Room-temperature photoluminescence (PL) from Si chemically etched (CE) in HF-HNO3-based solution has been observed. Scanning electron microscopy reveals that the etched Si has a surface morphology similar to that of luminescent porous Si fabricated by conventional anodization. PL spectra show an order of magnitude smaller luminescent intensity and a shorter wavelength intensity peak for CE Si. A CE Si thickness limitation was observed. The formation of CE Si can be readily explained by a local anodization model.

Thermal annealing studies of the photoluminescence (PL) intensity and Fourier-transform infrared spectroscopy have been performed concurrently on porous Si. A sharp reduction in the PL intensity is observed for annealing temperatures ≳300 °C and this coincides with desorption of hydrogen from the SiH2 surface species. A brief etch in HF can restore the luminescence of the samples annealed below 400 °C. We conclude that SiH2 is essential to the visible luminescence in porous Si.

The formation of photoluminescent porous Si in an &chant solution made from the HF-HNOs-CH,COOH system is reported. The porous Si is characterized on the basis of its photoluminescence (PL) spectra and the degradation of the PL during exposure to laser irradiation. The surface topography as characterized by atomic force microscopy (AFM) reveals features on the order of 400-600 A. The effect of annealing the porous Si in vacuum on the PL intensity is described and correlated to the breakdown of Si-H bonds on the porous Si surface.

The observation of photoluminescence (PL) spectral shifts during anodization of porous Si and after immersion in different chemical solutions is reported. These shifts in the PL spectra are attributed to changes in the surface chemistry achieved by changing the composition of the electrolyte in which the samples are immersed. Using this approach the emission has been repeatedly cycled (≳100 times) between green and red.

In situ scanning tunneling microscopy (STM) and ex situ atomic force microscopy (AFM) were used to examine the surface morphology of anodized p-St(i,00) electrodes in F -containing solutions. In addition to the formation of a mainly pitted and rough surface, in situ STM observation of anisetropic etching of St(100) in dilute (1%) HF showed the formation of well-defined features, such as peninsulas, a 27 ran wide V-groove, and many protruding 5 nm wide micropyramids.High-resolution in situ STM resolved atomic features at the V-groove limiting (111) facets. Although this slightly etched Si sample contained no quantum pillars, it luminesced orange under UV irradiation, in the same way as a porous Si layer prepared by anodization in a more concentrated HF (1:1 HF:EtOH) solution. A loosely bound surface porous Si layer as thick as 100 nm was revealed by AFM and a 2 ~m 2 square depression could be fabricated in this layer by exerting stronger compressive force. The chemical nature of the surface film prepared by anodic etching in 1:1 HF:EtOH was further probed by x-ray photoemission spectroscopy (XPS), transmission Fourier transform infrared spectroscopy (FTIR), and laser ionization microanalysis (LIMA) techniques. These results support the explanation that the photoluminescence from porous Si can be caused by a chemically modified (St/H/O) layer on the surface (e.g., a siloxene-iype material).Chemical and electrochemical etching of silicon has been applied to the fabrication of submicrometer features on the surface and the production of porous Si layers. ~ Because of the high porosity of porous St, it can be oxidized readily in an O2-rich environment to give a 1 ~m thick dielectric SiO2 layer for insulating electronic elements in integrated circuits. 2 Porous Si has als0 been suggested as a potential optical material for light emitting deyices. 3 Preferential (anisotropic) etching of Si along the (110) and (100) directions is used in microfabrication. 4 A typical chemical etching solution for Si contains an oxidant to react with the surface Si atoms to form higher oxidation states, such as Si(II) and St(IV), that react with F-species to produce soluble complexes. The oxidizing strength of the oxidant plays a crucial role in determining the shape of the etched surface features. Too strong an oxidant, like nitric acid (HNO3), leads to isotropic (orientation independent) etching. 5 Chemical etching of Si with an aqueous KOH solution is strongly anisotropic; this solution has been used to produce high aspect ratio surface features? Generally speaking, the etch rate of Si follows the order of (100) > (110) > (111). 4 The mechanism and causes of this anisotropic etching are of interest and have been studied in attempts to improve Si micromachining capabilities. 6' 7 One tentative model 4 involves correlating the dangling bond density on each of the low index Si surfaces with their reactivities, but the result failed to account for the marked difference in etch rate of 600:300:1 in 44 weight percent (w/o) KOH for the (100 ):...