Nanotexturing of GaN light-emitting diode material through mask-less dry etching

Abstract

We describe a new technique for random surface texturing of a gallium nitride (GaN) light-emitting diode wafer through a mask-less dry etch process. This involves depositing a sub-monolayer film of silica nanospheres (typical diameter of 200 nm) and then subjecting the coated wafer to a dry etch process with enhanced physical bombardment. The silica spheres acting as nanotargets get sputtered and silica fragments are randomly deposited on the GaN epi-layer. Subsequently, the reactive component of the dry etch plasma etches through the exposed GaN surface. Silica fragments act as nanoparticles, locally masking the underlying GaN. The etch rate is much reduced at these sites and consequently a rough topography develops. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) inspections show that random topographic features at the scale of a few tens of nanometres are formed. Optical measurements using angle-resolved photoluminescence show that GaN light-emitting diode material thus roughened has the capability to extract more light from within the epilayers.

Bottom-Up Assembly and Applications of Photonic Materials

“…Their process involves the deposition of monolayer of silica particles, which are then subjected to a dry etching process to create fragments that randomly deposit on the GaN surface. These fragments then serve as a mask when the substrate is exposed to dry plasma etching where the exposed GaN surface will be etched away [141]. Ng et al made use of nanosphere lithography to create a hexagonal array of air holes by dry etching a self-assembled silica monolayer on a GaN surface.…”

Enhancement of Light Output Power from LEDs Based on Monolayer Colloidal Crystal

“…37% enhancement of the LOP of the resultant GaN LED was achieved in comparison with the LED without surface texturing. Besides ordered surface textures, random topographic features at the scale of a few tens of nanometers have been recently demonstrated to enhance the LEE of GaN LED . As schematically illustrated in Figure c, a sub‐monolayer of 200 nm silica nanospheres was firstly coated on the surface of GaN epitaxial layer.…”

“…(c) Schematic diagrams of the fabrication process of nanotexturing a GaN surface. (d) Angular distribution of light from roughened GaN area (green line with triangles) and a smooth GaN area (blue line with squares) . Reproduced with permission.…”

“…Besides ordered surface textures, random topographic features at the scale of a few tens of nanometers have been recently demonstrated to enhance the LEE of GaN LED. [ 40 ] As schematically illustrated in Figure 3 c, a submonolayer of 200 nm silica nanospheres was fi rstly coated on the surface of GaN epitaxial layer. A dry etch process with enhanced physical bombardment was then performed.…”

Nanostructured graded-index antireflection layer formation on GaN for enhancing light extraction from light-emitting diodes

“…After this process the top glass plate was removed and the sample was found to be sparsely coated with a submonolayer coverage of randomly placed silica spheres. Further details of this technique have been published elsewhere [11]. Once the coating process was complete, the sample was placed inside a reactive ion etching tool chamber (Oxford Instruments System 100) and was subjected to a carefully optimized plasma process.…”