The characterization of high quality multicrystalline silicon by the electron beam induced current method

Abstract

Multicrystalline silicon (mc-Si) manufactured by a multi-stage solidification control casting method has been characterized by the electron beam induced current (EBIC) method. The average diffusion length of the ingot was over 250 µm, which was much longer than that of conventional mc-Si. The EBIC study revealed that the electrical activities of grain boundaries (GBs) varied with the ingot position due to the impurity contamination level. The main impurity detected was iron. The concentration of iron in the central position was much lower than that at the bottom and top positions. GBs in the central position showed no significant EBIC contrast at 300 K, suggesting low contamination level. GBs in the top and bottom positions, however, showed strong EBIC contrast at 300 K, suggesting high contamination level. At 100 K, a denuded zone with bright contrast developed around GBs in the top and bottom positions. The existence of the denuded zone suggested that impurities were gettered at the GBs. It was considered that the variation of the diffusion length in the ingot was related to the variation of recombination activities of GBs in the different positions, which mainly depended on the impurity contamination.

Influence of crystalline defects in Czochralski-grown Si multicrystal on minority carrier lifetime

“…Therefore, both crystalline defects and contaminated Fe impurities in cast-mc-Si are factors causing deterioration in the conversion efficiency of solar cells. The electrical properties at crystal defects in cast-mc-Si were evaluated by measuring the minority carrier lifetimes [9] and electron beam-induced current (EBIC) [6][7][8]10]. It has been reported that the minority carrier lifetime measured by the microwave detection of photo-conductive decay (m-PCD) method is especially low in regions where the density of sub-grain-boundaries is high [9].…”

“…EBIC contrast at sub-grain-boundaries was stronger than at random grain boundaries and coincidence site lattice boundaries such as S3, S9 and S27 [6,7], indicating that the sub-grain boundary acts as stronger recombination center. However, it is well known that Fe impurities in the cast-mc-Si concentrate around crystalline defects such as grain boundaries [6][7][8]10], and it is therefore very important to differentiate between the influence of crystalline defects and Fe contamination on carrier recombination in cast-mc-Si.…”

Electron‐beam‐induced current study of grain boundaries in multicrystalline Si

“…It is not necessary to stress that the key to improve the efficiency of mc-Si solar cell is the control of grain boundaries (GBs) and impurity contaminations. It is widely accepted that the GBs and sub-boundaries give serious suppression of solar cell efficiency [1][2][3][4].The impurity contamination, mainly Fe, also degrades the efficiency very much [5][6][7][8][9]. In commercial mc-Si wafers, these two defects closely interact with each other and determine the solar cell efficiency.…”

Investigation of Electric Properties Degradation of Multi-Crystalline Silicon Solar Cells

“…It gives us the information that except that the defects and grain boundary should influence cells LID, the impurity content of wafers also could make big contribution on cells LID. As the literatures introduction, the minority carrier lifetime is directly associated with impurity, defects, crystal boundary and so on (4). It is instructive examine if the LID in the cells is fully controlled by the degradation in minority carrier lifetime.…”