Carrier distribution imaging using ∂C/∂z-mode scanning nonlinear dielectric microscopy.

Scanning nonlinear dielectric microscopy (SNDM) can be used to visualize the carrier distribution in semiconductors with high sensitivity and spatial resolution. We recently proposed a complementary method named ∂C/∂z-SNDM that avoids the problem of contrast reversal. This paper describes a methodology for calculating the signal intensity in ∂C/∂z-SNDM using examples. For the simulation, the capacitance of a conductive-probe metal/oxide/semiconductor model was calculated and then the response signal for various probe-sample distances was analyzed. The simulation results confirm that the ∂C/∂z-SNDM signal intensity increases monotonically with dopant concentration, avoiding contrast reversal. Moreover, in addition to the fundamental (1ω) signal, higher-harmonic (2ω, 3ω) signals have sufficient intensities to be detected. The results suggest that the detection sensitivity for low dopant concentrations can be improved by conducting the measurement under an appropriate dc bias.