Ab Initio Study of Transition Levels for Intrinsic Defects in Silicon Nitride

作者：Di Valentin Cristiana^*; Palma Giorgio; Pacchioni Gianfranco

来源：Journal of Physical Chemistry C, 2011, 115(2): 561-569.

DOI：10.1021/jp106756f

The charge trapping properties of intrinsic defects in beta-Si(3)N(4) are investigated by means of density functional theory calculations using a hybrid exchange correlation functional that properly reproduces the band gap of the material. The following defects have been considered: an N vacancy, V(N), consisting of a N(3) Si* and a N(3) Si-Si N(3) adjacent units; an N vacancy saturated with H, V(N)(H) (N(3) Si-H and N(3) Si-Si N(3)); and a Si atom substitutional to N, Si(N), where Si is bound to three other Si atoms, Si(3) Si*. The analysis of the charge trapping ability is performed by computing the optical and thermodynamic transition levels between the 0 and 1 charge states of the defects, with an approach that goes beyond the single-particle approximation provided by the Kohn-Sham levels. The N vacancy turns out to be a deep trap for electrons, whereas the H impurity in the N vacancy and a Si atom substitutional for N are relatively shallow defects with thermodynamic 0/-1 transition levels at similar to 1 eV below the bottom of the conduction band. The results suggest that Si-Si bonds or tiny Si clusters formed inside Si(3)N(4) are responsible for the charge trapping behavior of this material in charge trapping memory devices.

• 出版日期2011-1-20