Light Extraction of Near-Infrared AlGaAs-Based LED Enhanced by Nanostructured Surface Morphology

To improve the light extraction efficiency of a planar AlGaAs-based light emitting diode (LED) (Device A), three novel LEDs with nanostructured surface morphologies are prepared using a surface texturing approach. We describe the fabrication of a nanostructured light extraction enhancement layer via the annealing of an evaporated Ag layer. Thermal annealing is used to induce the restructuring of a 15-25 nm layer of electron beam evaporated Ag into "nanoparticles", which are used as an etch mask to transfer a nanopattern into the n-AlGaAs layer. Then, the Ag is removed, and the remaining nanostructured n-AlGaAs surface improves the extraction of light from the device. The novel LEDs have three different nanostructured thicknesses, namely 15 nm (Device B), 20 nm (Device C), and 25 nm (Device D). The morphologies of the Devices B-D are analyzed by an atomic force microscope and a scanning electron microscope. Compared to the planar LED (Device A), the light output powers of the Devices B-D increases by 112.6%, 91.4%, and 63.5%, respectively. The nanopatterns can mitigate the abrupt change of the refractive indexes between the air and the semiconductor to increase the LEDs' light extraction efficiency. The surface texturing approach can be applied to commercial high-power LEDs.