Researchers from Ostendo Technologies demonstrated a novel monolithic InGaN-based LED that achieved three primary colors of light emitted from one device at selected current densities. They published their findings in a paper in AIP Advances.
The LED structure employed three different sets of quantum wells with specially designed intermediate carrier blocking layers(ICBLs) between them. The different sets of quantum wells create the red, green, and blue (RGB) colors. The LED was able to emit light from 460 to 650 nm, covering the entire visible spectrum.
The emission wavelength starts at 650 nm. Then, the wavelength decreases to 460 nm or lower as the injection current increases. The team noted that color mixing could be used to obtain many other colors.
The team also points out in the paper that having three separate colors from one emitter is highly desirable. According to the researchers, conventional RGB LEDs often suffer from low efficiency, high cost, large area, low yield, and low reliability. They assert that an LED like the one they demonstrated, once fully developed, might resolve these issues.
Multiple quantum wells (MQWs) heterostructures are most frequently used as optically active layers. According to the paper, increasing the number of active QWs can spread the injected carriers among the MQWs. The spreading of the injected carriers among the quantum wells decreases the average QW carrier population and minimizes the adverse effects on performance,
However, the researchers also noted that MQW active regions of electrically pumped devices suffer from the inhomogeneous distribution of the charge carriers (both electrons and holes), which are injected from opposite sides of the diode structure. This uneven and imbalanced carrier population of active QWs adversely affects the device performance.
They were able to suitably adjust the ICBLs thickness, Al/Ga compositions, and dopant concentrations, so both carriers (electrons and holes) can be preferentially attracted or blocked under a variety of current injection conditions. As a result, both carriers can be guided into targeted wells to obtain specific wavelengths emission.
In their tricolor LEDs with ICBLs, all three color emissions appeared under PL measurements. However, were able to achieve one dominate EL emission wavelength with high color purity at designated current densities.
The team anticipates that the technology could improve displays.
S. Hussein et al., “Growth of monolithic full-color GaN-based LED with intermediate carrier blocking layers,” AIP Advances. 6, 7 (2016). DOI: http://dx.doi.org/10.1063/1.4959897.