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Cryogenic microwave imaging of metal–insulator transition in doped silicon
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View: Figures


Image of FIG. 1.
FIG. 1.

(a) Schematic of the low temperature MIM setup, including a picture of the tip-sample assembly and the block diagram of the microwave electronics. The distance modulation is turned on for tip-sample approaching and off for scanning. (b) A typical approaching curve, in which the lock-in reading is recorded as a function of the tip-sample spacing (z-scanner voltage). The inset shows schematically the tip-sample distance modulation. The shielded cantilever probe is employed and the SEM picture of the Pt tip is shown. The scale bar equals to 2 μm.

Image of FIG. 2.
FIG. 2.

(a) Sketch of the cross section of the Si sample after ion-implantation and dopant diffusion. (b) AFM image of the sample surface, where the implanted region is slightly roughened due to the heavy dosage. (c) Simulated doping profile across the sample surface. The substrate background doping is also indicated (dashed line). The dotted line indicates the metal–insulation transition density of doped Si.

Image of FIG. 3.
FIG. 3.

(a) The simulated MIM-C (solid) and MIM-R (dotted) contrast as a function of the sample conductivity. Quasistatic potential distributions around the tip electrode corresponding to the insulating (blue), conductive (red), and the crossover (green) regions are shown (see text for details). (b) Surface conductivity profile across the sample with the same color codes of the three regions. (c) MIM-C and (d) MIM-R images at 4 K. Typical line cuts are shown in each image. Approaching curves at two points (green triangle and red circle) are plotted in dotted and solid lines on the right-hand side of (c) and (d). All scale bars are 1 μm.

Image of FIG. 4.
FIG. 4.

(a)–(d) MIM-R images at different temperatures. Insets show typical line cuts for each image. All scale bars are 1 μm.

Image of FIG. 5.
FIG. 5.

(a)–(c) Effect of electric fields on the MIM images at −4, 8, and 10 V, respectively. Cartoons of the carrier response to different dc biases are shown on top of the corresponding MIM-C images. The inset in (c) shows the MIM-R image at = 10 V. (d) MIM-C image at −2 V after a previous scan with = 10 V, showing the effect of carrier trapping at low temperatures. All scale bars are 1 μm.


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Cryogenic microwave imaging of metal–insulator transition in doped silicon