High power photoconductive switches of 4H SiC with Si3N4 passivation and n+ -GaN subcontact

The effect of a Si3N4 passivation layer on the breakdown voltage in 4H SiC high power photoconductive semiconductor switching devices has been investigated. An n+-GaN epitaxial layer was also used for these devices as a subcontact layer, which was between the contact metal and the high resistivity SiC bulk, to improve the ohmic contact and mitigate current spreading: the GaN subcontact layer protects the contact from damage occurring at high power levels. The Si3N4 passivation layer was grown by ultrahigh vacuum plasma enhanced chemical vapor deposition. By using the Si3N4 passivation, the dark leakage current of the devices was suppressed effectively and decreased by one order of magnitude, and the breakdown voltage of the switching devices was improved significantly from 2.9 to 5 kV without degrading the high photocurrent.