High‐Efficiency, High‐Power AlGaInP Thin‐Film LEDs with Micron‐Sized Truncated Cones as Light‐Extraction Structures

Micron‐sized truncated cones with a top surface diameter and a height on the order of the emission wavelength are prepared on the light‐extraction surface of a high‐power thin‐film AlGaInP red LED as the light‐extraction structure. An external quantum efficiency of ≈39.3% is obtained from a 1 × 1 mm2 device after resin encapsulation at an injection current of 120 mA at room temperature (≈25 °C). The light‐extraction process in this device is investigated by means of a finite‐difference time‐domain (FDTD) simulation and is compared with that in a conventional AlGaInP thin‐film LED with a randomly rough texture as the light‐extraction structure. It is found theoretically that the extraction efficiency of light per single surface incidence of the device with the micron‐sized truncated cones is a few tens of percent higher than that of a device with a randomly rough texture on the light‐extraction surface. The combined effect of evanescent wave scattering at facet edges and direct extraction through some specific facets is attributed to be the main mechanism responsible for the enhancement in the light‐extraction efficiency, based on the FDTD simulation. Truncated cones with dimensions on the order of the emission wavelength are prepared on the light‐extraction surface of a thin‐film type AlGaInP LED. Both theoretical simulation and device performances show that micron‐sized truncated cone is a promising light‐extraction structure to overcome the efficiency limit of the conventional random roughness structure for high‐efficiency, high‐power thin‐film LEDs.