Photoinduced Hysteresis Research Articles

Photoinduced Hysteresis of Graphene Field-Effect Transistors Due to Hydrogen-Complexed Defects in Silicon Dioxide.

Photoinduced hysteresis (PIH) of graphene field-effect transistors (G-FETs) has attracted attention because of its potential in developing photoelectronic or nonvolatile memory devices. In this work, we focused on the role of SiO2 dielectric layer on PIH, where G-FETs have only a SiO2 dielectric layer. Adsorbates are effectively removed before the PIH test. The effects of laser wavelength, laser power density, and temperature on the PIH are systematically investigated. The PIH is significantly enhanced by increasing the hydrogen flow in a hydrogen-atmosphere device thermal annealing. This strongly suggests proton-related defects that play a key role. The pure electronic process for PIH is further ruled out by the significant dependence of the doping rate on the temperature. A mechanism of PIH based on proton generation after hole trapping at [O3≡Si-H] is proposed. The proposed mechanism is well-supported by our experimental data: (1) the observed threshold photon energy for PIH is between 2.76 and 2.34 eV, which is close to the energy barrier for [O3≡Si-H], releasing a proton. (2) No obvious carrier mobility degradation after the PIH process suggests that the bulk defects in SiO2 are the major contributors rather than graphene/SiO2 interface defects. (3) The dependence of the doping rate on the temperature and the laser power density matches a theoretical model based on the random hopping of H+. The results in this work are also valuable for the study of degradation of other oxide dielectric materials in various field-effect transistors.

A Comparison of Photo-Induced Hysteresis Between Hydrogenated Amorphous Silicon and Amorphous IGZO Thin-Film Transistors.

We investigate photo-induced instability in thin-film transistors (TFTs) consisting of amorphous indium-gallium-zinc-oxide (a-IGZO) as active semiconducting layers by comparing with hydrogenated amorphous silicon (a-Si:H). An a-IGZO TFT exhibits a large hysteresis window in the illuminated measuring condition but no hysteresis window in the dark condition. On the contrary, a large hysteresis window measured in the dark condition in a-Si:H was not observed in the illuminated condition. Even though such materials possess the structure of amorphous phase, optical responses or photo instability in TFTs looks different from each other. Photo-induced hysteresis results from initially trapped charges at the interface between semiconductor and dielectric films or in the gate dielectric which possess absorption energy to interact with deep trap-states and affect the movement of Fermi energy level. In order to support our claim, we also perform CV characteristics in photo-induced hysteresis and demonstrate thermal-activated hysteresis. We believe that this work can provide important information to understand different material systems for optical engineering which includes charge transport and band transition.

Photo-activated oxygen sensitivity of graphene at room temperature

Photo-induced changes in the electrical conductivity and the sensitivity to oxygen gas of graphene sheets grown by chemical vapor deposition and transferred onto Al2O3 and SiO2 thin film substrates were studied at ambient conditions. The pristine graphene sensors were initially completely insensitive to oxygen gas at room temperature but showed significant (up to 100%) response when illuminated with weak ultraviolet (300 nm or 365 nm) light. Oxygen response was governed by Langmuir law and its activation was insensitive to humidity. The mechanism of sensitization is analyzed together with other photo-induced effects—negative persistent photo-conduction and photo-induced hysteresis of field effect transistor characteristics. While the reduction of conductivity in air is persistent effect, the oxygen sensitization and enlargement of hysteresis take place only under the direct influence of light. It is concluded that the charge traps with differently adsorbed oxygen and water are involved in these phenomena.

Low-voltage and hysteresis-free organic thin-film transistors employing solution-processed hybrid bilayer gate dielectrics

This study presents a promising approach to realize low-voltage (<3 V) organic thin-film transistors (OTFTs) exhibiting improved electrical and optical stability. Such device performance results from the use of solution-processed hybrid bilayer gate dielectrics consisting of zirconium dioxide (high-k dielectric) and amorphous fluoropolymer, CYTOP® (low-k dielectric). Employing a very thin amorphous fluoropolymer film reduces interfacial defect-states by repelling water molecules and other aqueous chemicals from an organic semiconductor active layer due to the hydrophobic surface-property. The chemically clean interface, stemming from decrease in density of trap states improves all the key device properties such as field-effect mobility, threshold voltage, and sub-threshold swing. Furthermore, degradation by electrical bias-stress and photo-induced hysteresis were suppressed in OTFTs employing hybrid bilayer gate dielectrics.

Light-induced hysteresis and recovery behaviors in photochemically activated solution-processed metal-oxide thin-film transistors

In this report, photo-induced hysteresis, threshold voltage (VT) shift, and recovery behaviors in photochemically activated solution-processed indium-gallium-zinc oxide (IGZO) thin-film transistors (TFTs) are investigated. It was observed that a white light illumination caused negative VT shift along with creation of clockwise hysteresis in electrical characteristics which can be attributed to photo-generated doubly ionized oxygen vacancies at the semiconductor/gate dielectric interface. More importantly, the photochemically activated IGZO TFTs showed much reduced overall VT shift compared to thermally annealed TFTs. Reduced number of donor-like interface states creation under light illumination and more facile neutralization of ionized oxygen vacancies by electron capture under positive gate potential are claimed to be the origin of the less VT shift in photochemically activated TFTs.

Investigation of Photo-Induced Hysteresis and Off-Current in Amorphous In-Ga-Zn Oxide Thin-Film Transistors Under UV Light Irradiation

We investigated the hysteresis and off-current (Ioff) of amorphous In-Ga-Zn oxide thin-film transistors illuminated by 400 nm light at various intensities. Both hysteresis and Ioff are induced by the ionized oxygen vacancy (Vo2+) that forms at the interface between the gate insulator and active layer. In our measurements, Ioff was much less than the estimated photocurrent. Ioff showed a rapid nonlinear increase with light intensity, while the photocurrent of a conventional crystalline semiconductor is expected to show a linear relationship. Furthermore, a numerical analysis suggested that the response time of Vo2+ should be considered when analyzing the hysteresis of these devices.

Dynamical model for spin-crossover solids. II. Static and dynamic effects of light in the mean-field approach

We have introduced a photoexcitation contribution in the dynamical model we previously presented (see previous paper), as an additional term in the rate transition, in order to reproduce the light induced thermal hysteresis effect, experimentally observed in the spin-crossover materials. The set of motion equations governing the evolution of the high-spin (HS) fraction of cooperative spin-crossover systems under light, is obtained. The mean-field treatment leads to a macroscopic master equation previously given on a phenomenological basis. With both the $\mathrm{HS}\ensuremath{\rightarrow}$ LS (low-spin) and $\mathrm{LS}\ensuremath{\rightarrow}$ HS transition rates terms, a model of general use is derived. This model describes the static and dynamic properties under light. We have investigated this model analytically, as far as possible. The properties under light involve two instabilities different in nature: the high-temperature instability, chiefly entropy driven, and the low-temperature one, light induced. We have determined the conditions for these instabilities to occur, and have examined their possible collapse. The described phenomena are discussed with respect to the available data on the photoinduced bistable regime: thermal hysteresis loops, optical hysteresis loops, and transient regimes. The kinetic dependence of the photoinduced hysteresis loops is calculated.

The photoinduced hysteresis phenomena in ferroelectric PZT films

Abstract The suppressing of the switchable remnant polarization in PZT films at illumination in the external field is observed This phenomenon is explained by the screening of the domain walls by the nonequilibrium carriers The experimental results are compared with the switching kinetics, suggested by Yshibashi and Takagi The comparison reveals also the influence of the nonequilibrium carriers on the domain-wall velocity and nucleation rate.

The bulk photovoltaic effect in ferroelectric Pb(Zr, Ti)O3 thin films

Abstract The bulk photovoltaic effect (BPE) has been investigated in lead zirconate titanate (PZT) thin films. Measurements of the kinetics, spectral distribution and photocurrent hysteresis loops have been made. In the extrinsic spectral region, the steady-state photocurrent is primarily due to the BPE, where the photovoltaic tensor component has been determined to be G31 = 10−9 cm/V. However, in the intrinsic region, the BPE has not been determined due to the strong contribution from photoinjection currents. Finally, it is shown that the BPE may be the driving force for photoinduced hysteresis changes in PZT thin films, particularly in the extrinsic spectral region.

Photo-induced and electrooptic properties of (Pb,La)(Zr,Ti)O3 films for optical memories

Abstract Photo-induced hysteresis changes and electrooptic effects in sol-gel Pb(Zr,Ti)O3 (PZT) and (Pb,La)(Zr,Ti)O3 (PLZT) films have been studied in an effort to evaluate these materials for optical memory applications. The films exhibit two distinct, but related, types of photo-induced changes in their hysteresis behavior: 1) a photo-induced change in the coercive voltage and 2) a photo-induced suppression of the switchable polarization. Both types of photo-induced hysteresis changes are due to trapping of photo-generated charge carriers at sites which minimize internal depolarizing fields. The photo-induced changes are reproducible and stable and are, thus, suitable for optical memory applications. In addition, polarization-dependent changes in the refractive indices can be the basis of a nondestructive optical readout technique. To characterize these electrooptic effects, a waveguide refractometry technique has been used to independently determine field-induced changes in the ordinary and extraordina...

Photo-Induced and Electrooptic Properties of (Pb,La)(Zr,Ti)O3 Films

AbstractPhoto-induced changes in the hysteresis behavior of sol-gel derived Pb(Zr,Ti)O3 (PZT) and (Pb,La)(Zr,Ti)03 (PLZT) films have been characterized. The film photosensitivity has been evaluated with respect to the magnitude of the effects, the time response and the spectral dependence. Photo-induced hysteresis changes exhibit a stretched-exponential time dependence, which implies a dispersive mechanism. The spectral dependence is strongly peaked at the band edge (∼3.4 eV), which indicates that generation of electron-hole pairs in the material is critical. The photo-induced hysteresis changes are reproducible and stable, which indicates that the controlling charge traps are stable. However, improvements in film photosensitivity will be required to develop these materials for optical memory applications.