Visible Color Tunable Emission in Three-Dimensional Light Emitting Diodes by MgO Passivation of Pyramid Tip.

We demonstrated visible color tunable three-dimensional (3D) pyramidal light emitting diodes by depositing the MgO on and near the tip of the pyramid as an insulating layer. Here, we show that the degradation of the materials (i.e., p-GaN) crystallinity and the built-in electric field due to the nanoscale geometry of the tip region is responsible for the large leakage current observed in LEDs. Confocal scanning electroluminescence microscopy images clearly showed that the intensity of the light emitted out of the side facet of the pyramid is much higher than that of the light extracted out of the tip surface, indicating that the MgO layer prohibited the carrier injection to the MQWs layer, suppressing the leakage occurring at or near the tip region of the pyramids. The color range of the LEDs can be also tuned by using the MgO layer, a blue-shift by 10.3 nm in the wavelength. This technique is simple and scalable, providing a promising solution for developing 3D pyramidal LEDs with low leakage current and controllable light emission.