The characteristics of Ge nanocrystals charge-storage memory stacks with NH3 plasma surface treatment of the tunneling oxide layer have been studied in this paper. The tunneling silicon oxide (TO) surface was nitrided by NH3 plasma treatment, which appears to modify the bonding type of the substrate surface and enhance the nucleation sites for Ge nanocrystals. The chemical bonding depth profile of the SixGe1-x/TO layers and the Ge nanocrystals structure were examined by X-ray photoelectron spectroscopy and transmission electron microscopy, respectively. The trap charge densities were estimated to be as high as 9.1 x 10(12) cm(-2) from hysteresis loop for +/- 10 V sweep. The nitrided interface (oxynitride) between the trapping layer and the tunneling silicon oxide has a bandgap lower than the silicon oxide, which causes an asymmetric tunneling barrier under programming and erasing conditions. An effective thinner barrier under programming bias results in enhanced programming speed due to improved carrier injection efficiency. It was also observed that the nitrided interface reduces Ge diffusion into the TO layer, which is known to result in degradation of the properties of Ge nanocrystal-based memory devices. (C) 2008 The Electrochemical Society.