Structural, electrical, and low-frequency-noise properties of amorphous-carbon-silicon heterojunctions

The structural, electrical, and low-frequency-noise properties of heterojun ctions of amor- phous-carbon (a-C) films grown on either n- or p-type singl e-crystal silicon are investigated. The a-C films were deposited by rf magn etron sputtering at room temperature with varying the substrate bias V-b, f rom +10 to -200 V. The study includes measurements of x-ray reflectivity (X RR), low-frequency noise at room temperature, and dark current-voltage (I-V ) and capacitance-voltage (C-V) characteristics over a wide temperature ran ge. Analysis of the XRR data indicates the presence of a thin SiC layer bet ween a-C and Si, with thickness increasing up to about 1.8 nm for V-b = -20 0 V. The results show that the noise properties of the devices are independ ent 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 lo wer 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 heterojunction s are governed by conventional heterojunction theory, while multistep tunne ling 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 .