Mar 3, 2017: When two quantum dot LEDs are brought in close proximity on a single chip, they can function as a tuneable, all-electric quantum light source. This was demonstrated by a team of researchers, who published a paper titled “Electrically driven and electrically tuneable quantum light sources”.
The researchers used an electrically excited driving LED, whose light excited quantum dots in the neighbouring diode. As a result, the researchers could tune the wavelength of the quantum dot emission from the neighbouring driven diode through the quantum confined Stark effect.
The researchers wanted to generate entangled photon pairs for quantum computing applications, through an on-chip in-plane excitation structure that could readily be integrated into semiconductor devices and photonic cavities.
The researchers demonstrated the method of producing electrically driven light from an electrically tuneable source. They designed 16 tuneable diode structures on a single chip. The structures comprised 180×210μm planar microcavity LEDs with a layer of InAs quantum dots embedded in a 10nm GaAs quantum well with Al0.75Ga0.25As barriers.
Multiple Distributed Bragg Reflectors (DBRs) was grown above and below the InAs quantum dot layer, and quantum well were used to form a half-wavelength cavity to increase the portion of QD light emitted vertically while acting as a horizontal waveguide for optical emission from the InAs wetting layer. A diode structure that can emit electrical excitation was formed out of the top DBR and the bottom DBR—doped p-type and n-type, respectively.
The researchers wanted to use light produced by one LED to excite the quantum dot in the neighbouring diode. The LED whose broadband light emission from the InAs wet layer is guided horizontally by the Bragg reflectors above and below the wetting layer. As the neighbouring LED is hit by a portion of the emitted light, a part of the light is absorbed by the wet layer, which in turn, generated excitons that was captured by the quantum dots in that neighbouring LED, leading to quantum light emission.
While the cavity mode of the planar microcavity matches the emission wavelength of the neighbouring quantum dots, it enhances the proportion of quantum dot emission. By varying the bias across the second LED, the wavelength can be tuned by Stark shifting the transitions, and the intensity of light emission from the neighbouring diode can be controlled by varying the voltage across the first LED.