We propose dual bias modulation electrostatic force microscopy (DEFM) for variable frequency measurements of surface depletion capacitance on a semiconductor. In DEFM, dual alternating current bias voltages at angular frequencies of ω1 and ω2 are applied to generate an electrostatic force, and we detect the high order term at an angular frequency of ω2 − 2ω1 in the electrostatic force from which a derivative of surface depletion capacitance by voltage (∂C/∂V) can be evaluated. Even with a fixed value of ω2 − 2ω1 at a specific resonant frequency of the cantilever, to ensure sufficient sensitivity of the electrostatic force, a pair of ω1 and ω2 can be varied; this enables variable frequency measurements of ∂C/∂V by DEFM. The validity of the quantitation and spatial resolution of DEFM were assessed through the analysis of metal-oxide-silicon and Zn(O, S)/Cu(In,Ga)(Se,S)2 samples.

We have proposed a method for quantitative capacitance measurements using frequency modulation electrostatic force microscopy (EFM) with a dual bias modulation method and demonstrated it on n- and p-type Si samples. First, we theoretically derived a conversion formula from a frequency shift of cantilever resonance in EFM into a capacitance value based on the parallel plate capacitor model, by which a pair of an EFM tip and a semiconductor sample is expected to be equivalently represented. Then the capacitance measurements were experimentally conducted on the n- and p-type Si substrates, and the acquired capacitance-voltage curves indicated that the obtained capacitance values were consistent with the expected ones and that the carrier densities evaluated from the depletion capacitances were also in good agreement with those evaluated by the conventional Hall effect measurements. From those results, the validity of our quantitative evaluation method has been well confirmed.

No abstract

We have proposed and demonstrated a direct imaging method in dual bias modulation electrostatic force microscopy (DI-DEFM) to observe the frequency response of the capacitance between a conductive tip and a sample in a single scan. In DI-DEFM, dual ac biases with different frequencies are simultaneously applied between the tip and the sample to generate an electrostatic force; the frequencies are switched between two pairs of frequency conditions, with a switching frequency . Then, the component in the electrostatic force is detected, similar to a heterodyne method, to analyze the frequency response of the capacitance. The validity of DI-DEFM is assessed through the image acquisition on a Cu(In,Ga)Se2 sample.

According to Onsager’s principle, electrical resistance R of general conductors behaves as an even function of external magnetic field B. Only in special circumstances, which involve time reversal symmetry (TRS) broken by ferromagnetism, the odd component of R against B is observed. This unusual phenomenon, called odd-parity magnetoresistance (OMR), was hitherto subtle (< 2%) and hard to control by external means. Here, we report a giant OMR as large as 27% in edge transport channels of an InAs quantum well, which is magnetized by a proximity effect from an underlying ferromagnetic semiconductor (Ga,Fe)Sb layer. Combining experimental results and theoretical analysis using the linearized Boltzmann’s equation, we found that simultaneous breaking of both the TRS by the magnetic proximity effect (MPE) and spatial inversion symmetry (SIS) in the one-dimensional (1D) InAs edge channels is the origin of this giant OMR. We also demonstrated the ability to turn on and off the OMR using electrical gating of either TRS or SIS in the edge channels. These findings provide a deep insight into the 1D semiconducting system with a strong magnetic coupling.