Growth of Thick InN by Molecular Beam Epitaxy
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Growth of Thick InN by Molecular Beam Epitaxy Hai Lu, William J. Schaff and Lester F. Eastman Department of Electrical and Computer Engineering, Cornell University Ithaca, NY 14853 J. Wu, Wladek Walukiewicz Lawrence Berkeley National Laboratory, Berkeley, CA 94720 David C. Look Semiconductor Research Center, Wright State University, Dayton, OH 45435 Richard J. Molnar MIT Lincoln Laboratory, Lexington, MA 02420 ABSTRACT In this study, InN films with thickness up to 7.5 micron were prepared by molecular beam epitaxy (MBE) on (0001) sapphire and quasi-bulk GaN templates. Previously it has been challenging to grow InN film much beyond 1 micron because the growing surface tended to become rough. Techniques to overcome this limit have been developed. Various buffer techniques were used and compared to optimize the epitaxial growth. It was found that with increasing film thickness, Hall mobility will monotonically increase, while carrier concentration decreases. Hall mobility beyond 2100 cm2/Vs with carrier concentration close to 3×1017 cm-3 was obtained at room temperature. Compared with the lowest carrier concentration ~2×1018 cm-3 obtained on thin InN films grown at the same condition, the conclusion is that impurities from the growth environment are not responsible for the high background doping of InN. Instead, some structural defects or substrate/buffer impurities may be the major source of the unintentional doping, which can be reduced by growing thicker films. Some results on Mg and Be doping of InN will be reported as well. To date, all Mg and Be doping attempts have resulted in n-type material.
INTRODUCTION Indium nitride, as an essential component in the III-nitride system, has attracted much attention recently. Knowing more about this material is very helpful to the design of novel IIInitride devices based on the concept of band-gap and strain engineering. During the past few years, many important improvements on the research of this material have been achieved. InN films with room temperature Hall mobility more than 1000 cm2/Vs and carrier concentration in the order of 1018 cm-3 have been produced by several groups in the world. [1,2] What more significant is the successful demonstration of the narrow bandgap (0.7 eV) of InN.[3-5] This discovery has two important implications. First, many theoretical studies and experimental explanations based on the predominantly reported bandgap (1.9 eV) of InN have to be updated. Second, InN and its related In-rich nitrides can be utilized in a new domain of applications. In
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the field of opto-electronics, III-nitride-based light emitters can be made over a broader wavelength range from infrared to ultraviolet. In our previous study, it was found that by increasing InN film thickness, the electrical properties of InN can be improved.[1] However, at the same time, it was also found that it is quite challenging to grow InN film much beyond 1 micron because the growing surface tends to become rough near 1 micron of thickness. As a result of the rough surfac
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