Light-emitting devices based on semiconductor quantum dots have been shown to be suitable for use in environments that include high levels of radiation that causes displacement damage in semiconductors - in particular, energetic protons. Conventional light-emitting diodes and other conventional optoelectronic devices become degraded rapidly by such radiation, giving rise to a need for radiation-hard devices. A preliminary confirmation of the feasibility of using semiconductor quantum dots to fill this need has been provided by experimental observations of radiation hardness in InxGa1-xAs/GaAs quantum dots.
For the experiments, specimens containing InxGa1-xAs/GaAs quantum dots [lenslike islands (≈5 nm thick and ≈25 nm in diameter) of InxGa1-xAs surrounded by GaAs] were fabricated by metal-organic chemical vapor deposition of In0.6Ga0.4As and GaAs on GaAs substrates. For comparison, specimens containing quantum wells (as distinguished from quantum dots) were also fabricated by stopping the growth of In0.6Ga0.4As before the onset of the Stranski-Krastanow transformation [in which quantum dots form spontaneously in a second semiconductor (in this case, In0.6Ga0.4As) deposited on a lattice-mismatched first semiconductor (in this case, GaAs) once the second semiconductor reaches a critical thickness, which is typically a few molecular layers].
In the experiments, the specimens were irradiated with protons at a kinetic energy of 1.5 MeV from a Van de Graaff generator. Next, the light-emitting properties of specimens that had been exposed to a range of proton doses were evaluated in terms of photoluminescence emitted by the specimens at various temperatures. The photoluminescence was excited by light at a wavelength of 514 nm from an argon-ion laser and measured by use of a cooled germanium detector and a lock-in detection technique.
The figure shows the measured integrated normalized photoluminescence intensities from the quantum wells and quantum dots as functions of the proton dose, the normalization being with respect to the zero-dose values. These plots suggest that quantum dots can tolerate about 50 to 100 times as much radiation as quantum wells can. The increase in radiation hardness of quantum dots over quantum wells is all the more significant in that quantum-well optoelectronic devices (e.g., light-emitting diodes) based on quantum wells have already been demonstrated to be an order of magnitude more radiation-hard than are the corresponding conventional optoelectronic devices (e.g., light-emitting diodes based on p/n junctions).
This work was done by Rosa Leon of Caltech for NASA's Jet Propulsion Laboratory.
NPO-21009
This Brief includes a Technical Support Package (TSP).
Semiconductor Quantum Dots as Radiation-Hard Light Emitters
(reference NPO21009) is currently available for download from the TSP library.
Don't have an account?
Overview
The document discusses the development and experimental validation of semiconductor quantum dots, specifically InGaAs/GaAs quantum dots, as radiation-hard light-emitting devices. Traditional optoelectronic devices, such as light-emitting diodes (LEDs) based on p/n junctions, are known to degrade rapidly in high-radiation environments, particularly due to energetic protons. This degradation necessitates the need for more resilient devices that can withstand such conditions.
The research, conducted by Rosa Leon at NASA's Jet Propulsion Laboratory, demonstrates that quantum dots exhibit significantly greater radiation hardness compared to conventional quantum wells and p/n-junction LEDs. Experimental results indicate that quantum dots can tolerate approximately 50 to 100 times more radiation than quantum wells, and about 1,000 times more than traditional p/n-junction LEDs. This enhanced tolerance is crucial for applications in environments with high radiation levels, such as space.
In the experiments, specimens containing InGaAs/GaAs quantum dots were fabricated using metal-organic chemical vapor deposition. The specimens were irradiated with protons at a kinetic energy of 1.5 MeV, and their light-emitting properties were evaluated through photoluminescence measurements. The results showed that quantum dots retained a greater proportion of their original photoluminescence compared to quantum wells when exposed to the same proton fluence, highlighting their superior performance in radiation environments.
The findings suggest that semiconductor quantum dots could be a viable solution for developing radiation-hard optoelectronic devices, which are essential for applications in space exploration and other high-radiation settings. The document emphasizes the significance of this research in advancing technology that can withstand extreme conditions, thereby enhancing the reliability and longevity of devices used in critical applications.
Overall, the work represents a promising step forward in the field of optoelectronics, showcasing the potential of quantum dots to revolutionize the design of light-emitting devices for use in challenging environments. The research underscores the importance of continued exploration and development of materials that can meet the demands of future technological applications in high-radiation scenarios.
