Local doping with focused laser beam writing was used to fabricate lateralnpn- andpnp-structures on modulation-doped Si/SiGe heterostructures. The electrical and optical properties of the achieved lateral potential modulation were analyzed for local B-doping onn-type Si/SiGe and P- and Sb-doping onp-type SiGe/Si. Focused laser beam written doped lines show a strongly nonohmicIVcharacteristic indicating the formation of a local insulating barrier in the two-dimensional carrier system. Such lateral structures can be used as photosensitive devices with responsivities up to106 A/Wcombined with a spatial resolution on the &mgr;m scale. ©1997 American Institute of Physics.