Temperature dependent carrier lifetime studies on Ti-doped multicrystalline silicon

Abstract

Carrier lifetime measurements were performed on deliberately Ti-doped multicrystalline silicon wafers using a temperature controlled photoconductance device. The dominant recombination center was found to be the double-donor level associated with interstitial titanium. The interstitial Ti concentrations in multicrystalline silicon wafers were determined by measuring the Shockley-Read-Hall time constant for holes and using the known values of the thermal velocity and capture cross section for holes of the double-donor level at different temperatures. The measured values of the Ti concentration were then used to determine the electron capture cross section of the double-donor level over the temperature range of 140-270°C via the measured values of the Shockley-Read-Hall time constant for electrons and the known thermal velocity. Multiphonon emission was found to be the most likely capture mechanism for this temperature range for electron capture into the double-donor level of Ti in silicon. The effective segregation coefficient for Ti was estimated by fitting Scheil's equation to the measured values of the Ti concentrations and their respective vertical positions in the ingot. If all Ti were present as the interstitial double-donor, a lower limit of 1.8ϫ 10 −6 can be ascribed to the segregation coefficient, which is very close to the equilibrium value.

Impact of Metal Contamination in Silicon Solar Cells

“…In the case of Cr, α is about 6%, which is reasonable considering that the diffusivity is 3 times smaller and the solubility is 1 order of magnitude smaller, in comparison to iron. In the case of titanium, we assume that the dominant recombination occurs through the double‐donor defect energy‐level as proposed by Paudyal et al29 This is reasonable due to the similarity between the samples investigated there and in this study (e.g., multicrystalline ingot prepared by intentional addition of Ti in the silicon melt). Using the electron‐capture cross section measured by Paudyal, α is as large as 90%.…”

“…However, to the extent of its validity (e.g., at lower concentrations), the estimation of α can give an indication of the impurity electrical activity. In Table 3, the values of σ n 28–30 used to calculate α are reported. It is evident that α is as low as 0.1% for Fe.…”

Defect Parameters Contour Mapping: A Powerful Tool for Lifetime Spectroscopy Data Analysis

“…Lifetime spectroscopy usually refers to injection‐dependent lifetime spectroscopy, i.e., IDLS, if performed at room temperature or temperature‐ and injection‐dependent lifetime spectroscopy, i.e., TIDLS, when the measurements are performed across a range of temperatures it proves the most effective in accurately determining the fundamental defect parameters such as its energy level in the band gap E t , the capture cross section ratio k ( σ n / σ p ), and the T ‐dependence of σ p and σ n . However, most of the reported studies make use of intentionally contaminated samples which means that, although extremely important to expand the general understanding about metal impurities impact on Si material, they rely on the a priori knowledge of the impurity identity introduced into the samples, and oftentimes its concentration.…”

Recombination parameters of lifetime-limiting carrier-induced defects in multicrystalline silicon for solar cells

“…18 This method is known as the temperature-and injection-dependent lifetime spectroscopy (TIDLS). 18,20 By plotting the DPSS curves at different temperatures together, the exact defect parameters should be identified by the intersections of the DPSS curves, if E t and k are assumed to be independent of temperature. 18 Recently, a customized TIDLS system has been developed in our laboratory.…”