Highly sensitive porous silicon based photodiode structures

Al/PS/c-Si photodiode structures were fabricated with a porous silicon (PS) layer of high porosity. Photosensitivity spectra, current-voltage (I-V) dependences at different temperatures, and electron beam induced current profiles were analyzed. Effects of annealing on the device characteristics were studied. The photosensitivity spectrum of the Al/PS/c-Si structures was found to be analogous to that of Al/c-Si structures. The photosensitivity value of as-prepared Al/PS/c-Si structures is 1.3 times that of an Al/c-Si Schottky diode in the wavelength range of 0.5-1.0 mu m. The photosensitivity of the annealed structure strongly depends on the reverse bias; it increases by more than two orders of magnitude (up to 10 A/W) when the reverse bias increases from 0 to 5 V. The I-V dependences indicate that band bending on the sides of the PS/c-Si heterointerface are in opposite directions. (C) 1997 American Institute of Physics. [S0021-8979(97)03121-6].