Organic semiconductors have many of the same physical properties as their inorganic silicon-based counterparts. However, they are cheaper to produce and are more flexible, potentially broadening the scope of their application.
While promising and backed by a significant amount of research, a drawback to these materials is that electrical charges move much slower than in their inorganic counterparts. This hurdle has been a long-standing barrier to applying organic semiconductors in fast-paced applications, such as communications electronics.
The Schottky diode, like all electronic diodes, allows an electrical current to pass through it in one direction but blocks flow in the other. The most important difference between it and the more ubiquitous p–n diode is that the Schottky diode can switch from conducting to nonconducting states much faster, a feature that makes them essential in radio-frequency applications.
The speed of Schottky diodes is generally limited by the device capacitance and resistance — an area of strength for organic semiconductors due to their low charge carrier mobility. These devices are conventionally assembled in sandwich-type architectures in which the semiconductors, metals, and electrical contacts are laid one on top of the other.
In a recent study published in Advanced Materials, the team at KAUST re-imagined this device architecture and placed the two electrical connections side-by-side. The organic semiconductor, referred to as C16IDT-BT, was placed in a tiny gap of just 25 nanometers in between the diodes. This structure gave the diodes an ultralow capacitance and resistance. They showed that this Schottky diode operated up to a frequency of 6 gigahertz (6 billion cycles per second). They were then able to extend this to 14 gigahertz 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,” said the study’s first author Kalaivanan Loganathan. “With the added advantage that they can be mass manufactured at low cost using solution processing.”
The team hopes to integrate their diodes into radio-frequency circuits, ID tags and wireless energy harvesting devices.
“Unlike their inorganic counterparts, organic semiconductors are cheap and easy to process via solution-based routes like printing or blade and die coating,” explained Loganathan. “To make this technology useful for the 5G frequency band, there is a need to fabricate organic Schottky diodes.”
Feature image credit © 2022 KAUST