THESIS
2013
xvi, 112 p. : ill. (some col.) ; 30 cm
Abstract
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 SiO
2 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% fo...[
Read more ]
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 SiO
2 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 SiO
2
nanorods with an average diameter of less than 400 nm were fabricated on 2 μm thick GaN
buffers and embedded into LED structures through nanoscale epitaxial lateral overgrowth.
Two simple and non-lithographic methods for SiO
2 nanorod fabrication were developed and
compared in this work. With SiO
2 nanorods surface coverage of 30%, 5 μm 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 SiO
2 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 μW 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.
Post a Comment