Abstract
Black silicon (b-Si) is currently being adopted by several fields of technology, and its potential has already been demonstrated in various applications. We show here that the increased surface area of b-Si, which has generally been considered as a drawback e.g. in applications that require efficient surface passivation, can be used as an advantage: it enhances gettering of deleterious metal impurities. We demonstrate experimentally that interstitial iron concentration in intentionally contaminated silicon wafers reduces from 1.7 × 1013 cm−3 to less than 1010 cm−3 via b-Si gettering coupled with phosphorus diffusion from a POCl3 source. Simultaneously, the minority carrier lifetime increases from less than 2 μs of a contaminated wafer to more than 1.5 ms. A series of different low temperature anneals suggests segregation into the phosphorus-doped layer to be the main gettering mechanism, a notion which paves the way of adopting these results into predictive process simulators. This conclusion is supported by simulations which show that the b-Si needles are entirely heavily-doped with phosphorus after a typical POCl3 diffusion process, promoting iron segregation. Potential benefits of enhanced gettering by b-Si include the possibility to use lower quality silicon in high-efficiency photovoltaic devices.
Highlights
Black silicon (b-Si) is currently being adopted by several fields of technology, and its potential has already been demonstrated in various applications
The lifetime in the b-Si half (720 μs) is more than two orders of magnitude higher than in the ungettered wafer (1.9 μs) and more than three times that of the gettered planar half (200 μs), implying a significantly higher cell efficiency potential for the b-Si wafers[27]. Since both halves have been passivated simultaneously, the lifetime difference is a direct result of differences in the wafer bulk, indicating more efficient gettering in b-Si
We have shown that the large surface area of b-Si, a considerable barrier for high efficiency b-Si solar cells in the past, can be used as an advantage to enhance gettering of detrimental metal impurities, iron
Summary
Black silicon (b-Si) is currently being adopted by several fields of technology, and its potential has already been demonstrated in various applications. A series of different low temperature anneals suggests segregation into the phosphorus-doped layer to be the main gettering mechanism, a notion which paves the way of adopting these results into predictive process simulators This conclusion is supported by simulations which show that the b-Si needles are entirely heavily-doped with phosphorus after a typical POCl3 diffusion process, promoting iron segregation. One advantage worth studying is the potentially enhanced gettering of metal impurities which are deleterious in several applications, including transistors and photovoltaic devices[7]. An idea of enhanced gettering via increased surface area in silicon solar cells was proposed by Dimassi et al.[18] They fabricated sacrificial porous silicon (PS) layers on Si wafers and demonstrated that the harmful impurities were gettered from the bulk material to the porous layer during thermal annealing due to the high surface reactivity of PS. We draw guidelines toward implementing these findings into predictive process simulators[23,24] via discussing the dominant gettering mechanisms and compare the experimental findings with simulations
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
