One of the most important aspects of nanotechnology is its multi-disciplinary aspect. The current structure of training program in most of the universities has some shortcomings for nanotechnology experts. Therefore training programs need to be optimized. The factors by which the way toward long-term goals of nanotechnology is being provided in time period less than 20 years are as follows: establishing research centers and applied laboratories of nanotechnology and multi-disciplinary research programs and groups in universities.
Hundreds of billions of dollars investments in the field of nanotechnology by developed countries like Japan and American indicates the nanotechnology’s universal importance. In Iran there is a great deal of scientific potential in order to conduct nanoelectronic researches. As a matter of fact, published articles in authoritative international journals and successful research projects represent that there is little distance between Iran and developed countries in this field; therefore, the competition is possible.
Research contexts in this laboratory include the factors like quantum transmission, single-electron devices, applying nanoparticles to fabrication of photodetectors with ZnO and molecular nanoelectronic. It has been predicted that by means of equipping the laboratory in future, it is possible to conduct practical activities like using electronic microscopes in order to measure atomic dimensions and molecular ordering, identifying three-dimensional features and nanoelectronic device surface, controlling molecular ordering and fabrication of photodetectors and so on.
Nanostructures can be metals, semiconductors and dielectrics which at least one of their dimensions is in nanometric range. This characteristic causes quantum confinement of electron motion and dependence of physical properties into the material dimensions. In other words, by decreasing dimensions of semiconductors, their behavior is complicated and new physical phenomena occur such as electron ballistic transport, tunneling, columbic blockage and so on that this in turn causes change of electrical and optical coordinates of devices. Therefore, it is important to investigate and explain these behaviors, obtain of electron motion equations and wave function and finally simulate and use of these property in nanoelectronic.
Nanoelectronic Lab includes two fundamental fields of molecular nanoelectronics and semiconductor nanoelectronics. Semiconductor nanoelectronics has three subsection of single electron devices and quantum dots (SET, QCA, RTD,…), nanofilms and nanofilters (TiO2, ZnO, …) and photodetectors and photocatalysts (Si, SiC, GaAs, ZnO, TiO2,…). Also, Molecular nanoelectronic filed has two subsets: molecular transistors and molecular cellular automats.
Fig. 1: Comparison of nanotools.
Fig.2: Taxonomy of Nanoelectronic devices.
FACULTY & STAFF
Mr Ehsan Rahimi
Fundamental research fields of this lab includes:
Investigation and analysis of quantum transport
Modeling of quantum transport in nanoelectronic devices
Simulation of these models for nanoelectronic devices
Fabrication of nanoelectronic devices
Fig.3: research fields of Nanoelectronic Lab.
Design and fabrication of Titanium Oxide thin film containing Ag nanoparticles
Sol gel process is a very good method for fabrication nanometric oxide films. This route has advantages including very high chemical purity, ability of phase change control and so on. After preparing sol, by using spin coater apparatus and choosing desirable pressure and speed, homogenous layer is formed on the substrate (quartz or glass) and is annealed in oven. Then, Produced film is analyzed by UV-Vis spectrometer and absorption and transmittance spectra of thin film are obtained.
Fig. 4: Sol formation stages.
Design and simulation of dynamical circuit model for QCA cells
QCA dynamical cells are modeled and simulated by using equations obtained of kirchhoff's voltage-current circuit laws and equal circuit design of QCA clocked circuits. Dynamical relations of Pauli spin matrix and following dynamical relations of coherence vectors for Design of dynamical circuit model can be obtained from calculation of Hamiltonian circuit and using Heisenberg image relations. In mathematics expression of coherence vector, a part of state variables is related to correlation between QCA cells. For this resean, temporal depecdence of elements of correlation matrix of two cells is calculated and therefore complete equations of QCA dynamical model are obtained.
Fig. 5: QCA cells.
Design and simulation of Ag nanoparticles effects on electrical and optical coordinates of Titanium Oxide thin films
By using numerical methods, effects of diameter and figure of nanoparticles on electrical and optical coordinations of titanium oxide thin film are investigated. Some of them are absorption, diffraction, reflection, transport and energy gap. By using optical parameters, refraction and dielectric coefficients and conduction can be obtained. In addition, polarization, absorption and reflection of n doped layer can be obtained. Also, Ag nanoparticles effects on quantum efficiency, optical current, dark current, noise, NEP and photodetection ability in TiO2 photodetectors are analyzed and simulated.
Design and simulation of single molecular transistors
MOSFET size reduction results in decreasing of cannel length to a few tens of nanometers. Hence, in general all device dimensions including oxide thickness, attachment depth, length and width of cannel and isolation distance change and quantum effects will be dominated.
Fig. 6: Design of single molecular transistor.
In simplest model, a molecular device includes one molecule that attached to two metal electrodes that have roles of source and drain. Complicated goal of molecular electronic is implantation of a molecular transistor with three terminals which can switch current between two branches by changing applied external electrical field to the third branch of individual molecule. Effects of applying external electric field in direction of molecular length as drain-source voltage and also electrical field perpendicular to transport direction as gate voltage onto the applied field molecules are investigated. Effects of increasing acceptors and donors groups in benzene molecule to the parameters of chosen molecules and calculation of voltage-current properties are studied.
Fig. 7: Model of single molecular devices.
Investigation of single electron components and transistors
Single electron tunneling transistors are devices which using tunneling quantum effect to control and determine electron movement. Single electron devices include single electron transistors (SET) and single electron memories (SEM). Their advantages are low consumption power, high switching speed and their ability of increasing density of integration. Unlike field effect transistors, single electron devices work according to quantum phenomena (tunneling effect). In these devices, some electrons which have Fermi energy can tunnel through dielectric material even in classic condition that their energy is much lower than necessary energy to dominate on the potential barrier.
Design and simulation of ZnO based UV photodetectors with improving of quantum efficiency & dark current
In this project, the current transport mechanism of ZnO-based metal-semiconductor-metal ultraviolet photodetectors with various contact electrodes is discussed and simulated. The simulation is based on the thermionic emission theory and tunneling effects. It was found that the lowest dark current, 6.04×10-10A at 3V biased, is obtained when the RU contact electrode is used. Moreover, it is shown that in order to achieve a large schottky barrier height on ZnO and more reduction of dark current, one can insert a thin oxide layer between contacts and ZnO layer. Also, the influence of the thickness of the insulator layer on the dark current of the MIS photodetector has been analyzed. Based on the simulations results, the dark current at 3V photodetector biased, with various thicknesses of interfacial insulator layer 3, 5, 7 and 10nm is 2.87×10-11, 8.23×10-13, 2.36×10-14 and 1.15×10-16A, respectively. Furthermore, quantum efficiency in our simulations with an antireflection coating has been improved. It is found that in these devices, the quantum efficiency with TiO2 thin oxide with thickness of 1nm is 46.7%.