Solution-Cast Semiconductor Outperforms Conventional Chips

In recent years, alternative methods for building electronic and optoelectronic devices have been explored. Now researchers at the University of Toronto in Canada have developed ultrasensitive solution-processed quantum dot photodetectors that may be of value for many communications, imaging and monitoring applications. The devices, which they describe in the July 13 issue of Nature, offer a large device area, flexibility and convenient materials integration at low cost, compared with conventional semiconductor devices.

The investigators created photoconductive detectors by spin-coating quantum dots from a solution onto gold-interwoven electrodes. Processed from a chloroform solution, the quantum dot nanocrystals enabled easy integration with any substrate. Furthermore, their transport and trap state properties can be separately controlled via the engineering of ligands, receptor-binding compounds, and the oxidation of nanoparticle surfaces either before or after film formation.

Following the spin-coating process, the film was given a two-hour bath in methanol. After the solvent had evaporated, the scientists observed an interelectrode separation of 5 μm and a metal electrode height of 100 nm. The thickness of the light-sensitive nanoparticle layer was 800 nm.

The researchers found that the devices exhibited a photoconductive gain with increased responsivity. According to the report, the best devices demonstrated a normalized detectivity of 1.8 × 10¹³ jones (1 jones = 1 cm Hz^1/2 W^–1) at 1.3 μm at room temperature, while previous records of photoconductive detectors lie in the 10¹¹- to 10¹²-jones range.