Vertically-stacked LEDs with invariance of color Chromaticity

This study investigated the variance of color chromaticity of a vertically-stacked LEDs device with respect to the viewing angles. The LED chips with truncated inverted pyramid geometry were fabricated by laser micromachining. The sidewalls of the truncated inverted pyramid LED chips were coated with a thin layer of highly reflective silver film. The red, green and blue truncated inverted pyramid LED chips were vertically-stacked to form the white LEDs with color tunable function. A well mix of colors from the polychromatic LED chips was achieved in the layout of the vertically-stacked LEDs without utilizing additional optics. Compared to the commercial RGB LEDs, the stacked LEDs device showed insignificant angular dependence of color chromaticity. A luminous efficacy of 33 lm/W was achieved without any optimization of the fabrication process.

Research highlights
► Laser micromachining was used to fabricate angled sidewall LED chips.
► Vertically-stacked LEDs produce highly uniform white light emission.
► Angled sidewall LED were coated with highly reflective silver films minimizes sidewall emissions.
► Vertically-stacked LEDs show invariance of color chromaticity with viewing angle