Fig. 2: In-depth analysis of the NDT phenomenon.

a OM image of the PG-NDT device for KPFM analysis, where the length of the scale bar denoted in the OM image is 10 μm. b VCPD profile from points A to B under the positive and negative VG values. c Height and width of the potential barrier and/or well, which were extracted under the positive and negative VG values. d Modified Richardson plot of the PG-NDT device (top) and distribution of ΔVCPD extracted from the inset KPFM mapping image (bottom). e Energy band diagrams and ID−VG curves of the PG-NDT device at three different gate voltage regions. From VG = 20 V to the vicinity of VG = 0 V (left), from the vicinity of VG = 0 V to the vicinity of VG = −10 V (middle), and from the vicinity of VG = −10 V to VG = −20 V (right).