Ohmic contacts, including materials and processes for forming n-type ohmic contacts on n-type semiconductor substrates at low temperatures, are disclosed. Materials include reactant layers, n-type dopant layers, capping layers, and in some instances, adhesion layers. The capping layers can include metal layers and diffusion barrier layers. Ohmic contacts can be formed on n-type semiconductor substrates at temperatures between 150 and 250° C., and can resist degradation during operation.