Peak-tracking scanning capacitance force microscopy with multibias modulation technique

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, omega(1), omega(2), and omega(m), are applied together with DC voltage, VDc, to generate an electrostatic force, and high-order components at the angular frequencies of omega(2) - 2 omega(1) and omega(2) - 2 omega(1) - omega(m), which represent a voltage derivative of a capacitance (partial derivative C/partial derivative V) and a second-order derivative of the capacitance (partial derivative C-2/partial derivative V-2), respectively, are extracted from the electrostatic force. Then, a DC voltage, V-p, giving the peak of partial derivative C/partial derivative V is determined from V-DC to be adjusted to nullify the omega(2) - 2 omega(1) - omega(m) component using a feedback controller. From the obtained values of V-p and partial derivative C/partial derivative 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-DC 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 Cu(In, Ga)Se-2 material to discuss the effects of surface depletion and deep-level states, from which the validity of PT-SCFM has been examined.

Automated summary

This paper proposes peak-tracking scanning capacitance force microscopy (PTSCFM) for capacitance-voltage (C-V) measurements. PT-SCFM can extract the main feature of the C-V curve without the need for a DC voltage sweep. It allows for simultaneous imaging of the distribution of C-V values and topography, and enables analysis based on frequency dependence.