  Electrodes in close proximity to an active area of a device are required for
sufficient electrical control. The integration of such electrodes into optical
devices can be challenging since low optical losses must be retained to realise
high quality operation. Here, we demonstrate that it is possible to place a
metallic shallow phosphorus doped layer in a silicon micro-ring cavity that can
function at cryogenic temperatures. We verify that the shallow doping layer
affects the local refractive index while inducing minimal losses with quality
factors up to 10$^5$. This demonstration opens up a pathway to the integration
of an electronic device, such as a single-electron transistor, into an optical
circuit on the same material platform.
