Fex Ge1- x/Ge amorphous heterojunction diodes with p-Fex Ge1-x ferromagnetic semiconductor layers are grown on single-crystal Ge substrates of p-type,n-type and intrinsic semiconductors,respectively.The I-V curves of pFe0.4 Ge0.6 /p-Ge diodes only show slight changes with temperature or with magnetic field.For the p-Fe0.4 Ge0.6 /nGe diode,good rectification is maintained at room temperature.More interestingly,the I-V curve of the pFe0.4Ge0.6/i-Ge diode can be tuned by the magnetic field,indicating a large positive magnetoresistance.The resistances of the junctions decrease with the increasing temperature,suggesting a typical semiconductor transport behavior.The origin of the positive magnetoresistance is discussed based on the effect of the electric and magnetic field on the energy band structures of the interface.In the past decades,ferromagnetic semiconductors (FMSs),which can be used as spin current sources,have received much attention due to their potential application in the next generation of information technology.In 1996,Ohno et a/.… reported molecular beam epitaxial (Ga,Mn)As FMSs,which show a wellaligned ferromagnetic order and an anomalous Halleffect.In 2002,Park et al.[2]