An interface state mediated junction leakage mechanism induced by a single polyhedral oxide precipitate in silicon diode

Abstract

The impact of an oxide precipitate on the junction leakage of a silicon p/n diode was investigated. A 70–100 nm diam single polyhedral oxide precipitate was placed in the depletion region of a p+/n junction by hydrogen annealing and polishing a Czochralski grown silicon wafer. In the reverse-bias current–voltage (I–V) curve, an anomalous hump structure was observed. This excess leakage component exhibited a flicker-type low frequency noise. Functional decomposition of the I–V curves demonstrated that a single gap state regulates the leakage current and that two distinct physical processes are involved in the leakage mechanism. The temperature and electric field dependence of the processes revealed that the gap state was a shallow attractive Coulomb center and that electric carriers were supplied to the Coulomb center by phonon-assisted tunneling and emitted from the center by the Poole–Frenkel mechanism. The presence of excessive low frequency noise indicated spatial proximity between the Coulomb center and the oxide precipitate. Computer simulations of the electric field around the oxide precipitate suggested that the center is doubly charged. Based on these findings, a leakage model was proposed. In the vicinity of the oxide precipitate, a few interstitial oxygen atoms are thought to be clustered to form a shallow double donor. The electric field facilitates the hopping of electrons from the valence band into the oxygen donor via interface states on the exterior of the oxide precipitate. Electrons are then emitted onto the conduction band by the Poole–Frenkel mechanism. Charge state transitions of traps inside the oxide precipitate generate a low frequency electric field fluctuation. The field fluctuation is then amplified by the Poole–Frenkel mechanism into the excessive low frequency noise in the leakage current. Thus a clear case of the detrimental impact of a shallow Coulomb center associated with an extended defect is established.