Single crystal wurtzite GaN on (111) GaAs with AlN buffer layers grown by reactive magnetron sputter deposition
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T. K. Gustafson University of California, 183M Cory, Berkeley, California 94720 (Received 16 November 1992; accepted 20 May 1993)
We report the growth conditions necessary for highly oriented wurtzite GaN films on (111) GaAs, and single crystal GaN films on (111) GaAs using AIN buffer layers. The GaN films and AIN buffers are grown using rf reactive magnetron sputter deposition. Oriented basal plane wurtzite GaN is obtained on (111) GaAs at temperatures between 550 and 620 °C. However, using a high temperature 200 A AIN buffer layer epitaxial GaN is produced. Crystal structure and quality are measured using x-ray diffraction (XRD), reflection electron diffraction (RED), and a scanning electron microscope (SEM). This is the first report of single crystal wurtzite GaN on (111) GaAs using AIN buffer layers by any growth technique. Simple AIN/GaN heterostructures grown by rf reactive sputter deposition on (111) GaAs are also demonstrated.
I. INTRODUCTION Gallium nitride is a promising material in the development of short-wavelength light emitting devices (LED) due to its 3.4 eV direct band gap. However, two principal factors have limited GaN blue LED development: controllable p-type doping and substrates for epitaxial growth. P-type conduction has now been demonstrated in Mg-doped GaN films grown by metalorganic chemical vapor deposition (MOCVD) and can be enhanced using low energy electron beam irradiation.1'2 Neither bulk GaN nor AIN crystals are yet available; therefore, alternate substrates must be used. Large lattice and thermal expansion differences between GaN and the substrate create interface strain and dislocations that will degrade p-n junction performance. GaN is typically grown on sapphire substrates despite a 16% lattice mismatch. Attempts on other substrates include silicon,3"7 gallium arsenide,3-8"14 gallium phosphide,3 silicon carbide,15"17 and magnesium oxide.18 Aluminum nitride has been used effectively by many researchers as a thin-film buffer layer on sapphire for improved GaN growth.19'20 Table I summarizes the material data for GaN and substrates considered for wurtzite GaN heteroepitaxy. The lattice parameter for the (111) cubic crystals (GaAs, Si) is given as the effective spacing in the (111) plane corresponding to "a" of the wurtzite crystal for easier comparison. Sapphire data are also translated into the wurtzite system. Despite the large lattice mismatch, GaAs is a desirable substrate due to its large role in the electrooptic industry. If GaN could be grown epitaxially on GaAs, device integration would be possible. Zinc-blende
crystals in the (111) direction differ from wurtzite basal planes only by the stacking order of their planes. Few researchers have used GaAs as substrates for GaN growth, possibly because early comparisons showed sapphire produced smoother and more oriented GaN films.8 Cubic GaN, grown by gas-source molecular beam epitaxy (MBE), has been reported on (001) GaAs.9"13 Recent work in Japan has also shown oriented wurtzite GaN on (111) GaAs, using gas-source MBE.9 Howe
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