Peak-tracking scanning capacitance force microscopy with multibias modulation technique

Abstract

Abstract Scanning capacitance force microscopy (SCFM) is a good method for capacitance measurements using electrostatic force detection. However, to obtain an entire capacitance–voltage (C–V) curve by SCFM, a sweep of a direct current (DC) bias voltage is required at a certain fixed point on a sample surface during scan suspension, and thus the measurements become very time-consuming when we want to observe some types of image related with C–V characteristics. In this paper, we propose peak-tracking scanning capacitance force microscopy (PTSCFM) for the purpose of extracting the main feature of the C–V curve without DC voltage sweep. In PT-SCFM, alternating current voltages at three different angular frequencies, ω 1, ω 2, and ω m , are applied together with DC voltage, V D C , to generate an electrostatic force, and high-order components at the angular frequencies of ω 2 − 2 ω 1 and ω 2 − 2 ω 1 − ω m , which represent a voltage derivative of a capacitance ( ∂ C / ∂ V ) and a second-order derivative of the capacitance ( ∂ 2 C / ∂ V 2 ), respectively, are extracted from the electrostatic force. Then, a DC voltage, V p , giving the peak of ∂ C / ∂ V is determined from V D C to be adjusted to nullify the ω 2 − 2 ω 1 − ω m component using a feedback controller. From the obtained values of V p and ∂ C / ∂ V at V p , the C–V curve can be outlined. In PT-SCFM, the distributions of those values are simultaneously imaged together with a topography without V D C sweep, and when we operate PT-SCFM under various modulation frequency conditions, analyses similar to those based on the frequency dependence of the C–V property are realized. We have applied the PT-SCFM to a microcrystalline C u ( I n , G a ) S e 2 material to discuss the effects of surface depletion and deep-level states, from which the validity of PT-SCFM has been examined.