Optical response of the Al/a-SiC/c-Si(p)/Au heterojunction structure

In the present work, structures of the form Al/a-SiC/c-Si(p)/Au were fabricated and their optical response was studied in the wavelength region from 350 up to 1000 nm for different thicknesses of the amorphous material, from 600 up to 10,000 Angstrom, as well as the diffusion length of the a-SiC was determined. The spectral response of the Al/a-SiC/c-Si(p)/Au structures for thicknesses, d, of a-SiC > 1000 Angstrom exhibits a maximum value at 800 nm, whereas in the region of wavelengths from 400 up to 600 nm appears a loss mechanism, which may be attributed to the recombination of photogenerated hole-electron pairs in the neutral region of a-SiC. This loss mechanism disappears when the thickness of the neutral region of the amorphous thin film is smaller than the diffusion length of a-SiC. In this case (i.e. for d < 1000 Angstrom), the spectral response of the Al/a-SiC/c-Si(p)/Au structures exhibits an almost constant value of quantum efficiency over the range of wavelengths from 550 up to 850 nm. This, combined with the relatively high variable values of quantum efficiency over the range of wavelengths from 350 up to 550 run, makes these structures interesting as optical sensor devices. Finally, the minority carrier (holes) diffusion length of a-SiC was determined, using an optical method applicable to one-sided crystalline Si homojunctions, and it was found to be equal to 800 Angstrom. (C) 2002 Elsevier Science Ltd All rights reserved.