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...[ Read more ]

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 > 10⁷ 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.