In recent years, a variety of solid-state qubits has been realized, including quantum dots [1,2], superconducting tunnel junctions [3,4] and point defects [5,6]. Due to its potential compatibility with existing microelectronics, the proposal by Kane [7,8] based on phosphorus donors in Si has also been pursued intensively [9,10,11]. A key issue of this concept is the readout of the 31 P quantum state. While electrical measurements of magnetic resonance have been performed on single spins [12,13], the statistical nature of these experiments based on random telegraph noise measurements has impeded the readout of single spin states. In this letter, we demonstrate the measurement of the spin state of 31 P donor electrons in silicon and the observation of Rabi flops by purely electric means, accomplished by coherent manipulation of spin-dependent charge carrier recombination between the 31 P donor and paramagnetic localized states at the Si/SiO2 interface via pulsed electrically detected magnetic resonance. The electron spin information is shown to be coupled through the hyperfine interaction with the 31 P nucleus, which demonstrates the feasibility of a recombinationbased readout of nuclear spins.Since the detection of single charges has become technically straight forward, it is widely believed [7,8,10,11,12] that the realization of spin-to-charge transfer is the key prerequisite for a successful implementation of single spin phosphorus ( 31 P) readout devices, capable of determining the actual spin state (spin up | ↑ or spin down | ↓ ). Different approaches to the electrical spin readout of 31 P-donor electron spins have been proposed based on spin-dependent transitions between neighboring 31 P atoms [7,8,10,11]. Since the states involved are energetically degenerate, these spin-to-charge transfer schemes are rather difficult to realize. Alternatively, spin-dependent transitions involving dissimilar paramagnetic states might be easier to detect as proposed by Boehme and Lips [14]. Spin-dependent charge carrier transport and recombination are known at least since 1966 [15], when Schmidt and Solomon already observed spin-dependent recombination involving 31 P donors in silicon. However, it was not demonstrated until 2003 [16] that the much more sensitive electrical detection of spins via resonant changes of recombination processes is also able to reflect coherent spin motion, which is necessary for a readout of the spin quantum state as opposed to a mere detection of the presence of spins. Figure 1(a) illustrates the readout scheme based on spin-dependent recombination demonstrated in this paper. In order to probe 31 P donor electron spins, spindependent excess charge carrier recombination through so-called P b0 centers is used. P b0 centers are trivalent Si atoms at the interface between crystalline silicon (c-Si) and silicon dioxide (SiO 2 ) that introduce localized, paramagnetic states in the Si band gap and dominate electron trapping and recombination at the interface [17,18]. If a neutral P b0 center is locate...
We have investigated the role of doping and paramagnetic states on the electronic transport of networks assembled from freestanding Si nanocrystals (Si-NCs). Electrically detected magnetic resonance (EDMR) studies on Si-NCs films, which show a strong increase of conductivity with doping of individual Si-NCs, reveal that P donors and Si dangling bonds contribute to dark conductivity via spin-dependent hopping, whereas in photoconductivity, these states act as spin-dependent recombination centers of photogenerated electrons and holes. Comparison between EDMR and conventional electron paramagnetic resonance shows that different subsets of P-doped nanocrystals contribute to the different transport processes.
The structural and electrical properties before and after laser annealing of spin-coated films of doped silicon nanocrystals (ncs) produced from the gas phase are presented. While the as-deposited films form a porous network of ncs and show only weak electrical conductivity independent of the doping level, a laser annealing step leads to sintering and melting of the particles and tremendously increases the lateral conductivity. By controlled doping of the initial particles, the conductivity can be further enhanced by seven orders of magnitude reaching values of up to 5 Ω−1 cm−1. The conductivity is found to increase with the doping concentration for highly doped samples while it is independent of the doping level below a critical concentration of 1019 cm−3. The results are discussed within a compensational model taking into account the defect concentration from electron paramagnetic resonance measurements and the activation energies of the electrical conductivity. Surface segregation of phosphorus during growth is identified as the origin of the apparently small phosphorus doping efficiency.
The electrical detection of spin echoes via echo tomography is used to observe decoherence processes associated with the electrical readout of the spin state of phosphorus donor electrons in silicon near a SiO 2 interface. Using the Carr-Purcell pulse sequence, an echo decay with a time constant of 1.7 ± 0.2 µs is observed, in good agreement with theoretical modeling of the interaction between donors and paramagnetic interface states. Electrical spin echo tomography thus can be used to study the spin dynamics in realistic spin qubit devices for quantum information processing.
Freestanding silicon nanocrystals (Si‐ncs) offer unique optical and electronic properties for new photovoltaic, thermoelectric, and other electronic devices. A method to fabricate Si‐ncs which is scalable to industrial usage has been developed in recent years. However, barriers to the widespread utilization of these nanocrystals are the presence of charge‐trapping defects and an oxide shell formed upon ambient atmosphere exposure hindering the charge transport. Here, we exploit low‐cost post‐growth treatment routes based on wet‐etching in hydrofluoric acid plus surface hydrosilylation or annealing enabling a complete native oxide removal and a reduction of the defect density by up to two orders of magnitude. Moreover, when compared with only H‐terminated Si‐ncs we report an enhancement of the conductivity by up to a factor of 400 for films of HF etched and annealed Si‐ncs, which retain a defect density below that of untreated Si‐ncs even after several months of air exposure. Further, we demonstrate that HF etched and hydrosilylated Si‐ncs are extremely stable against oxidation and maintain a very low defect density after a long‐term storage in air, opening the possibility of device processing in ambient atmosphere.
We have produced networks of surface-oxidized and hydrogen-terminated silicon nanocrystals (Si-NCs), both intrinsic and n-type doped, on flexible plastic foil from nanoparticle inks. The charge transport in these networks was comprehensively studied by means of time-dependent conductivity, steady-state current versus voltage characteristics, and steady-state photocurrent measurements as a function of incident light intensity. These measurements were complemented by surface chemistry and structural/morphological analysis from Fourier transform infrared spectroscopy and electron microscopy. Whereas H-terminated Si-NC networks function as semiconductors (both in air and in vacuum), where conductivity enhancement upon impurity doping and photoconductivity were observed, these characteristics are not present in networks of surface-oxidized Si-NCs. For both network types, the observation of a power law behavior for steady-state current versus voltage and a current decaying with time at constant bias indicate that charge transport is controlled by space-charge-limited current (involving trap states) via percolation paths through the networks. We have also monitored the evolution of the networks (photo)conductivity when the internanocrystal separating medium formed by Si–H bonds is progressively replaced by a native oxide upon exposure to air. Although a decrease in the (photo)conductivity is observed, the networks still behave as semiconductors even after a long-term air exposure. From an analysis of all (photo)current data, we deduce that in networks of oxidized Si-NCs inter-NC charge transfer requires the participation of oxide-related electronic states, whereas in H-terminated Si-NC networks direct inter-NC charge transfer plays a major role in the overall long-range conduction process.
The hyperfine interaction of phosphorus donors in fully strained Si thin films grown on virtual Si 1−x Ge x substrates with x ≤ 0.3 is determined via electrically detected magnetic resonance. For highly strained epilayers, hyperfine interactions as low as 0.8 mT are observed, significantly below the limit predicted by valley repopulation. Within a Green's function approach, density functional theory (DFT) shows that the additional reduction is caused by the volume increase of the unit cell and a local relaxation of the Si ligands of the P donor.
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