Passivation and characterization of charge defects in ambipolar silicon quantum dots

Spruijtenburg, Paul C.; Amitonov, Sergey V.; Mueller, Filipp; Wiel, Wilfred G. van der; Zwanenburg, Floris A.

doi:10.1038/srep38127

Cited by 22 publications

(32 citation statements)

References 49 publications

(57 reference statements)

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“…Their very flexible design has enabled single and double quantum dots [6][7][8][9] , spin read-out via Pauli spin blockade [10][11][12][13][14][15] , charge sensing experiments with a quantum point contact 16 and dispersive read-out 17 , single qubits 10,[18][19][20][21] and two-qubit logic gates 22 in quick succession. With the demonstration of these building blocks, the reproducible fabrication of fully gate-tuneable devices receives increased attention 23,24 . The formation of unintentional quantum dots [25][26][27] poses a substantial problem, since they can capacitively couple to the intended quantum dot and disturb both transport and charge sensing measurements.…”

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confidence: 99%

Palladium gates for reproducible quantum dots in silicon

Brauns

Amitonov

Spruijtenburg

et al. 2018

Sci Rep

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We replace the established aluminium gates for the formation of quantum dots in silicon with gates made from palladium. We study the morphology of both aluminium and palladium gates with transmission electron microscopy. The native aluminium oxide is found to be formed all around the aluminium gates, which could lead to the formation of unintentional dots. Therefore, we report on a novel fabrication route that replaces aluminium and its native oxide by palladium with atomic-layer-deposition-grown aluminium oxide. Using this approach, we show the formation of low-disorder gate-defined quantum dots, which are reproducibly fabricated. Furthermore, palladium enables us to further shrink the gate design, allowing us to perform electron transport measurements in the few-electron regime in devices comprising only two gate layers, a major technological advancement. It remains to be seen, whether the introduction of palladium gates can improve the excellent results on electron and nuclear spin qubits defined with an aluminium gate stack.

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confidence: 99%

Palladium gates for reproducible quantum dots in silicon

Brauns

Amitonov

Spruijtenburg

et al. 2018

Sci Rep

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“…By choosing a mid-gap silicide, ambipolar operation is realized in a simple, highly compact design, as no complementary charge reservoirs are required. So far, ambipolar silicon QDs have only been implemented by integrating separate n-and p-type contacts to the same channel, enlarging the device's footprint [33][34][35][36][37] . The NiSi electrodes are formed by EBL, Ni evaporation, lift-off and low-temperature silicidation annealing at 475 • C for 30 min in an argon ambient.…”

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confidence: 99%

Ambipolar quantum dots in undoped silicon fin field-effect transistors

Kuhlmann

Deshpande

Camenzind

et al. 2018

Applied Physics Letters

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We integrate ambipolar quantum dots in silicon fin field-effect transistors using exclusively standard complementary metal-oxide-semiconductor fabrication techniques. We realize ambipolarity by replacing conventional highly-doped source and drain electrodes by a metallic nickel silicide with Fermi level close to the silicon midgap position. Such devices operate in a dual mode, either as classical field-effect or single-electron transistor. We implement a classical logic NOT gate at low temperature by tuning two interconnected transistors into opposite polarities. In the quantum regime, we demonstrate stable quantum dot operation in the few charge carrier Coulomb blockade regime for both electrons and holes.Quantum information can be encoded in the spin state of a single electron or hole confined to a semiconductor quantum dot (QD) 1-3 . Several material systems have been explored in the search of a highly coherent spin quantum bit (qubit). Silicon (Si) is a particularly promising material platform for scalable spin-based quantum computing because of its fully developed, industrial manufacturing processes, which enable reliable and reproducible fabrication at the nanometer scale 4-6 . Furthermore, natural silicon consists of 95 % non-magnetic nuclei (92 % 28 Si, 3 % 30 Si), suppressing hyperfine-induced decoherence 7-9 . A nearly nuclear-spin-free environment can additionally be engineered by means of isotopic purification 10 . Electron spins in silicon are also subject to a weak spin-orbit interaction (SOI) and can thus be almost completely isolated from environmental noise 11 . As a result, an excellent dephasing time T * 2 of 120 µs has been demonstrated for the electron spin qubit in isotopically enriched silicon (≥ 99.9 % of 28 Si) 5 .For scalable quantum circuits, qubit control via electric rather than magnetic fields is more promising in terms of speed and hardware implementation. In this regard, the hole spin represents an attractive alternative to its electron counterpart [12][13][14] . The asymmetry of the silicon band structure with respect to the conduction (CB) and valence bands (VB) manifests itself in different characteristics for electrons and holes. While the electron Bloch function has s-wave symmetry, the hole has p-wave symmetry. Consequently, hole spins experience a weaker hyperfine, yet stronger SOI, which enables fast, all-electrical spin manipulation 15-17 . Despite these potential benefits, hole spin qubits in silicon are still largely unexplored. Recently, qubit functionality with fast, purely electrical, two-axis control was shown for a hole spin, yet with inferior coherence compared to the electron spin 6 .Usually, either electrons 18-21 or holes 6,17,22-24 are confined in silicon QDs. Ambipolar devices, by contrast, can be operated in both the electron and hole regime [25][26][27][28][29][30][31][32] . For planar silicon metal-oxide-semiconductor (MOS) QD structures, ambipolar behavior was demonstrated by integrating both n-and p-type reservoirs on the same device 33-37 . Ambipolar dev...

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“…The covering Al 2 O 3 layer allows for annealing without dewetting, because it caps the entire structure and contains hydrogen as described in section II. This process is shown to reduce charge defects to a substantial degree 28,73 .…”

Section: The Si/sio 2 Interfacementioning

confidence: 98%

A fabrication guide for planar silicon quantum dot heterostructures

Spruijtenburg¹,

Amitonov²,

Wiel³

et al. 2018

Nanotechnology

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We describe important considerations to create top-down fabricated planar quantum dots in silicon, often not discussed in detail in literature. The subtle interplay between intrinsic material properties, interfaces and fabrication processes plays a crucial role in the formation of electrostatically defined quantum dots. Processes such as oxidation, physical vapor deposition and atomic-layer deposition must be tailored in order to prevent unwanted side effects such as defects, disorder and dewetting. In two directly related manuscripts written in parallel we use techniques described in this work to create depletion-mode quantum dots in intrinsic silicon, and low-disorder silicon quantum dots defined with palladium gates. While we discuss three different planar gate structures, the general principles also apply to 0D and 1D systems, such as self-assembled islands and nanowires. 1 arXiv:1709.08866v3 [cond-mat.mes-hall] Feb 2018Dealing with the fragility of the quantum coherent state is one of the key issues on the road to meet the limits posited by quantum computation schemes 1 . It is the coupling of quantum states to states in an unknown environment which is the driver for decoherence. The properties of the environment therefore dictate the performance of a quantum bit (qubit).Creating qubits in the solid state means that the environment consists of many different materials and structures used in device construction. give rise to interactions detrimental to qubit creation and readout.The hyperfine interaction of nuclear spins in the host material and the qubit is one such effect. The non-zero-spin isotopes in a material create a nuclear-spin-bath and cause decoherence of the quantum state. This is the motivation for the use of isotopically purified silicon as a host material for spin qubits 9,10 . The purified silicon, now containing predomi-Si, results in a zero-nuclear-spin isotope system, and eliminates the fluctuations in the spin bath, which are detrimental.Field noise, such as charge-and spin-noise 11 can also influence the lifetime of the quantum state. One strategy to deal with these fluctuations is to tune the quantum dots to certain regimes in phase space where the energy levels of interest are insensitive to these fields. This can happen in the clock transition of Bi dopants in Si 12 , by dressing qubits and tuning them appropriately 13 , or for hybrid quantum dots. 14 Another effect that can influence quantum states are fluctuations in the electrochemical potential at longer timescales. These have been shown to occur due to charge offsets fluctuating over time in glassy media and their intrinsic two-level systems (TLS). 15,16Finally, unintentional quantum dots, charge traps, or charge defects can influence a de- This article has the intention to provide a foothold for entrants in the field (e.g. starting graduate students) and elucidate mechanisms that need to be taken into account when designing and fabricating these devices in the solid state. It can be read back to front, and may also serve well ...

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Passivation and characterization of charge defects in ambipolar silicon quantum dots

Cited by 22 publications

References 49 publications

Palladium gates for reproducible quantum dots in silicon

Palladium gates for reproducible quantum dots in silicon

Ambipolar quantum dots in undoped silicon fin field-effect transistors

A fabrication guide for planar silicon quantum dot heterostructures

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