CHARACTERIZATION OF STAIN ETCHED POROUS SI WITH PHOTOLUMINESCENCE, ELECTRON-PARAMAGNETIC-RESONANCE, AND INFRARED-ABSORPTION SPECTROSCOPY

Porous Si (PS) layers are prepared by stain etching in a HF/NaNO2 solu tion on both p- and n-type crystal Si substrates, and are characterize d by photoluminescence (PL), electron paramagnetic resonance (EPR), an d infrared absorption (IR) spectroscopy. The PL spectra under 488 nm l aser excitation exhibit a strong peak at 680-720 nm for various sample s of different substrate parameters and remain stable upon aging in ai r or gamma irradiation; as-etched (approximately 20 min in air before measurement) and aged (for up to six months) samples show no detectabl e EPR signal but the gamma-irradiated samples show an isotropic g = 2. 006 signal of peak-to-peak linewidth of 1.1 mT supporting an amorphous Si structure; the IR spectra show both hydrogen and oxygen related IR modes in the as-etched samples and the former decreases with aging ti me in air while the latter increases. Comparing our results with those of anodically etched PS samples we conclude that: (1) the PL peak pos ition of the stain PS seems to be unique and stable as compared with t hat of the anodic PS varying in 620-830 nm; (2) the isotropic EPR sign al of the stain PS reflects no crystallinity, in contrast with the ani sotropic signal of the anodic PS; and (3) obvious oxidation in the as- etched stain PS is also in contrast with the nonobservation of oxygen- related IR modes in the as-etched anodic PS. We discuss the results in terms of structural properties and PL mechanism of PS.