Electrical characterization of an operating Si pn-junction diode with scanning capacitance microscopy and Kelvin probe force microscopy

Electrical characterization of an operating pn-junction diode is performed with scanning capacitance microscopy (SCM) and Kelvin probe force microscopy (KPFM) with submicron scale resolution. We image the spatial distribution of the carrier density inside a diode with SCM and the potential distribution on the surface of the operating diode with KPFM. The surface potential distribution measured at reverse bias is different from that in bulk. The potential drop is extended deep into a lightly p-doped region at reverse bias. The positive fixed oxide charge of 1–2×1011/cm2 would explain the modified potential drop: A known detrimental effect in such a device. The potential distribution at forward bias is nearly bulklike. The potential drops only near the metal–semiconductor junction.