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Double-heterojunction Nanorods and Light-sensitive LEDs


By
Mohsen Alowayed

July 26, 2017 - Posted in Discussion
‚ÄčOne of the recent developments in optoelectronic devices is the so called double-heterojunction nanorod (DHNR). It is comprised of a rod of low band gap quantum dots with a diameter around 5 nm, the ends of which are covered by two materials of higher band gap (see Figure 1). Since all three materials are in contact, it allows the formation of both type I and type II heterojunctions (see Figure 2).

 
 
 
Figure 1: Schematic diagram of a single DHNR structure [1].

Figure 2: Energy band diagram of DHNR with type I heterojunction between CdS and CdSe as well as between CdSe and ZnSe, and type II heterojuciton between CdS and ZnSe [2].

The benefits of having both types of heterojunctions for optical devices are numerous, and include: efficient carrier injection, low threshold voltage, and reduced heating. Quantum dots also have some benefits such as high photoluminescence and control of optoelectronic properties. DHNRs thus combine these desirable properties into one structure.

A recent application of DHNRs was the realization of light-sensitive LEDs. The LEDs can both emit and detect light. Electroluminescence is aided by the type I heterojunction and photovoltaics is aided by type II heterojunction. The mode of operation (emitting or detecting) can be changed by switching the direction of the bias imposed on the device. The device can also be operated in alternating bias to allow dual mode operation (see Figure 3).


Figure 3: Demonstration of a light sensitive LED in dual mode operation. The LED is connected to a circuit that allows automatic brightness adjustment [2].

There are many exciting applications for light-sensitive LEDs including bidirectional device-to-device communication, new types of interfaces and interactivity, and energy harvesting. And such advancements were made possible by DHNRs. It is interesting to think where those nanostructures will be useful next.

 

References:

[1] Oh, N. et al. Double-heterojunction Nanorods. Nat. Commun. 5:3642 doi: 10.1038/ncomms4642 (2014)

[2] Oh, N. et al. Double-heterojunction nanorod light-responsive LEDs for display applications. Science 355, 616-619 (2017)

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