Noncontact evaluation of electrical passivation of oxidized silicon using laser terahertz emission microscope and corona charging

We evaluated electrical passivation of crystalline silicon wafers possessing oxidized layers using a laser terahertz (THz) emission microscope, measuring waveforms of laser-excited THz emission from those surfaces with a corona charging setup to tune surface potential without electrical contact. The THz waveform strongly correlated to the surface potential, evaluated by measuring surface photovoltage using a Kelvin probe when the surface was depleted or inverted. The waveform also correlated to the potential of the surface in the accumulation mode and inverted near the flatband condition. The minority carrier lifetime agreed with the theoretically determined dependence on the charge density. These results indicate that the surface potential of a semiconductor covered by an insulator which can be charged by the corona charging setup can be evaluated by assessing the THz emission. Further, such a sample can also be used as a reference to quantitatively relate the waveform of the THz emission and the internal field of surface band bending in semiconductors. Published under license by AIP Publishing.