Quantum Dot Lasers Closer to Electric-Pumping

Colloidal quantum dots (CQDs) are highly promising materials for light amplification thanks to their efficient photoluminescence, tunable emission wavelength and low-cost synthesis. (Source: NTU)

Scientists from Nanyang Techno­logical University in Singapore have developed a way to make colloidal quantum dots (CQD) produce laser light with the help of an electric field. CQDs are semi­conductor nano­particles that can generate vivid and saturated colours of light effi­ciently, which are used to make display screens of many electronic devices. Though CQDs should be promising as laser materials, they are not yet practical since they need to be powered by another source of light energy via optical pumping. However, this renders them too bulky for use in semi­conductor electronics.

Over the last few years, researchers have tried various approaches to make it easy to use CQDs in lasers, including electro­chemical methods or chemical doping. These approaches require the use of harsh chemical solvents or oxygen-free environments in their production, and so have been limited to lab-scale experiments. Steve Cuong Dang together with Yu Junhong, have demons­trated how an electric field can help CQDs emit laser light while using only a fraction of the energy tradi­tionally required to drive a laser.

In their experiments, the scientists embedded CQDs between two electrodes, which provides an electric field to control and change the pro­perties inside the CQDs. By manipulating these properties, the scientists lowered the energy threshold needed for lasing by around 10 per cent, bringing the prospect of CQD lasers closer to reality. This threshold reduction is the first time researchers have lowered it using an electric field, instead of difficult-to-employ electro­chemical methods.

Being able to build low-cost, small size lasers that are elec­trically driven in a wide range of colours is the holy grail for many optical and opto­electronic researchers. Lasers are the backbone technology for various industries including medical, security and consumer electronics, and are essential to the development of laser televisions. “Our successful experiment brings us one step closer towards developing single-material full-colour lasers that can be elec­trically pumped. That achievement would eventually make it possible to put lasers on chip inte­grated systems used in consumer elec­tronics and the Internet of Things” said Dang, from the School of Electrical and Electronic Engi­neering (EEE).

Colloidal Quantum Dots are easily and eco­nomically produced in simple liquid-phase chemical syntheses, and their optical and electronic properties can be altered and controlled by varying the particle size. Colloidal nano­materials are attrac­tive to laser makers due to their low-cost, tune-able emission colour and high emission efficiency. However getting them to lase currently requires fast, intense and coherent optical pumping, whereas electric pumping is slow, weak and incoherent.

Together with his colla­borators Hilmi Volkan Demir and Wang Hong from EEE, and Sum Tze Chien from the School of Physical and Mathe­matical Sciences, Dang showed that applying an electric field lowers the lasing threshold of CQDs, and could lead to viable electrically-pumped CQD lasers. Demir said, “The next big challenge in laser research is to develop nano-scale lasers and integrate them into on-chip photonic devices and ultra­sensitive sensors. This would bring signi­ficant impacts to modern society especially in data and infor­mation processing, that is driving the 4th industrial revolution. Achieving it would be a major advance within Singapore’s Industry 4.0 trans­formation.” The team is now looking to research further into making tiny CQD lasers on a chip and to work with industry partners keen to develop the tech­nology into proof-of-concept devices with practical appli­cations. (Source: NTU)

Reference: J. Yu et al.: Electrically control amplified spontaneous emission in colloidal quantum dots, Sci. Adv. 5, eaav3140 (2019); DOI: 10.1126/sciadv.aav3140

Link: Centre of Excellence for Semiconductor Lighting and Displays, School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore, Singapore

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