Rapid Photoluminescence Intensity Degradation in Porous Silicon
- PDF / 325,708 Bytes
- 6 Pages / 420.48 x 639 pts Page_size
- 86 Downloads / 258 Views
RAPID PHOTOLUMINESCENCE INTENSITY DEGRADATION IN POROUS SILICON *
**
*
P. BASMAJI , A.A. BERNUSSI , J.C. ROSSI and B. MATVIENKO * IFQSC - USP - 13560 - S&o Carlos - SP - Brazil ** CPqD - Telebras - 13085 - Campinas - SP - Brazil
*
ABSTRACT Rapid photoluminescence intensity degradation are observed in porous silicon layers formed at different preparation conditions. The decay rate, ranging from 0.5 to tens of seconds, is found to be a function of illumination intensity, sample temperature and emission wavelength. We attributed the degradation effect to photochemical reactions on the surface.
INTRODUCTION Visible luminescence at room temperature from anodized porous silicon (PS) has been a subject of great interest due to the possibility of fabricating light-emitting devices for optoelectronic applications [1-4]. The origin of this luminescence is not clear at the present. Quantum confinement effects and SiHX complex formation have been suggested as possible explanations for visible luminescence in porous silicon (5,6]. In spite of the efficient light emission achieved in these materials, luminescence intensity degradation has also been observed [7,8]. An understanding of the degradation mechanisms is important for further device development from these materials. In this work we present results of photoluminescence (PL) properties of porous silicon layers obtained under different measurement conditions and different sample preparations. We observed that the PL intensity decreases with time. The time decay rate is a function of the illumination intensity, the temperature of the sample and the emission wavelength. We tentatively associate the decrease in luminescence efficiency after a long illumination time to photochemical reactions on the surface during the PL measurements.
EXPERIMENTAL DETAILS The porous silicon layers were formed by anodization of p-type silicon wafers (1-10 0 cm) using different current densities and times. We have used both (100) and (111) oriented Si substrates. Photoluminescence measurements were carried out at room temperature or at 77K using the 488 nm (or 458 rm) line of an argon laser as excitation source with power densities Wm2 ranging from 0.01 to 10 W/cm2. The emitted radiation was dispersed by a 0.25 meter single grating monochromator and detected with a S1 photomultiplier.
RESULTS AND DISCUSSIONS The PL spectra from porous silicon usually exhibit broad Mat. Res. Soc. Symp. Proc. Vol. 283. @1993 Materials Research Society
234
bands with 0.3-0.5 eV half-widths. The peak emission wavelength strongly depends on the sample preparation conditions. For our samples, we obtained emission lines with peaks from 550 nm (2.254 eV) to 850 nm (1.458 eV). Figure 1 shows a typical room temperature PL spectrum of an air exposed porous silicon layer, anodized for 150 min with a current density of 15 mA/cm2. The spectrum exhibits a broad band centered at 776 nm (1.60 eV) of 0.4 eV. with a full width at half maximum (FWHM) During our measurements we observed that the PL intensity decreases wit
Data Loading...
