| InGaN/GaN-based light emitting diodes (LEDs) grown on Si have generated intensive research interest due to silicon's low cost, large size availability and good thermal conductivity. However, GaN grown on Si normally suffers from large dislocation density and tensile stress due to the huge mismatch in the lattice constant and thermal expansion coefficient between GaN and Si.;This thesis focuses on developing high-quality and crack-free InGaN/GaN-based blue, green and yellow LEDs with embedded SiO2 nanorods. GaN buffers were firstly optimized using a source flow ratio modulation method and an AlN/AlGaN superlattice interlayer. After optimization, crystalline quality, surface morphology and stress status were all improved. Moreover, light output power (LOP) was improved by 66% for InGaN/GaN blue LEDs.;To further enhance the internal and external quantum efficiencies, high density SiO2 nanorods with an average diameter of less than 400 nm were fabricated on 2 microm thick GaN buffers and embedded into LED structures through nanoscale epitaxial lateral overgrowth. Two simple and non-lithographic methods for SiO2 nanorod fabrication were developed and compared in this work. With SiO2 nanorods surface coverage of 30%, 5 microm thick crack-free InGaN/GaN-based blue LEDs were grown with smooth surfaces. The LOP was raised by 40% compared to those without nanocomponents.;The LED structures with embedded SiO2 nanorods were also extended to emit longer wavelength to fill the "green gap". For 505 nm green LEDs, the optical power was as high as 0.65 mW at 20 mA. Moreover, for the first time, yellow InGaN/GaN MQW LEDs on Si substrates were demonstrated whose LOP and peak wavelength were 31 microW and 565 nm at 20 mA current injection. Low temperature characteristics of green and yellow LEDs were also described and discussed.;In the last section of this thesis, a method to remove light absorptive Si substrates and fabricate vertical LEDs was described, in which the LOP was enhanced by 30% over planar LEDs on Si. |
