室温辐照吸杂研究和应用于提高硅太阳电池效率的探索

The presence of transition-metal impurities is vitally harmful to the performance of solar cells. All the reported gettering methods for transition-metal impurities need high-temperature processes. Beginning with an observation on an abnormal novel phenomenon, we have systemally studied on the room temperature radiation gettering of transition metals in the bulk of Si, and put forward two patents and two papers. Trough many experiments, we have proved that in the condition of introducing surface defect region as gettering sinks, 60Co γ-ray radiation or 3-5MeV electron irradiation both with a very small dose (e.g. 50Gy) can stimulate the gettering of Au in the bulk of Au-implanted Si samples, i.e. the distribution of Au markedly shifts toward the surface gettering defect region at room temperature. The present application aims at: elucidating the mechanism of the room-temperature radiation gettering of Au in Si, Which type of transition-metal impurities other than Au in Si wafers with gettering defects can also have the room-temperature radiation gettering effect? What are the mechanisms on the roles of the gettering defect region and the two types of radiation? How to optimize the gettering defect region and the radiation parameters to fully play the room-temperature gettering effect? Combining the optimized gettering defect region with optimized small dose γ-ray radiation or electron irradiation, Au and some other transition metals in the active region of Si solar cells can be gettered to the gettering defect region under room temperature. As a result, the efficiencies of Si solar cells can be improved with very low cost (due to the very low cost of very small dose radiation and that of forming the gettering defect region).

过渡金属杂质对太阳电池的性能有多方面危害。已有对过渡金属杂质的吸杂都在高温进行。我们在太阳电池研究中从发现反常的新现象开始到系统研究，提出两项专利和两篇论文，都涉及硅中过渡金属的室温辐照吸杂。我们以多种实验证明：在具有表面吸杂缺陷区的前提下，很低剂量（如50Gy）60Co伽玛射线或3-5 MeV电子辐照激励下，离子注入Si中Au的分布在室温下移向表面吸杂缺陷区。本申请拟研究：阐明我们发现的Si中Au室温辐照吸杂的机制；除Au外，Si中还有什么杂质也有类似的室温辐照吸杂效应？吸杂缺陷区、伽玛射线和电子辐照各起什么作用？如何优化吸杂缺陷区和辐照参数，使之充分发挥室温吸杂作用？探索将优化的吸杂缺陷区与很低剂量伽玛射线或高能电子辐照相结合，在室温下将硅太阳电池有源区中Au等过渡金属杂质驱赶到吸杂缺陷区，从而实现很低成本下提升硅太阳电池的效率（很低剂量辐照和引入缺陷区的成本都很低）。

我们团队于2013年发现：在等离子体处理导致表面缺陷区的基础上，低剂量60Co伽玛射线的激励能在室温下将Si中Au原子部分地提取到Si表面。在此基础上，本项目的研究中有如下进展：一，与60Co伽玛射线相比，5MeV电子辐照对Si中Au原子有明显更强的吸杂效应。二，对于重要化合物半导体GaAs中重要杂质Cr的研究证明，等离子体处理GaAs表面加上60Co伽玛射线辐照能在室温下将GaAs体内部分的Cr提取到GaAs表面。三，对于重要化合物半导体GaN中Pt的研究证明，等离子体处理GaN表面, 加上60Co伽玛射线辐照能在室温下将GaN体内部分的Pt提取到GaN表面。实验还证明，与60Co伽玛射线相比，5MeV电子辐照对GaN中Pt原子有明显更强的吸杂效应。上述原创性的等离子体处理与辐照相结合的室温吸杂效应与方法对如何降低半导体中有害杂质的浓度有重要意义。在本项目研究的基础上，我们将进一步研究本吸杂方法在提高太阳电池效率和光电探测器灵敏度方面的应用。