THESIS
2014
xii, 77 pages : illustrations ; 30 cm
Abstract
III-nitrides are one of the most important semiconductors since silicon, offering
high-carrier saturation velocity, high breakdown field strength and hence enormous
opportunities in RF/power electronics. Due to the lack of native substrates, III-nitrides
are normally heteroepitaxially grown on lattice-mismatched substrates, such as silicon,
sapphire and silicon carbide. However, high-density dislocations, unintentional
doping from the substrates and other issues arising from mismatched heteroepitaxy
may degrade device electrical properties and cause reliability concerns. To resolve
these problems and unleash the full potential of III-nitrides, both advanced epitaxy
techniques and innovative device architectures need to be engineered.
This thesis focuses on the growth of high-pe...[
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III-nitrides are one of the most important semiconductors since silicon, offering
high-carrier saturation velocity, high breakdown field strength and hence enormous
opportunities in RF/power electronics. Due to the lack of native substrates, III-nitrides
are normally heteroepitaxially grown on lattice-mismatched substrates, such as silicon,
sapphire and silicon carbide. However, high-density dislocations, unintentional
doping from the substrates and other issues arising from mismatched heteroepitaxy
may degrade device electrical properties and cause reliability concerns. To resolve
these problems and unleash the full potential of III-nitrides, both advanced epitaxy
techniques and innovative device architectures need to be engineered.
This thesis focuses on the growth of high-performance III-nitrides high electron
mobility transistors (HEMTs) by metalorganic chemical vapor deposition (MOCVD)
and their monolithic integration with light emitting diodes (LEDs). AlGaN/AlN/GaN
HEMTs were grown and optimized on sapphire substrates with enhanced buffer
resistivity and electron mobility. Key factors impacting the resistivity of the buffer
were studied for growth on Si substrates. MOCVD in situ deposited SiN
x was also
investigated and successfully applied to SiN
x/AlN/GaN
metal-insulator-semiconductor HEMTs as gate insulation and surface passivation. A
maximum drain current of 1550 mA/mm and an on/off-state current ratio > 10
7 have
been achieved.
Finally, monolithic integration of HEMTs and LEDs was demonstrated with both
selective epitaxial removal (SER) and selective epitaxial growth (SEG) methods. It
was found that the SEG method yield better results as SER led to degradation of the
LED performance by plasma damage of the p-GaN surface during the removal
process. The integrated HEMT-LEDs by SEG exhibited a peak transconductance of
246 mS/mm, similar to conventional HEMTs, and a forward voltage of 3.7 V at 20
mA, comparable to stand-alone LED devices. Blue light emission modulation by gate
biasing of the HEMT was also demonstrated.
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