Field Emission Properties of Ion Beam Synthesized SiC/Si Heterostructures by MEVVA Implantation
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DIHU CHEN*, S. P. WONG*# , W.Y. CHEUNG*, E.Z. LUO*, W. WU*, J.B. XU*, I.H. WILSON*, and R.W.M. KWOK ** *Department of Electronic Engineering and Materials Science & Technology Research Centre, The Chinese University of Hong Kong, Shatin, Hong Kong China "**Departmentof Chemistry and Materials Science & Technology Research Centre, The Chinese University of Hong Kong, Shatin, Hong Kong China
ABSTRACT Planar SiC/Si heterostructures were formed by high dose carbon implantation using a metal vapor vacuum arc ion source. The variations of the field emission properties with the implant dose and annealing conditions were studied. A remarkably low turn-on field of 1V/ptm was observed from a sample implanted at 35 keV to a dose of I.0x10 18 cm-2 with subsequent annealing in nitrogen at 1200 0C for 2h. The chemical composition depth profiles were determined from x-ray photoelectron spectroscopy and the surface morphology was observed by atomic force microscopy. The formation of a thin surface stoichiometric SiC layer and the formation of densely distributed small protrusions on the surface are believed to be the two factors responsible for the efficient electron field emission.
INTRODUCTION The wide band-gap, high breakdown field strength, high thermal conductivity and high electron saturation velocity of SiC have made it an attractive material for applications in hightemperature, high-frequency and high-power devices. Since the first report on the formation of CSi bonds by carbon implantation into silicon [1], there has been a considerable amount of effort to synthesize SiC thin layers using ion implantation [2-10]. Our previous results [6-10] have shown that there are new features in the process of synthesizing SiC layers by implantation using a metal vapor vacuum arc (MEVVA) ion source, which was first developed by Brown el al [11], because of the high instantaneous input power density due to pulse mode operation. In particular, a remarkably low turn-on field of electron field emission of 1 V/pm has been observed from these implanted planar SiC/Si heterostructures prepared under appropriate conditions [10]. In this work, we shall report in more detail the recent results of our study on the field emission properties of these SiC/Si heterostructures prepared by MEVVA implantation.
Author to whom correspondence should be addressed; electronic mail: [email protected] 199 Mat. Res. Soc. Symp. Proc. Vol. 509 ©1998 Materials Research Society
EXPERIMENTAL The MEVVA implantation was performed at an energy of 35 keV to doses ranging from 5x1017to 1.2x10 18cm"2 . The pulse length of the MEVVA source was set at 1.2 ms and a typical repetition rate of 10 Hz was used, resulting in an average beam current density of about 15 4tA/cm 2. The substrates used were (100) n-Si wafers of resistivity 0.01-0.02 f)cm. Thermal annealing was performed at 1200'C in nitrogen for various time intervals. The chemical composition depth profiles and the chemical states of the C and Si atoms were determined by xray photoelectron spectroscopy (XPS)
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