Meyer Neldel Energy Research Articles

Electric field dependent activation energy of electron transport in fullerene diodes and field effect transistors: Gill’s law

The electric field and temperature dependence of the electron mobility is studied comparatively in the bulk of fullerene (C60) diodes and at the interface with dielectric of organic field effect transistors (OFETs). Electron mobility values follow a Poole–Frenkel-type electric field dependence in both types of devices. The activation energy for electron transport is electric field dependent and follows the square root law of field in both devices as predicted by Gill’s law. The same Gill’s energy EGill=34 meV is measured in diodes and OFETs, which corresponds well to Meyer–Neldel energy (EMN=35 meV). It is shown that both the electric field and charge carrier concentration must be accounted for the description of disordered charge transport.

Modeling of Polycrystalline Organic Thin-Film Transistor and Schottky Diode for the Design of Simple Functional Blocks

ABSTRACTWe present analytical models for organic thin film transistors (OTFTs) and Schottky diodes based on polycrystalline semiconductors. The OTFT model is developed using a well-established approach previously developed for polysilicon, with slight modification for organics. The model predicts voltage and temperature dependencies on the various device and circuit parameters. A good agreement is obtained with experimental data of TIPS-based OTFTs. Essential parameters such as the characteristic temperature and Meyer-Neldel Energy extracted using the model with TIPS OTFTs data were in agreement with those obtained from Schottky diode measurements.

Meyer–Neldel rule for charge carrier transport in fullerene devices: A comparative study

Charge transport is comparatively studied in the bulk and at the interface of disordered fullerene films fabricated using physical vapour deposition. Charge carrier concentration and temperature dependent electron mobilities are comparatively studied using charge extraction by linearly increasing voltage (CELIV) technique and organic field-effect transistors (OFET) measurements. Electron mobility is at least two orders of magnitude higher than hole mobility in the fullerene films. Lower mobility values and stronger concentration dependence in diodes is observed. Carrier concentration dependent activation energy is experimentally measured in both types of devices. Larger activation energy for electron transport is required at lower carrier concentrations. Meyer–Neldel rule (MNR) for electron mobility is observed in both the bulk of the fullerene films and in the transistor channel at the interface. Meyer–Neldel energy ( E MN = 35 meV), which is interpreted as disorder parameter, is the same in both device geometries, which suggest that the level of disorder and energetical landscape for charge transport is similar in the bulk of fullerene films and at the interface with the insulator. Disorder formalism is used to qualitatively explain that either carrier concentration or the nature of non-equilibrium charge carrier transport in CELIV compared to steady-state OFET measurements is responsible for observed transport properties.

Further Meyer–Neldel Rule for Thermally Activated High Field Conduction in Thin Films of Glassy Se100−xSbx Alloys

In the present work, we report the applicability of the further Meyer–Neldel rule in thin films of glassy Se100−xSbx alloys for thermally activated high field conduction using two different methods. In first case, the temperature dependence of dc conductivity is studied at different electric fields without changing the composition of the glassy system, whereas, in the second case, the composition itself varies at a particular electric field. A strong correlation between prefactor σ00 and Meyer–Neldel energy in both cases is also observed. The observation of the correlation between prefactor σ00 and Meyer–Neldel energy can be described by multiple excitations stimulated by phonon energy as described by Yelon and Movaghar.

Dependence of Meyer–Neldel energy on energetic disorder in organic field effect transistors

Meyer–Neldel rule for charge carrier mobility was studied in C60-based organic field effect transistors (OFETs) fabricated at different growth conditions which changed the degree of disorder in the films. The energetic disorder in the films was found to correlate with a shift in the Meyer–Neldel energy, which is in excellent agreement with the predictions of a hopping-transport model for the temperature dependent OFET mobility in organic semiconductors with a Gaussian density-of-states (DOS). Using this model the width of the DOS was evaluated and it was found to decrease from 88 meV for the films grown at room temperature to 54 meV for films grown at 250 °C.

Further MN rule in thermally activated a.c. conduction of Se–Te–Sb chalcogenide glasses

Temperature and frequency dependence of a.c. conductivity have been studied in glassy Se 70Te 30− x Sb x (4 ≤ x ≤ 10) alloys. The observation of Further Meyer–Neldel rule in case of a.c. conductivity is reported. The observation of the correlation between Meyer–Neldel pre-factor σ 00 and Meyer–Neldel energy is explained by multiple excitations stimulated by optical phonon energy as described by Yelon and Movaghar.

Effect of Film Morphology on Charge Transport in C60-based Organic Field Effect Transistors

AbstractThe critical factor that limits the efficiencies of organic electronic devices is the low charge carrier mobility which is attributed to disorder in organic films. In this work we study the effects of active film morphology on the charge transport in Organic Field Effect Transistors (OFETs). We fabricated the OFETs using different substrate temperature to grow different morphologies of C60 films by Hot Wall Epitaxy. Atomic Force Microscopy images and XRD results showed increasing grain size with increasing substrate temperature. An increase in field effect mobility was observed for different OFETs with increasing grain size in C60 films. The temperature dependence of charge carrier mobility in these devices followed the empirical relation named as Meyer-Neldel Rule and showed different activation energies for films with different degree of disorder. A shift in characteristic Meyer-Neldel energy was observed with changing C60 morphology which can be considered as an energetic disorder parameter.

Improvement in the determination by 1/f noise measurements of the interface state distribution in polysilicon thin film transistors in relation with the compensation law of Meyer Neldel

Low-frequency (1/f) noise is studied in N-channel furnace solid phase crystallized (FSPC) and in laser solid phase crystallized (LSPC) polysilicon thin film transistors (TFTs) biased from weak to strong inversion. Noise analysis is supported by the theory of charge carrier trapping/detrapping at the interface tunneling into gate oxide traps. The distribution of interface trap states (NT) is deduced from the number of carriers trapped into the oxide. Noise measurements for devices biased from weak to moderate inversion allow the determination of the distribution of deep level trap states associated with dangling bond-type defects (NTdb), whereas measurements from moderate to strong inversion give the distribution of shallow level trap states (NTts) associated with strained bond defects. The noise analysis clearly shows that the slope of both exponential distributions equals to the reverse of the Meyer Neldel energy EMN (0.035 and 0.055 eV for FSPC and LSPC TFTs, respectively). For LSPC devices the resulting distribution of interface states (NT=NTdb+NTts) is one decade lower and it is attributed to the effects of the laser annealing on the active layer crystal quality.

Further MN rule for thermally activated high field conduction in bulk samples of glassy Se 100− xSb x alloys

In the present paper, we report the observation of the Meyer–Neldel rule (MNR) in thermally activated high field conduction in bulk samples of glassy Se 100− x Sb x alloys. We have investigated Meyer–Neldel rule by two different approaches. In first approach, the temperature dependence of d.c. conductivity is studied at different electric fields without changing the composition of the glassy system. In the second approach, the composition itself varies at a particular electric field. We found that the conductivity obeys the Meyer–Neldel rule as the pre-exponential factor depends on activation energy. We also found a strong correlation between pre-factor σ 00 and Meyer–Neldel energy in both cases. The observation of the correlation between pre-factor σ 00 and Meyer–Neldel energy can be described by multiple excitations stimulated by phonon energy as described by Yelon and Movaghar.

Further Meyer–Neldel rule in thermally activated crystallization of chalcogenide glasses

This paper reports the observation of the Further Meyer–Neldel rule in thermally activated crystallization in Se 80− x Te 20 M x (M = Ag, Cd, In and Sb); 0 ⩽ x ⩽ 15 chalcogenide glasses. We have investigated Further Meyer–Neldel rule by two different approaches. In the first case, the different sets of Meyer–Neldel pre-factor K 00 and Meyer–Neldel energy E MN are obtained by changing the composition (i.e., value of x ) of a particular glassy system keeping the third element (i.e., value of M) constant. In the second case, the different sets of Meyer–Neldel pre-factor K 00 and Meyer–Neldel rule energy E MN are obtained by changing the third element in a particular glassy system keeping the composition constant. The results are explained using the conception of thermal phonons in thermally activated crystallization analogous to optical phonons in thermally activated electric conduction.

Compensation effect in thermally activated photoconduction in amorphous thin films of Se75In25− x Pb x alloys

In the present paper, we report the observation of the compensation effect (also known as Meyer–Neldel rule) in thermally activated photoconduction in thin films of Se75In25− x Pb x . The Meyer–Neldel rule was investigated via two different approaches. In the first, the light intensity was varied while measuring the photoconductivity in amorphous thin films of each sample instead of the changing composition of the glassy system. In the second approach, the composition itself was varied at a particular intensity. The observation of the correlation between pre-factor σ 00 and Meyer–Neldel energy can be described by multiple excitations stimulated by optical phonon energy as described by Yelon and Movaghar [Phys. Rev. Lett. 65 618 (1990)].

Observation of Meyer–Neldel rule in amorphous thin films of Se100−xSbx in presence of light

In the present paper, we report the thermally activated conductivity in thin films of Se100−xSbx in presence of light of different intensities. We found that the conductivity obeys the Meyer–Neldel rule as the pre-exponential factor depends on activation energy. We also found a strong correlation between prefactor σ00 and Meyer–Neldel energy. The origin of the correlation and the MN rule can be described by multiple excitations stimulated by optical phonon energy as described by Yelon and Movaghar. The value of optical phonon energy calculated by experimental data is in good agreement with the YM model which suggests that the optical phonons are the source of the excitation energy in such processes.

Influence of disorder on the electron transport properties in fluorinated copper-phthalocyanine thin films

Electron transport in polycrystalline thin films of fluorinated copper phthalocyanine is investigated by space charge limited current, photoconductivity, and field-effect transistor measurements in the temperature range from 200 to 300 K. In this region the conductivity follows the Meyer–Neldel rule. The Meyer–Neldel energy EMN is connected to the characteristic energy of the exponential tail state distribution of localized states determined by voltage-dependent space charge limited current spectroscopy. Moreover, a correlation of the conductivity prefactor and EMN is observed revealing a maximum energy barrier of 0.52 eV for the relaxation of trapped electrons.

The Meyer–Neldel rule in organic thin-film transistors

We have measured and analyzed the temperature and gate voltage dependencies of the field-effect mobility in organic thin-film transistors. We find that the mobility prefactor increases exponentially with the activation energy in agreement with the Meyer–Neldel rule. This behavior is demonstrated in the mobility data of solution-processed pentacene, poly(2,5-thienylene vinylene) and in mobility data reported in literature. Surprisingly, the characteristic Meyer–Neldel energy for all analyzed materials is close to 40 meV. Possible implications for the charge transport mechanism in these materials are discussed.