Semiconductor Film Thickness Research Articles

Evolution of surface and interface in soluble acene/polymer blends and its critical effects on gas diffusion dynamics in gas sensors

Organic field-effect transistor (OFET)-based gas sensors are highly valued for their sensitivity, cost-effectiveness, and operation at room temperature, making them ideal candidates for gas detection applications. For gas sensor performance, gas molecules must not only adsorb onto the organic semiconductor surface but also diffuse into the organic semiconductor-insulator interface that the conductive channel is formed. Therefore, the thickness of the active OSC layer is crucial in determining the efficiency of gas diffusion and the overall sensing response. This study analyzed the impact of semiconductor thin film thickness on gas sensing properties by adjusting the thickness of crystalline organic semiconductors. Using 6,13-bis(triisopropylsilylethynyl)pentacene (TIPS-pentacene), known for its excellent response toward NO2, surface and interface characteristics were modulated through a blend approach. With all other conditions constant, the semiconductor film thickness significantly influenced NO2 detection properties, with the highest sensitivity observed in films around 10 nm thick. A quantitative analysis using Langmuir isotherms demonstrated that reducing the OSC layer thickness from 20 nm to 10 nm could enhance the response speed by a factor of five. Furthermore, the limit of detection (LOD) for TIPS-pentacene films at this reduced thickness was found to be in the low parts per billion (ppb) range.

Performance analysis of OTFT with varying semiconductor film thickness for future flexible electronics

The goal of this study was to get a deeper understanding of the intricate impact of organic semiconductor thickness on the performance of devices, using a thorough and meticulous investigation at the microscopic level incorporating the density of defect model using using Silvaco ATLAS TCAD Simulator. The present work thoroughly investigates the relationship between the thickness of semiconductors and important performance parameters, such as hole concentration, electric potential, electric field, and Hole QFL. The comprehensive insights derived from this research not only enhance the comprehension of device physics but also provide a framework for the systematic enhancement of electronic devices. The widespread use of organic thin film transistors (OTFT) in future Flexible electronics, particularly in display and memory circuits, necessitates the incorporation of low voltage, high speed, and low cost characteristics.

A method for measuring and correcting errors in the thickness of semiconductor thin films based on reflection spectroscopy fitting technology

The thickness of semiconductor thin films stands as a pivotal parameter dictating their operational efficacy, directly shaping their applications in the realms of electronics and optoelectronics. Nevertheless, the quandary of measuring the thickness of widely utilized hundred-micron-scale semiconductor wafers continues to vex researchers. Existing measurement techniques grapple with issues of inadequate precision, poor stability, and sluggish measurement speeds. To surmount this challenge, this study innovatively devises a method employing reflective spectral fitting technology for film thickness measurement coupled with adaptive correction. This approach integrates an enhanced frequency fitting technique, endowing it with the capability for swift and stable measurements of hundred-micron-scale semiconductor thin films. Simultaneously, addressing measurement errors stemming from complex environmental factors in industrial production, the paper proposes a thickness correction method based on carrier interference principles. This correction method ensures precise thickness calibration even when the sample isn't perfectly perpendicular to incident light, significantly augmenting measurement accuracy and stability. Experimental data demonstrates that employing the proposed methodology enhances measurement accuracy by approximately 50 % and elevates measurement stability by about 80 % compared to existing methods. Particularly noteworthy is its capability to maintain high measurement precision and stability even when the sample isn't entirely perpendicular to incident light. The calibrated measurements exhibit around a 55 % reduction in error compared to uncorrected results. This study presents an efficient and accurate solution for the challenging task of measuring hundred-micron-scale semiconductor thin film thickness in industrial settings.

Detection of H2S gas sensing performance of sol gel prepared metal oxide (In2O3, SnO2, Sn doped In2O3) thin films

Gas monitoring and control of hazardous and polluting gases (CO, H2S, CH4, H2, NH3, and alcohol) are required in industrial and laboratory applications where air quality must be regulated to protect public health, the environment, and security. Transparent conducting metal oxide semiconductors (TCO) have been shown to be extremely sensitive to both reducing and oxidising gases. They are caused by a lack of oxygen, also known as anion deficit. The present emphasis of scientific and technical endeavours is to improve the selectivity, stability, and practicability of response. Wide bandgap semiconducting oxides such as SnO2, In2O3 and Sn doped In2O3 have long been employed in gas sensing. The sensitivity of the gas sensor has increased as the thickness of the metal oxide semiconductor film or particle used to produce it has decreased. In the presence of reducible gases and adsorbed oxygen on the crystal surface, the conductivity is lowered by surface potential, when SnO2 is heated to high temperature, however, conductivity increases noticeably for In2O3 and indium tin oxide films. Indium oxide and tin oxide gas sensors detected H2S gas at working temperatures of 115 °C and 120 °C, respectively. Response and recovery times for indium oxide ranged from 10 s to 26 s and 34 s to 91 s, respectively, and for tin oxide from 3 s to 37 s and 82 s to 40 s. At 100 °C working temperature, ITO sensors with 10% tin concentration had the highest H2S sensitivity.

Investigation on Atomic Bonding Structure of Solution-Processed Indium-Zinc-Oxide Semiconductors According to Doped Indium Content and Its Effects on the Transistor Performance.

The atomic composition ratio of solution-processed oxide semiconductors is crucial in controlling the electrical performance of thin-film transistors (TFTs) because the crystallinity and defects of the random network structure of oxide semiconductors change critically with respect to the atomic composition ratio. Herein, the relationship between the film properties of nitrate precursor-based indium-zinc-oxide (IZO) semiconductors and electrical performance of solution-processed IZO TFTs with respect to the In molar ratio was investigated. The thickness, morphological characteristics, crystallinity, and depth profile of the IZO semiconductor film were measured to analyze the correlation between the structural properties of IZO film and electrical performances of the IZO TFT. In addition, the stoichiometric and electrical properties of the IZO semiconductor films were analyzed using film density, atomic composition profile, and Hall effect measurements. Based on the structural and stoichiometric results for the IZO semiconductor, the doping effect of the IZO film with respect to the In molar ratio was theoretically explained. The atomic bonding structure by the In doping in solution-processed IZO semiconductor and resulting increase in free carriers are discussed through a simple bonding model and band gap formation energy.

Inkjet‐Printed Narrow‐Channel Mesoporous Oxide‐Based n‐Type TFTs and All‐Oxide CMOS Electronics

AbstractOxide semiconductors are becoming the materials of choice for modern‐day display industries. The performance of solution‐processed oxide thin film transistors (TFTs) has also improved dramatically over the last few years. However, while oxygen deficient n‐type semiconductors can demonstrate excellent electronic transport, the performance of p‐type materials has remained unsatisfactory. Consequently, only the n‐type semiconductor‐based pseudo‐complementary metal oxide semiconductor (CMOS) technology has attracted tremendous interests recently; yet, the high power dissipation remains a problem. Here, this work demonstrates all‐oxide CMOS invertors with high‐performance narrow‐channel n‐type TFTs, which can compensate for the limited carrier mobility of the p‐type transistors. These n‐type TFTs are fabricated with polymer‐templated mesoporous In2O3 and with a device geometry that allows near‐vertical current transport, thereby rendering the TFT channel lengths to be equal to the semiconductor film thickness (≈50 nm). Unprecedented On‐current (1.02 mA µm−1) and transconductance (950 µS µm−1) are achieved. The CuO‐based p‐type TFTs also show a device mobility of no less than 0.5 cm2 V−1 s−1. The printed all‐oxide CMOS inverters are found to operate at very low supply voltages and demonstrate sharp transfer curves with maximum signal gain of 31 and low power dissipation of only 4 nW, at a supply voltage of 1 V.

Modeling of thickness-dependent energy level alignment at organic and inorganic semiconductor interfaces

We identify a universality in the Fermi level change of Van der Waals interacting semiconductor interfaces. We show that the disappearing of quasi-Fermi level pinning at a certain thickness of semiconductor films for both intrinsic (undoped) and extrinsic (doped) semiconductors over a wide range of bulk systems including inorganic, organic, and even organic–inorganic hybridized semiconductors. The Fermi level (EF) position located in the energy bandgap was dominated by not only the substrate work function (Φsub) but also the thickness of semiconductor films, in which the final EF shall be located at the position reflecting the thermal equilibrium of semiconductors themselves. Such universalities originate from the charge transfer between the substrate and semiconductor films after solving one-dimensional Poisson's equation. Our calculation resolves some of the conflicting results from experimental results determined by using ultraviolet photoelectron spectroscopy (UPS) and unifies the general rule on extracting EF positions in energy bandgaps from (i) inorganic semiconductors to organic semiconductors and (ii) intrinsic (undoped) to extrinsic (doped) semiconductors. Our findings shall provide a simple analytical scaling for obtaining the “quantitative energy diagram” in the real devices, thus paving the way for a fundamental understanding of interface physics and designing functional devices.

Wrapped Channel FET (WCFET)

In this article, we examined the electrical characteristic of proposed new device structure, Wrapped Channel Field Effect Transistor (WCFET). Results of WCFET have been analyzed using Atlas 3-D simulator. WCFET shows better transfer characteristics with ON-current ION of ~10-6A and leakage current IOFF of ~10-16 A. Optimization of device characteristics has done with doping concentration (ND), gate work function (ΦG) and spacer dielectric. Impact of gate length and semiconductor film thickness variation on drain current, subthreshold slope (SS) and DIBL are also investigated. Further, effects of various gate dielectric materials such as SiO2, Si3N3, HfO2 and TiO2 are examined w.r.t. switching characteristics of WCFET. To validate of device compatibility with power supply scaling, we inspected full range variation of VDS ≈ (0.05V-to-0.7V) on transfer characteristics.

3D interconnected nanoporous Ta3N5 films for photoelectrochemical water splitting: thickness-controlled synthesis and insights into stability

Solar-driven photoelectrochemical (PEC) water splitting is a promising technology for sustainable hydrogen production, which relies on the development of efficient and stable photoanodes for water oxidation reaction. The thickness and microstructure of semiconductor films are generally crucial to their PEC properties. Herein, three-dimensional (3D) interconnected nanoporous Ta3N5 film photoanodes with controlled thickness were successfully fabricated via galvanostatic anodization and NH3 nitridation. The porous Ta3N5 nanoarchitectures (NAs) of 900 nm in thickness showed the highest PEC performance due to the optimal light-harvesting and charge separation. Compared with the hole-induced photocorrosion, the electrochemical oxidation at high anodic potentials resulted in severer performance degradation of Ta3N5. Although the surface oxide layer on deteriorated Ta3N5 photoanodes could be removed by NH3 re-treatment, the PEC performance was only partially recovered. As an alternative, anchoring a dual-layer Co(OH)x/CoOOH co-catalyst shell on the porous Ta3N5 NAs demonstrated substantially enhanced PEC performance and stability. Overall, this work provides reference to controllably fabricate 3D nanoporous Ta3N5-based photoanodes for efficient and stable PEC water splitting via optimizing the light absorption, hole extraction, charge separation and utilization.

PRISA: a user-friendly software for determining refractive index, extinction co-efficient, dispersion energy, band gap, and thickness of semiconductor and dielectric thin films

A user-friendly software PRISA has been developed to determine optical constants (refractive index and extinction co-efficient), dispersion parameters (oscillator energy and dispersion energy), absorption co-efficient, band gap and thickness of semiconductor and dielectric thin films from measured transmission spectrum, only. The thickness, refractive index, and extinction co-efficient of the films have been derived using Envelope method proposed by Swanepoel. The absorption co-efficient in the strong absorption region is calculated using the method proposed by Connel and Lewis. Subsequently, both direct and indirect bandgap of the films is estimated from the absorption co-efficient spectrum using Tauc plot. The software codes are written in Python and the graphical user interface is programmed with tkinter package of Python. It provides convenient input and output of the measured and derived data. The software has a feature to cross check the results by retrieving transmission spectrum using the values of refractive index, extinction co-efficient, and thickness obtained from Envelope method. The performance of the software is verified by analyzing numerically generated transmission spectra of a-Si:H amorphous semiconductor thin films, and experimentally measured transmission spectra of electron beam evaporated HfO2 dielectric thin films as examples. PRISA is found to be much simpler and accurate as compared to the other freely available softwares. To help researchers working on thin films, the software is made freely available at https://www.shuvendujena.tk/download.

3D versus 2D Electrolyte–Semiconductor Interfaces in Rylenediimide‐Based Electron‐Transporting Water‐Gated Organic Field‐Effect Transistors

AbstractWater‐gated organic field‐effect transistors (WGOFETs) are relevant devices for use in the fields of biosensors and biosystems. However, real applications require very stringent performance in terms of electrochemical stability and charge mobility to the organic semiconductor in contact with an aqueous environment. Here, a comparative study of two small‐molecule electron‐transporting perylenediimide semiconductors, which differ only in the N‐substituents named PDIF‐CN2 and PDI8‐CN2 is reported. The two materials present similar solid‐state arrangements but, while the PDI8‐CN2 shows a more 3D growth modality and electron mobility independent of the semiconductor layer thickness (≈10−4 cm2 V−1 s−1), the PDIF‐CN2 has an almost‐2D growth modality and the mobility increases with the semiconductor film thickness, reaching a maximum value of ≈5 × 10−3 cm2 V−1 s−1 at 30 nm. Above this thickness, the PDIF‐CN2 switches to a more 3D growth modality, and the mobility drops by one order of magnitude. XRR analysis indicates that a PDIF‐CN2 film can be modeled as a dense layered structure in which each layer is decoupled from the others due to the presence of fluorocarbon‐chains. The availability of additional pathways for charge transport from buried layers and the 2D versus 3D growth can explain the mobility dependence on the film thickness.

Analysis of Nanoporous Semiconductor Film Thickness Effect on Short Circuit Current Density of β-Carotene Dye based DSSC: Theoretical and Experimental Approach

Dye-sensitized solar cells (DSSC) made of TiO 2 have received increasing attention since O’Regan and Gratzel published their work in Nature in 1991 [1]. Some studies have been conducted to determine the effect of the TiO 2 electrode thickness on the DSSC performance. Nevertheless, the effect of the electrode thickness on the J–V characteristics, especially the short circuit current density ( J sc ), has not been adequately addressed. Therefore, in this investigation, parametric analyses were conducted to study the DSSC electrode thickness effect on J sc . Diffusion model was used to derive the equation of nanoporous semiconductor film thickness ( d ) dependence on J sc . TiO 2 paste was prepared using same method as Ref. [2]. The cells I-V curve were characterized using a computerized digital multi-meter (Keithley 2400) with a variable load. The cells short circuit current ( J sc ) data gotten from the I-V characterization were plotted as the function of the thickness of TiO 2 films. The result of the data plot was then compared and fitted with the theoretical modelling result. It is apparent that the DSSC performance largely depends on the TiO2 film thickness. The results was also showed that the diffusion model provided good approximation to describe the dependence of J sc on the film thickness of DSSC. DOI: http://dx.doi.org/10.17977/um024v4i12019p001

Achieving a broad-spectrum photovoltaic system by hybridizing a two-stage thermoelectric generator

A novel solar hybrid system (SHS) that couples a two-stage thermoelectric generator (TTEG) to a dye-sensitized solar cell (DSSC) is put forward to broadbandly capture the inlet sunlight, in which the TTEG considers Thomson effect as well as Peltier effect and Seebeck effect. The mathematical relationship between the TTEG dimensionless operating electric current and the DSSC operating electric current is determined. Theoretical calculation indicates the maximum power output density (MPOD) and maximum energy efficiency (MEE) of DSSC are, respectively, 77.82 W m−2 and 4.94%, and the MPOD and MEE of SHS are, respectively, improved by 4.33% and 64.25% in comparison with the single DSSC. Moreover, the MPOD and MEE of SHS with Thomson effect are 1.49% and 0.05% smaller than that without Thomson effect, respectively. Exhaustive parametric studies are conducted to examine the dependence of SHS performance on comprehensive designing parameters and operating conditions, including temperature difference between operating temperature and environment temperature, Schottky barrier, thickness of porous nano-TiO2 semiconductor film, thermoelectric element (TEE) number ratio of top stage to bottom stage, total number of TEE, length and cross-sectional area of semiconductor legs. The obtained results are helpful for designing and optimizing such an actual SHS.

Thickness dependent studies of hetero-junction solar cell synthesized on quartz substrate by spray pyrolysis technique

Variable thickness hetero-junction solar cells synthesized on quartz substrate by spray pyrolysis technique synthesized quartz based solar cells have been found to possess cell parameters such as open circuit voltage, saturation current density, fill factor and efficiency in the range of 191 – 449 mV, 2 × 10 -9 – 0.11 × 10 -6 A cm -2 , 15 – 20 % and 0.2 × 10 -9 – 3.35 × 10 -6 % at 206 mW/cm 2 (at air mass 5.6), respectively. Series and shunt resistance of the solar cells have been found to vary with the thickness of semiconductor films. Thick film solar cells are found to possess reasonably good cell parameters compared to thin film solar cells due to enhancement of charge concentration, mobility, grain size, variation of optical band gap, excesses atomic percentage of Ti, Cu, Te, Sn elements in TiO 2 , CuO, CdTe, SnS films and less structural defects, increment of activation energy as well as existence of mixed phase at the Schottky barrier. The optical response of hetero-junction solar cells is found to be thickness dependent. Good rectifying characteristic has been reported in the present work for both thick and thin hetero-junction solar cells. All the measurements have been performed in air without protection against oxygen gas or moisture, which shows the stability of spray pyrolyzed thin films.

Optimizing and Implementing Light Trapping in Thin-Film, Mesostructured Photoanodes.

Stable semiconductor photoelectrodes for water splitting often exhibit long absorption lengths and poor properties for the efficient separation and transport of photogenerated charges. We propose a combination of resonant and geometric light trapping for thin-film, mesostructured α-Fe2O3 photoanodes to engineer enhanced light management and increase the photocurrent density. Simulations of the electromagnetic wave propagation on accurate mesostructures were used to optimize the semiconductor film thickness and the electrode morphology for maximum light absorption. Local photocurrent densities at the semiconductor-electrolyte interface were calculated via a probabilistic charge collection model. The findings of the numerical model were translated into photoanodes by a novel fabrication process based on template stripping. The developed experimental platform is versatile and enables to fabricate electrodes with various shapes and precise control on the mesostructure. We successfully demonstrated the fabrication of α-Fe2O3 photoanodes with arrays of wedge structures in the micrometer range on a flexible substrate that benefits from resonant and geometric light trapping.

Understanding Thickness-Dependent Electrical Characteristics in Conjugated Polymer Transistors With Top-Gate Staggered Structure

Ketopyrrolopyrrole-thieno[3,2-b] thiophene (DPPT-TT) and indacenodithiophene-co-enzothiadiazole (IDT-BT) were employed for organic field-effect transistors (OFETs) to understand the effects of semiconductor channel thickness on electrical properties. The mobility was found nearly constant, whereas the threshold voltage, contact resistance, and subthreshold slope reached an optimum at a semiconductor layer thickness of about 40 nm. This value was related to the height of the source/drain electrodes. The device performance could be degraded when the thickness of semiconductor film is higher or lower than this critical value. Two different mechanisms are proposed to explain the experimental results.

Absorption enhancement in methylammonium lead iodide perovskite solar cells with embedded arrays of dielectric particles.

In the field of hybrid organic-inorganic perovskite based photovoltaics, there is a growing interest in the exploration of novel and smarter ways to improve the cells light harvesting efficiency at targeted wavelength ranges within the minimum volume possible, as well as in the development of colored and/or semitransparent devices that could pave the way both to their architectonic integration and to their use in the flowering field of tandem solar cells. The work herein presented targets these different goals by means of the theoretical optimization of the optical design of standard opaque and semitransparent perovskite solar cells. In order to do so, we focus on the effect of harmless, compatible and commercially available dielectric inclusions within the absorbing material, methylammonium lead iodide (MAPI). Following a gradual and systematic process of analysis, we are capable of identifying the appearance of collective and hybrid (both localized and extended) photonic resonances which allow to significantly improve light harvesting and thus the overall efficiency of the standard device by above 10% with respect to the reference value while keeping the semiconductor film thickness to a minimum. We believe our results will be particularly relevant in the promising field of perovskite solar cell based tandem photovoltaic devices, which has posed new challenges to the solar energy community in order to maximize the performance of semitransparent cells, but also for applications focusing on architectonic integration.

Full-band quantum simulation of electron devices with the pseudopotential method: Theory, implementation, and applications

This paper presents the theory, implementation, and application of a quantum transport modeling approach based on the nonequilibrium Green's function formalism and a full-band empirical pseudopotential Hamiltonian. We here propose to employ a hybrid real-space/plane-wave basis that results in a significant reduction of the computational complexity compared to a full plane-wave basis. To this purpose, we provide a theoretical formulation in the hybrid basis of the quantum confinement, the self-energies of the leads, and the coupling between the device and the leads. After discussing the theory and the implementation of the new simulation methodology, we report results for complete, self-consistent simulations of different electron devices, including a silicon Esaki diode, a thin-body silicon field effect transistor (FET), and a germanium tunnel FET. The simulated transistors have technologically relevant geometrical features with a semiconductor film thickness of about 4 nm and a channel length ranging from 10 to 17 nm. We believe that the newly proposed formalism may find applications also in transport models based on ab initio Hamiltonians, as those employed in density functional theory methods.

Comparative analysis of the thickness and electrical conductivity of thin chalcogenide semiconductor films

The structure and thickness of zinc and cadmium chalcogenide semiconductor films are studied by X-ray radiography. The film thickness is shown to be comparable with the half-value layer depth. The electrical conductivity of the films increases upon heating in the hydrogen atmosphere and decreases upon heating in carbon oxide. The opposite trend is observed in the ratio between the electrical conductivity and band gap of the initial and oxidized film surfaces.

The polarization approach to registration femtosecond time slots based stimulated photon echo on the exciton states

It is reported about the first experiments on the registration of a femtosecond time interval using the effect of non-Faraday rotation of the plane polarization of the stimulated photon echo. The experiment was performed at room temperature in a three-layer semiconductor film thickness of 300 nm, obtained by magnetron sputtering. The fundamental difference of this effect from the Faraday’s effect was shown. We give conclusions about the possibility of femtosecond time intervals registration at room temperature with an accuracy of 25 fs in the polarization principle of action, rather than spectral.