Organic semiconductors share many of the physical properties as their inorganic counterparts, such as silicon-based semiconductors, and are made using solvent-based processing techniques. This makes them cheaper and more flexible, but a significant drawback is that electrical charges move more slowly in organic materials. According to KAUST (King Abdullah University of Science and Technology) in Saudi Arabia this drawback is a barrier to applying organic semiconductors for use in applications such as radio-frequency electronics.
“Unlike their inorganic counterparts, organic semiconductors are cheap and easy to process via solution-based routes like printing or blade and die coating,” said Ph.D. student Kalaivanan Loganathan, working with Thomas Anthopoulos. “To make this technology useful for the 5G frequency band, there is a need to fabricate organic Schottky diodes.”
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The Schottky diode allows current to pass through in one direction but blocks flow in the other. The most important difference between the more ubiquitous p–n diode and the Schottky diode is that the latter can switch from the conducting to the non-conducting state much faster, making them essential in radio-frequency applications.
The speed of Schottky diodes is generally limited by the device capacitance and the resistance. But organic semiconductors are often associated with high capacitance and resistance due to their low charge carrier mobility. They are mostly employed in conventional sandwich-type architecture in which the semiconductors, metals and electrical contacts are laid one on top of the other.
Loganathan and the team are said to have reimagined this device architecture and placed the two electrical connections side-by-side. The organic semiconductor - C16IDT-BT - was placed in a gap of 25nm in between the diodes which gave the diodes ultralow capacitance and resistance.
They showed that this Schottky diode operated up to a frequency of 6GHz. They were then able to extend this to 14GHz by chemically doping the semiconductor with the addition of another molecule.
“Our results show that organic semiconductors are capable of operating in the 5G frequency range, like their inorganic counterpart, with the added advantage that they can be mass manufactured at low cost using solution processing," Loganathan said in a statement.
The team is looking to integrate their diodes into radio-frequency circuits, ID tags and wireless energy harvesting devices. Their findings have been published online in Advanced Materials.
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