Structural optimization of SUTBDG devices for low-power applications
ABSTRACT In this paper, we investigate the impact of physical structure on the performance of symmetric ultrathin body double-gate devices for low-operating-power (LOP) applications. Devices with regular raised source/drain (S/D) structures have optimal spacer thicknesses governed by a tradeoff between fringing capacitance and series resistance. Expanded S/D structures improve on regular raised S/D structures by slowing down the increases in both fringing capacitance with gate height and series resistance with spacer thickness. The cost is more chip area and process complexity. Pure high-κ gate dielectrics raise the off-state current (IOFF) due to the fringing field-induced barrier lowering effect. Suppressing the IOFF increase requires either a significant reduction in equivalent oxide thickness or a significant shift in gate work function. If the gate work function is tuned to maintain a fixed IOFF, devices with less abrupt S/D-channel junctions suffer a drive current (ION) degradation, and devices with weakly coupling S/D and relatively thick bodies gain improvements in ION. The ION of a device with metal S/D is significantly lower than required for LOP applications, if the S/D Schottky barrier height (SBH) is over 200 meV. We also briefly discuss the impact of mobility degradation on this structural optimization.
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ABSTRACT: Quantum transport simulation in DoubleGate (DG) MOSFETs using the Non-Equilibrium Green's function Formalism (NEGF) in both coupled-mode space (CMS) and real space (RS) is reported. The transport models were implemented in the same simulator and used to simulate near-and long-term's targets of the ITRS for DG MOSFETs. The CMS presents the advantage of simulation time reduction without significant loss of accuracy, when sufficient number of modes is used. The computational burden is reduced by a factor of 7 comparing with RS and the percentage error in the terminal current is less than 0.2 % for the year 2017 target device of the ITRS.Engineering and Technology (ICET), 2012 International Conference on; 01/2012
Conference Paper: Simulation Study of Schottky Contact Based Single Si Wire Solar Cell[Show abstract] [Hide abstract]
ABSTRACT: We simulate single silicon nanowire (SiNW) solar cells with dissimilar work function metal contacts. Both short circuit current (ISC) and open circuit voltage (VOC) have been investigated. Effects of nanowire dimension, minority carrier lifetime, and contact metal work function difference are understood through simulations. Both ISC and VOC increase with nanowire length but saturate due to minority carrier recombination. The saturation length is found to be five times the diffusion length. The larger the contact work function difference, the more improved the solar cell characteristics. Large work function differences may also avoid need for any doping in axial p-i-n nanowire solar cells. Saturation in ISC as well as degradation in current density with length can be minimized by spreading the contacts along the length of the nanowire.Photovoltaic Specialist Conference (PVSC), 2014 IEEE 40th; 06/2014
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ABSTRACT: We study solar cell properties of single silicon wires connected at their ends to two dissimilar metals of different work functions. Effects of wire dimensions, the work functions of the metals, and minority carrier lifetimes on short circuit current as well as open circuit voltage are studied. The most efficient photovoltaic behavior is found to occur when one metal makes a Schottky contact with the wire, and the other makes an Ohmic contact. As wire length increases, both short circuit current and open circuit voltage increase before saturation occurs. Depending on the work function difference between the metals and the wire dimensions, the saturation length increases by approximately an order of magnitude with a two order magnitude increase in minority carrier length. However current per surface area exposed to light is found to decrease rapidly with increase in length. The use of a multi-contact interdigitated design for long wires is investigated to increase the photovoltaic response of the devices.Solar Energy Materials and Solar Cells 11/2014; 130:456-465. DOI:10.1016/j.solmat.2014.07.015 · 5.03 Impact Factor