Cryogenic scanning probe characterization of semiconductor nanostructures

Eriksson, Mats; Beck, R. G.; Topinka, M. A.; Katine, J. A.; Westervelt, R. M.; Campman, K. L.; Gossard, A. C.

doi:10.1063/1.117801

Cited by 148 publications

(161 citation statements)

References 1 publication

Supporting

Mentioning

156

Contrasting

Order By: Relevance

“…2d implies an effective lever arm of α tip = 1/10.8. This is a reasonable value, consistent with the expected tip-sample mutual capacitance [25][26][27] .…”

Section: Methodssupporting

confidence: 87%

Scanning-probe spectroscopy of semiconductor donor molecules

et al. 2008

View full text Add to dashboard Cite

Semiconductor devices continue to press into the nanoscale regime, and new applications have been proposed for which a single dopant atom acts as the functional part of the device 1-3 . Moreover, because shallow donors and acceptors are analogous to hydrogen atoms, experiments on small numbers of dopants have the potential to be a testing ground for fundamental questions of atomic and molecular physics 4,5 . Although dopant properties are well understood with respect to the bulk, the study of configurations of dopants in small numbers is an emerging field 6,7 . Here we present local capacitance measurements of electrons entering silicon donors in a gallium arsenide heterostructure. To the best of our knowledge, this study is the first example of single-electron capacitance spectroscopy carried out directly with a scanning probe tip 8 . The precise position with respect to tip voltage of the observed single-electron peaks varies with the location of the probe, reflecting a random distribution of silicon within the donor plane. In addition, three broad capacitance peaks are observed independent of the probe location, indicating clusters of electrons entering the system at approximately the same voltages. These broad peaks are consistent with the addition energy spectrum of donor molecules, effectively formed by nearest-neighbour pairs of silicon donors.Electron tunnelling spectroscopy through isolated dopants has been observed in transport studies 9,10 . In addition, Geim and coworkers identified resonances due to two closely spaced donors, effectively forming donor molecules 11 . Rather than measuring transport current, our scanning-probe method is essentially a capacitance technique 8,12 . In contrast to the work of Geim et al., the measurements show discernible peaks attributed to successive electrons entering the molecules.Our method is an extension of scanning charge accumulation imaging 12 . Figure 1a shows the experiment schematically. The key component is a metallic tip with an apex of radius ∼ 50 nm, connected directly to a charge sensor, which achieves a sensitivity of 0.01e/ √ H z (ref. 13). For the capacitance spectroscopy measurements reported here, the tip's position is fixed (that is, not scanned) at a distance of ∼1 nm from the sample surface. We then monitor the tip's a.c. charge q tip in response to an a.c. excitation voltage V exc applied to an underlying electrode, as a function of d.c. bias voltage V tip . As detailed in the Methods section, if the quantum system below the tip can accommodate additional charge, the excitation voltage causes it to resonate between the system and the underlying electrode-giving rise to an enhanced capacitance,The first observations of donor-layer capacitance peaks acquired with our method probed a gallium arsenide heterostructure sample grown by molecular beam epitaxy, for which the donor layer was bulk-doped with Si at a density of 10 24 m −3 . To achieve better characterized results that would be more conducive to analysis, we used a GaAs [001] heterostructure...

show abstract

“…2d implies an effective lever arm of α tip = 1/10.8. This is a reasonable value, consistent with the expected tip-sample mutual capacitance [25][26][27] .…”

Section: Methodssupporting

confidence: 87%

Scanning-probe spectroscopy of semiconductor donor molecules

et al. 2008

View full text Add to dashboard Cite

show abstract

“…This approach allows either modulation of the strength of a preexisting scattering site or the generation of an artificial scattering site. In scanning gate microscopy (SGM) [16,17], a charged tip is scanned above the device of interest, and the effect of the induced potential fluctuation on the conductance in the device is monitored. Over the past few years, scanning gate microscopy has been used to investigate transport phenomena in a variety of low-dimensional systems like quantum dots [18][19][20][21], quantum-point contacts [22], and two-dimensional electron gases [23][24][25][26].…”

Section: Experimental Methodsmentioning

confidence: 99%

Spatially Resolved Study of Backscattering in the Quantum Spin Hall State

et al. 2013

View full text Add to dashboard Cite

The discovery of the quantum spin Hall (QSH) state, and topological insulators in general, has sparked strong experimental efforts. Transport studies of the quantum spin Hall state have confirmed the presence of edge states, showed ballistic edge transport in micron-sized samples, and demonstrated the spin polarization of the helical edge states. While these experiments have confirmed the broad theoretical model, the properties of the QSH edge states have not yet been investigated on a local scale. Using scanning gate microscopy to perturb the QSH edge states on a submicron scale, we identify well-localized scattering sites which likely limit the expected nondissipative transport in the helical edge channels. In the micron-sized regions between the scattering sites, the edge states appear to propagate unperturbed, as expected for an ideal QSH system, and are found to be robust against weak induced potential fluctuations.

show abstract

“…We also observe two unanticipated phenomena in high-mobility samples. In our highest-mobility sample we observe an almost complete absence of sharp impurity or defect scattering, indicated by the complete suppression of quantum coherent interference fringes.Also, branched flow through the chaotic potential of a high-mobility sample remains stable to significant changes to the initial conditions of injected electrons.Scanning gate microscopy (SGM) images of electron flow in two-dimensional electron gases (2DEGs) [8][9][10][11][12][13][14][15][16][17][18] provide direct spatial information not available in conventional electrical transport measurements. Our SGM studies show how varying disorder affects electron flow, and enable us to infer information about the disorder potential in our different samples.…”

mentioning

confidence: 99%

Unexpected features of branched flow through high-mobility two-dimensional electron gases

et al. 2007

View full text Add to dashboard Cite

GaAs-based two-dimensional electron gases (2DEGs) show a wealth of remarkable electronic states [1][2][3] , and serve as the basis for fast transistors, research on electrons in nanostructures 4,5 , and prototypes of quantum-computing schemes 6 . All these uses depend on the extremely low levels of disorder in GaAs 2DEGs, with low-temperature mean free paths ranging from microns to hundreds of microns 7 . Here we study how disorder affects the spatial structure of electron transport by imaging electron flow in three different GaAs/AlGaAs 2DEGs, whose mobilities range over an order of magnitude. As expected, electrons flow along narrow branches that we find remain straight over a distance roughly proportional to the mean free path. We also observe two unanticipated phenomena in high-mobility samples. In our highest-mobility sample we observe an almost complete absence of sharp impurity or defect scattering, indicated by the complete suppression of quantum coherent interference fringes.Also, branched flow through the chaotic potential of a high-mobility sample remains stable to significant changes to the initial conditions of injected electrons.Scanning gate microscopy (SGM) images of electron flow in two-dimensional electron gases (2DEGs) [8][9][10][11][12][13][14][15][16][17][18] provide direct spatial information not available in conventional electrical transport measurements. Our SGM studies show how varying disorder affects electron flow, and enable us to infer information about the disorder potential in our different samples. Achieving a detailed picture of the disorder potential 19, 20 may help to understand why exotic electron organization emerges in some 2DEGs and not others, and to aim for ever weaker disorder or even tailored disorder 21 .By analyzing the differences between images of flow in our samples, we find that the highermobility samples are increasingly dominated by small-angle scattering instead of hard-scattering 22 .2 Finally, we investigate an unusual property of electron flow through such a small-angle scattering disorder potential: though the disorder potential is classically chaotic, branches of flow are stable to significant changes in initial conditions.On each of three 2DEG samples defined in GaAs/AlGaAs heterostructures (Table 1), we use a home-built scanning gate microscope to image the flow of electrons emanating from a split-gate quantum point contact (QPC) 23, 24 at 4.2 K, as schematically shown in Fig. 1d. Using a recently established technique 9-15 , we measure the conductance across the QPC while scanning a sharp conducting tip ∼20 nm above the surface of the sample. We negatively bias the tip to create a depletion region in the 2DEG below. When the tip is above a region of high electron flow from the QPC, it backscatters electrons through the QPC, reducing the measured conductance. By scanning the tip and recording the drop in conductance ∆G for each tip location, we thus image electron flow. Images of flow gathered in this way have been found to accurately reproduce the under...

show abstract

Cryogenic scanning probe characterization of semiconductor nanostructures

Cited by 148 publications

References 1 publication

Scanning-probe spectroscopy of semiconductor donor molecules

Scanning-probe spectroscopy of semiconductor donor molecules

Spatially Resolved Study of Backscattering in the Quantum Spin Hall State

Unexpected features of branched flow through high-mobility two-dimensional electron gases

Contact Info

Product

Resources

About