Photocurrent spectrum measurements of doped black silicon

摘要

Photocurrent spectra of doped black silicon (BSi) samples were investigated using metal-semiconductor-metal (MSM) structure. The BSi samples were fabricated through femtosecond-laser doping method. Two pieces of samples were annealed in nitrogen ambient for 30 minutes at different temperatures 350 ℃ and 700 ℃. One control sample remains without annealing. It was found that the doped black silicon samples have an electron mobility as low as 40~50 cm~2/V s but a conductivity as high as 4 ~ 5 Scm~(-1). The high conductivity allows making electrodes by directly contacting metal stripes onto the black silicon surfaces. For the sample without annealing, its photocurrent spectrum covers a wavelength range from 400 nm to 1200 nm. For the sample annealed at 350 ℃, no significant improvement was found except disappearance of a defect induced photocurrent peak at 660 nm. Further annealing at 700 ℃, as observed for the third sample, was found to greatly help enhance photoresponse in the wavelength range from 400 nm to 800 nm. The photocurrent spectra under different biases were also measured. With the increasing of bias from 0 to 0.6 V, the peak photoresponse was enhanced by about 5 times while large dark current brought in substantial noise level as well.