Single-electron transistor based on modulation-doped SiGe heterostructures

Notargiacomo, A.; Gaspare, L. Di; Scappucci, Giordano; Mariottini, G.; Evangelisti, F.; Giovine, E.; Leoni, R.

doi:10.1063/1.1592883

Cited by 23 publications

(19 citation statements)

References 11 publications

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“…The 2DEG is separated from the donors by a 140 Å Si 0.7 Ge 0.3 spacer layer, and the phosphorus donors lie in a 140 Å Si 0.7 Ge 0.3 layer capped with 35 Å of Si at the surface. The electron density in the 2DEG is 4ϫ10 11 cm Ϫ2 and the mobility is 40 000 cm 2 /V s at 2 K. Ohmic contacts to the 2DEG are formed by Au/Sb metal evaporation and sintering at 400°C for 10 min.…”

Section: 9mentioning

confidence: 99%

“…The fabrication of highly isolated Schottky top gates is particularly difficult. 10,11 Due to the lattice mismatch between layers of different Ge fraction, misfit dislocations must be present to relieve the strain in the SiGe buffer layer. Misfit dislocations terminate in threading arms running up to the heterostructure surface, and these threading arms may play a role in forming a conductive path between top Schottky contacts and the 2DEG later.…”

Section: 9mentioning

confidence: 99%

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Coulomb blockade in a silicon/silicon–germanium two-dimensional electron gas quantum dot

Klein

Slinker

Truitt

et al. 2004

Applied Physics Letters

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We report the fabrication and electrical characterization of a single electron transistor in a modulation doped silicon/silicon-germanium heterostructure. The quantum dot is fabricated by electron beam lithography and subsequent reactive ion etching. The dot potential and electron density are modified by laterally defined side gates in the plane of the dot. Low temperature measurements show Coulomb blockade with a single electron charging energy of 3. Silicon-germanium modulation doped field-effect transistors ͑MODFETs͒ are potentially attractive devices for high-speed, low noise communications applications, where low cost and compatibility with complementary metaloxide-semiconductor logic are desirable.1 Because the silicon quantum well containing the electrons is strained by up to 2%, the electron mobility of these structures is as much as a factor of five larger than that of unstrained silicon fieldeffect transistors ͑FET͒ at room temperature, offering the prospect of high speed operation. At low temperatures, electron mobilities as high as 5.2ϫ10 5 cm 2 /V s have been reported, 2,3 raising the possibility of lithographically patterned quantum devices.Development of quantum devices in silicon MODFETs is of particular interest, because silicon is unique among the elemental and binary semiconductors in that it has an abundant nuclear isotope of spin zero. Silicon also has very small spin orbit coupling. Together, these two features provide only weak channels for electron spin relaxation; the electron spin dephasing time T 2 for phosphorus-bound donors has been measured to be as long as 3 ms at 7 K. 4 Kane has pointed out the advantages of nuclear spins in silicon for quantum computation, 5 and his scheme has been extended to electrons in SiGe heterostructures.6 Following Loss and DiVincenzo, 7 specific schemes have been proposed for spin-based quantum computation in silicon-germanium electron quantum dots. 8,9Here we demonstrate a quantum dot fabricated in a layered silicon/silicon-germanium ͑Si/SiGe͒ heterostructure that includes a strained Si quantum well containing a twodimensional electron gas ͑2DEG͒. Even with recent advances in the growth of high mobility SiGe modulationdoped heterostructures, producing lithographically defined n-type quantum dots with periodic Coulomb blockade has been challenging. The fabrication of highly isolated Schottky top gates is particularly difficult. 10,11 Due to the lattice mismatch between layers of different Ge fraction, misfit dislocations must be present to relieve the strain in the SiGe buffer layer. Misfit dislocations terminate in threading arms running up to the heterostructure surface, and these threading arms may play a role in forming a conductive path between top Schottky contacts and the 2DEG later. We have avoided this problem by fabricating a dot with highly isolated side gates formed from the 2DEG itself.The Si/SiGe heterostructure used here was grown by ultrahigh vacuum chemical vapor deposition.2 The 2DEG sits near the top of 80 Å of strained Si grown on a s...

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Section: 9mentioning

confidence: 99%

Section: 9mentioning

confidence: 99%

Coulomb blockade in a silicon/silicon–germanium two-dimensional electron gas quantum dot

Klein

Slinker

Truitt

et al. 2004

Applied Physics Letters

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“…While SET development for laboratory applications have reached a mature state in heterosystems based on III-V compound semiconductors, only few Si/SiGe SETs have been reported 8,9,10 . Moreover, none of these was achieved by the usual split-gate technique that is considered a precondition for efficient coupling of quantum dots and for high integration.…”

mentioning

confidence: 99%

Single-electron transistor in strained Si/SiGe heterostructures

Berer

Pachinger

Pillwein

et al. 2006

Physica E: Low-dimensional Systems and Nanostructures

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A split gate technique is used to form a lateral quantum dot in a two-dimensional electron gas of a modulation-doped silicon/silicon-germanium heterostructure. e-beam lithography was employed to produce split gates. By applying negative voltages to these gates the underlying electron gas is depleted and a lateral quantum dot is formed, the size of which can be adjusted by the gate voltage. We observe single-electron operation with Coulomb blockade behavior below 1K. Gate leakage currents are well controlled, indicating that the recently encountered problems with Schottky gates for this type of application are not an inherent limitation of modulation-doped Si/SiGe heterostructures, as had been speculated. With the introduction of the Si/SiGe heterobipolar transistor into large scale production, Si-based heterostructures have become an important material system for electronic high-performance device with full compatibility with standard Si technologies 1 . Meanwhile, the first digital CMOS circuits with selectively grown SiGe epilayers are commercially available, 2 and intense research and development is dedicated to the fabrication of SiGe pseudosubstrates and SiGe-on-insulator substrates for further device applications. In terms of basic research, great effort is directed toward spintronic and quantum computing as potential techniques for future computation and encrypting facilities 3,4 . Si-based heterostructures have distinct advantages in these fields because of the extremely long spin coherence times 5,6 , which are attributed to the small spin-orbit interaction, and the low natural abundance of isotopes with nuclear spin. Moreover, in this material system the interaction between the spins of the conduction electrons and the nuclei can be further reduced or even completely suppressed by employing enriched 28 Si, and Ge with a depleted 73 Ge isotope. This way, matrix materials free of nuclear spins are conceivable in addition to the unrivalled ultra-large scale integration capabilities of Si technologies.On a device level, single electron transistors (SET) with carrier confinement in all three directions of space are considered a key-component for spin manipulation and programmable entanglement 7 . While SET development for laboratory applications have reached a mature state in heterosystems based on III-V compound semiconductors, only few Si/SiGe SETs have been reported 8,9,10 . Moreover, none of these was achieved by the usual split-gate technique that is considered a precondition for efficient coupling of quantum dots and for high integration. It was pointed out in some of these papers that a lateral quantum dot cannot be achieved by Schottky split gates due to detrimental leakage currents through threading dislocations in the crystal and Fermi level pinning. Here we demonstrate that excessive leakage currents are not an intrinsic limitation of modulation-doped Si/SiGe heterostructures: Our split-gate SETs show well-behaved Coulomb blockade and very low leakage currents of the Pd Schottky gates.A high-mobi...

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“…Further progress was hampered by difficulties with leakage currents and parallel conduction paths 14,15 , and unavoidable defects associated with the growth of strained heterostructures. However, spurred on by quantum computing, and new technologies like atomic layer oxide deposition, some important technological hurdles have been overcome.…”

Section: Introductionmentioning

confidence: 99%

Quantum dots and etch-induced depletion of a silicon two-dimensional electron gas

Klein

Lewis

Slinker

et al. 2006

Journal of Applied Physics

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The controlled depletion of electrons in semiconductors is the basis for numerous devices. Reactive-ion etching provides an effective technique for fabricating both classical and quantum devices. However, Fermi level pinning can occur, and must be carefully considered in the development of small devices, such as quantum dots. Because of depletion, the electrical size of the device is reduced in comparison with its physical dimension. To investigate this issue, we fabricate several types of devices in silicon-germanium heterostructures using two different etches, CF4 and SF6. We estimate the depletion width associated with each etch by two methods: (i) conductance measurements in etched wires of decreasing thickness (to determine the onset of depletion), (ii) capacitance measurements of quantum dots (to estimate the size of the active region). We find that the SF6 etch causes a much smaller depletion width, making it more suitable for device fabrication.

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Single-electron transistor based on modulation-doped SiGe heterostructures

Cited by 23 publications

References 11 publications

Coulomb blockade in a silicon/silicon–germanium two-dimensional electron gas quantum dot

Coulomb blockade in a silicon/silicon–germanium two-dimensional electron gas quantum dot

Single-electron transistor in strained Si/SiGe heterostructures

Quantum dots and etch-induced depletion of a silicon two-dimensional electron gas

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