Nonpolar a-plane AlGaN epi-layers were grown on a semi-polar r-plane sapphire substrate with an innovative two-way pulsed-flows metal organic chemical vapor deposition growth technology. A root-mean-square value of 1.79 nm was achieved, and the relative light transmittance of the a-plane AlGaN epi-layer was enhanced by 36.9%. These results reveal that the innovative growth method is able to improve the surface morphology and reduce the defect density in nonpolar a-plane Al _x Ga_{1– x} N epi-layers, particularly those with an Al composition greater than 0.5, which are key materials for the fabrication of nonpolar AlGaN-based high light emission efficiency deep-ultraviolet light-emitting diodes.

GaN-based light-emitting diodes (LEDs) on patterned sapphire substrate (PSS) with patterned composite SiO₂/Al₂O₃ passivation layers and TiO₂/Al₂O₃ distributed Bragg reflector (DBR) backside reflector have been proposed and fabricated. Highly passivated Al₂O₃ layer deposited on indium tin oxide (ITO) layer with excellent uniformity and quality has been achieved with atomic layer deposition (ALD) technology. With a 60 mA current injection, an enhancement of 21.6%, 59.7%, and 63.4% in the light output power (LOP) at 460 nm wavelength was realized for the LED with the patterned composite SiO₂/Al₂O₃ passivation layers, the LED with the patterned composite SiO₂/Al₂O₃ passivation layers and Ag mirror + 3-pair TiO₂/SiO₂ DBR backside reflector, and the LED with the patterned composite SiO₂/Al₂O₃ passivation layer and Ag mirror + 3-pair ALD-grown TiO₂/Al₂O₃ DBR backside reflector as compared with the conventional LED only with a single SiO₂ passivation layer, respectively.

The surface chemical state and local electronic structure of Al_xGa_1-xN (x = 0~0.45) epi-layers have been systematically investigated by X-ray photoelectron spectroscopy (XPS) and extended X-ray absorption fine structure (EXAFS) spectroscopy. The results show that the surface of Al_xGa_1-xN is a composite of oxide and nitride of gallium and aluminum. In addition, it was identified that the Ga-O components were converted to Al-O components when the Al_xGa_1-xN sample was exposed to air. The EXAFS analysis also reveals that the Ga-N and Ga-Al bond lengths are independent of the Al composition, whereas the Ga-Ga bond length is a function of Al composition.

Al₂O₃/GeO_x/Ge gate stack fabricated by an in situ cycling ozone oxidation (COO) method in the atomic layer deposition (ALD) system at low temperature is systematically investigated. Excellent electrical characteristics such as minimum interface trap density as low as 1.9 × 10¹¹cm⁻²eV⁻¹ have been obtained by COO treatment. The impact of COO treatment against the band alignment of Al₂O₃ with respect to Ge is studied by x-ray photoelectron spectroscopy (XPS) and spectroscopic ellipsometry (SE). Based on both XPS and SE studies, the origin of gate leakage in the ALD-Al₂O₃ is attributed to the sub-gap states, which may be correlated to the OH-related groups in Al₂O₃ network. It is demonstrated that the COO method is effective in repairing the OH-related defects in high-k dielectrics as well as forming superior high-k/Ge interface for high performance Ge MOS devices.