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T13.01 - Growth of GaN on Sapphire, Si (111), and Ge/Si (111) Using a Pulsed Electron Beam Deposition (PED) Process 
December 5, 2014   9:00am - 9:15am

This presentation will describe results recently obtained with pulsed electron beam deposition (PED) of GaN on c-plane sapphire, silicon (111), and 2 nm germanium coated silicon (111) substrates. The PED technique is potentially useful for growth of III-nitrides at lower substrate temperatures, a capability that can allow use of new buffer layer materials, introduction of chemically dissimilar lattice-matched materials, and help solve wafer bowing and cracking problems during growth. The introduction of this technique could lead to improvements in device quality and fabrication of vertical LED structures. In this study, GaN was deposited on sapphire at a substrate temperature of 750°C, and on silicon (111) and Ge/Si (111) at 600°C in a UHP N2 (15 mTorr) environment, without any surface pre-treatment such as pre-nitridation. A high power electron gun pulse (Neocera, Inc) was used to ablate the GaN target (1” dia. x 0.250” thick, 99.99% pure) stationed at a 5 cm vertical distance from the substrate. The electron pulses were generated at 15KV, 0.3 J/pulse at 1 Hz for initial few nm of growth, and then increased to a 3 Hz pulse rate. Scanning electron microcopy (SEM), X-ray diffraction (XRD), Rutherford backscattering (RBS), and optical absorption characterization were performed. SEM imaging confirmed a rough surface morphology with the presence of 30 nm to 300 nm scaled GaN crystallites for the GaN/Sapphire sample, while smaller but more coalesced crystallites of 30-50 nm size were observed for the GaN/Si (111) and GaN/Ge/Si (111) samples. The average film thickness was 350 nm, yielding a growth rate of 0.16 angstrom/pulse. XRD θ-2θ scans from 2θ = 0° to 2θ = 70° for the GaN on sapphire sample showed only two other peaks, besides the peaks from the sapphire, near 2θ = 34.6°. The peaks near 2θ = 34.6° consist of a stronger peak at 34.668° and a much weaker peak at 36.903°. These peaks correspond to the (0002) and (10-11) orientations for GaN, respectively. XRD scans for the GaN/Si (111) and GaN/Ge/Si (111) samples showed only a polar GaN (0002) peak at 34.7°. The XRD results clearly show that the deposited GaN material is not polycrystalline. Optical absorption spectroscopy over a 1.2 eV to 6.2 eV spectral range, for the GaN/Sapphire sample, showed an abrupt absorption edge at 3.4 eV, a clear indication of interband transitions in binary GaN. These results confirm that our PED-grown GaN is highly c-axis oriented and suitable for the initial growth of GaN on various substrate materials.

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