Self-aligned double injection-function contact mitigating short channel effects in sub-micron channels of solution processed indium gallium zinc oxide

We propose and demonstrate self-aligned Double Injection Function Thin Film Transistor (DIF-TFT) architecture that mitigates short channel effects in 200nm channel on a non-scaled insulator (100nm SiO2). In this conceptual design, a combination of an ohmic-like injection contact and a high injection-barrier metal allows maintaining the high ON currents while suppressing the drain-induced barrier lowering. Using an industrial 2D device simulator (Sentaurus), we propose two methods to realize the DIF concept and we use one of them to experimentally demonstrate a DIF-TFT based on solution processed IGZO. Using molybdenum as the ohmic contact and platinum as the high injection barrier, we compare three transistor’s source-contacts: ohmic, Schottky, and double injection function. The fabricated DIF-TFT exhibits saturation at sub 1V drain bias with only about a factor of 2 loss in ON current compared to the ohmic contact.

Wavelength conversion through plasmon-coupled surface states

Surface states generally degrade semiconductor device performance by raising the charge injection barrier height, introducing localized trap states, inducing surface leakage current, and altering the electric potential. We show that the giant built-in electric field created by the surface states can be harnessed to enable passive wavelength conversion without utilizing any nonlinear optical phenomena. Photo-excited surface plasmons are coupled to the surface states to generate an electron gas, which is routed to a nanoantenna array through the giant electric field created by the surface states. The induced current on the nanoantennas, which contains mixing product of different optical frequency components, generates radiation at the beat frequencies of the incident photons. We utilize the functionalities of plasmon-coupled surface states to demonstrate passive wavelength conversion of nanojoule optical pulses at a 1550 nm center wavelength to terahertz regime with efficiencies that exceed nonlinear optical methods by 4-orders of magnitude.

Enhancement of Charge Injection in Organic Field-Effect Transistors Through Semiconducting Organic Buffer Layer

We investigate the effect of a semiconducting organic buffer layer (SOBL) on the injection and transport of charges in organic field-effect transistors (OFETs). Here, two different injection barriers at the source/organic semiconductor interface are respectively studied with the aid of a numerical simulation: one is intermediate (0.4 eV), and the other is large energy barriers (0.6 eV). The introduction of nanostructure buffer layer, or SOBL, exhibits the decrease of potential loss at the contact interfaces, improving the electrical performance of the OFETs. It is also found that the energy level as well as the mobility of the SOBL plays an important role in determining the injection properties at the metal/organic hetero-interfaces and thus improving the device performance. Our systematic investigation on the injection barrier by the introduction of the nanostructure buffer layer will provide a useful guideline for the fabrication of high-performance FETs with molecular semiconductors.

Innovative Incorporation of Poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) as Hole Carrier Transport Layer and as Anode for Organic Solar Cells Performance Improvement

In this work, we present a comparative study of benzoid poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) as electrode and as hole carrier transport layer (HTL) in the manufacture of organic photovoltaic devices using Fischer metal-carbene complexes. The performance of the different devices was evaluated for solar cell applications. Scanning electronic microscopy (SEM) and X-ray diffraction (XRD) were used to characterize the thin films that integrated the devices. A more ordered and crystallized active film microstructure is observed when using benzoid PEDOT:PSS as nucleation layer. The optical gap for both direct and indirect electronic transitions was evaluated from ultraviolet-visible spectroscopy data (UV-vis), as well as the absorption coefficient (α), and the values are in the range of 2.10–2.93 eV. Photovoltaic devices with conventional architecture, using two different chromium carbenes as active layers, were manufactured, and their electrical behavior was studied. The devices were irradiated with different wavelengths between the infrared and ultraviolet regions of the electromagnetic spectrum. Using the PEDOT:PSS film as hole carrier transport layer (HTL) decreases the slope on the ohmic and space charge limited current (SCLC) regions and eliminates the trap-charge limited current (T-CLC) mechanism. Furthermore, a saturation current of ~1.95 × 10−10 A and higher current values ~1.75 × 10−2 A at 4 V, ~4 orders in magnitude larger were observed. The PEDOT:PSS films as HTL in the devices reduced the injection barrier, thus showing a better performance than as anodes in this type of organic solar cells.

Prediction of a Two-Transistor Vertical QNOT Gate

A new design of quaternary inverter (QNOT gate) is proposed by means of finite-element simulation. Traditionally, increasing the number of data levels in digital logic circuits was achieved by increasing the number of transistors. Our QNOT gate consists of only two transistors, resembling the binary complementary metal-oxide-semiconductor (CMOS) inverter, yet the two additional levels are generated by controlling the charge-injection barrier and electrode overlap. Furthermore, these two transistors are stacked vertically, meaning that the entire footprint only consumes the area of one single transistor. We explore several key geometrical and material parameters in a series of simulations to show how to systematically modulate and optimize the quaternary logic behaviors.