Yang Ji-Hui, Shi Lin, Wang Lin-Wang, Wei Su-Huai
National Renewable Energy Laboratory, Golden, CO 80401, USA.
Suzhou Institute of Nano-Tech and Nano-Bionics, Chinese Academy of Sciences, Suzhou 215125, China.
Sci Rep. 2016 Feb 16;6:21712. doi: 10.1038/srep21712.
Non-radiative recombination plays an important role in the performance of optoelectronic semiconductor devices such as solar cells and light-emitting diodes. Most textbook examples assume that the recombination process occurs through a single defect level, where one electron and one hole are captured and recombined. Based on this simple picture, conventional wisdom is that only defect levels near the center of the bandgap can be effective recombination centers. Here, we present a new two-level recombination mechanism: first, one type of carrier is captured through a defect level forming a metastable state; then the local defect configuration rapidly changes to a stable state, where the other type of carrier is captured and recombined through another defect level. This novel mechanism is applied to the recombination center Te(cd)(2+) in CdTe. We show that this two-level process can significantly increase the recombination rate (by three orders of magnitude) in agreement with experiments. We expect that this two-level recombination process can exist in a wide range of semiconductors, so its effect should be carefully examined in characterizing optoelectronic materials.
非辐射复合在诸如太阳能电池和发光二极管等光电子半导体器件的性能中起着重要作用。大多数教科书中的例子都假定复合过程通过单个缺陷能级发生，在此过程中一个电子和一个空穴被捕获并复合。基于这一简单图景，传统观点认为只有带隙中心附近的缺陷能级才可能是有效的复合中心。在此，我们提出一种新的双能级复合机制：首先，一种载流子通过一个缺陷能级被捕获形成亚稳态；然后局部缺陷构型迅速转变为稳定状态，在此状态下另一种载流子通过另一个缺陷能级被捕获并复合。这种新颖的机制应用于碲化镉中的复合中心Te(cd)(2+)。我们表明，这一双能级过程能够显著提高复合率（提高三个数量级），与实验结果相符。我们预计这种双能级复合过程可能存在于多种半导体中，因此在表征光电子材料时应仔细研究其影响。
