Ricerc@Sapienza

New research aims to improve quantum dot LEDs (QD-LEDs) by using a new generation of the nanosized, engineered semiconductor particles specifically tailored to have reduced wasteful charge-carrier interactions that compete with the production of light. Incandescent light bulbs convert only 10 percent of electrical energy into light, with the remaining 90 percent lost to heat. They are being replaced worldwide with less-wasteful fluorescent light sources, but the most efficient approach is direct conversion of electricity into light using electroluminescent devices such as LEDs. In the last decade, vigorous research in QD-LEDs has led to dramatic improvements in their performance, to the point where it nearly meets the requirements for commercial products. One outstanding challenge in the field is the so-called efficiency roll-off (known also as ¿droop¿), or the drop in efficiency at high currents. The use of nanophotonics will be instrumental in the ongoing quest to minimize the effects of droop on the performance of QD-LEDs. The light-emitting material at the heart of current state of the art devices is indeed represented by small, nm-sized islands of InAs, which produce light when excited with an electric pulse. These QDs are surrounded by photonic crystal, which serves as an optical cavity, confining light inside the LED and forcing it to resonate at a single frequency: in other words, it enables single-mode operation for the device. Without these nanophotonic ingredients, i.e., QDs and photonic crystal, it is impossible to make an LED efficient, single-mode and fast; all at the same time.
In this present project, we will try to show that a focused laser beam can be used to control spatially the photoluminescence emission energy of a hydrogenated (InGa)(AsN). This laser writing effect will prove the breaking of N-H bonds and can be used to manipulate the electronic activity of the N- and H-atoms. Laser writing of the electronic activity of H-atoms in InGaAsN and other III-Vs could open up interesting possibilities for low-cost and high-speed nanofabrication techniques in nanophotonics. The laser writing will not only remove the H, but also control the electrostatic potential, triggering the diffusion of charged impurities in the regions above and below the QD and creating a preferential path for charged carriers. In turn, this will activate a nanoscale region of the LED to emit light.
To create site-controlled nanoscale light emitting spots or ordered LED arrays by laser writing using hydrogenated (InGa)(AsN) p-i-n diodes, exploiting a new. The laser-driven diffusion of H to fabricate a nanoscale LED in dilute nitrides has never been reported before. Moreover, the possibility to define nanoscale current channels without the deep etching and lateral oxidation will lead to longer lifetime, as well as improved performances at high-current densities. If used in laser optical interconnect systems already exist, but their new nanoscale LED setup improves the energy efficiency 2,000 times, sipping just 0.25 femto-joules per bit sent as compared to a laser's 500 femto-joules. In spite of this low power consumption, chips using the LEDs will reportedly be capable of transfer speeds of 10Gbps. This data speed is achieved through using single-mode LEDs: normal LEDs give off light at a range of frequencies, whereas this design will create a single frequency of light. Electricity is applied to dots of InGaAsN, which give off light as current passes through them. This is then focused by a photonic crystal, created by putting an array of holes into a semiconductor, which both forces the light to resonate at the desired frequency and acts as a focusing mirror, creating a beam of light.

References:

1.https://www.theverge.com/2011/11/17/2568275/nanoscale-led-optical-data-t...
2.http://www.augustinefou.com/2011_11_13_archive.html#axzz4jIAEaqAr
3. http://onlinelibrary.wiley.com/doi/10.1002/adma.200904409/full