Thin Film Semiconductor Devices Research Articles

Two-Dimensional Linear Elasticity Equations of Thermo-Piezoelectric Semiconductor Thin-Film Devices and Their Application in Static Characteristic Analysis

Two-Dimensional Linear Elasticity Equations of Thermo-Piezoelectric Semiconductor Thin-Film Devices and Their Application in Static Characteristic Analysis

Stabilizing Schottky junction in conjugated polymer diodes enables long-term reliable radio-frequency energy harvesting on plastic

Due to their inherent flexibility, solution-processable conjugated polymers are increasingly being considered for the cost-effective production of thin-film semiconductor devices used in Internet of Everything (IoE) applications. With considerable improvements in charge carrier mobilities, the final challenge impeding the commercialization of conjugated polymers may be improving their environmental and electrical stabilities. Recent studies have improved the stability of computing devices (i.e., transistors) by eliminating interface traps and water molecules within conjugated polymers. However, the stability issue of Schottky diodes, which play a crucial role in configuring thin-film IoE devices used in wireless communication and energy harvesting, has been largely overlooked. This study reveals that aluminum, which is commonly used as a cathode metal in polymer Schottky diodes, creates a nonstoichiometric effect when deposited on conjugated polymers, thereby leading to the formation of charge traps over time, which reduces the rectification ratio of the Schottky diodes and induces a significant bias stress effect during operation. To address this issue, we introduce a zinc-oxide sacrificial interlayer between the conjugated polymer and cathode. This interlayer effectively eliminates the penetrated Al metal or ionized Al-induced nonstoichiometric effect without reducing the charge injection efficiency, achieving exceptional environmental and operational stability. The printed polymer Schottky diodes demonstrate consistent rectifying operation at 13.56 MHz for several months with negligible changes in electrical characteristics.

Nanocrystal Quantum Dot Devices: How the Lead Sulfide (PbS) System Teaches Us the Importance of Surfaces.

Semiconducting thin films made from nanocrystals hold potential as composite hybrid materials with new functionalities. With nanocrystal syntheses, composition can be controlled at the sub-nanometer level, and, by tuning size, shape, and surface termination of the nanocrystals as well as their packing, it is possible to select the electronic, phononic, and photonic properties of the resulting thin films. While the ability to tune the properties of a semiconductor from the atomistic- to macro-scale using solution-based techniques presents unique opportunities, it also introduces challenges for process control and reproducibility. In this review, we use the example of well-studied lead sulfide (PbS) nanocrystals and describe the key advances in nanocrystal synthesis and thin-film fabrication that have enabled improvement in performance of photovoltaic devices. While research moves forward with novel nanocrystal materials, it is important to consider what decades of work on PbS nanocrystals has taught us and how we can apply these learnings to realize the full potential of nanocrystal solids as highly flexible materials systems for functional semiconductor thin-film devices. One key lesson is the importance of controlling and manipulating surfaces.

Centers of cold electron emission from molybdenum thin films

Thin-film semiconductor devices and functional metal-oxide-semiconductor structures have drawn attention as being applicable for on-chip electronics. Similar structures, however, were also reported to be promising as efficient sources of electrons. This paper presents the results of scanning electron microscopy analysis of molybdenum thin films capable of low-macroscopic-field electron emission. Supposedly, the images show the centres of cold-field emission at different stages of their life cycles from activation to destruction. It is assumed that initially continuous Mo films experience dewetting under heating and ion bombardment, which are caused by the emission current flow. The results contribute to understanding the mechanism of low-field emission from thin metal films, which seems to be different from those previously proposed for thin carbon coatings.

Optical and Electrical Properties of Organic Semiconductor Thin Films on Aperiodic Plasmonic Metasurfaces.

Metal electrodes are playing an increasingly important role in controlling photon absorption and in promoting optimal light management in thin-film semiconductor devices. For organic optoelectronic devices, the conventional fabrication approach is to build the device on top of a transparent electrode, with metal electrode deposition as the last step. This makes it challenging to control the surface of the metal electrode to promote good light management properties. An inverted fabrication approach that builds the device on top of a metal electrode makes it possible to control the morphology of the metal surface independently of the organic semiconductor active layer to achieve a variety of photonic and plasmonic behaviors useful for devices. However, there are few reports of inverted fabrication of organic optoelectronic devices and its impacts on device properties. Silver (Ag) is the most suitable metal for fabrication of nanostructured electrodes with plasmonic behavior (i.e., plasmonic electrodes) because of its low parasitic absorption loss and high reflectivity. In this project, we describe the facile fabrication of silver nanoparticle (AgNP) aperiodic plasmonic metasurfaces and study their physical and optical characteristics. Then, we investigate the photonic and electrical behaviors of the aperiodic plasmonic metasurfaces when interfaced with poly(9,9-dioctylfluorene-alt-benzothiadiazole) (F8BT) organic semiconducting polymer thin films. The luminescence quantum yield of F8BT thin films increases from 29% on planar Ag up to 66% on AgNP metasurfaces due to the Purcell effect and the improved extraction of emission coupled to surface plasmon polariton modes. In particular, we show that plasmonic enhancement can overcome ohmic losses associated with metals and metal-induced exciton quenching. According to the current-voltage characteristics of hole-only devices with and without aperiodic plasmonic metasurfaces, we conclude that AgNP aperiodic plasmonic metasurfaces have comparable electrical behavior to planar metal electrodes while having superior light management capability.

Hierarchical flower-like Cu3BiS3 thin film synthesis with non-vacuum chemical bath deposition technique

Now-a-days, the progress of thin film semiconductor devices such as CdTe, Cu(In,Ga)Se2 has remarkable development in the field of thin film photovoltaics. The toxicity of cadmium and limited availability of indium impose the search for alternative materials. At this juncture, Cu3BiS3 is one of the promising emerging materials with favorable properties like high absorption coefficient and direct bandgap. Furthermore, the entire ingredients essential for Cu3BiS3 synthesis are cost effective, non-toxic and plenteously accessible in the Earth’s crust. In the present work, hierarchical flower-like Cu3BiS3 thin films were effectively synthesized on a glass substrate by non-vacuum chemical bath deposition method. The XRD approves the amorphous nature of hierarchical flower-like Cu3BiS3 thin films. Raman spectrum ensured the pure phase of Cu3BiS3 by major vibrational peaks at 285 and 468 cm−1. Moreover, SEM shows the formation of hierarchical flower-like nanostructure of Cu3BiS3 thin films. Wettability study of Cu3BiS3 thin films exhibited hydrophobic behavior. The absorption coefficient and the optical bandgap of Cu3BiS3 thin films were found to be 105 cm−1 and 1.73 eV respectively. These hierarchical flower-like Cu3BiS3 thin films may be useful as absorbing layer in the photovoltaic solar cell.

3D Hybrid Small Scale Devices.

Interfacing nano/microscale elements with biological components in 3D contexts opens new possibilities for mimicry, bionics, and augmentation of organismically and anatomically inspired materials. Abiotic nanoscale elements such as plasmonic nanostructures, piezoelectric ribbons, and thin film semiconductor devices interact with electromagnetic fields to facilitate advanced capabilities such as communication at a distance, digital feedback loops, logic, and memory. Biological components such as proteins, polynucleotides, cells, and organs feature complex chemical synthetic networks that can regulate growth, change shape, adapt, and regenerate. Abiotic and biotic components can be integrated in all three dimensions in a well-ordered and programmed manner with high tunability, versatility, and resolution to produce radically new materials and hybrid devices such as sensor fabrics, anatomically mimetic microfluidic modules, artificial tissues, smart prostheses, and bionic devices. In this critical Review, applications of small scale devices in 3D hybrid integration, biomicrofluidics, advanced prostheses, and bionic organs are discussed.

Open-source parametric 3-D printed slot die system for thin film semiconductor processing

Slot die coating is growing in popularity because it is a low operational cost and easily scaled processing technique for depositing thin and uniform films rapidly, while minimizing material waste. The complex inner geometry of conventional slot dies require expensive machining that limits accessibility and experimentation. In order to overcome these issues this study follows an open hardware approach, which uses an open source 3-D printer to both fabricate the slot die and then to functionalize a 3-D slot die printing system. Polymer materials are tested and selected for compatibility with common solvents and used to fabricate a custom slot die head. This slot die is then integrated into a 3-D printer augmented with a syringe pump to form an additive manufacturing platform for thin film semiconductor devices. The full design of the slot die system is disclosed here using an open source license including software and operational protocols. This study demonstrates that functional lab-grade slot dies may be 3-D printed using low-cost open source hardware methods A case study using NiO2 found an RMS value 0.486 nm, thickness of 17–49 nm, and a maximum optical transmission of 99.1%, which shows this additive manufacturing approach to slot die depositions as well of fabrication is capable of producing viable layers of advanced electronic materials. Using this method, a cost savings of over 17,000% was obtained when compared to commercial slot die systems for laboratories.

Flexible Semiconductor Technologies with Nanoholes-Provided High Areal Coverages and Their Application in Plasmonic-Enhanced Thin Film Photovoltaics

Mechanical flexibility and advanced light management have gained great attentions in designing high performance, flexible thin film photovoltaics for the realization of building-integrated optoelectronic devices and portable energy sources. This study develops a soft thermal nanoimprint process for fabricating nanostructure decorated substrates integrated with amorphous silicon solar cells. Amorphous silicon (a-Si:H) solar cells have been constructed on nanoholes array textured polyimide (PI) substrates. It has been demonstrated that the nanostructures not only are beneficial to the mechanical flexibility improvement but also contribute to sunlight harvesting enhancement. The a-Si:H solar cells constructed on such nanopatterned substrates possess broadband-enhanced light absorption, high quantum efficiency and desirable power conversion efficiency (PCE) and still experience minimal PCE loss even bending around 180°. The PCE performance without antireflection coatings increases to 7.70% and it improves 40% compared with the planar devices. Although the advantages and feasibility of the schemes are demonstrated only in the application of a-Si:H solar cells, the ideas are able to extend to applications of other thin film photovoltaics and semiconductor devices.

Electrothermal Simulation of Large-Area Semiconductor Devices

The lateral charge transport in thin-film semiconductor devices is affected by the sheet resistance of the various layers. This may lead to a non-uniform current distribution across a large-area device resulting in inhomogeneous luminance, for example, as observed in organic light-emitting diodes (Neyts et al., 2006). The resistive loss in electrical energy is converted into thermal energy via Joule heating, which results in a temperature increase inside the device. On the other hand, the charge transport properties of the device materials are also temperature-dependent, such that we are facing a two-way coupled electrothermal problem. It has been demonstrated that adding thermal effects to an electrical model significantly changes the results (Slawinski et al., 2011). We present a mathematical model for the steady-state distribution of the electric potential and of the temperature across one electrode of a large-area semiconductor device, as well as numerical solutions obtained using the finite element method.

Development of a new Schiff-base semiconducting material for thin film active device and analysis of its charge transport mechanism

Schiff-base compounds have rarely been employed in optoelectronics. Herein, we report the optical and electrical properties of a Schiff-base compound, 1,4-bis-(quinolin-6-yl iminomethyl)benzene (BQB), in detail. The electrical properties of BQB have been studied with a thin film made of it. The results of electrical conductivity and measurement of optical band gap of BQB encouraged us to examine its potential application in metal (Al)-semiconductor Schottky diode. I–V measurement of ITO/BQB/Al configuration illustrated its Schottky behavior with a moderate rectification ratio at applied bias potential of ±1.0 V. The characteristic diode parameters were obtained. The device showed a good ideality factor of 1.2 and low barrier height of 0.44 eV. Charge transport properties through the metal semiconductor junction, which is critical for device performance, were analyzed by space charge-limited current theory. In this regard, mobility–lifetime product, carrier density, density of states at Fermi level and diffusion length was estimated. The results show that this new Schiff-base compound has the potential for successful application in thin film semiconductor device.

Thin-film organic semiconductor devices: from flexibility to ultraflexibility

Flexible thin-film organic semiconductor devices have received wide attention due to favorable properties such as light-weight, flexibility, reproducible semiconductor resources, easy tuning of functional properties via molecular tailoring, and low cost large-area solution-procession. Among them, ultraflexible electronics, usually with minimum bending radius of less than 1 mm, are essential for the development of epidermal and bio-implanted electronics, wearable electronics, collapsible and portable electronics, three dimensional (3D) surface compliable electronics, and bionics. This review firstly gives a brief introduction of development from flexible to ultraflexible organic semiconductor electronics, and design of ultraflexible devices, then summarizes the recent advances in ultraflexible thin-film organic semiconductor devices, focusing on organic field effect transistors, organic light-emitting diodes, organic solar cells and organic memory devices.

Anchoring Molecules on the Surface of ZnO and Effects on Intergranular Transport Properties

Improving electrical conductivity in thin film semiconductor devices such as solar cells, thermoelectric modules, or transparent conducting devices, remains a key point for better performances. As polycrystalline films have the favor of the industry for their lower fabrication cost, the limitation of the current is most of the time attributed to charge scattering at the grain boundaries due to high energy barriers at the interface between grains.(1) This work focuses on the understanding of intergranular electrical conductivity in the view of improving thin film semiconductor performances deposited via a soft chemistry deposition routes. In this goal, ZnO:Al was chosen as a model doped semiconductor for our investigations as it is a reference material in many semiconductor applications (sensors, solar cells, transparent conducting oxides)(2). Many studies have already demonstrated the role of adsorbed species onto ZnO thin films and nanostructures surfaces to improve sensor selectivity or charge transfer in dye sensitized solar cells for instance (3). With this in mind, we have performed liquid phase adsorption studies of organic molecules onto ZnO particles through solution conductimetry and IR. A theoretical modeling of the energy level of anchoring molecules was performed in order to fit the LUMO level to the conduction band. Conjugated and thiophene based molecules with different substituents and lengths were selected. Conductivity on pressed powders was studied as a function of the applied pressure to show the effect of the grain boundaries and of the powder compaction. A conclusion was drown on the participation of these molecules and their LUMO levels in the electrical conductivity of ZnO:Al. This study allows quantitative determination adsorbates on ZnO surface and puts into perspective the investigation of better matches between LUMO and conduction band. Literature: 1. Greuter F, Blatter G. Electrical properties of grain boundaries in polycrystalline compound semiconductors. Semicond Sci Technol. 1990;5(2):111. 2. Klaus Ellmer, Andreas Klein, Bernd Rech. Transparent Conductive Zinc Oxide. Springer Series in Material Science. 2008. 3. Galoppini E. Linkers for anchoring sensitizers to semiconductor nanoparticles. Coord Chem Rev. 2004 juillet;248(13–14):1283–97.

Simplified method for the evaluation of the reverse dark current–voltage characteristic of thin film devices

An algorithm that simplifies the evaluation of the reverse dark current–voltage (J–V) characteristic of semiconductor thin film devices is presented. This algorithm, recognized with the symbols “0KRDA”, is an approximation of the SRH formalism that can be used when the dangling bond density is modeled with either the Uniform Density Model or with the Defect Pool Model. The 0KRDA is designed to replace the 0K‐Simmons–Taylor approximation (0KSTA) in reversed biased junctions operating under dark conditions. The dependence of the current density J with respect to the applied voltage V predicted with SRH formalism is well replicated by the 0KRDA. The small differences obtained in the calculated reverse dark currents can be removed by neglecting the contribution of gap states with energies closer than kT/5 to the intrinsic trap level. The transport physic controlling the shape of reverse dark J–V curves of thin film devices can be more easily visualized with the 0KRDA.

Direct determination of doping concentration and built-in voltage from extraction current transients

We have extended the analytical framework of the charge extraction by linearly increasing voltage (CELIV) theory to the case with doping, taking the effect of built-in voltage, diffusion and band-bending into account. Not taking the built-in voltage into account in dark CELIV will lead to an underestimation of the charge carrier density, while the mobility is overestimated. Furthermore, based on the analysis we propose to use CELIV in the doping-induced capacitive regime for direct determination of doping concentration and built-in voltage from extraction current transients in the time-domain of doped thin-film semiconductor devices. The analytical framework is confirmed numerically with a one-dimensional drift–diffusion model and experimentally on aged P3HT:PCBM bulk heterojunction solar cell devices. An excellent agreement between the experimental extraction current transients and the analytical prediction is found. The presented analytical treatment is not limited to sandwich-type thin-film devices, but is more general and the technique can also be extended to pn-junctions.

Electron transport across π-stacked oligophenyls system: A density functional theory approach

To understand the π–π stacking interaction between layers of graphenes or polymers, parallel oligophenyls with π-stacked units have been studied with non-equilibrium Green’s function formalism and first-principle density functional theory from two aspects. With the increasing number of π-stacked units, the π–π stacking interaction between parallel oligophenyl chains is enhanced whereas the coupling between the central molecules and the electrodes is weakened. The two effects reach a balance in the parallel oligophenyls with 5 π-stacked units. The π–π stacking interaction is weakened exponentially with the separating distance. Large separating distance impedes electrons to pass through parallel molecules. These results provide a fundamental discussion on issues related to conjugated polymers and, in particular, organic semiconductor thin film devices.

Angular dependence of light trapping in In0.3Ga0.7As/GaAs quantum-well solar cells

The dependence of light trapping effects in In0.3Ga0.7As/GaAs quantum-well solar cells on wavelength and incident angle is experimentally characterized and analyzed. Separation of active device layers from their epitaxial growth substrate enables integration of thin-film semiconductor device layers with nanostructured metal/dielectric rear contacts to increase optical absorption via coupling to both Fabry-Perot resonances and guided lateral propagation modes in the semiconductor. The roles of Fabry-Perot resonances and coupling to guided modes are analyzed via photocurrent response measurements and numerical modeling for light incident at angles of 0° (normal incidence) to 30° off normal. Light trapping enables external quantum efficiency at long wavelengths as high as 2.9% per quantum well to be achieved experimentally, substantially exceeding the ∼1% per quantum well level typically observed. Increased long wavelength quantum efficiency is shown in experimental measurements to persist with increasing angle of incidence and is explained as a consequence of the large number of guided modes available in the device structure.

Changes to the Editorial Board

It is the Editor-in-Chief's pleasure to welcome Dr. Bang-Lin Lee to the Editorial Board of the IEEE Electron Device Letters. A biography and sketch of Dr. Lee's areas of research interest are provided. His subject areas are thin-film transistors and organic semiconductor devices.

Effect of carrier gas temperature on pentacene thin film formation by organic vapor-jet printing techniques

Organic vapor jet printing (OVJP) is a powerful mask-free continuous method of fabricating organic thin film semiconductor devices. In the technique, vaporized organic compounds are carried by an inert carrier gas and jet-sprayed onto a substrate through a nozzle. During the printing process, the carrier gas temperature is controlled by an outer temperature control system. The morphology and electrical properties of organic thin films fabricated in this way can vary depending on the carrier gas temperature. This paper examines the effects of carrier gas temperature on OVJP systems. Pentacene thin films were fabricated, and their properties were compared with predicted behavior based on numerical simulations. Carrier gas temperatures exceeding 413K yielded bulk-mode pentacene thin films with high electrical mobilities. The temperature of the carrier gas was a significant factor in determining behavior and properties of the film.

Predicting organic thin-film transistor carrier type from single molecule calculations

The hole- or electron-conducting ability of functionalized acene-derivative organic molecular semiconductor thin-films can be predicted by electrochemical measurements of the frontier molecular orbital energies. We find that PM6 calculations using a Conductor-like Polarizable Continuum Model (CPCM) solvent are in complete qualitative agreement with the electrochemical results, and B3LYP/6-311+G(d,p)//B3LYP/6-31G(d) CPCM calculations are in quantitative agreement with the electrochemical results, given a suitable linear scaling function presented in this paper. These calculated electrochemical results can thus be used to predict the charge-carrier type of the resulting thin-film organic semiconductor device, enabling rapid computational screening of new materials. We also examine the role of internal reorganization energy and dielectric medium shifts to modify carrier conduction. Neither effect is large enough to explain the experimental results, demonstrating the importance of the relative orientations and packing of the molecules in the thin-film.