The potential of microLEDs is well known but several challenges remain before ramping up to large scale consumer applications. To form RGB microLED displays, typical approaches are to use a pick and place process to transfer discrete R, G and B pixels or to use native blue LEDs as the light source for subsequent colour conversion, to red and green.
Plessey’s latest patented growth approach creates both native blue and native green emission layers on the same wafer. The monolithic formation of two colours significantly simplifies display manufacture. Green microLEDs have high efficiency with a narrow spectral width resulting in an excellent colour gamut when operating alongside the high performance blue microLEDs.
The monolithic integration of both the native blue and green microLEDs on the same Silicon substrate is the result of a concerted effort aimed at solving several challenges previously considered insurmountable. Among the issues preventing the integration of multiple wavelength diode junctions are, firstly, a magnesium memory effect and diffusion from the p-type cladding of the lower junction into the upper junction.
An additional process challenge to the integration of blue and green microLEDs is the precise tuning of the thermal budget during the growth of the second junction to prevent indium phase separation in the blue active region. Plessey has precisely engineered the thermal budget to maintain high efficiency (IQE), low defectivity and high electrical conductivity required for high brightness display applications.