Abstract: Stable ohmic contacts play the important role in the normal operation of semiconductor devices. At present，Au /AuGeNi alloy is used as the electrode material of n type GaAs. The process is complex and the cost is high.In this paper，a new type of ohmic contact electrode material Ag /Co doped amorphous carbon film for semi-insulated GaAs and its preparation process are introduced to make it easy for readers to understand the process and technology of semiconductor devices.

Key words: semi-insulated GaAs, ohmic contact, photoconductivity