Colloidal quantum dot field-effect transistors: From electronic circuits to light emission and detection

Colloidal quantum dots (QDs) recently triggered great attention from the optoelectronics community due to their utterly fascinating physical properties. The most important for optoelectronics is the size-dependent absorption and emission of light, what has allowed QDs to become the active layer of solar cells, light-emitting diodes, photodetectors, water splitting photoelectrodes, field effect transistors, etc.
This thesis is devoted to the fabrication and investigation of various types of field-effect transistors (FETs), based on lead sulfide (PbS) QDs. In order to get tuneable FETs characteristics, double gate QDs FETs were introduced, using a ferroelectric polymer as a dielectric material for the top gate and silicon dioxide as the bottom gate. Further, QDs FETs were used as n-type part of CMOS-like inverter, in combination with carbon nanotubes as the p-type material. The inverter featured sub-1V operation, with the highest reported static gain and noise margins for that voltage.
Near-infrared light emission is another interesting application of PbS QDs, and the first fully solid QDs light-emitting FET is reported in this thesis. The device shows not only interesting application prospects modulating simultaneously optical and electrical signals, but is also used to study the physical properties of QDs films.
To bring the QDs FETs closer to industrial application, lithographically patterned FETs were fabricated, for medium-frequency optoelectronics. Lithographical processing does not compromise the quantum confinement of PbS QDs film as confirmed by the responsivity of a phototransistor. Moreover, the cut-off frequency (400 kHz) could be measured precisely for the first time for this type of samples.