Dispersive Fourier Transform Spectroscopy Of Free-Standing Porous Silicon Films
- PDF / 320,075 Bytes
- 5 Pages / 414.72 x 648 pts Page_size
- 77 Downloads / 198 Views
ABSTRACT We have investigated optical constants of free-standing porous silicon films by dispersive Fourier transform spectroscopy (DFTS) in the NIR-VIS range. This allows the spectral variation of both the absorption coefficient and the refractive index of a material to be determined from the measurements of the attenuation and phase shift imposed on an electromagnetic wave by its interaction with a specimen. Using these optical constants, we have studied the complex dielectric function and the complex conductivity. To avoid the additive error in the absorption spectra arising from the pseudocoherence, we measured the transmission spectra by conventional Fourier transform spectroscopy (FTS). Using the refraction spectrum derived from the DFTS measurements, we have corrected for reflection losses in calculation of the absorption spectrum from the FTS transmission spectrum. The changes in the absorption coefficient and the refractive index due to oxidation, which is the most common aging phenomenon in porous silicon, have been studied using samples with different types of oxidization. INTRODUCTION The demonstration of efficient visible photoluminescence at room temperature [1] has resulted in tremendous interest in the optoelectronic properties of porous silicon. The capability of porous silicon to guide, modulate and detect light has aroused hopes of achieving silicon based integrated optoelectronics. Several of these possible applications have been already demonstrated in practice (see e.g. [2]). The refractive index of porous silicon can be tuned over a wide range by varying the porosity. Even after anodization, one can tune the refractive index using oxidation treatment. Several papers dealing with the porous silicon refractive index have been published and more of the investigations have been done using a spectroscopic ellipsometry or reflectance measurements. In this paper, the porous silicon refractive index and the attenuation index have been determined for the first time using dispersive transmission Fourier transform spectroscopy of free-standing porous silicon films. In DFTS, the complex refractive index is measured through the sample with a thickness of several microns, not only from the topmost layer. A knowledge of the complex refractive index allows one to calculate several parameters which define the optical behaviour of the matter for the electromagnetic field considered. The changes in the complex refractive index due to oxidation have also been studied. The most common aging phenomenena in porous silicon have been used: UV-illumination induced oxidation, ethanol treatment and wet oxidation in a humid atmosphere. These oxidation types are usually present when one works with porous silicon in laboratory air. 323 Mat. Res. Soc. Symp. Proc. Vol. 486101998 Materials Research Society
EXPERIMENT The samples were prepared by anodizing the Si (100) wafers in a HF (40%) and ethanol mixture (1:1). The etching time varied from 3 to 6 min. and the current density was 50-200 mA/cm 2 . The resistivity of the p
Data Loading...
