An asymmetry metal-semiconductor-metal (MSM) structure has been demonstrated in SiGe/Si heterojunction photodetector (HPD) to suppress the dark current of conventional symmetry MSM structure, but the photocurrent are about the same for all symmetry and asymmetry structures. In our study, the Ni, An, and Cr metals were employed and we found that the Ni/SiGe/Si/Au asymmetry MSM heterojunction photodetector exhibits the lowest dark current for all symmetry and asymmetry structures. Compared to symmetry Ni/SiGe/SiNi MSM HPD, the dark current of asymmetry Ni/SiGe/Si/Au MSM HPD was reduced by a magnitude of 127 at an applied reverse bias voltage of 5 V. Moreover, the photo to dark current ratio was also enhanced by 78.6 for the Ni/SiGe/Si/Au asymmetry one at 5 V reverse bias, which exhibits a photoresponsivity of 16.57 A/W. (c) 2006 Elsevier B.V. All rights reserved.