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In the family of amorphous semiconductors, non-oxide chalcogenide glasses (ChGs) are in the spotlight because of their widespread applications in various scientific and industrial fields. In this p...

This paper is devoted to investigating the description of the q-deformed multiple-trapping equation for charge carrier transport in amorphous semiconductors. For this, we at first modified the multi–trapping model (MTM) of charge carriers in amorphous semiconductors from time-of-flight (TOF) transient photo-current in the framework of the q-derivative formalism, and then, we have constructed, our simulated current by using a method based on the Laplace method. This method is implemented in a program proposed recently by [14] which allows us to construct a current using the Padé approximation expansion.

Surface-enhanced Raman scattering (SERS) spectroscopy on semiconductors has attracted increasing attention due to its high spectral reproducibility and unique selectively to target molecules. Recently, endeavors have been made in fabricating novel SERS-active semiconductor substrates and exploring new enhancement mechanisms to improve the sensitivity of semiconductor substrates. This Minireview explains the enhancement mechanism of the semiconductor SERS effect in a brief tutorial and summarize recent developments of novel semiconductor substrates, in particular with regard to the remarkable SERS activity of amorphous semiconductor nanomaterials. Potential applications of semiconductor SERS are also a key issue of concern. We discuss a variety of promising applications of semiconductor SERS in the fields of in situ analytical chemistry, spectroelectrochemical analysis, biological sensing, and trace detection.

Η ΔΙΑΤΡΙΒΗ ΜΟΥ ΕΣΤΙΑΖΕΤΑΙ ΣΕ ΔΥΟ ΘΕΜΑΤΑ: ΣΤΟ ΠΡΩΤΟ, Η ΑΙΧΜΗ ΑΠΟΡΡΟΦΗΣΗΣ ΤΟΥ ΑΜΟΡΦΟΥ ΥΔΡΟΓΟΝΩΜΕΝΟΥ ΠΥΡΙΤΙΟΥ ΜΕΤΡΙΕΤΑΙ ΜΕ ΜΕΓΑΛΗ ΑΚΡΙΒΕΙΑ ΣΕ ΕΥΡΕΙΑ ΠΕΡΙΟΧΗ ΘΕΡΜΟΚΡΑΣΙΩΝ: 100K-500K ΓΙΑ ΔΕΙΓΜΑΤΑ ΠΑΡΑΣΚΕΥΑΣΜΕΝΑ ΜΕ ΔΙΑΦΟΡΕΤΙΚΕΣ ΜΕΘΟΔΟΥΣ. Η ΠΕΙΡΑΜΑΤΙΚΗ ΤΕΧΝΙΚΗ ΠΟΥ ΧΡΗΣΙΜΟΠΟΙΕΙΤΑΙ ΑΦΟΡΑ ΣΕ ΜΕΤΡΗΣΕΙΣ ΔΙΑΠΕΡΑΤΟΤΗΤΑΣ ΚΑΙ ΑΝΑΚΛΑΣΤΙΚΟΤΗΤΑΣ. ΤΑ ΑΠΟΤΕΛΕΣΜΑΤΑ ΣΧΕΤΙΚΑ ΜΕ ΤΗΝ ΜΕΤΑΒΟΛΗ ΤΟΥ ΧΑΣΜΑΤΟΣ ΣΥΜΦΩΝΟΥΝ ΠΟΛΥ ΚΑΛΑ ΜΕ ΤΗΝ ΒΙΒΛΙΟΓΡΑΦΙΑ. Η ΜΕΤΑΒΟΛΗ ΤΗΣ ΠΑΡΑΜΕΤΡΟΥ ΟΥΡΜΠΑΧ ΑΠΟ ΤΟΥΣ100K ΣΤΟΥΣ 500K ΒΡΕΘΗΚΕ ΜΙΚΡΟΤΕΡΗ ΑΠΟ 5MEV. ΤΟ ΑΠΟΤΕΛΕΣΜΑ ΑΥΤΟ ΕΙΝΑΙ ΣΕ ΣΥΜΦΩΝΙΑ ΜΕ ΠΡΟΣΦΑΤΕΣ ΜΕΤΡΗΣΕΙΣ ΑΛΛΗΣ ΟΜΑΔΑΣ ΠΟΥ ΧΡΗΣΙΜΟΠΟΙΗΣΕ ΤΕΛΕΙΩΣ ΔΙΑΦΟΡΕΤΙΚΗΤΕΧΝΙΚΗ, ΕΝΩ ΑΝΤΙΤΙΘΕΤΑΙ ΣΤΟΝ ΓΕΝΙΚΑ ΠΑΡΑΔΕΚΤΟ ΣΥΣΧΕΤΙΣΜΟ ΜΕΤΑΞΥ ΤΟΥ ΧΑΣΜΑΤΟΣΚΑΙ ΤΗΣ ΠΑΡΑΜΕΤΡΟΥ ΟΥΡΜΠΑΧ ΠΟΥ ΠΡΟΤΑΘΗΚΕ ΑΠΟ ΤΟΝ CODY. ΟΣΟΝ ΑΦΟΡΑ ΤΟ ΔΕΥΤΕΡΟΘΕΜΑ, ΜΕΛΕΤΑΜΕ ΘΕΩΡΗΤΙΚΑ ΤΗΝ ΕΠΙΔΡΑΣΗ ΤΗΣ ΑΤΑΞΙΑΣ ΣΤΗΝ ΔΙΑΔΟΣΗ ΗΛΕΚΤΡΟΜΑΓΝΗΤΙΚΩΝ ΚΥΜΑΤΩΝ ΜΕΣΑ ΣΕ ΔΥΑΔΙΚΕΣ ΠΟΛΥΣΤΡΩΜΑΤΙΚΕΣ ΔΟΜΕΣ. ΘΕΩΡΟΥΜΕ ΔΟΜΕΣ ΜΕ ΑΤΑΞΙΑ ΣΤΟ ΠΑΧΟΣ ΤΩΝ ΣΤΡΩΜΑΤΩΝ. ΤΑ ΑΠΟΤΕΛΕΣΜΑΤΑ ΔΕΙΧΝΟΥΝ ΜΙΑ ΚΑΤΑ ΜΕΣΟ ΟΡΟ ΕΚΘΕΤΙΚΗ ΜΕΙΩΣΗ ΤΗΣ ΠΥΚΝΟΤΗΤΑΣ ΤΗΣ ΗΛΕΚΤΡΟΜΑΓΝΗΤΙΚΗΣ ΕΝΕΡΓΕΙΑΣ, ΚΑΘΩΣ ΠΡΟΧΩΡΑΜΕ ΑΠΟ ΤΗΝ ΕΛΕΥΘΕΡΗ ΕΠΙΦΑΝΕΙΑ ΤΗΣ ΔΟΜΗΣ, ΣΤΟ ΕΣΩΤΕΡΙΚΟ. ΤΟ ΜΗΚΟΣ ΕΝΤΟΠΙΣΜΟΥ, ΤΟ ΧΑΡΑΚΤΗΡΙΣΤΙΚΟ ΜΗΚΟΣ ΠΟΥ ΣΧΕΤΙΖΕΤΑΙ ΜΕ ΤΗΝ ΕΚΘΕΤΙΚΗ ΑΥΤΗ ΜΕΙΩΣΗ, ΥΠΟΛΟΓΙΖΕΤΑΙ ΑΡΙΘΜΗΤΙΚΑ, ΚΑΘΩΣ ΚΑΙ ΑΝΑΛΥΤΙΚΑ ΣΤΟ ΠΛΑΙΣΙΟ ΠΡΟΣΕΓΓΙΣΗΣ. (ΠΕΡΙΚΟΠΗ ΠΕΡΙΛΗΨΗΣ)

Orientador: Francisco das Chagas Marques Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin Resumo: Neste projeto de tese de mestrado apresentamos os resultados de medidas de ressonância paramagnética eletrônica (RPE), realizadas em filmes de nitreto de carbono amorfo (a-C1-xNx(:H)), depositados por duas técnicas diferentes, conhecidas como: Glow Discharge (GD) e Dual Ion Beam Assisted Deposition (DIBAD). Os principais parâmetros obtidos como: A concentração de centros paramagnéticos (CCP), fator (ou valor) g e largura de linha (.Hpp), típicos para a espectroscopia de RPE, são analisados em termos das mudanças promovidas pelo nitrogênio incorporado em nossas amostras de a-C1-x Nx(:H), ao lado de resultados já publicados por outros grupos em temas próximos ao aqui desenvolvido. Diferente da tendência apresentada por outros filmes de carbono amorfo (a-C), depositados por diferentes técnicas, onde se observa que a CCP aumenta, ~10 20 cm -3 , conforme o gap óptico diminui, ~1,0 eV, este último em função da presença de clusters grafíticos maiores, nossas amostras de a-C, principalmente aquelas depositadas por DIBAD, mostram-se claramente fora deste comportamento, como será apresentado, com uma concentração de centros paramagnéticos da ordem de 10 18 cm -3 para um gap óptico de 0 eV. Atribuímos a este comportamento, uma diferenciação entre quais tipos de centros paramagnéticos (localizados ou itinerantes), em função do tamanho do gap óptico, são os responsáveis pelo sinal de RPE observado Abstract: In this present work, measures of Electron Paramagnetic Resonance (EPR) on amorphous carbon nitride films (a-C1-x Nx(:H)), deposited by two different techniques known as Glow Discharge (GD) and Dual Ion Beam Assisted Deposition (DIBAD), will be presenting. The parameters like Paramagnetic Centers Concentration (PCC), g value and linewidth, ordinary within the EPR spectroscopy, are analyzed as the nitrogen is incorporated promoting some structural changes into the our a-C1-x Nx(:H) samples, and besides to results reporting by others groups working in subjects close to that here developed. Differently of the behavior showed by others amorphous carbon films (a-C) deposited by several different ways, where the paramagnetic centers get rise, ~10 20cm -3 , as the optical gap drops, ~ 1.0 eV, due the presence of the largest clusters of graphite sheets, our a-C samples, mainly the ones deposited by DIBAD, presenting in a straight disagree according to this trend, as it will be later explored, with a PCC around 10 18 cm -3 and a 0 eV for the optical gap. We have attributed to this behavior, a transition between localized and itinerant centers, respectably for large and small gap, whose are the responsible for the EPR signal observed Mestrado Física da Matéria Condensada Mestre em Física

Orientador: Francisco das Chagas Marques Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin Resumo: Nesta tese estudamos a influência da incorporação de nitrogênio nas propriedades termomecânicas e estruturais em matrizes de carbono amorfo hidrogenado (a-C:H) e não hidrogenado (a-C). Duas técnicas de deposição foram utilizadas para o crescimento dos filmes. Os filmes hidrogenados foram preparados utilizando um sistema de glow discharge e as não hidrogenadas foram preparadas por IBAD. Um estudo preliminar foi feito em função do bias e a pressão do metano CH4, com o objetivo de escolher duas condições para a incorporação de nitrogênio. Deste primeiro estudo foi observado um aumento do coeficiente de dilatação térnica dos filmes de a-C:H com o aumento das ligações sp2. A partir desta série, uma segunda série de amostras com matriz tipo diamond-like e graphite-like de a-C:H foram estudadas, nas quais observamos que independente da matriz, a incorporação de nitrogênio produz um aumento no coeficiente de dilatação térnica (CTE) de até 9x10-6 C-1 para cerca de 6% de nitrogênio, próximo do valor do CTE do grafite (8x10-6C-1). A influência do nitrogênio no carbono amorfo aumenta a geração das hibridizações sp e sp2, o qual facilita a fornação de clusters grafíticos dentro dos filmes de a-C:H:Nx. O empilhamento dos clusters e a influência destes no CTE dos filmes são amplamente discutidos, para o qual técnicas espectroscópicas como Raman, infravermelho e perda de energia dos elétrons (EELS) são estudadas nesta tese. Por outro lado, para ter uma visão mais clara da influência do N, amostras com matrizes não hidrogenadas de a-C foram preparadas pela técnica de IBAD. Com nesta técnica temos filmes de a-C:Nx com altas concentrações de nitrogênio (até ~30%). Foi observado que mesmo com altas concentrações de N, o CTE dos filmes de a-C:Nx não consegue atingir valores acima de 5xl0-6 C-1. Este fato, faz pensar que o hidrogênio cumpre um papel muito importante no ernpilhamento dos clusters grafíticos. A partir das medidas feitas pela técnica de TIB (o qual foi desenvolvido em nosso laboratório e utilizado para medir o stress, CTE e módulo biaxial dos filmes) e a Nanoindentação obtivemos separadamente o módulo de Young (E) e a razão de Poisson (v), nas três séries de amostras estudadas. Os resultados são discutidos como uma função dos tipos de hibridizações dos filmes de a-C:H, a-C:H:Nx e a-C:Nx Abstract: In this work, we studied thenno mechanical and structural properties of hydrogenated amorphous carbon (a-C: H), hydrogenated carbon nitride (a-C:H:Nx) and carbon nitride (a-C:Nx) thin films. Two techniques were used to prepare the samples: glow discharge for depositing hydrogenated amorphous carbon (a-C:H) and carbon nitride (a-C:H:Nx) and ion beam assisting deposition (IBAD) for unhydrogenated amorphous carbon nitride (a-C:Nx) films. The curvature of the film/substrate composites was measured using the thermally induced bending (TIB) technique in order to determine the stress of the films. By varying the temperature and using films deposited in several different substrates one was able to obtain the coefficient of thermal expansion (CTE) and the biaxial modulus (E/(l-v)) of the films. Complementarily to this technique, we perfonned nanohardness measurements, which also allows to obtaining the elastic constant (E/(1-v2)) as well. Using both techniques, TIB and nanohardness, we determined, for the first time, separately the Young's modulus (E) and the Poisson's ratio (v) of a-C:H, a-C:H:Nx and a-C:Nx. These thermomechanical properties were investigated as a function of sp2-bond, or graphite's cluster, concentrations, using the following techniques: EELS, infrared spectroscopy, visible and ultraviolet Raman spectroscopy. The influence of the incorporation of nitrogen in the hydrogenated and unhydrogenated matrixes is discussed. We observed that the CTE of a-C:H depends strongly on the concentration of Sp2 sites approaching the value for graphite as the concentration tends to 100 %. The nitrogen incorporation increases the cluster formation in matrixes, inducing a substantial increase of the CTE of the fi1ms. On the other hand, in the matrix free of hydrogen it was observed that the CTE is not strongly influenced by the nitrogen concentration. These observations indicate that hydrogen plays an important role on the value of the CTE in amorphous carbon nitrogen films Doutorado Física da Matéria Condensada Doutor em Ciências

In this paper, we revisit the state-of-the-art amorphous semiconductor InGaZnO4 (a-IGZO), and demonstrate the application of a-IGZO thin film as an electron transporting layer (ETL) for efficient perovskite solar cells (PSCs) by a solution process. The champion device using such a-IGZO ETL has achieved an efficiency of 17.4%. The outstanding performance is attributed to the excellent properties of a-IGZO oxide thin films, including high carrier concentration, high electron mobility and high transparency. Our results definitely revel that amorphous semiconductors (e.g. a-IGZO) offer some unique features and have a great potential for large-area perovskite solar cells.

The photoelectrochemical (PEC) properties of sputtered aluminum doped hydrogenated amorphous silicon carbide thin films grown on p-type crystalline silicon substrates were investigated in 1 M H 2 S O 4 solution under chopped light illumination. Optical and structural properties of the top absorber layer were systematically assessed after post-deposition isochronical annealing treatments. Samples exhibited a noticeable improvement of the opto-electronic properties after thermal treatments. In addition, an abrupt enhancement of the photocurrent was observed reaching a saturation value of 17 mA cm−2 at −1.75 V vs. Ag/AgCl (3.5 M KCl). In this research we propose that this enhancement effect is associated to a charge transfer kinetic mechanism influenced by surface states and the p-type substrate. The latter most likely due to the space charge region extending beyond the absorber layer reaching the substrate. Current density-potential and electrochemical impedance spectroscopy measurements in dark revealed a reduction of the S i O 2 native layer at cathodic potentials higher than −1 V vs. Ag/AgCl (3.5 M KCl), which contributes to the high charge transfer kinetic of the system. We believe that these results will contribute to understand the substrate influence in the PEC performance of top absorber layers in multilayer structures for solar water splitting.

Chalcogenide glasses have evidently become the most popular materials in the field of electronics, communication, medicine, military, chemical sensing, and detection. Consequently, it is essential to study the characteristic features of these materials for their better use in future applications. Chalcogenide glasses are one of the most studied amorphous semiconductors. To date, various types of glasses are fabricated and their properties have been studied by many researchers. The present paper focuses on the various processes for the synthesis of chalcogenide glasses, their optical properties, electrical properties, and diverse applications. In the end, we have also summarized the present and future challenges in this field.

A new method for measuring the free carriers lifetime () and the density of localised states (DOS) in amorphous semiconductors is described. The method is based on the analysis of transient photoco...

Thin films of Se based chalcogenide glassy alloys Ge10-xSe60Te30Inx (x = 0, 2, 4, 6) were deposited on to glass substrate by vacuum evaporation technique. Glassy nature of the film has been confirm...

The authors wish to thank fruitful discussions with Prof Jeffery Gray, Prof Peter Bermel, and Prof Mark Lundstrom at Purdue University. This paper is based upon work supported in part under the US-India Partnership to Advance Clean Energy-Research (PACE-R) for the Solar Energy Research Institute for India and the United States (SERIIUS), funded jointly by the U.S. Department of Energy (Office of Science, Office of Basic Energy Sciences, and Energy Efficiency and Renewable Energy, Solar Energy Technology Program, under subcontract DE-AC36-08GO28308 to the National Renewable Energy Laboratory, Golden, Colorado) and the Government of India, through the Department of Science and Technology under subcontract IUSSTF/JCERDC-SERIIUS/2012 dated November 22, 2012.

The thin films of As40Se60 and As40Se50Ge10 were prepared on glass substrates by thermal evaporation method with thickness 1000 nm. The prepared films were amorphous in nature which was confirmed t...

A link between the morphological characteristics and the electric properties of amorphous layers is established by means of atomic, conductive, electrostatic force and thermal scanning microscopy. Using amorphous Ta 2 O 5 (a-Ta 2 O 5 ) semiconductive layer, it is found that surface profile gradients (morphological gradient), are highly correlated to both the electron energy gradient of trapped electrons in interactive Coulombic sites and the thermal gradient along conductive paths and thus thermal and electric properties are correlated with surface morphology at the nanoscale. Furthermore, morphological and electron energy gradients along opposite conductive paths of electrons intrinsically impose a current stability anisotropy. For either long conductive paths ( L > 1 μm) or along symmetric nanodomains, current stability for both positive and negative currents i is demonstrated. On the contrary, for short conductive paths along non-symmetric nanodomains, the set of independent variables ( L, i ) is spanned by two current stability/intability loci. One locus specifies a stable state for negative currents, while the other locus also describes a stable state for positive currents.

A detailed study of the electronic properties of thin (>20 nm) anodic TiO2 potentiostatically grown on titanium in two different solutions is presented. The results show that the nature of the anodizing solution affects the electronic properties of the anodic film and, more specifically, the density of electronic states (DOS) distribution. Different DOS were derived from the experimental data analyzed according to the theory of amorphous semiconductor (a-SC) Schottky barrier. It is shown that the usual non-linear and frequency dependent Mott-Schottky plots are in agreement with expected theoretical behavior of a-SC Schottky barrier.

We explore some aspects of the optimization of amorphous semiconductors as well as low- and high-dielectric-constant (low-/high-k) materials viewed purely from the perspective of percolation and topological constraint theories. We specifically illustrate how percolation, constraint theory, and mean network coordination, 〈r〉, play underlying roles in determining the electrical and mechanical properties of amorphous semiconducting and dielectric materials as well as interfaces that are important for modern micro-/nanoelectronic devices.

We present an ab initio computational study of triplet exciton diffusion in four phosphorescent emitters commonly used in organic light-emitting diodes (OLEDs). By kinetic Monte Carlo simulations, triplet diffusion lengths are obtained for these emitters in neat films and as a guest in two different hosts. The triplet transfer rates governing the diffusion contain a transfer integral factor that includes both Förster and Dexter contributions and a Franck-Condon weighted density of vibrational states that includes the coupling to all intramolecular vibrations in a fully quantum mechanical way. We find that at guest concentrations around 10 mol% the Förster transfer contribution is most important. At larger concentrations of about 30–40 mol% the Dexter contribution becomes dominant. We show that obtaining the triplet transfer rates by the semiclassical Marcus theory yields diffusion lengths that are too short and that using a simple cubic lattice in combination with the often used Miller-Abrahams rates instead of using a real morphology with the ab initio rates leads to an underestimation of the diffusion lengths due to transfers down in energy that are too slow.

An ordered semiconductor has a crystalline lattice in which charge carriers move around by the Gaussian process of normal diffusion. The mean square displacement (MSD) of these charge carriers is proportional to time. On the contrary, the movement of carriers in a material with a non-crystalline structure such as amorphous semiconductors is considered to be non-Gaussian in nature. In this case, MSD is proportional to some power of time. Diffusion in this type of transport mechanism is classified as anomalous diffusion. The usual drift-diffusion equation (DDE) cannot adequately describe this process because it has non-Gaussian and dispersive transport mechanisms. Fractional calculus has been used to generalize the standard DDE to a time fractional equation in order to include the hereditary effects of the carrier transport. For power devices, the distribution and conduction of heat is the primary criteria considered when making a device. Therefore, an equation for heat conduction is added to the model for inclusion of variable temperature. The coupled system is solved using a Numerical scheme wherein Finite Difference method has been employed to discretize the Riemann - Liouville time derivative of order α and the space variable. The effects of different physical factors such as light intensity, heat and applied electric field are discussed with the help of graphical illustrations.

The article discusses how bonding concepts have allowed the development of amorphous semiconductors, in particular the 8−N rule of bonding, the doping mechanism in a-Si:H, the weak effect of disorder on s states in amorphous oxide semiconductors, the strong effect of disorder on p states in amorphous carbon, and the effect of the change from resonant bonding to simple molecular covalent bonding in chalcogenide phase change materials.

A physics-based model for electron and hole mobility in an amorphous semiconductor is developed to estimate the mobility limits of an amorphous semiconductor. The model involves band tail state trapping of a diffusive (Brownian motion) mobility and accounts for both drift- and diffusion-induced transport, as normally encountered in the operation of a thin-film transistor. Employing this model leads to a predicted maximum mobility of ~70 cm 2 V -1 s -1 (~10 cm 2 V -1 s -1 ) for electrons (holes).

It is known that impact ionizations occur in amorphous materials such as Se and SiO2 under exposures to high dc fields, pulsed-laser exposures, and high-energy radiations. These processes have been explored from different perspectives, including avalanche carrier multiplications, laser fabrications, and x-ray detections. The present work tries to clarify the relations between such phenomena. Characteristic differences of the ionizations in crystalline and non-crystalline forms are also considered. Among recent topics, specifically interesting is the laser excitation that can produce intense light pulses with the duration between femto- and nano-second ranges, which cover collision times governing impact ionization and electron-lattice interactions. For SiO2, we can connect the collision times with related mean free paths estimated from dc studies. By contrast, optical studies are still insufficient for chalcogenides, except for amorphous Ge2Sb2Te5 films.

In amorphous semiconductors and insulators, the using conductivity formulas are semi-empirical and have no satisfying physical explanations. A conductivity equation has been derived by Debye for the response of ideal materials which is rarely observed in practice, but a general conductivity equation which includes the previous empirical equations via a correct choice of arbitrary parameters and moreover totally theoretical derivation had to be generated. Hence, to determine the motion of electrons in the amorphous environment, we defined the equation of motion including viscous forces as a function of coordinates, their derivatives and time variables. We developed a fractional form of this equation over these three variables and finally obtained the most generalized equation of motion, which counts the overall interactions by a fractional form as a variation of two variable. The improved formula, called the stretched Havriliak–Negami equation, has the same form and behavior as the semi-empirical equation and reducible to the Cole–Cole and Cole–Davidson-type of conductivity.

Over a decade, transparent amorphous oxide semiconductors (TAOSs) have well demonstrated the advantages of electronic devices based on transparent amorphous semiconductors (TASs). However, it has been rather difficult to obtain p-type TAS to date. Therefore, it would be attractive if the p-type TAS is realized. In this paper, we propose a material design concept of p-type TAS and an example, a-Cu-Sn- I. The proposed solution-processable p-type a-CuSnI thin films exhibits a large Hall mobility of 9 cm2V−1s−l, and a promising energy-level for conventional optoelectronics including OLEDs and solar cells.

© 2018 American Physical Society. Based on a rational classification of defects in amorphous materials, we propose a simplified model to describe intrinsic defects and hydrogen impurities in amorphous indium gallium zinc oxide (a-IGZO). The proposed approach consists of organizing defects into two categories: point defects, generating structural anomalies such as metal - metal or oxygen - oxygen bonds, and defects emerging from changes in the material stoichiometry, such as vacancies and interstitial atoms. Based on first-principles simulations, it is argued that the defects originating from the second group always act as perfect donors or perfect acceptors. This classification simplifies and rationalizes the nature of defects in amorphous phases. In a-IGZO, the most important point defects are metal - metal bonds (or small metal clusters) and peroxides (O-O single bonds). Electrons are captured by metal - metal bonds and released by the formation of peroxides. The presence of hydrogen can lead to two additional types of defects: metal-hydrogen defects, acting as acceptors, and oxygen-hydrogen defects, acting as donors. The impact of these defects is linked to different instabilities observed in a-IGZO. Specifically, the diffusion of hydrogen and oxygen is connected to positive- and negative-bias stresses, while negative-bias illumination stress originates from the formation of peroxides. ispartof: PHYSICAL REVIEW APPLIED vol:9 issue:5 status: published

Near-room-temperature electronic transport of annealing induced semiconducting crystallites embedded within its amorphous counterpart is treated within the effective-medium approach. As such, the mixtures transport coefficients become smooth functions of those of its two components. Carrier mobilities in the crystallites are assumed much larger than those of the amorphous phase. Nonetheless, crystallites act as macroscopic traps when their carriers energies lie below those in the amorphous phase. Then the mixtures dc conductivity falls below that of the amorphous phase at low enough carrier concentrations. However, with increasing carrier concentration the shifting chemical potential diminishes this trapping effect enabling crystallites larger mobilities to drive the mixtures electrical conductivity above that of the amorphous phase. Meanwhile the Seebeck coefficient remains insensitive to the annealing-induced introduction and growth of embedded crystallites. These features are qualitatively similar to those reported for an amorphous organic polymer with annealing-induced embedded crystallites., Comment: 14 pages including 7 figures

We present a microscopic interpretation for the appearance and behaviour of subgap states in stoichiometric and oxygen-deficient, amorphous In–Zn–O (a-IZO) and In–Sn–O (a-ITO) derived from a density functional theory analysis using a self-interaction-correction scheme. Our findings concerning the defect structures and the resulting deep levels are qualitatively similar to earlier results on a-IGZO and a-ZTO and in agreement with recent experimental results. Based on our extensive set of DFT results for In-, Sn-, Zn- based oxides we develop a general concept of the subgap states which is applicable to these systems. Electronic defect levels in the lower half of the band gap are created by undercoordinated oxygen atoms while local oxygen deficiencies cause defect levels in the upper part of the band gap.

A physics-based model for transport in an amorphous semiconductor is developed to estimate the mobility limits of oxide TFTs. The model involves band tail state trapping of a diffusive mobility. Simulation reveals a strong dependence on the Urbach energy. This consideration makes it difficult to realize a highperformance p-type oxide.

In this work, both experiments and simulations were employed to study Cu ion's role in light soaking effect of CdTe solar cells. Both experiment and simulation show Cu ion's migration under forward-bias could cause device performance enhancement. As consistent results are achieved from both aspects, we conclude that migration of Cu ions or other charged species could be the cause of device performance enhancement observed in light soaking experiments.

© 2016 The Author(s).A link between the morphological characteristics and the electric properties of amorphous layers is established by means of atomic, conductive, electrostatic force and thermal scanning microscopy. Using amorphous Ta2O5 (a-Ta2O5) semiconductive layer, it is found that surface profile gradients (morphological gradient), are highly correlated to both the electron energy gradient of trapped electrons in interactive Coulombic sites and the thermal gradient along conductive paths and thus thermal and electric properties are correlated with surface morphology at the nanoscale.Furthermore, morphological and electron energy gradients along opposite conductive paths of electrons intrinsically impose a current stability anisotropy. For either long conductive paths (L .>. 1. μm) or along symmetric nanodomains, current stability for both positive and negative currents . i is demonstrated. On the contrary, for short conductive paths along non-symmetric nanodomains, the set of independent variables (L, i) is spanned by two current stability/intability loci. One locus specifies a stable state for negative currents, while the other locus also describes a stable state for positive currents.

Orientador: Leandro Russovski Tessler Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Física Gleb Wataghin Resumo: Este trabalho fornece caracterização ótica e estrutural de filmes finos compostos por nitreto de silício amorfo hidrogenado dopado com térbio (a-SiNx:H) ¿ crescidos por deposição química a vapor assistida por plasma gerado através de ressonância ciclotrônica de elétrons (ECR PECVD) e por pulverização catódica reativa em radiofrequência (reactive RF-Sputtering) ¿ com o propósito de avançar a investigação em fabricação de novos materiais e dos mecanismos da emissão de luz de íons de Tb quando diluídos em materiais baseados em silício. A fotoluminescência (PL) atribuída aos filmes de a-SiNx:H foi investigada em termos das condições de deposição e correlacionadas com suas propriedades estruturais e de recozimento pós-deposição. Entre as propriedades caracterizadas estão: estequiometria, taxa de deposição, índice de refração, coeficiente de extinção, bandgap ótico E04, concentração de térbio e vizinhança química presente ao redor de íons Tb3+. Concentrações de Tb da ordem de 1.8 at.% ou 1.4×?10?^21 at/cm^3 foram obtidas em amostras crescidas por Sputtering enquanto que concentrações de 14.0 at.%, ou da ordem ?10?^22 at/cm^3, puderam ser obtidas em amostras crescidas por ECR PECVD. Em Sputtering, a incorporação de Tb varia linearmente com a área recoberta por pastilhas de Tb4O7 em pó, enquanto que em PECVD, a incorporação de Tb é inversamente proporcional e pode ser ajustada sensivelmente pelo fluxo de gás SiH4. Forte emissão de luz, atribuída às transições eletrônicas em Tb3+ (PL do Tb), foi obtida em filmes não-recozidos que possuíam bandgap estequiométrico (E04 = 4.7 ± 0.4 eV and x = 1.5 ± 0.2). Espectros de PL do Tb não mostraram mudanças significativas no formato e na posição dos picos de emissão devido a alterações na temperatura de recozimento, nas condições de deposição ou entre amostras crescidas por diferentes técnicas de deposição. Entretanto, esses parâmetros influenciaram fortemente a intensidade da PL do Tb. Estudos da estrutura fina de absorção de raios-X (XAFS) em filmes crescidos por sputtering mostraram a estabilidade da vizinhança química ao redor dos íons Tb3+ mesmo em altas temperaturas (1100ºC). Investigações por sonda atômica tomográfica (APT) não encontraram formação de nanoclusters envolvendo ou não Tb, mesmo após recozimentos em altas temperaturas. Isso sugere que a excitação de Tb3+ deve ocorrer através da própria matriz hospedeira amorfa e não por mudanças no campo cristalino e, portanto, na força de oscilador das transições eletrônicas do Tb3+. Caracterização da densidade de ligações Si-H por espectroscopia infravermelha a transformada de Fourier (FTIR) em filmes recozidos em diferentes temperaturas foi relacionada com a intensidade da PL do Tb. Ela mostra que um decréscimo na densidade das ligações Si-H, que está relacionada a um aumento na concentração de ligações pendentes de Si (Si-dbs), resulta em filmes com maior intensidade na PL do Tb. Portanto, isso sugere que a excitação de Tb3+ parece acontecer através de transições envolvendo Si-dbs e estados estendidos, o que é consistente com o modelo de excitação Auger por defeitos (DRAE) Abstract: This work offers optical and structural characterization of terbium (Tb) doped hydrogenated amorphous silicon nitrides thin films (a-SiNx:H) grown by electron cyclotron resonance plasma-enhanced chemical vapor deposition (ECR PECVD) and reactive RF-Sputtering with the purpose of advancing the investigation in fabrication of novel materials and the mechanisms of light emission of Tb ions when embedded in Si-based materials. Photoluminescence (PL) of a-SiNx:H films were investigated and correlated with the deposition conditions, structural properties, and post-deposition thermal treatments (isochronal annealing under flow of N2). Among the characterized properties are: film stoichiometry, deposition rate, refractive index, extinction coefficient, optical bandgap, terbium concentration, and the chemical neighborhood around Tb ions. Tb concentrations of about 1.8 at.% or 1.4×?10?^21 at/cm^3 have been achieved in Sputtering system while concentrations of 14.0 at.%, or about ?10?^22 at/cm^3, could be achieved in ECR PECVD samples. In Sputtering, Tb incorporation varies linearly with the covered area of the Si target by Tb4O7 powder pellets, while in PECVD, Tb incorporation is inversely proportional to and can be sensitively adjusted through SiH4 gas flow. Bright PL attributed to Tb3+ electronic transitions (Tb PL) were obtained in as-deposited films with stoichiometric bandgaps (E04 = 4.7 ± 0.4 eV and x = 1.5 ± 0.2). The Tb PL spectra did not show any significant change in shape and in PL peak positions due to alterations in annealing temperature, deposition conditions or due to the used deposition method. However, these parameters strongly affected Tb PL intensity. Studies of X-ray absorption fine structure (XAFS) in Sputtering grown films show the stability of the chemical neighborhood around Tb3+ under annealing conditions even after thermal treatments at temperatures as high as 1100ºC. Atom probe tomography (APT) investigation also found no formation of nanoclusters of any type (involving Tb ions or not) after high temperature annealing treatments suggesting that Tb3+ excitation should come from the amorphous host matrix itself and not by changes in crystal field and thus in oscillator strength of Tb3+ electronic transitions. Fourier transform infrared spectroscopy (FTIR) characterization of Si-H bond density in films treated atin different annealing temperatures were crossed correlated with Tb PL intensity. It shows that a decrease in Si-H bond density, related to increase in Si dangling bonds (Si-dbs) concentration, results in greater Tb PL intensity. Thus, it suggests that excitation of Tb3+ happens through transitions involving silicon dangling bonds and extended states, consistent with the defect related Auger excitation model (DRAE) Doutorado Física Doutor em Ciências CNPQ 142174/2012-2 CAPES 010308/2014-08

Thickness and compositional dependence of optical properties of Pb9Se71Ge20−xSnx (8 ≤ x ≤ 12) glass has been studied. Various optical constants such as refractive index, extinction coefficient and optical band gap have been determined by analyzing optical transmittance data in the wavelength range of 200–3,500 nm. Density of localized states and disorder plays a crucial role in deciding the optical properties of amorphous semiconductors. Refractive index and extinction coefficient increase as Sn content increase in material. With the rise in thickness, there may be increase in order of short range order of the film and continuous random network simultaneously, result in reduced band gap. The isoelectronic substitutions of Ge by Sn in the glassy system also contribute to reduction in optical band gap of the material.

The structure of chalcogenide vitreous semiconductors (CVSs) As33.3Se33.3S33.4 and As33.3Se33.3Te33.4 and the influence on them of samarium additives is studied using the technique of X-ray diffraction. The observed peculiarities of the diffraction picture are explained by the Elliott void-cluster model. The structural parameters of CVS materials As33.3Se33.3S33.4 and As33.3Se33.3Te33.4 with and without admixtures of samarium are determined.

The effect of the preillumination on the dark and the photo-conductivity of the TlGaSe2 layered semiconductor is investigated within the temperature range of 80–300 K. After the illumination predominantly at high temperatures, a substantial decrease in both dark and photo-conductivities was observed. Observed phenomena resemble the Staebler–Wronski effect, which is typical for the amorphous semiconductors. The main contribution of this work is to show that the TlGaSe2 single crystals with well apparent crystalline structure can demonstrate certain characteristics peculiar to amorphous semiconductors.

Al-induced crystallization (AIC) of amorphous SixGe1–x (a-SixGe1–x) alloys with compositions over the entire range of the isomorphous Si–Ge system has been investigated. The crystallization progress was monitored by dedicated in situ x-ray diffraction analysis while gradually increasing the annealing temperature. Auger sputter-depth profiling was applied to investigate the occurrence of Al-induced layer exchange of the Al and a-SixGe1–x sublayers after complete crystallization. A-SixGe1–x alloys with x 0.41 show largely different AIC behaviors with respect to crystallization rate and possible layer exchange of the Al and a-SixGe1–x sublayers upon crystallization. A thermodynamic model for AIC of a-SixGe1–x alloys is presented, which well explains these experimental observations and thereby demonstrates the dominant role of interface thermodynamics in the AIC process of amorphous semiconductors. The model can be used to predict the AIC behaviors of a-SixGe1–x alloys over the entire composition range at specified annealing temperatures.

The influence of the transparent conducting oxide (TCO) topography was studied on the performance of a silicon oxide intermediate reflector layer (IRL) in a-Si/μc-Si tandem cells, both experimentally and by 3-D optical simulations. Therefore, cells with varying IRL thickness were deposited on three different types of TCOs. Clear differences were observed regarding the performance of the IRL as well as its ideal thickness, both experimentally and in the simulations. Optical modeling suggests that a small autocorrelation length is essential for a good performance. Design rules for both the TCO topography and the IRL thickness can be derived from this interplay.

The present letter extends the prior findings on self-induced heating of solid state field emission devices. It was found that a vacuum diode (base pressure $\sim10^{-9}$ Torr), that makes use of graphite-rich polycrystalline diamond as cathode material, can switch from diode regime to resistor regime, to glow discharge plasma regime without any external perturbation, i.e. all transitions are self-induced. Combined results of in situ field emission microscopy and ex situ electron microscopy and Raman spectroscopy suggested that the nanodiamond cathode of the diode heated to about 3000 K which caused self-induced material evaporation, ionization and eventually micro-plasma formation. Our results confirm that field emission, commonly called cold emission, is a very complex phenomenon that can cause severe thermal load. Thermal load and material runaway could be the major factors causing vacuum diode deterioration, i.e. progressive increase in turn-on field, decrease in field enhancement factor, and eventual failure., Comment: 6 pages, 5 figures

The hole current in amorphous films of N,N′-di(1-naphthyl)-N,N′-diphenyl-(1,1′-biphenyl)-4,4′-diamine (α-NPD) strongly depends on substrate temperature during vacuum deposition (Tsub) and is the highest at a Tsub value of around 275 K. However, the reason for this enhancement of hole current at this Tsub is not clearly understood. In this study, we performed thermally stimulated current (TSC) measurements, which is a versatile method used to obtain information about carrier traps, on α-NPD films. The TSC results revealed that hole traps were uniformly distributed throughout the films and that hole traps were the shallowest for films fabricated at a Tsub value of around 275 K. Thus, the shallowest hole traps at this Tsub are believed to be one reason for the highest hole current for α-NPD films. This is the demonstration of how Tsub affects carrier traps, contributing to a better understanding of the underlying physics in organic amorphous films.The hole current in amorphous films of N,N′-di(1-naphthyl)-N,N′-diphenyl-(1,1′-biphenyl)-4,4′-diamine (α-NPD) strongly depends on substrate temperature during vacuum deposition (Tsub) and is the highest at a Tsub value of around 275 K. However, the reason for this enhancement of hole current at this Tsub is not clearly understood. In this study, we performed thermally stimulated current (TSC) measurements, which is a versatile method used to obtain information about carrier traps, on α-NPD films. The TSC results revealed that hole traps were uniformly distributed throughout the films and that hole traps were the shallowest for films fabricated at a Tsub value of around 275 K. Thus, the shallowest hole traps at this Tsub are believed to be one reason for the highest hole current for α-NPD films. This is the demonstration of how Tsub affects carrier traps, contributing to a better understanding of the underlying physics in organic amorphous films.

We develop a band fluctuations model which describes the absorption coefficient in the fundamental absorption region for direct and indirect electronic transitions in disordered semiconductor materials. The model accurately describes both the Urbach tail and absorption edge regions observed in such materials near the mobility edge in a single equation with only three fitting parameters. An asymptotic analysis leads to the universally observed exponential tail below the bandgap energy and to the absorption edge model at zero Kelvin above it, for either direct or indirect electronic transitions. The latter feature allows the discrimination between the absorption edge and absorption tails, thus yielding more accurate bandgap values when fitting optical absorption data. We examine the general character of the model using a dimensionless joint density of states formalism with a quantitative analysis of a large amount of optical absorption data. Both heavily doped p type GaAs and nano crystalline Ga 1 x Mn x N, as examples for direct bandgap materials, as well as amorphous Si H x , SiC H x and SiN x , are modeled successfully with this approach. We contrast our model with previously reported empirical models, showing in our case a suitable absorption coefficient shape capable of describing various distinct materials while also maintaining the universality of the exponential absorption tail and absorption edge

Програма моделювання аморфних напівпровідникових приладів (ASDMP), розроблена професором P. Chatterjee і широко підтверджена експериментальними результатами, є детальною програмою, де рівняння Пуассона і рівняння безперервності електронів і дірок розв’язуються одночасно без жодного спрощення. Вона враховує кінетику захоплення і рекомбінації через стани у забороненій зоні. У цій програмі щільність станів моделюється за допомогою стандартної моделі (SM). Така модель описує дефекти двома гаусіанами поблизу центра забороненої зони та двома хвостами, експоненціально розподіленими за енергією, і припускає, що щільність станів однорідна у просторі. Defect pool model (DPM) є вдосконаленою моделлю формування дефектів у гідрогенізованому аморфному кремнії на основі ідеї, що сітка невпорядкованих атомів a-Si:H має великий спектр локальних середовищ, в яких може бути сформований дефект. Таким чином, ці дефекти вибирають місця, де їх енергія утворення мінімальна, і це стає можливим з рухом водню.Використовуючи підхід до опису дефектів, ми розробили чисельну DPM і застосували її у ASDMP при термодинамічній рівновазі. Ми використали ASDMP, щоб отримати щільність станів у кожній позиції сонячного елемента на основі стандартної структури p-i-n. Показано вплив допінгу на концентрацію дефектів та досліджено вплив положення рівня Фермі на розподіл щільності станів. Ми визнали використання ASDMP ключовим результатом того, що негативно заряджені дефекти в матеріалі n-типу розташовані нижче за енергією, ніж позитивно заряджені дефекти в матеріалі p-типу, навіть якщо енергія кореляції позитивна.Ми розрахували електричне поле і діаграми смуг при термодинамічній рівновазі як з DPM, так і з SM. Ми показали, що електричне поле, отримане від DPM, сильніше поблизу інтерфейсів і нижче в об'ємі, де діаграми смуг більш плоскі. Така поведінка електричного поля, розрахованого за даною моделлю, підкреслюється зі збільшенням нахилу хвостів валентної зони. Amorphous Semiconductor Device Modeling Program (ASDMP), developed by Professor P. Chatterjee and widely validated by experimental results, is a detailed program where the Poisson’s equation and the electron and hole continuity equations are simultaneously solved without any simplifying assumption. It takes into account the trapping and recombination kinetic through the gap states. In this program, the density of states is modeled using the standard model (SM). Such a model describes the defects by two Gaussians near the center of the gap and two tails exponentially distributed in energy, and assumes the density of states homogenous in space. The defect pool model (DPM) is an improved model for defect formation in hydrogenated amorphous silicon based on the idea that the a-Si:H network has a large spectrum of local environments at which a defect could be formed. So, these defects choose the sits where their formation energy is minimal and this becomes possible with hydrogen motion. Using the defect pool approach, we have developed a numerical DPM and inserted it in ASDMP at thermodynamic equilibrium. We have used ASDMP to get the density of states in each position of a solar cell based on a standard p-i-n structure. We have shown the effect of doping on defect concentration and studied the impact of the position of Fermi level on the distribution of the density of states. We recognized using ASDMP the key result that negatively charged defects in n-type material are situated lower in energy than positively charged defects in p-type material even when the correlation energy is positive. We calculated the electric field and the band diagrams at thermodynamic equilibrium both with the DPM and the SM. We showed that the electric field obtained from the DPM is stronger near the interfaces and lower in the bulk where the band diagrams are flatter. This behavior of the electric field calculated with this model is accentuated with the increase of the slope of the valence band tails.

Nanoscale (30–100 nm) films of BiFeO3/BaTiO3/Ni0.5Zn0.5Fe2O4 complex composition have been obtained by the pulsed-laser deposition method. Optical properties of the films were studied in the wavelength range of 250–1000 nm. It is shown that the optical properties of amorphous films deposited at room temperature are explained by the Tauc model for amorphous semiconductors. An increase in the optical gap from 1.7 to 1.95 eV was observed with decreasing film thickness. Allowed direct-band transitions (Eg = 3.1 eV) were observed after annealing of films independent of their thickness.

Although the steady-state secondary photoconductivity in amorphous semiconductors is fairly well understood, photocarrier transport with a subpicosecond time resolution (the THz region in the frequency domain) is still not clear. The frequency response of short-lived photocarriers in the THz region is discussed in a-Si:H here. It is shown that THz-photoconductivity is highly influenced by the mesoscopic inhomogeneity (10-nm scale) originating from potential fluctuations. This behavior is basically the same as observed in the radio-frequency (RF) range.

We fabricated amorphous silicon n-i-p solar cells with two types of nanopatterned back reflectors using stencil lithography. One reflector type has a plasmonic grating that is embedded in the ZnO layer; the other one has a metallic grating patterned on top of the Ag layer. From comparing the short-circuit current densities of the two device types, we conclude that light trapping through grating coupling is more efficient than coupling of light through the excitation of localized surface plasmons. The back reflectors were patterned with dot arrays by evaporation of Ag through millimeter-size stencil membranes. The stencils themselves were patterned by wafer-scale nanosphere lithography. The dot arrays have a periodicity of 428 nm and efficiently scatter light in the near-infrared wavelength range. Both back reflectors types lead to the same morphology for the silicon films. This allows us a fair comparison of the two light coupling mechanisms. We found a 14% and 19% short-circuit current density enhancement for the plasmonic and for the metallic grating, respectively. The external quantum efficiency gains between 550 and 650 nm show similar guided modes resonances for both device types, but the excitation is stronger for the device with the metallic grating.