Quantitative carrier lifetime measurement with micron resolution

Abstract

In the last fifteen years the measurement of the spatially resolved carrier lifetime has emerged as a valuable tool for the characterization of silicon wafers and solar cells. In most of the available measurement methods, the spatial resolution is constrained to the order of several 10 to 100 µm by the diffusion length of the charge carriers. In this paper we introduce a contactless quantitative technique to determine the Shockley-Read-Hall lifetime with a spatial resolution of 1µm. This technique is based on high injection microphotoluminescence spectroscopy and allows a quantitative analysis of microscopic defects such as grain boundaries and metal precipitates by virtue of the high spatial resolution

Microscale Characterization of Surface Recombination at the Vicinity of Laser-Processed Regions in c-Si Solar Cells

“…Due to such small spot size, the excitation power density on the sample surface resulted to be in the order of 8x10 4 W/cm 2 , leading to a density of photo-generated carriers well above 10 18 cm −3 . As reported by Gundel et al [19], under these high injection levels, Auger recombination limits the carrier diffusion length to 1 µm or less, which therefore, gives us a spatial resolution for the PL measurements in the order of the laser beam spot size. For micro-Raman measurements, the light excitation was made by the same diode-pumped SSL (wavelength of 785 nm), and again the light beam was focused onto the sample surface by the same Leica 50x microscope objective.…”

Effects of photon reabsorption phenomena in confocal micro-photoluminescence measurements in crystalline silicon

“…The incident light is absorbed in the sub-surface region and notably for silicon the absorption depth varies between 100 nm and 10 lm for characteristic excitation wavelengths of 400 and 785 nm, respectively. As pointed out by Gundel et al, 15 due to the high carrier densities achieved in micro-PL measurements, the diffusion of photo-generated carriers is limited by Auger recombination, and therefore, the charge carrier profile is typically confined close to the illuminated surface.…”

“…A diagram of the Witec setup can be found elsewhere. 15 A diode-pumped laser with a wavelength of 532 nm was used as the excitation source, resulting in a light penetration depth of about 1 lm. Two different Plan Achromat microscope objectives (Olympus 50Â, Numerical Aperture (NA) ¼ 0.8 and Olympus 20Â, NA ¼ 0.45) optimized for near-infrared (NIR) detection were used to focus the laser light beam onto the sample surface.…”

Quantitative Surface Recombination Imaging of Single Side Processed Silicon Wafers Obtained by Photoluminescence Modeling

“…In some cases non-uniform carrier profiles have been analytically modeled and utilized to derive quantities sensitive to the carrier profile [7][8][9]. More advanced techniques also used multidimensional numerical device modeling [10][11][12][13][14].…”