VISIBLE-LIGHT EMISSION-SPECTRA OF INDIVIDUAL MICROSTRUCTURES OF POROUS SI

We have measured the spectra of visible light emitted from the individual structures of porous Si (PS) below the probe tip of the scanning tunneling microscope (STM), and found that the peak energy of the emission spectrum shifts with the size of nanometer-scale structures on the PS surface. Samples with a PS layer similar to 50 nm thick were formed by anodic etching of p(+)Si(100) substrates (similar to 0.005 Omega cm). The STM images show that protrusions whose dimensions are 3-10 nm in diameter are distributed on the PS surface. The peak energy of the STM light emission spectrum shifts from similar to 1.7 to similar to 2.1 eV as the diameter of the structure below the STM tip decreases from similar to 9 to similar to 3 nm. The measured peak shift with the size of the structure is consistent with the shift of the energy gap predicted on the basis of a quantum confinement model. (C) 1995 American Institute of Physics.