We report the characterisation of printed circuit boards (PCB) metal powder filters and their influence on the effective electron temperature which is as low as 22 mK for a quantum dot in a silicon MOSFET structure in a dilution refrigerator. We investigate the attenuation behaviour (10 MHz-20 GHz) of filter made of four metal powders with a grain size below 50 μm. The room-temperature attenuation of a stainless steel powder filter is more than 80 dB at frequencies above 1.5 GHz. In all metal powder filters, the attenuation increases with temperature. Compared to classical powder filters, the design presented here is much less laborious to fabricate and specifically the copper powder PCB-filters deliver an equal or even better performance than their classical counterparts. © 2013 AIP Publishing LLC. [http://dx
In this letter we report single-hole tunneling through a quantum dot in a two-dimensional hole gas, situated in a narrow-channel field-effect transistor in intrinsic silicon. Two layers of aluminum gate electrodes are defined on Si/SiO2 using electron-beam lithography. Fabrication and subsequent electrical characterization of different devices yield reproducible results, such as typical MOSFET turn-on and pinch-off characteristics. Additionally, linear transport measurements at 4 K result in regularly spaced Coulomb oscillations, corresponding to single-hole tunneling through individual Coulomb islands. These Coulomb peaks are visible over a broad range in gate voltage, indicating very stable device operation. Energy spectroscopy measurements show closed Coulomb diamonds with single-hole charging energies of 5-10 meV, and lines of increased conductance as a result of resonant tunneling through additional available hole states.In order for sufficient coherent operations to be performed in a proposed quantum computer [1], the quantum states of the corresponding qubits are required to be long-lived. In the scheme proposed by Loss and DiVincenzo [2], quantum logic gates perform operations on coupled spin states of single electrons in neighboring quantum dots. Most experiments have focused on quantum dots formed in III-V semiconductors, especially GaAs [3, 4]; however, electron spin coherence in those materials is limited by hyperfine interactions with nuclear spins and spin-orbit coupling. Group IV materials are believed to have long spin lifetimes because of weak spin-orbit interactions and the predominance of spin-zero nuclei. This prospect has stimulated significant experimental effort to isolate single charges in carbon nanotubes [5,6], Si/SiGe heterostructures [7,8], Si nanowires [9], planar Si MOS structures [10], and dopants in Si [11][12][13]. Silicon not only holds promise for very long coherence times [14], but also for bringing scalability of quantum devices one step closer, and has thus attracted much attention for quantum computing purposes [15,16].Recently, coherent driven oscillations of individual electron and nuclear spins in silicon were reported [17,18]. The spin resonance was magnetically driven by sending alternating currents through a nearby microwave line. A technologically more attractive way is electric-field induced electron spin resonance, as demonstrated in quantum dots made in GaAs/AlGaAs heterostructures [19][20][21], InAs nanowires [22], and InSb nanowires [23]. Electrical control of single spins requires mediation by either hyperfine or spin-orbit interaction. Although the latter is too weak for electrically driven spin resonance of electrons in silicon, the spin-orbit interaction for holes may well facilitate hole spin resonance by means of electric fields.
In this Report we show the role of charge defects in the context of the formation of electrostatically defined quantum dots. We introduce a barrier array structure to probe defects at multiple locations in a single device. We measure samples both before and after an annealing process which uses an Al2O3 overlayer, grown by atomic layer deposition. After passivation of the majority of charge defects with annealing we can electrostatically define hole quantum dots up to 180 nm in length. Our ambipolar structures reveal amphoteric charge defects that remain after annealing with charging energies of 10 meV in both the positive and negative charge state.
We report electrical transport measurements on a gate-defined ambipolar quantum dot in intrinsic silicon. The ambipolarity allows its operation as either an electron or a hole quantum dot of which we change the dot occupancy by 20 charge carriers in each regime. Electron-hole confinement symmetry is evidenced by the extracted gate capacitances and charging energies. The results demonstrate that ambipolar quantum dots offer great potential for spin-based quantum information processing, since confined electrons and holes can be compared and manipulated in the same crystalline environment.
We report single-charge transport in ambipolar nanoscale MOSFETs, electrostatically defined in near-intrinsic silicon. We use the ambipolarity to demonstrate the confinement of either a few electrons or a few holes in exactly the same crystalline environment underneath a gate electrode. We find similar electron and hole quantum dot properties while the mobilities differ quantitatively like in microscale devices. The understanding and control of individual electrons and holes are essential for spin-based quantum information processing.
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