Transient Electroluminescence

To deal with the injection inefficiency caused by Schottky contacts, I developed an AC carrier injection architecture, a device concept that is capable of efficiently injecting carriers in various excitonic systems, including monolayer semiconductors (Nat. Comm. 2018), with demonstrations of bright light-emitting devices from infrared to ultraviolet regimes. Ohmic contacts to both carrier types are typically a requirement for high-performance light-emitting diodes but are challenging to achieve in practice. This fundamental challenge can be resolved by leveraging transient-mode device operation. Using monolayers as an example in this dopant-less device (monolayer semiconductors have significant Schottky barriers at metal-semiconductor junctions), an AC voltage is applied to a gate electrode to generate alternating electron and hole populations in the thin semiconductor film. During the ac transients, steep band bending is created at the metal-semiconductor junction, which leads to large tunneling currents that surmount the Schottky barrier height. As a result, bright EL is achieved at high injection levels.