Preparation of InN and InN-Based Heterostructures by Molecular Beam Epitaxy
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Preparation of InN and InN-Based Heterostructures by Molecular Beam Epitaxy
Hai Lu, William J. Schaff, Jeonghyun Hwang, and Lester F. Eastman Department of Electrical and Computer Engineering, Cornell University Ithaca, New York 14853 ABSTRACT InN is an important III-V compound semiconductor with many potential microelectronic and optoelectronic applications. In this study, we prepared epitaxial InN on (0001) sapphire with an AlN buffer layer by molecular beam epitaxy, and its variation, migration enhanced epitaxy. A series of samples were grown with different substrate temperatures ranging from 360oC to 590oC. The optimum growth temperature for InN was found to be between 450oC and 500oC. We also found that thicker AlN buffer layers result in the best InN quality. With increasing thickness of an AlN buffer layer, the Hall electron mobility of InN increases while the carrier concentration decreases. The surface morphology is also improved this way. Hall mobility greater than 800 cm2/Vs with carrier concentration 2-3×1018 cm-3 at room temperature can be routinely obtained for ~0.1µm thick InN films. Various InN-based heterostructures with AlInN or AlN barrier were fabricated. X-ray diffraction study clearly shows the barrier and InN layers. A 2-dimensional electron gas resulting from polarization induced electrons was observed in capacitance-voltage measurements. Some results on Mg doping of InN will be discussed as well.
INTRODUCTION Indium nitride, an important III-V compound semiconductor with many potential applications, has attracted much attention recently. [1] Although the band gap of InN is 1.89eV at room temperature, which is smaller than that of GaN at 3.39eV, it is larger than that of GaAs at 1.42eV, and is certainly large enough for many high-power applications. More importantly, the inherent material characteristics of InN make it superior to GaN in some very important aspects. Much higher peak drift velocity and peak overshoot velocity compared with GaN and AlN are predicted by theoretical calculations. [2-4] However, due to the difficulties in preparation of high-quality InN, it is less studied than GaN, GaInN and other nitride compounds. One main difficulty is the lack of suitable substrate material. The lattice mismatch between InN and α-Al2O3 (0001) substrates, which are widely used, is about 25%. This large mismatch can result in an extremely high density of structural defects. The other main difficulty is the low dissociation temperature of InN. As a result, the preparation of InN requires a low growth temperature. Meanwhile, for common III-nitride epitaxy techniques, such as metalorganic vapor phase epitaxy (MOVPE) and molecular bean epitaxy (MBE), low growth temperature means a short migration distance of group-III atoms. That is, many group-III atoms will have less energy to travel long enough on the surface to locate their energy minimum sites before they react with N to form small less mobile nitride islands. As a result, nitride film with high defect density can form. In this study, we rep
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