Non-polar GaN film growth on (0 1 0) gallium oxide substrate by metal organic chemical vapor deposition
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To achieve the first demonstration of non-polar a-plane gallium nitride (GaN) epitaxy on (0 1 0) gallium oxide substrates by metal organic chemical vapor deposition (MOCVD), a low temperature AlGaN nucleation layer was engineered. Specific low temperature AlGaN growth parameters were necessary because the gallium oxide substrate begins to decompose at ;600 °C in the ambient of H2. To achieve a smooth GaN epitaxial surface, low V/III molar ratio, and low pressure were required. To characterize the GaN film, AFM along with an orientation-dependent crystal tilt mosaic study by X-ray diffraction was performed. We effectively reduced threading dislocation density by applying in situ SiN interlayers grown by MOCVD. The oxygen contamination in the GaN film was found to originate from the substrate decomposition during GaN growth and can be reduced more than 10 times by using GaN buffer layer grown under N2 ambient.
I. INTRODUCTION
Gallium oxide (Ga2O3) has attracted great interest because of its potential for the next-generation of power electronics. The advantage Ga2O3 has over other materials, such as GaN and SiC, is that Ga2O3 has a larger band gap of 4.8–4.9 eV, a higher estimated breakdown field of 8 MV/cm, 1 and a lower cost to produce the native substrates.2,3 The electron mobility of ;100 cm2/V s in Ga2O3 at room temperature has been reported4,5 and could be higher with further improved material quality. It has been estimated that the Baliga’s figure of merit of b-Ga2 O3 is more than four times larger than those of 4H–SiC and GaN.1 Extensive studies have been performed on material growth6,7 as well as physical properties, like the thermal conductivity and the dielectric constant. 8,9 Both lateral transistors 1,10,11 and vertical Schottky diodes4,6 have been fabricated on Ga2O3 with the hope of demonstrating a better figure of merit (FOM) than GaN and SiC. However, the development of vertical Ga2O3 transistors is currently limited by the lack of stable p-type doping. The valence band offset between GaN and b-Ga2O3 was reported to be 1.4 eV.12 This indicates the conduction band offset is less than 0.1 eV, making it very attractive to integrate GaN-based devices with Ga2O3 substrates or even Ga2O3 devices because of the availability of both n-type and p-type doping capability in GaN, and the possible vertical conduction Contributing Editor: Don W. Shaw a) Address all correspondence to this author. e-mail: [email protected] This paper has been selected as an Invited Feature Paper. DOI: 10.1557/jmr.2017.126
between GaN and Ga2O3. But this approach requires high-quality hetero-epitaxy as well as in-depth understanding of the growth mechanisms for GaN and Ga2O3 materials. This paper will make preliminary exploration in this area. II. EXPERIMENT
Epitaxy of c-plane GaN has been achieved on b-Ga2O3 substrates with different orientations including ( 2 0 1), (1 0 0), (1 0 1), (3 1 0), (3 1 0) by MBE, HVPE, and MOCVD methods.14–23 c-Plane GaN LED devices have also been demonstrated on (1 0 0) b-Ga 2O3 substrates.21,22 Since Ga2O3 can b
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