading to the increase of the drain current and the apparent field-effect mobility. The phenomena expected with the device simulation were experimentally confirmed in typical BGBC pentacene thin-film transistors. The 5-nm-thick p+ layers, located 10 nm (or 20 nm) over the source-drain electrodes, were prepared by coevaporation of pentacene and 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane as an acceptor dopant. Since the molecular doping in this study can increase the drain current without positive shift of threshold voltage, p+ layers were formed precisely on top of the source-drain regions. This study shows that common inferior characteristics of bottom-contact OTFT devices mainly derive from the supply shortage of charge carriers to the channel region. The importance of reliable molecular doping techniques or heavily doped semiconductor materials for improving OTFT device performance is clearly suggested.

Experimental and numerical analysis of channel-length-dependent electrical properties in bottom-gate, bottom-contact organic thin-film transistors with Schottky contact

“…Current-voltage curves measured for the pentacene OTFTs were also numerically examined by using a thinfilm organic transistor advanced simulator (TOTAS) [23,24]. In p-channel operation of OTFTs, holes are injected from the source electrode to the active semiconductor layer under a reverse bias condition.…”

Effects of the F4TCNQ-Doped Pentacene Interlayers on Performance Improvement of Top-Contact Pentacene-Based Organic Thin-Film Transistors

“…The μ FE value of Device 1 was enhanced by a factor of 1.6 and the on/off current ratio was enhanced by a factor of 1.5 compared with the control sample. This appreciable improvement in the electrical performance of Device 1 could be attributed to the F 4 TCNQ:pentacene ratio being appropriate and to the charge density at interface between the S/D electrodes and the pentacene channel being high, improving charge injection [ 12 , 16 ]. However, the μ FE value of the devices decreased with a decrease in the F 4 TCNQ concentration of the F 4 TCNQ-doped pentacene interlayer.…”

Experimental and Numerical Investigation of Contact Doping Effects in Dinaphthothienothiphene Thin‐Film Transistors

“…Currently, carrier doping limited to surrounding part of contact electrodes (contact doping) has been widely applied as a formation method of low-resistance contact in OTFT [5][6][7]. However, as a subject to realize devices with OTFTs, a problem on contact resistance caused on interface between contact electrode and organic semiconductor film still remains.…”

“…However, as a subject to realize devices with OTFTs, a problem on contact resistance caused on interface between contact electrode and organic semiconductor film still remains. Currently, carrier doping limited to surrounding part of contact electrodes (contact doping) has been widely applied as a formation method of low-resistance contact in OTFT [5][6][7]. However, doping structure with molecular dopant [8] is not understood sufficiently due to its complexity and activation rate of dopant is far from 100%, that is, not being efficient doping, so that carrier density control and measurement with high reliability have not been established.…”