Figure 1

(Top) (a) X-STM topographic image of an InAsP quantum dot ($V=+1.7\mathrm{V}$; $I=300\mathrm{pA}$). The $Z$ contrast of the dot is $200\pm 20\mathrm{pm}$. (b)–(e) STS measurements obtained at $T=4\mathrm{K}$ on bare $\mathrm{InP}(1\overline{1}0)$ surface [(b)—dark blue line], and on an InAsP quantum dot at various locations [(c)—green line, (d)—red line, (e)—black line]. The spectra are shifted for clarity. Signal was integrated for 20 ms at each point. (Bottom) (f) Quantum dot derivative image where the locations of STS spectra (b)–(e) are indicated by crosses with corresponding colors. (g)–(m) $16\mathrm{nm}\times 32\mathrm{nm}$-size $dI/d{V}_{\mathrm{sample}}$ maps measured, respectively, at 0.974, 1.024, 1.085, 1.143, 1.197, 1.250, and 1.289 V corresponding to the arrows on the above STS measurements curve. Each picture has its own arbitrary color scale.Reuse & Permissions

Figure 2

$dI/d{V}_{\mathrm{sample}}$ as a function of the applied voltage and of the distance from the dot center along the quantum dot base, measured on three different InAsP quantum dots labeled QD1 (a), QD2 (b), and QD3 (c) with an apparent width and height of 30 and 3.8 nm, 30 and 5.9 nm, 42 and 5.9 nm, respectively. The observation of the (010) state on QD2 suggests a larger depth for this dot compared with QD1 and QD3. The conductance is averaged along the growth axis over a 10 nm window centered on the middle of the dot. For each plot, the differential conductance integrated along the dot base is shown (arbitrary scales). The dependence of the $(n00)$ level energy as a function of the quantum numbers, for the three dots, is shown in (d).Reuse & Permissions

Figure 3

(a) QD geometry used for simulation. The QD (green) is surrounded by InP (blue) and vacuum. (b)–(j) Measured $dI/d{V}_{\mathrm{sample}}$ maps ($15\mathrm{nm}\times 45\mathrm{nm}$) and simulations of the electronic wave function spatial distribution ($15\mathrm{nm}\times 60\mathrm{nm}$) for the electronic states of QD3. The simulations display the square modulus of the wave function in the plane separating the semiconductor from the vacuum, corresponding to the red area of (a). Calculations assume an apparent width and height of the dot of, respectively, 56 and 5.6 nm. The dot depth is chosen equal to 5 nm. Each picture has its own arbitrary color scale.Reuse & Permissions