Photovoltaic evidence for interface-trapped charge in X-ray-irradiated oxidized n-type silicon wafers

It is found that the AC surface photovoltage (SPV) increases after X-ray irradiation (8 kGy(Si)=0.8 Mrad (Si)) in an air-free dry-oxidized and hydrogen-annealed n-type silicon (Si) wafer with resistivity 0.1 Omega m. Since the AC SPV is known to increase as the depletion layer becomes wider, the present phenomenon means that negative interface-trapped charge due to X-ray-induced interface traps must be dominant in the wafer. This result is also supported by the fact that the AC SPV in an as-oxidized n-type Si wafer with native high interface trap density (D_it) is higher than that in a hydrogen-annealed wafer with resultant low D_it.