Microwave-assisted transport in a single-donor silicon quantum dot

Abstract

Single donors in semiconductor nanostructures represent a key element to develop spin related quantum functionalities in atomic scale devices. Quantum transport through a single Arsenic donor in the channel of a Silicon nano-field effect transistor under microwave irradiation is investigated. The device is characterized at mK temperatures in the regime of Coulomb-blockade. Photon assisted tunneling and microwave induced electron pumping regimes are revealed respectively at low and high microwave power. At sufficiently high power, the microwave irradiation induces tunneling through the first excited energy level of the D 0 energy of the donor. Such microwave assisted transport at zero bias enhances the resolution in the spectroscopy of the energy levels of the donor. 1 I. INTRODUCTION Single and double atom impurities in semiconductor nanostructures are of major interest for their key role in atomic scale devices for electronics and spintronics [1, 2, 3, 4, 5, 6]. The first observation of a single As atom in a Silicon nanostructure [7, 8] opened the route to the spectroscopy of donor atoms by means of quantum transport measurements. Isolated dopants in the channel of a silicon NanoFET behave as atomic-like systems with one or two electrons in a central 1/r attracting Coulomb potential. Donors can be characterized in terms of energy levels, associated to the D 0 and D − states, known in bulk Silicon [9]. A direct measure of the degree of hybridization of the electron wavefunction between the donor potential and the interfacial well has been performed in a Si nanostructure [8]. The separation of the conduction peaks, observed by applying a gate voltage to a nanostructure, and the threshold voltage, is proportional to the energy level position with respect to the conduction band edge [7, 8]. An isolated, diffused dopant embedded in the Si inversion layer of a nanostructure acts as a quantum dot (Single Donor Quantum Dot, SDQD) at cryogenic temperatures [7, 10]. Above the conduction band edge, further quantized energy levels are due to the quantum dot formed in the Si channel by electrostatic confinement.A microwave field, thanks to the variety of its couplings with the single atom and its environment, provides an unique tool to explore quantum transport and spin properties. In quantum information processing applications, microwave irradiation should drive electron spin resonance of Zeeman spin doublets and single spin manipulation with pulses of appropriate duration as already observed in GaAs systems [11]. In Si the observation and the control of single electron spin resonance has not been demonstrated yet due to the small linewidth (expected to be of the order on one gauss) [12] if compared to the typical resolution of superconducting cryomagnets ordinarily used for quantum transport measurements, contrarily to GaAs where the spin orbit effect broadens the line to tens of gauss [11,13,14], and to the competition of such effect with photon assisted tunneling in terms of current variation [20].When a quantum dot is i...

Adiabatic charge control in a single donor atom transistor

“…The presence of the donor in the quantum device is due to the diffusion of few donors from the source and the drain to the nanometric channel. [6,7] Only some samples exhibit the conduction due to one or few donors with including both a metallic quantum dot and a donor quantum dot (Figure 3 b). Figure 3 b shows the simulation of a system made by a metallic quantum dot and a donor in parallel.…”

“…[3,5] Single atom spintronics and solid state qubits are among the most relevant exploitation opportunities for the ultimate Si-based nanostructures in which a single donor is an essential part of the working principle of the device. Coulomb blockade of single donors in NanoFETs has been previously reported [3,[5][6][7][8] by studying the sequential tunneling through D 0 and D − states, also under microwave irradiation. [6] By operating the sample in Coulomb blockade regime, we show that the electrons bound to a donor close to the oxide interface and those in another electrostatic quantum dot confined at the oxide interface are differently coupled respectively to the control gate and the back gate.…”

“…Coulomb blockade of single donors in NanoFETs has been previously reported [3,[5][6][7][8] by studying the sequential tunneling through D 0 and D − states, also under microwave irradiation. [6] By operating the sample in Coulomb blockade regime, we show that the electrons bound to a donor close to the oxide interface and those in another electrostatic quantum dot confined at the oxide interface are differently coupled respectively to the control gate and the back gate. We consequently tune the system among different charge states.…”

Towards room temperature solid state quantum devices at the edge of quantum chaos for long-living quantum states

“…Later, single electron effects have been observed in donor at the silicon/silicon oxide interface. [23] Individual atoms centered between the source and the drain of a small device provide the energy levels for sequential tunneling, in which an impurity was randomly diffused from the doping of one of the contacts. The presence of the individual atom is observed by looking at the quantum transport of the device at cryogenic temperature [24,25,26].…”

Microwave Effects in Silicon Low Dimensional Nanostructures

“…We investigated the effects of an rf field applied to commercial flash memories based on Si technology with nominal n-channel dimensions of 50 nm width and an effective length of less than 70 nm. 27 The contacts are doped with arsenic and the channel with boron. Few As atoms can also diffuse in a random number in the channel.…”