Micro/nano Processing And Optical Properties Of GaN Nanorod-arrays

LED(Light emitting diode) based on III group nitride(such as GaN) has been widely used in lighting and display fields owing to its environmental protection, energy saving, small body and long lifetime. The epitaxial growth and chip production techniques of two-dimensional LEDs have gradually matured and realized the industrialization process up to date. Compared with the conventional two-dimensional LED, a new three-dimensional(3D) LED has recently shown huge advantages in weakening polarization effects and increasing light extraction efficiency because of its unique 3D structure. In this thesis, we reported on the fabrication and optical properties of 3D GaN and InGaN/GaN nanostructures. The main results are as follows:(1) 3D GaN nanostructures with well-aligned nano-cones have been prepared via a laser interference lithography + inductively coupled plasma(ICP)etching method. The effect of radio frequency(RF) power and KOH solution etching on morphologies and optical properties of the GaN nano-cones has been studied by scanning electron microscopy(SEM), energy dispersive spectroscopy(EDS), room-temperature and low-temperature photoluminescence(PL)measurements. Our results show that the sidewall obliquity of GaN nano-conesincreases from 63° to 80° with the increase of RF power from 60 W to 120 W,while their height and PL intensity peak at the RF power of 80 W. After etching with KOH solution the nano-cones’ surface was obviously roughened and their PL intensity increased by around 60%, although their internal quantum efficiency determined by low-temperature PL measurement was only increased by 6%. The enhanced PL intensity could be mainly ascribed to the improved light extraction efficiency and/or light absorption efficiency.(2) The well-aligned GaN based InGaN/GaN nanorods have been prepared using a lithography + ICP etching method. The effect of RF power and KOH solution etching on morphologies, strain and optical properties of the InGaN/GaN nanorods has been studied by SEM, Raman and room-temperature PL measurements. Our results show that the sidewall obliquity of InGaN/GaN nanorods increases from 71° to 90° with the increase of RF power from 60 W to120W, while their height and PL intensity peak at the RF power of 100 W and80W, respectively. The PL intensity of the InGaN/GaN nanorods(RF=80 W) is13 times the amount of the original 2D InGaN/GaN structure. Our results show that the strains of 2D InGaN/GaN structure and InGaN/GaN nanorods(RF=80W) are-0.84% and-0.5%, respectively, implying the stress of InGaN/GaN nanorods has been partially relaxed. The increase in PL intensity of the InGaN/GaN nanorods could be due to the relaxation of compressive stress,which can weak the piezoelectric polarization in the InGaN/GaN multiple quantum wells. After etching with KOH solution the InGaN/GaN nanorods’ surface was obviously roughened and their PL intensity increased by around48%, which could be ascribed to the relaxation of compressive stress in InGaN/GaN nanorods and the improved light extraction efficiency.