Electrostatic effects in coupled quantum dot-point contact-single electron transistor devices

Abstract

We study the operation of a system where quantum dot (QD) and point contact (PC) defined in a two-dimensional electron gas of a high-mobility GaAs/AlGaAs heterostructure are capacitively coupled to each other and to metallic single electron transistor (SET). The charge state of the quantum dot can be probed by the point contact or single electron transistor. These can be used for sensitive detection of terahertz radiation. In this work, we explore an electrostatic model of the system. From the model, we determine the sensitivity of the point contact and the single electron transistor to the charge excitation of the quantum dot. Nearly periodic oscillations of the point contact conductance are observed in the vicinity of pinch-off voltage. They can be attributed to Coulomb blockade effect in a quasi-1D channel because of unintentional formation of small quantum dot. The latter can be a result of fluctuations in GaAs quantum well thickness. V C 2012 American Institute of Physics. [http://dx

Detection of Coherent Terahertz Radiation from a High-Temperature Superconductor Josephson Junction by a Semiconductor Quantum-Dot Detector

“…every time an electron leaves the QD because of the capacitive coupling C QD SET between the SET and the QD, where C QD Σ is the total capacitance of QD, and δV period G is the CBO period. For the present device, the shift is approximately 20% of δV period G [24]. When the gate voltage V G is fixed, then the electron excitations are seen as steplike changes of the SET current; see Fig.…”

“…The detector is designed in such way that charge excitations of the QD are probed by a sensitive electrometer (SET). Details of the fabrication and the operation of the SET can be found elsewhere [24,25]. Coulomb blockade oscillations (CBOs) of the SET current are shown in Fig.…”

“…For a multiexcited QD, the energy of a terahertz photon may not be enough to overcome the potential barrier forming the QD. We can estimate the order of excitation needed for such a situation by invoking the charging energy of the QD, approximately 80 μeV [24]. Excitation of each electron out of the QD decreases the potential of the electrons in the QD by 80 μeV so that the excitation of a dozen electrons should completely block further excitation.…”

Compact Remote Spectral Terahertz Imager

“…We have evidence that photo-response in our detector is due to resonant excitation of the plasma waves in the 2DEG upon absorption of terahertz photons. The rectification of these plasma waves at a non-uniform potential profile is then detected with the narrow conductive channel [11]. The explanation is widely accepted for the operation at low temperatures, below 4 K, where coherent plasma waves can be easily excited.…”

“…However, they did not allow to get spectroscopy information remotely. Recent progress in compact high power spectral terahertz sources, like resonance tunnelling diodes (RTD) [9], heterodyne [10] and direct spectral detectors [11] opens way to the next step in technology-a remote terahertz spectroscopy. One can envisage a remote spectroscopy system: an array of spectral sensors detects incoherent radiation reflected by the objects when consecutively illuminated by a number of narrow spectrum terahertz sources.…”