Researchers develop three-atom-thick semiconductor transparent LED
Scientists at the American Berkeley University have developed a transparent LED a few millimeters wide, whose semiconducting material is only three atoms thick. This could eventually be used for ‘invisible’ displays.
The LED uses monolayers of different semiconductor materials, including molybdenum disulfide and tungsten disulfide, each of which emits a different color of light. Those compounds belong to the category of transition metal dichalcogenides, the semiconducting equivalents of graphene. Like graphene, they form monolayers, but three atoms thick instead of one atom. The trouble with semiconductors made up of these monolayers is that there isn’t much material to make efficient contact points for the electrodes.
The researchers solved this problem by using a single contact point on the semiconductor. The semiconductor material forms the source and is placed on doped silicon, which acts as a gate. Underneath is a layer of silicon oxide that forms the gate oxide. The electrodes are made of indium tin oxide, which is also optically transparent. When alternating current is used and the polarity changes, the positive and negative charges are simultaneously present in the semiconductor, creating light and thus the electrons lose energy in the form of a photon.
The scientists from the University of California state that the materials used are so thin and flexible that a screen made of the LEDs can be made transparent and will have no trouble with angular surfaces. According to the researchers, this LED, which is currently still a proof-of-concept, can eventually be used in places where invisible screens are needed. The screen can then be printed on a wall or on someone’s skin, as it were. In the latter case it concerns, for example, luminous tattoos.
The researchers recognize that there are still many challenges to be overcome and research is needed before these LEDs can actually be used in practice. For example, the efficiency of the LED is still at one percent, while commercially used LEDs often have an efficiency of around thirty percent. Although the thickness can remain very small, according to researchers, the LEDs can ultimately achieve a high light intensity by making the length and width of the LEDs relatively large.
The research was recently published in the scientific journal Nature Communications, under the title ‘Large-area and bright pulsed electroluminescence in monolayer semiconductors’.