| With increasing device integration and miniaturization, it is desirable to grow Al-Ga-N optoelectronic devices on inexpensive, large size Si wafers. The latter enables seamless integration of optical components with conventional electronics. However, Si has large lattice and thermal expansion mismatches with group-III nitrides, and absorbs visible and UV light emitted by active nitride layers. To circumvent these difficulties, unique hybrid substrates were developed based on HfxZr1-xB2(0001) buffered Si(111) including on-axis and miscut geometries. The work described in this dissertation focuses on epitaxial synthesis, characterization, and theoretical description of strain, thermoelastic behavior, and electronic structure of thick ZrB2 films and associated heterostructures including Si/ZrB2/HfxZr1-xB2, Si/ZrB 2/HfB2 and Si/HfxZr1-xB2.;Optical quality ZrB2 films up to 500 nm thick were obtained via reactions of carefully tuned Zr(BH4)/H2 admixtures using gas source molecular beam epitaxy (GS-MBE). A residual tensile strain persisted in these films, independent of thickness, and it vanished at the growth temperature of 900°C. Comparison of the lattice mismatch between sapphire (Al2O3), silicon carbide (SiC), and bulk ZrB 2 substrates with GaN films over 20-900°C illustrated superior structural and thermal characteristics of the boride templates. Measurements and density functional theory (DFT) simulations of the boride dielectric function and reflectivity indicated metallic Drude behavior across the IR range. At higher energies (2-7 eV) additional spectral features were identified to be interband transitions.;The ZrB2 films were used as strain-compensating buffers to fabricate HfxZr1-xB2 including HfB2 . Ellipsometry indicated that the band structure and reflectivity evolved smoothly from ZrB2 to HfB2, paving the way for the fabrication of optimized hybrid substrates, enabling large scale nitride integration with Si technologies via simultaneous optical and strain engineering. The Hf xZr1-xB2/Si technology was utilized to grow Al xGa1-xN via displacement reactions of D2GaN 3 vapors and Al atoms at unprecedented low temperatures (650-700°C), compatible with Si processing. The films exhibited strong cathodoluminescence with narrow peak widths comparable to those observed in MOCVD samples grown at 1100°C. The formation of GaN was investigated theoretically using first principle simulations. |
