Solid State Phenomena Vols. 121-123

Abstract: For compatibility with present CMOS devices, the single-electron transistor (SET) is preferably made in silicon. In this paper, a Si-based SET with in-plane side gates is proposed, which is fabricated in a SIMOX (Separation by IMplanted OXygen) wafer using electron beam lithography (EBL) with high-resolution SAL601 negative e-beam resist and inductively coupled plasma (ICP) etching. Carefully controlled the process, the SET with a 70-nm-radius Coulomb island is successfully fabricated. The Rds-T characteristics of the SET indicate that the device has typical semiconductor characteristics and the co-tunneling phenomena is impossible to occur. The Ids-Vds characteristics of the SET at different values of Vg (-10 V, 0 V, 10 V) measured at the temperature of 2 K all show Coulomb staircases. And the good reproducibility of the Ids-Vds characteristics can also be realized. The corresponding dIds/dVds-Vds characteristics show the clear differential conductance oscillations at 2 K. The Ids-Vg curve at Vds = 0.1 V and Vg = 10 V approximately exhibits Coulomb oscillations. The fabrication process is quite easy and this kind of Si-based SET has the advantages of simplicity, IC-orientation and compatibility with traditional CMOS process.

Abstract: The electrical transport properties of C70 and C60 fullerene peapods are investigated. We report the fabrications and performances of field-effect transistors (FETs) based on C70 and C60 fullerene peapods. A large percentage of the fullerene peapod-FETs we fabricated exhibit ambipolar characteristics with high Ion/Ioff ratio at room temperature in air. The origin of ambipolar behavior is qualitatively discussed.

Abstract: The device characteristics of the nanoscale metal/insulator tunnel transistor are investigated by solving the ballistic quantum transport equation in the device. The device performance in terms of the transfer characteristics, the drain output, and the threshold voltage change is assessed as the channel length is gradually reduced down to a few nanometer. We have found that the device characteristics remain almost the same if the channel length is reduced to around 10 nanometer, but below it, the device performance becomes drastically degraded. Effects of other device parameters such as the channel depth, tunnel barrier height, and the gate dielectric constant are also discussed.

Abstract: Ballistic electron emission microscopy (BEEM) is a new method by apply the spatial resolution capabilities of the scanning tunneling microscope (STM) to investigate electron transport properties in the quantum dots. This method requires three terminals: a sharp tip to inject electrons, a conductive layer and a semiconductor substrate. The transport-related properties of the sample can be obtained by using the characteristic of the injected and collected electrons. In this paper proposed a BEEM model for the silicon quantum dots (Si-QDs) on SiO2 layer prepared by LPCVD technique. SiO2 layer was thermally grown on p-type Si (100) wafer in dry O2 atmosphere and a thin gold layer cap used to provide a conductive layer on top of the Si-QDs for the BEEM characterization.

Abstract: We designed the monolithic opto-electronic integrated circuit composed by Resonant Tunnelling Diodes (RTD) and Heterojunction Phototransistor (HPT). Circuit simulation of RTD and HPT integration is firstly processed. The material structure and technological process of the device is introduced in detail. A good characteristic is obtained with high Peak-to-valley current ratio.

Abstract: Fabrication of semiconductor nanostructures such as quantum dots (QDs), quantum rings (QRs) has been considered as the important step for realization of solid state quantum information devices, including QDs single photon emission source, QRs single electron memory unit, etc. To fabricate GaAs quantum rings, we use Molecular Beam Epitaxy (MBE) droplet technique in this report. In this droplet technique, Gallium (Ga) molecular beams are supplied initially without Arsenic (As) ambience, forming droplet-like nano-clusters of Ga atoms on the substrate, then the Arsenic beams are supplied to crystallize the Ga droplets into GaAs crystals. Because the morphologies and dimensions of the GaAs crystal are governed by the interplay between the surface migration of Ga and As adatoms and their crystallization, the shape of the GaAs crystals can be modified into rings, and the size and density can be controlled by varying the growth temperatures and As/Ga flux beam equivalent pressures(BEPs). It has been shown by Atomic force microscope (AFM) measurements that GaAs single rings, concentric double rings and coupled double rings are grown successfully at typical growth temperatures of 200°C to 300°C under As flux (BEP) of about 1.0×10-6 Torr. The diameter of GaAs rings is about 30-50 nm and thickness several nm.

Abstract: Anomalously high values of power α (1.6 < α < 12) are found in power laws in conductance versus energy relationships in carbon-nanotube peapod quantum dots, encapsulating a chain of C60 molecules. This power is controllable by the applied back gate voltage. Atomic-like behaviors with doubly degenerate ground states are also found by single electron spectroscopy. They reveal that a portion of power originates from the Tomonaga-Luttinger liquid via the occupied electronic levels, which originate from the subbands unique to the peapods. This observation also clarify that the encapsulated C60 molecules do not directly contribute to the above quantum phenomena in peapods.

Abstract: Starting from a mean field calculation for the static capacitance of a MIS-nanostructure with a near back gate [P.N. Racec, E. R. Racec and U. Wulf, Phys. Rev. B 65, 193314, (2002)] we develop an approach to determine the equivalent small-signal circuit. The analyzed system has an open character, taken into account in the Landauer-Büttiker formalism. The Coulomb interaction is treated in Hartree approximation. Consistent with our static calculations we determine the charge-charge correlation function in the random phase approximation to find the ac-admittances. The small-signal circuit consists of a voltage-dependent capacitance and a resistance in series. Beyond a characteristic frequency c ν they become frequency dependent. The characteristic frequency is given by the life time of specific resonance which develops in the system.