Preliminary Characterization of GaN MBE Epitaxial Layers Grown on Nanoporous 6H-SiC Substrates
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Preliminary Characterization of GaN MBE Epitaxial Layers Grown on Nanoporous 6H-SiC Substrates J. T. Wolan,1 A. Gopalkrishna,1 S. E. Saddow,2 M. Mynbaeu,3 H. Morkoç,4 M. Reshchikov,4 F. Yun,4 V. Dmitriev,5 and C.E.C. Wood6 1
Dave C. Swalm School of Chemical Engineering, Mississippi State, MS 39762-9595 Emerging Materials Research Laboratory, Department of Electrical & Computer Engineering, Mississippi State, MS 39762-9571 3 Ioffe Institute, St. Petersburg, Russia 4 Virginia Commonwealth University, Department of Electrical Engineering 5 TDI, Inc., Gaithersburg, MD, 20877 6 Office of Naval Research Arlington, VA 2
Abstract We report on the growth and quality of plasma enhanced molecular beam epitaxy (PEMBE) of an n-GaN layer grown on a 6H-SiC substrate, which was prepared to be half nanoporous. A layer of nanoporous SiC was fabricated on a half section of n-type, on-axis (0001)Si face 41 mm commercial wafer by surface anodization. Following H-plasma surface cleaning and in-situ thermal annealing, a 0.7µm thick silicon doped GaN film was deposited at a growth rate of 0.35µm/hr. Substrate temperature during GaN growth was 709oC with a chamber pressure of 1.9 x 10 -5 Torr. Results of X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) characterization suggest improved chemical quality of the film grown on the nanoporous section. Photoluminescence (PL) data indicate greatly reduced nonradiative recombination in the epi layer grown on the nanoporous as compared to the control surface. Introduction The GaN based heterojunction system possesses many characteristics that are highly attractive for high-power/frequency devices, emitters and detectors, the details of which have been discussed in recent reviews and texts [1-7]. Even though extraordinary advances have been made in a relatively short time, there are key issues yet to be adequately addressed on the way to realizing the full potential of nitrides. The most immediate problem is the defects caused by lack of native substrates [8]. While the ubiquitous sapphire substrates may produce acceptable results for the time being, one or more of the following will soon be required: high breakdown voltage, high thermal conductivity, reduced low and high frequency noise in devices, and malfunction free device operation. These will require greatly improved lattice and stacking match between the epitaxial layer and substrate. Ideally, bulk GaN crystals would be used for substrates; however, those currently available do not exceed a few millimeters in size. SiC is an attractive substrate for epitaxial growth of GaN films exhibiting excellent lattice, stacking and thermal compatabilities. Due to high SiC thermal conductivity (~ 4 W/cm-K) and cleavage possibilities, this system is particularly attractive for high-power/frequency electronic and photonic applications. This is due, in part, to their desirable material properties such as, high breakdown fields, high thermal conductivity; high-saturated electron velocities and large electron mobilities [9-12]. In
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