Doping semiconductor with metals will change their electrical and optical properties.
For example, Ga and Al are used to dope silicon to make it p-type. Similarly for other semiconductors there exist different metals for doping. On the other hand gold has detrimental effect on frequency response of silicon devices.
The quantity and type of doping will depend on what type (p- or n-) semiconductor you want to produce and to what end. In order words, the optimal property you are seeking depends on what/ where your intend to use the doped SC. Hope this helps.