Spectroscopy of few-electron single-crystal silicon quantum dots

Abstract

A defining feature of modern CMOS devices and almost all quantum semiconductor devices is the use of many different materials. For example, although electrical conduction often occurs in single-crystal semiconductors, gates are frequently made of metals and dielectrics are commonly amorphous. Such devices have demonstrated remarkable improvements in performance over recent decades, but the heterogeneous nature of these devices can lead to defects at the interfaces between the different materials, which is a disadvantage for applications in spintronics and quantum information processing. Here we report the fabrication of a few-electron quantum dot in single-crystal silicon that does not contain any heterogeneous interfaces. The quantum dot is defined by atomically abrupt changes in the density of phosphorus dopant atoms, and the resulting confinement produces novel effects associated with energy splitting between the conduction band valleys. These single-crystal devices offer the opportunity to study how very sharp, atomic-scale confinement--which will become increasingly important for both classical and quantum devices--influences the operation and performance of devices.

Quantum dot spectroscopy using a single phosphorus donor

“…2b (again marked by the vertical dashed yellow line). Here we also observe conductance features beyond the edges of blockaded SET current in the Coulomb diamonds, corresponding to excited states either of the leads or the SET quantum dot [8]. Since these conductance lines only appear parallel to the left edges of the diamonds, we can conclude that the quantum dot is much more strongly coupled to the source lead than to the drain lead [13].…”

“…The electronic structure of an isolated quantum dot in the few-electron regime [8][9][10][11] is experimentally accessible using tunnel spectroscopy [12] and transport spectroscopy measurements [13]. Here the electronic structure can be determined from conductance variations as a function of source-drain and gate voltages.…”

The many aspects of quantum dots

“…It is also possible to make a quantum dot by trapping a single molecule or nanoparticle between two electrodes, by attaching electrodes to a nanotube or to graphene, or by modulating the level of doping in a single crystal of a semiconductor 4 . Moreover, further variety is possible because the nanoparticles trapped between the electrodes can, for example, be metallic, ferromagnetic or superconducting 5 Essential characteristics of quantum dots include the fact that the energy levels occupied by the charge carriers are quantized, as in atoms and molecules, and that the bandgap between the conduction and valence bands increases as the dot gets smaller, which decreases the wavelength at which they fluoresce.…”

Transport through an impurity tunnel coupled to a Si/SiGe quantum dot

“…Phosphorus donors also have nuclear spins with extremely long coherence times [5][6][7] . Although donor-based quantum devices can be fabricated with near-atomically precise placement of donors 8,9 , even when well-placed, donors are very small, making it difficult to control and change the tunnel couplings between them with gate voltages. In contrast, tunnel couplings are easily tunable in gate-defined quantum dots, and high-quality quantum dots hosting at least four different types of spin qubits have been demonstrated semiconductor materials [10][11][12][13][14][15][16][17][18][19][20][21][22] .…”