Single-hole tunneling through a two-dimensional hole gas in intrinsic silicon

Abstract

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.

Spin-orbit interactions in inversion-asymmetric two-dimensional hole systems: A variational analysis

“…Therefore, we have included both k-linear and k-cubed terms in Eq. (25 16. We obtain p D = 5.4 × 10 13 m −2 , so that the linear-k contribution is essentially negligible for our range of densities.…”

“…The search for semiconductor systems with strong spin-orbit coupling has led naturally to lowdimensional hole systems. [7][8][9] Despite the promising advances of recent years, in particular in the experimental state of the art, [10][11][12][13][14][15][16][17][18][19][20][21][22] functional hole spin-based devices are yet to be realized. In particular, a comprehensive understanding of the interaction between a hole's spin and its solid-state environment is far from complete.…”

Spin blockade in hole quantum dots: Tuning exchange electrically and probing Zeeman interactions

“…The period of the anisotropic leakage is critically dependent on the relative magnitude of Zeeman interaction terms linear and cubic in the magnetic field. The current and singlet-triplet exchange splitting can be effectively adjusted by an appropriate choice of field direction, providing a simple control variable for quantum information processing and a way of tailoring magnetic interactions in hole spin qubits.Spin-based quantum information processing platforms relying on hole quantum dots (QDs) have recently attracted considerable attention [1][2][3][4][5][6][7][8][9][10][11], since they permit long spin coherence and electrically driven spin resonance thanks to the strong hole spinorbit (SO) interaction [12][13][14][15][16][17][18][19][20]. Owing to their effective spin J = 3 2 , spin dynamics in hole systems often exhibits physics not found in electron systems [21][22][23][24][25][26].…”

Quantum information density scaling and qubit operation time constraints of CMOS silicon-based quantum computer architectures

“…Indeed, hyperfine interaction and magnetic field fluctuations, that are mainly responsible for decoherence in III-V semiconductors due to the high density of spin-carrying nuclei, are effectively inhibited by utilizing purified 28 Si. 25,35,46,93 Alternatively, hole spin qubits could be considered in the future [53][54][55][56] to reduce hyperfine interaction. Another significant noise component arises from the interface in the case of Si-SiO 2 QDs in particular.…”