The structural, electrical, and low-frequency-noise properties of heterojunctions of amor- phous-carbon (a-C) films grown on either n- or p-type single-crystal silicon are investigated. The a-C films were deposited by rf magnetron sputtering at room temperature with varying the substrate bias V-b, from +10 to -200 V. The study includes measurements of x-ray reflectivity (XRR), low-frequency noise at room temperature, and dark current-voltage (I-V) and capacitance-voltage (C-V) characteristics over a wide temperature range. Analysis of the XRR data indicates the presence of a thin SiC layer between a-C and Si, with thickness increasing up to about 1.8 nm for V-b = -200 V. The results show that the noise properties of the devices are independent of the SiC interlayer and the a-C film deposition conditions, while the noise of the a-C/n-Si heterojunctions is about four orders of magnitude lower than that of the a-C/p-Si heterojunctions. Analysis of the I-V and C-V data shows that the rectification properties of the a-C/n-Si heterojunctions are governed by conventional heterojunction theory, while multistep tunneling is the current conduction mechanism in a-C/p-Si heterojunctions due to a high density of interface states. (C) 2001 American Institute of Physics. References: 33
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