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Ultra-shallow quantum dots in an undoped GaAs/AlGaAs two-dimensional electron gas
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View: Figures


Image of FIG. 1.
FIG. 1.

(a) MBE layers used in the undoped heterostructures. (b) Carrier density versus overall topgate voltage for the V625 and V627 undoped 2DEGs. The capacitance is dominated by the 500 nm-thick polyimide layer. (c) Leakage current (right) to the 2DEG as the overall topgate is swept, with the accompanying two-terminal conductance between a pair of ohmic contacts (left). (d) Mobility versus electron density for undoped wafers V625 and V627, as well as various other doped wafers in shallow 2DEGs. 4–14 Lines through data points indicate a gated measurement. The legend indicates the 2DEG depth below the surface.

Image of FIG. 2.
FIG. 2.

(a) Micrograph of a dot with the same dimensions as the one reported here. The surface gates t1, t2, and t3 are held together at the same voltage. Gates b1 and b2 control the left and right barriers, and gate pg is the plunger. (b) Leakage characteristics of surface gates defined by e-beam lithography, in another similar device. (c) Measured differential conductance G (with 20 μV AC excitation), showing CB oscillations from a quantum dot on wafer V627. All CB data were obtained at an overall topgate voltage of 8.0 V ( ). Gates t1, t2, t3, b1, and b2 are all held at 0.900 V while pg is swept. CB peaks marked with # and are further analyzed in Figure 4 . (d) The dot is in the weak coupling regime. (e) Even at high temperature, the CB peaks are well resolved, indicative of a large charging energy.

Image of FIG. 3.
FIG. 3.

Source-drain bias spectroscopy. The dot is in a slightly different regime than shown in Figure 2 : gates t1 = t2 = t3 = 0.836 V, b1 = 0.862 V, b2 = 0.918 V, and the overall topgate at 8 V. Parameters extracted from this data set are: the charging energy (U = 1.25 meV), the single-particle energy level spacing ( ), the plunger gate lever arm ( ), the plunger capacitance ( ), and the total capacitance ( ).

Image of FIG. 4.
FIG. 4.

In all panels above, symbols are experimental data from the CB peaks marked # and in Figure 2 , solid lines are fits to equations, and dashed lines are guides to the eye. Extracted from DC bias spectroscopy, the value was used in these fits (e-beam gates were biased at the same voltages as described in Fig. 2 ). (a)–(b) The solid line is a fit to Eq. (2) . (c)–(d) Below 800 mK, the inverse of CB peak maximum height (Gmax) is proportional to temperature. Paired panels (a)/(c) and (b)/(d) suggest only a single energy level is involved in transport for CB peaks # and . (e) FWHM of both peaks against electron temperature. (f) Electron temperature deduced from fits of the data to Eq. (1) .


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Ultra-shallow quantum dots in an undoped GaAs/AlGaAs two-dimensional electron gas