Analyzing the Surface Passivity Effect of Germanium Oxynitride: A Comprehensive Approach through First Principles Simulation and Interface State Density

High-purity germanium (HPGe) detectors, which are used for direct dark matter detection, have the advantages of a low threshold and excellent energy resolution. The surface passivation of HPGe has become crucial for achieving an extremely low energy threshold. In this study, first-principles simulations, passivation film preparation, and metal oxide semiconductor (MOS) capacitor characterization were combined to study surface passivation. Theoretical calculations of the energy band structure of the -H,-OH, and -NH2 passivation groups on the surface of Ge were performed, and the interface state density and potential with five different passivation groups with N/O atomic ratios were accurately analyzed to obtain a stable surface state. Based on the theoretical calculation results, the surface passivation layers of the Ge2ON2 film were prepared via magnetron sputtering in accordance with the optimum atomic ratio structure. The microstructure, C-V, and I-V electrical properties of the layers, and the passivation effect of the Al/Ge2ON2/Ge MOS were characterized to test the interface state density. The mean interface state density obtained by the Terman method was 8.4 × 1011 cm-2 eV-1. The processing of germanium oxynitrogen passivation films is expected to be used in direct dark matter detection of the HPGe detector surface passivation technology to reduce the detector leakage currents.