A new kind of microLEDs’ array technology that aims to answer ultrahigh brightness, narrow optical aperture, low power consumption and small footprint requirements for Augmented Reality glasses applications will be discussed.
GaN sub-micrometer (“nano”) rods are grown directly on large size microelectronic silicon wafers with further LED structure resulting in self-standing “nanoLEDs”. NanoLEDs size allows to array them in such a way it builds a photonic crystal tuned to the desired emission wavelength and designed so that propagative modes are only allowed into a narrow cone normal to the array plane. It results in intrinsic directivity of light emission without a need for additional microlenses, meaning that instead of losing 90% of the light not entering the AR glasses optics (waveguides, for instance) most of it becomes useful raising significantly the overall system power efficiency. The number of nanoLEDs to maintain efficient photonic effect is discussed and leads to µm range subpixel capability, other advantageous consequences of such a resonant coupling are discussed, while single color arrays results are presented.
Furthermore, quantum well Indium composition can be modulated by playing on local fill-factor, basically size and pitch of the nanorods, thus changing the quantum well emission wavelength. By adding fill-factor constrain to photonic crystal design for directivity it is possible to grow in a single run three colors (R,G,B) patterns with most of above advantages, including directivity of light emission. Design trade-off and perspectives are discussed and results on actual microLEDs presented. This technology opens path to single chip >6000ppi RGB ultra-compact and highly efficient micro display designs.