Anderson’s negative- U chemistry in amorphous silicon nitride: A complex system approach
- Woon Ih Choi
- Bokyeom Kim
- Uihui Kwon
- Yong-Hee Cho
- Won-Joon Son
- Hawoong Jeong
- Richard Dronskowski
- Dae Sin Kim
2025-10-24
P. W. Anderson introduced a negative- U (i.e., attractive electron-electron interaction) to describe the scarcity of singly occupied spin states in amorphous materials. To uncover the underlying chemistry behind this phenomenon, we combined structural sampling with quantum-chemical analysis of amorphous silicon nitride (a-SiN x ) based on DFT. Our analysis demonstrates that coordination defects act as charge traps, with a density on the order of 10 21 per cubic centimeter. These defects render singly occupied electronic states energetically less favorable than paired or fully emptied states, primarily due to electron donor-acceptor interactions. Furthermore, excess charge trapping occurs through chemical bond reorganization, which disrupts the balance of existing electron and hole traps. In addition, we found that in Si-rich a-SiN x , various Si─Si bonding networks exhibit power-law–like size distribution, where larger networks are associated with deeper trap levels. These findings explain why a-SiN x has been used as a charge storage layer in the charge trap flash memory.