Influence Of RTP On The Behavior Of Impurities And Deffects In Multicrystalline Silicon

Cast multicrystalline silicon is one of the main solar materials in photovoltaic industry. High density of impurities and defects, such as dislocations and grain boundaries, play a crucial role on the degradation of mc-Si solar cells performance. Understanding the properties of these impurities and defects as well as their impacts on the quality of mc-Si could help us find the way to reduce the cost of mc-Si solar cells and produce high quality mc-Si ingots. The effects of thermal annealing on the behavior of impurities and defects in mc-Si were investigated in this paper. And the effect of the transition metals, such as copper, iron and nickel, on the minority lifetime in mc-Si after RTP was also investigated.One-step and two-step annealing have greatly effect on the dislocation morphotogy in mc-Si. The size of dislocations is bigger at low temperature than that of high temperature. But the density of dislocations is smaller at low temperature than that of high temperature. The bulk density of defects rised with the annealing temperature after two-step annealing.The minority carrier lifetime decreased obviously after RTP at temperatures from 750℃to 950℃, especially for the sample annealed at 950℃for 30s. However, the minority carrier lifetime increased sharply when the RTP temperature is 1050℃, and the largest lifetime value is 4.3 times than the initial value. On the other hand, the minority carrier lifetime is affected obviously by the annealing time, and the minority carrier lifetime increased as the annealing time increased.The effects of the transition metals,such as copper, iron, nickel, on the minority lifetime in mc-Si subjected rapid thermal process are investigated. It is found that the minority carrier lifetime of the as-grown samples and transition-metal contaminated samples decreased obviously at conventional annealing temperature 1000℃for 2 hours. The minority carrier lifetime of the as-grown samples increased obviously after RTP at high temperatures, and the lifetime of wafers after annealing decreases silightly with increasing of annealing temperature but has a recovery after RTP at 1000℃. The minority carrier lifetime changed following copper and nickel contamination at mid and low temperature(below 900℃). However, the minority carrier lifetime decreased sharply following copper, iron and nickel contamination at high temperatures (1000℃,1100℃). These results indicated that high temperature RTP could improve the minority carrier lifetime of wafers with low-impurity concentration, but they have a negative effect on wafers with high-impurity concentration.