Weak Bonds in Amorphous Semiconductors

Abstract

In this paper, we would like to point out the important role played by the presence of weak bonds in various kinds of amorphous semiconductors. Most atoms have a normal structure bonding (NSB) configuration even in amorphous semiconductors. Only a small fraction of atoms have a deviant electronic configuration (DEC), that is, coordination number different from NSB. Besides such atoms, it is possible that atoms with a largely prolonged bond are present. So far several proposals for the existence of such weak bonds in amorphous semiconductors have been done. One of the authors (T.S.) suggested that defects in chalcogenide glasses are not three-fold coordinated chalcogens but positively and negatively charged dangling bonds with the positively charged ones interacting with neighboring lone-pair, making weak bonds.¹ In hydrogenated amorphous silicon (a-Si:H), the ESR signals with g = 2.0043 and g = 2.013 were ascribed to unpaired spins in the antibonding and bonding states of weak Si-Si bonds, respectively.^2,3 Very recently, we attributed the ESR hyperfine lines (ESR-HFL) observed in P-doped a-Si:H^4,5 to an electron in the antibonding state of a weak Si-P bond, and the change of the Si-P bond length according to its charge state was suggested.⁶