Faruque M. Hossain

High mobility thin film transistors with transparent ZnO channels

We have fabricated high performance ZnO thin film transistors (TFTs) using CaHfOx buffer layer between ZnO channel and amorphous silicon?nitride gate insulator. The TFT structure, dimensions, and materials set are identical to those of the commercial amorphous silicon (a-Si) TFTs in active matrix liquid crystal display, except for the channel and buffer layers replacing a-Si. The field effect mobility can be as high as 7 cm2?V-1?s-1 for devices with maximum process temperature of 300?C. The process temperature can be reduced to 150?C without much degrading the performance, showing the possibility of the use of polymer substrate.

Modeling and simulation of polycrystalline ZnO thin-film transistors

Thin-film transistors (TFTs) made of transparent channel semiconductors such as ZnO are of great technological importance because their insensitivity to visible light makes device structures simple. In fact, there have been several demonstrations of ZnO TFTs achieving reasonably good field effect mobilities of 1–10 cm2/V s, but the overall performance of ZnO TFTs has not been satisfactory, probably due to the presence of dense grain boundaries. We modeled grain boundaries in ZnO TFTs and performed simulation of a ZnO TFT by using a two-dimensional device simulator in order to determine the grain boundary effects on device performance. Polycrystalline ZnO TFT modeling was started by considering a single grain boundary in the middle of the TFT channel, formulated with a Gaussian defect distribution localized in the grain boundary. A double Schottky barrier was formed in the grain boundary, and its barrier height was analyzed as a function of defect density and gate bias. The simulation was extended to TFTs ...

Diamond integrated quantum photonics

Diamond is a leading contender as the material of choice for the quantum computer industry. This potential arises mainly from the quantum properties of color centers in diamond. However, before diamond can realize its full potential, the technology to fabricate and sculpt diamond as well as, if not better than, silicon must be developed. A comprehensive processing capability for diamond that will allow the fabrication of qubits and their associated photonic structures is required. Here we describe the remarkable properties of diamond color centers, and the techniques being developed to engineer qubits and sculpt monolithic structures around them. Finally we outline some of the new proposals that use engineered diamond to realize tasks not possible with existing technologies.

Nano-manipulation of diamond-based single photon sources

The ability to manipulate nano-particles at the nano-scale is critical for the development of active quantum systems. This paper presents a technique to manipulate diamond nano-crystals at the nano-scale using a scanning electron microscope, nano-manipulator and custom tapered optical fibre probes. The manipulation of a approximately 300 nm diamond crystal, containing a single nitrogen-vacancy centre, onto the endface of an optical fibre is demonstrated. The emission properties of the single photon source post manipulation are in excellent agreement with those observed on the original substrate.

A highly efficient two level diamond based single photon source

An unexplored diamond defect center that is found to emit stable single photons at a measured rate of 1.6 MHz at room temperature is reported. The center, identified in chemical vapor deposition grown diamond crystals, exhibits a sharp zero phonon line at 734 nm with a full width at half maximum of ∼4 nm. The photon statistics confirm that the center is a single emitter and provides direct evidence of a true two level single quantum system in diamond.

All-Graphene Planar Self-Switching MISFEDs, Metal-Insulator-Semiconductor Field-Effect Diodes

Graphene normally behaves as a semimetal because it lacks a bandgap, but when it is patterned into nanoribbons a bandgap can be introduced. By varying the width of these nanoribbons this band gap can be tuned from semiconducting to metallic. This property allows metallic and semiconducting regions within a single Graphene monolayer, which can be used in realising two-dimensional (2D) planar Metal-Insulator-Semiconductor field effect devices. Based on this concept, we present a new class of nano-scale planar devices named Graphene Self-Switching MISFEDs (Metal-Insulator-Semiconductor Field-Effect Diodes), in which Graphene is used as the metal and the semiconductor concurrently. The presented devices exhibit excellent current-voltage characteristics while occupying an ultra-small area with sub-10 nm dimensions and an ultimate thinness of a single atom. Quantum mechanical simulation results, based on the Extended Huckel method and Nonequilibrium Greens Function Formalism, show that a Graphene Self-Switching MISFED with a channel as short as 5 nm can achieve forward-to-reverse current rectification ratios exceeding 5000.

High Performance Graphene Nano-ribbon Thermoelectric Devices by Incorporation and Dimensional Tuning of Nanopores

Thermoelectric properties of Graphene nano-ribbons (GNRs) with nanopores (NPs) are explored for a range of pore dimensions in order to achieve a high performance two-dimensional nano-scale thermoelectric device. We reduce thermal conductivity of GNRs by introducing pores in them in order to enhance their thermoelectric performance. The electrical properties (Seebeck coefficient and conductivity) of the device usually degrade with pore inclusion; however, we tune the pore to its optimal dimension in order to minimize this degradation, enhancing the overall thermoelectric performance (high ZT value) of our device. We observe that the side channel width plays an important role to achieve optimal performance while the effect of pore length is less pronounced. This result is consistent with the fact that electronic conduction in GNRs is dominated along its edges. Ballistic transport regime is assumed and a semi-empirical method using Huckel basis set is used to obtain the electrical properties, while the phononic system is characterized by Tersoff empirical potential model. The proposed device structure has potential applications as a nanoscale local cooler and as a thermoelectric power generator.

All-Graphene Planar Double Barrier Resonant Tunneling Diodes

In this work, we propose an atomically-thin all-graphene planar double barrier resonant tunneling diode that can be realized within a single graphene nanoribbon. The proposed device does not require any doping or external gating and can be fabricated using minimal process steps. The planar architecture of the device allows a simple in-plane connection of multiple devices in parallel without any extra processing steps during fabrication, enhancing the current driving capabilities of the device. Quantum mechanical simulation results, based on non-equilibrium Greens function formalism and the extended Huckel method, show promising device performance with a high reverse-to-forward current rectification ratio exceeding 50 000, and confirm the presence of negative differential resistance within the devices current-voltage characteristics.

Reactivity of ideal and defected rutile TiO2 (110) surface with oxygen

Abstract First principles pseudopotential density functional calculations have been performed to investigate the reactivity of O2 on ideal and defected surface of rutile TiO2 (110). All ionic positions are allowed to relax on slab geometry with periodic boundary conditions. The results reveal that both the molecular and dissociated adsorption of O2 is most favourable on a defective surface in the presence of titanium vacancy and a substantial change in surface relaxation was observed. This remarkable surface ionic displacement and titanium vacancy induced acceptor-like environment favoured in stable adsorption of oxygen for both molecular and dissociated states. The least favourable adsorption or no adsorption of O2 is observed on an ideal surface.

A graphene nanoribbon neuro-sensor for glycine detection and imaging

Glycine acts as a neurotransmitter in the Central Nervous System (CNS) and plays a vital role in processing of motor and sensory information that control movement, vision, and audition. Glycine detection and imaging can lead to a greater understanding of how this information is processed in the CNS. Here, we present a neuro-sensor for the detection and imaging of Glycine molecules, based on a zigzag Graphene Nanoribbon device structure. An energetically stable Nitrogen Vacancy (NV) center is introduced in the device to enable its use in neuronal imaging applications. We demonstrate, by using the Density Functional Theory and Nonequilibrium Greens Function method, that the device detects the attachment of a single Glycine molecule to its edges by significant changes in its conductance. The attachment of Glycine induces current channels around the NV center increasing the current flow through the device. In absence of Glycine, the presence of the NV center suppresses current flow through the device, signif...