Photocurrent Engineering of Silicon Nanowire Field‐Effect Transistors by Ultrathin Poly(3‐hexylthiophene)

Photoresponse on the silicon nanowire (SiNW) and organic semiconductor interfaces embedding an insulating barrier is understood by a photogating effect associated with charge separations. Still elusive one is when the thickness of organic semiconductor is decreased down to a few molecular layers, where the photoresponse can be strongly altered by the spatial confinement of photoinduced carriers. In this work, the photoresponse modulation of SiNW field‐effect transistors coated with an ultrathin organic semiconductor poly(3‐hexylthiophene) (P3HT) is reported, where the P3HT layer thickness is changed by an order of magnitude. In the absence of laser illumination, the P3HT interface on SiNW slightly decreases the SiNW channel current, irrespective of the P3HT thickness. Upon the laser illumination, the thick case of P3HT layers (≈100 nm) supports the dissociation of photoinduced electrons and holes, hence the photogating effect largely decreases the SiNW channel current. When the P3HT layer thickness is decreased down to the P3HT hole diffusion length (≈8.5 nm), the photoinduced P3HT holes screen out the P3HT interface states, effectively increasing the SiNW channel current up to the intrinsic level. The method of engineering the organic semiconductor thickness suggests a complementary optoelectronic operation, verifying the controllable photoresponse within a compact nanodevice. For the modern nanoscale electronics, the increased surface‐to‐volume ratio renders that the device performance becomes more dependent on the surrounding environmental conditions such as organics incorporated. In this work, the authors show that the photoresponse of such nanodevices can be significantly altered when polymers poly(3‐hexylthiophene) with different thicknesses are integrated with the current state‐of‐the‐art silicon nanowire field‐effect transistors.