We report on issues associated with the metalorganic chemical vapor deposition growth of ScGaN and YGaN. Based on the proposed bandgaps of ScN (2.15 eV), YN (0.8 eV) and the known bandgap of GaN (3.4 eV), we expected that LEDs could be fabricated from the UV (410 nm) to the IR (1600 nm), resulting in LED over all visible wavelengths for solid state lighting However, due to the low volatility of scandium and yttrium metalorganic precursors, we were only able to incorporate doping level concentrations of these atoms into a GaN film. This report highlights the difficulties encountered during the growth of these alloys and how some of these difficulities were overcome. We also investigated the nitridation of thin scandium metal films deposited on GaN using pulsed laser deposition. GaN was also grown on these thin ScN films to as a means to lower the GaN dislocation density.
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Extended AbstractThe most energy efficient solid state white light source will likely be a combination of individually efficient red, green, and blue LED. For any multi-color approach to be successful the efficiency of deep green LEDs must be significantly improved. While traditional approaches to improve InGaN materials have yielded incremental success, we proposed a novel approach using group IIIA and IIIB nitride semiconductors to produce efficient green and high wavelength LEDs.To obtain longer wavelength LEDs in the nitrides, we attempted to combine scandium (Sc) and yttrium (Y) with gallium (Ga) to produce ScGaN and YGaN for the quantum well (QW) active regions. Based on linear extrapolation of the proposed bandgaps of ScN (2.15 eV), YN (0.8 eV) and GaN (3.4 eV), we expected that LEDs could be fabricated from the UV (410 nm) to the IR (1600 nm), and therefore cover all visible wavelengths. The growth of these novel alloys potentially provided several advantages over the more traditional InGaN QW regions including: higher growth temperatures more compatible with GaN growth, closer lattice matching to GaN, and reduced phase separation than is commonly observed in InGaN growth. One drawback to using ScGaN and YGaN films as the active regions in LEDs is that little research has been conducted on their growth, specifically, are there metalorganic precursors that are suitable for growth, are the bandgaps direct or indirect, can the materials be grown directly on GaN with a minimal defect formation, as well as other issues related to growth.The major impediment to the growth of ScGaN and YGaN alloys was the low volatility of metalorganic precursors. Despite this impediment some progress was made in incorporation of Sc and Y into GaN which is detailed in this report. Primarily, we were able to incorporate up to 5x10 18 cm -3 Y atoms into a GaN film, which are far below the alloy concentrations needed to evaluate the YGaN optical properties.After a no-cost extension was granted on this program, an additional more "liquid-like" Sc precursor was evaluated and the nitridation of Sc metals on GaN w...