Metal-organic Metal Research Articles

Frequency and voltage dependent electrical responses of poly(triarylamine) thin film-based organic Schottky diode

A metal-organic-metal (MOM) type Schottky diode based on poly (triarylamine) (PTAA) thin films has been fabricated by using the spin coating method. Investigation of the frequency dependent conductance-voltage (G-V-f ) and capacitance-voltage (C-V-f ) characteristics of the ITO/PTAA/Al MOM type diode were carried out in the frequency range from 12 Hz to 100 kHz using an LCR meter at room temperature. The frequency and bias voltage dependent electrical response were determined by admittance-based measured method in terms of an equivalent circuit model of the parallel combination of resistance and capacitance (RC circuit). Investigation revealed that the conductance is frequency and a bias voltage dependent in which conductance continuous increase as the increasing frequency, respectively. Meanwhile, the capacitance is dependent on frequency up to a certain value of frequency (100 Hz) but decreases at high frequency (1 – 10 kHz). The interface state density in the Schottky diode was determined from G-V and C-V characteristics. The interface state density has values almost constant of 2.8 x 1012 eV−1 cm−2 with slightly decrease by increasing frequencies. Consequently, both series resistance and interface trap density were found to decrease with increasing frequency. The frequency dependence of the electrical responses is attributed the distribution density of interface states that could follow the alternating current (AC) signal.

Charge density at the contacts of symmetric and asymmetric organic diodes

The organic diode, or metal-organic-metal (MOM) structure, is constituent key building block of organic-devices. The physical understanding and performance evaluation of these devices usually require proper modeling and simulation of the metal-organic structure. A topic of major concern in the simulation of the MOM structure, although frequently mishandled, is the selection of proper boundary conditions at the metal-organic interface. In this work, we determine the boundary conditions for the charge density at the metal-organic contact. Symmetric and asymmetric organic diodes with unipolar and bipolar conduction are analyzed. Using experimental current-voltage curves, an analytical method to determine the value of the charge density at the contacts is proposed. In single-carrier diodes, we observe that the charge concentration at the interface due to injection follows a power-law function of the current in metal-organic contacts in drift-dominated transport. This boundary condition is the way to introduce the contact effects in models. The contact affects the other regions (e.g., the bulk) as a boundary condition. This boundary condition for the charge density keeps information about the limited recombination velocity at the contacts and the contribution from space charge limited conduction (SCLC) in the bulk. In diffusion-dominated transport, at low bias close to the diode’s built-in voltage, the charge density at the contact is almost constant with the current. The complete relation between charge and current for injecting electrodes, extracted from the analysis of single-carrier diodes, can be used as boundary condition in bipolar devices.

Low-frequency noise properties of metal–organic–metal ultraviolet sensors

For this study, the metal–organic–metal (MOM) ultraviolet (UV) sensors with organic 4,4′,4′′-tris[3-methylphenyl(phenyl)amino]triphenylamine (m-MTDATA) thin films of various thicknesses were fabricated successfully, and their low-frequency noise (LFN) characteristics were also analyzed. The findings revealed that the UV-to-visible rejection ratio of the fabricated 80-nm-thick m-MTDATA UV sensor was approximately 7.81 when biased at 5 V, with a cutoff at 220 nm. With an incident light wavelength of 220 nm and an applied bias of 5 V, the measured responsivity of the 80-nm-thick m-MTDATA UV sensor was found to be 2.84 × 10−4 A/W. Furthermore, a noise-equivalent power (NEP) of 9.8 × 10−11 W and a detectivity (D*) of 8.3 × 108 cm Hz0.5 W−1 can be achieved using the fabricated 80-nm-thick m-MTDATA UV sensor.

Photoluminescence emission from Alq3 organic layer in metal–Alq3–metal plasmonic structure

The emission properties of an organic layer embedded in a metal–organic–metal (MOM) structure were investigated. A partially radiative odd-SPW as well as a non-radiative even-SPW modes are supported by hybridization of the SPW modes on the opposite organic/metal interface in the structure. Because of the competition by this radiative SPW, the population of excitons that recombine to form non-radiative SPW should be reduced. This may account for why the photoluminescence intensity of the MOM sample is higher than that of an organic–metal sample even though the MOM sample has an additional metal layer that should intuitively act as a filter.

Memory effect in thin films of insulating polymer andC60 nanocomposites

We describe the use of C60 fullerene molecules as the charge storage medium in an insulating poly-vinyl-phenol (PVP)polymer. The simple metal–organic–metal (MOM) sandwich structure devices depositedfrom solution exhibit distinct high and low conduction states, which can be used toprogram read, write and erase memory operations. The charge transfer and retention inC60 molecules at room temperature has been confirmed by capacitance–voltage and Ramanspectroscopy measurements. Conducting atomic force microscopy has been used todemonstrate that high and low conductance states persist even at the nanoscale.