On Modeling Trivalent Dangling Bonds with Bivalent Levels

Abstract

We examine the treatment of the hydrogenated Amorphous silicon (a-Si:H) dangling-bond defect used in the Analysis of microelectronic and Photonic Structures (AMPS) computer model and in other models of a-Si:H semiconductor devices. The dangling bond defect (D) is trivalent, with two correlated electronic levels in the gap. However, Modelers typically employ two uncorrelated bivalent levels to represent D; this introduces fictitious neutral dangling bond (D°) levels whenever D is charged. We find that the bivalent (AMPS) representation captures the important aspects of D physics and introduces only small errors into simulations. To reach this conclusion, we examine charge density and recombination and compare the trivalent D defect and its bivalent representation in both thermal equilibrium and non-equilibrium (illuminated) cases. The charge density is identical, implying that band bending computed by the simulation is accurate. We find errors in the recombination rate for the bivalent representation are normally less than or equal to σ⁰/σ^ch, where σ° is the capture cross section of D⁰ and σ^ch is the capture cross section of a charged state of D. Typically Modelers use σ⁰/σ^ch of 1:10 to 1:100 yielding insignificant errors in the recombination rate with the uncorrelated bivalent representation.