Monolithic integration of RGB LEDs and Integrated RF electronics for LiFi


Building on the work in the platform our approach is to use nitrides where they can be efficient and fast enough by using semi-polar or non-polar for green and yellow combined with other CS for longer wavelengths. We will use multiple selective area growth steps to integrate CS/Si structures with several different epitaxy designs on the same substrate.


 

III-nitride semiconductors have direct bandgaps across their entire composition range, covering the complete visible spectrum and a major part of the ultraviolet (UV). The large range of bandgap also facilitates high power and RF electronics. The last two decades have seen dramatic advances in the development of III-nitrides (specifically for polar c-plane growth), whose emergence is significantly changing many aspects of our lives, through for example, its application in efficient white light sources and high efficiency cellular radio base station power amplifiers. However, the main achievements are limited to device types and/or bandgaps where the polar nature of the material has limited effect. Polar GaN intrinsically poses a number of fundamental issues. The polar orientation generates the quantum confined Stark effect (QCSE) due to the polarisation induced piezoelectric fields, leading to long recombination lifetime and low quantum efficiency. The long lifetime due to polar GaN (typically 10s ns) also limits application in RF applications and in LiFi (simultaneous illumination and visible light communication) due to the limited bandwidth (typically MHz). These factors become a severe issue for longer wavelength green emitters and still longer wavelengths e.g. yellow are precluded by the challenge of incorporating a large Indium fraction into polar InGaN. Polar nitrides are prone to efficiency droop affecting today’s InGaN LEDs, which is a significant reduction in quantum efficiency with increasing current. At the currents required for practical applications the QE falls by up to 50% from its peak. This is again more severe for green and yellow emitters.
Building on the work in the platform our approach is to use nitrides where they can be efficient and fast enough by using semi-polar or non-polar for green and yellow combined with other CS for longer wavelengths. We will use multiple selective area growth steps to integrate CS/Si structures with several different epitaxy designs on the same substrate.
In completing this high level integration, we will consider if all CS on Si devices need to be comparable with their CS alternatives in terms of performance in order to provide an integrated performance advantage and select the best route for overall performance.

 

 

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