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In this letter, a novel ammonium fluoride pretreatment (AFP) method has been proposed to improve the morphology and thermal stability of NiGe on bulk germanium devices. The root mean square roughness of NiGe film has been obviously decreased using the AFP method, indicating more smooth and flat NiGe surfaces formed compared with samples by hydrochloric acid and hydrofluoric acid pretreatments. Also, the thermal stability of NiGe film has been enhanced, since uniform NiGe film can be formed at temperature as high as 600°C. In addition, NiGe/n-Ge Schottky diodes have been fabricated to illustrate the benefits of AFP method in Ge-based devices. Better rectifying performance has been achieved using the AFP method from the benefit of suppressing reverse current about one order of magnitude, compared with the hydrochloric acid treated sample. Thus, both the material properties and electrical characteristics of NiGe film have been effectively improved by the simple AFP technique, revealing its potential for Ge-based process technology.