Extraordinarily Weak Temperature Dependence of the Drain Current in Small‐Molecule Schottky‐Contact‐Controlled Transistors through Active‐Layer and Contact Interplay

Abstract

Low saturation voltages and extremely high intrinsic gain can be achieved in contact‐controlled thin‐film transistors (TFTs) with staggered device architecture, enabled by the energy barrier introduced at the source contact. The resulting device, the source‐gated transistor (SGT), is limited in its usefulness by the high temperature dependence of the drain current induced by the source energy barrier. Here, the interaction between the thermal characteristics of the source contact and the semiconductor to show drastically reduced temperature dependence for SGTs based on organic semiconductors (OSGTs) is exploited. This extraordinarily weak temperature dependence of the drain current is observed regardless of the height of the source energy barrier (27.8% in OSGTs with Ti contacts compared to 22.1% when using Au contacts, over a 34 K range). The reduction in mobility of the semiconductor offsets an increase in thermionic‐field emission of charge carriers at the source. This is a first for SGTs and provides a route to removing one of the last hurdles to their wider adoption. The OSGTs with Ti contacts also demonstrate: drain‐current saturation at very low drain‐source voltages (saturation factor of 0.22); noteworthy stability after 70 days; and minimal drain‐current variation with channel length or illumination.

High gain complementary inverters based on comparably-sized IGZO and DNTT source-gated transistors

“…30 At high absolute gate-source voltage, both transistors exhibit negative differential resistance in the output curves. This has been observed in several SGT implementations 26,30,32 and will be investigated separately. Nevertheless, flat output characteristics are obtained across a large range of operating conditions.…”

“…24 In principle, the channel length could also be reduced significantly without suffering from deleterious scaling effects. 25,26 Highly pertinent to digital logic applications, by relying on the contact barrier introduced at the source electrode to tailor the current density, the two transistors show similar on-current levels, which permits close to equal sizing in the circuit layout.…”

Organic Source‐Gated Phototransistors with > 104 Photo‐To‐Dark Current Ratio in the Visible Range at Zero Gate‐Source Bias

“…The slope of the linear regime is comparatively steeper and there is negative differential resistance (NDR) after saturation. [14] The Ni-contact devices, however, demonstrate behavior that is typical of SGTs, with low saturation voltages. The ideal flat saturation that leads to extremely high intrinsic gain [19,20] in these devices is absent, due to the NDR.…”

“…Here, we present small-molecule dinaphtho[2,3-b:2′,3′f ]thieno [3,2-]thiophene (DNTT, Figure 1c) [12] organic SGTs (OSGTs, Figure 1d) [13,14] and their behavior when exposed to an optical stimulus in the visible range. DNTT OPTs have been implemented in gesture recognition [7] and are capable of low light detection in the pW cm −2 range, [6] with a sensitivity to ultraviolet (UV) and blue light (peak wavelength 𝜆 = 450 nm).…”

“…Second, we show some of the benefits of fabricated OSGTs in accordance with well-established operating principles, including their unique temperature dependence as DNTT OSGTs, which has been previously observed in a different contact metal. [14] Finally, we operate the structures as OPSGTs under illumination in the visible range.…”