Improvement of AlGaN-based deep-ultraviolet light emitting diodes performance with a nano-textured/roughened sapphire substrate

Performance improvement of the fabricated AlGaN-based deep-ultraviolet light emitting diode (DUV LEDs) on sapphire with nano-textured/roughned substrate is reported. The output optical powers as well as the current-voltage characteristics of the processed devices with and without textured/roughened substrate are compared. Lapping/polishing and dry-etching techniques were employed for nano-texturing/roughening of the substrate. Magnetron dry etching was performed using a mixed CF$_{2}$Cl$_{2}$/Ar feed gases followed by an inductively coupled plasma (ICP) etching in BCl$_{3}$/Cl$_{2}$ plasma chemistry. An etching rate of $\sim $145 nm/min for the sapphire was easily obtained. The result show that the optical emission power of the fabricated devices with textured/roughened sapphire substrate is higher as compared to similar un-textured/roughened devices. Based on the analysis, it is concluded that a textured/roughened substrate surface with an RMS $\sim $ 15 -- 25 nm shows improved light extraction efficiency, which is the result of the reduced internal reflection of the light caused by the nano-textured/roughened surface profile thereby causing deviation for critical angle.