Safa Kasap

Safa Kasap

University of Saskatchewan

H-index: 49

North America-Canada

About Safa Kasap

Safa Kasap, With an exceptional h-index of 49 and a recent h-index of 29 (since 2020), a distinguished researcher at University of Saskatchewan, specializes in the field of electronic materials, optoelectronic and photonic materials, devices, detectors, photoconductors.

His recent articles reflect a diverse array of research interests and contributions to the field:

29 December 2023 Professor Patrick McNally Dublin City University, Ireland Former Deputy Editor-in-Chief

Improved temporal performance and optical quantum efficiency of avalanche amorphous selenium for low dose medical imaging

The effect of excited-state absorption on up-conversion photoluminescence behavior in erbium-ion doped gallium lanthanum sulphide-oxide glasses

X-ray induced reduction of Sm3+ into Sm2+ in Li2CaSiO4 and its potential for radiation measurement applications

Roadmap on chalcogenide photonics

Recent advances in radiophotoluminescence materials for luminescence dosimetry

Direct conversion X-ray detectors with 70 pA cm− 2 dark currents coated from an alcohol-based perovskite ink

Time‐of‐flight transient photoconductivity technique

Safa Kasap Information

University

University of Saskatchewan

Position

Professor of Electrical Engineering

Citations(all)

15744

Citations(since 2020)

5744

Cited By

12529

hIndex(all)

49

hIndex(since 2020)

29

i10Index(all)

244

i10Index(since 2020)

98

Email

University Profile Page

University of Saskatchewan

Safa Kasap Skills & Research Interests

electronic materials

optoelectronic and photonic materials

devices

detectors

photoconductors

Top articles of Safa Kasap

29 December 2023 Professor Patrick McNally Dublin City University, Ireland Former Deputy Editor-in-Chief

Authors

Safa Kasap

Journal

Journal of Materials Science: Materials in Electronics

Published Date

2024/2

With much sadness, we announce the passing away of Professor Patrick McNally, who unexpectedly left us on December 29, 2023. Professor McNally was an editorial member, Editor and then the Deputy Editor-in-Chief of this journal for 20+ years. He was much liked and much respected by his colleagues in the journal and served the scientific publishing community with high-spirited enthusiasm and unselfish dedication. As the Deputy Chief Editor, he had to deal with numerous misconduct and fraudulent data complaints. He investigated each with utmost integrity and did not leave any stone unturned until he arrived at a just decision, even if it meant retracting a paper. We all trusted his judgement and we all appreciated the endless time and effort he put into maintaining the journal’s high standards. He became a role model to new editors. Professor McNally also promoted the involvement of more women in …

Improved temporal performance and optical quantum efficiency of avalanche amorphous selenium for low dose medical imaging

Authors

Corey Orlik,Sébastien Léveillé,Salman M Arnab,Adrian F Howansky,Jann Stavro,Scott Dow,Safa Kasap,Kenkichi Tanioka,Amir H Goldan,Wei Zhao

Journal

Journal of Medical Imaging

Published Date

2024/1/1

PurposeActive matrix flat panel imagers (AMFPIs) with thin-film transistor arrays experience image quality degradation by electronic noise in low-dose radiography and fluoroscopy. One potential solution is to overcome electronic noise using avalanche gain in an amorphous selenium (a-Se) (HARP) photoconductor in indirect AMFPI. In this work, we aim to improve temporal performance of HARP using a novel composite hole blocking layer (HBL) structure and increase optical quantum efficiency (OQE) to CsI:Tl scintillators by tellurium (Te) doping.ApproachTwo different HARP structures were fabricated: Composite HBL samples and Te-doped samples. Dark current and optical sensitivity measurements were performed on the composite HBL samples to evaluate avalanche gain and temporal performance. The OQE and temporal performance of the Te-doped samples were characterized by optical sensitivity …

The effect of excited-state absorption on up-conversion photoluminescence behavior in erbium-ion doped gallium lanthanum sulphide-oxide glasses

Authors

Mikhail M Voronov,Alexander P Skvortsov,Alexander B Pevtsov,Chris Craig,Daniel W Hewak,Cyril Koughia,Safa Kasap

Journal

Journal of Luminescence

Published Date

2023/5/1

Abstract Photoluminescence (PL) of Er 3+ ions embedded in GaLaS (O) glass at excitation wavelengths of 488, 532, 660, 808, and 980 nm has been studied. Typical cases at which the ratios of the optical transition intensities have no dependence on the pumping intensity have been considered. For the case of pumping at the 488 nm wavelength the method of extrapolation coefficients, which reveals the up-conversion nature of PL “mimicking” a “normal” PL, has been demonstrated. The thermal coupling of S 3/2 4 and H 11/2 2 manifolds, which are responsible for the intense PL in the green region of the visible spectral range, is discussed.

X-ray induced reduction of Sm3+ into Sm2+ in Li2CaSiO4 and its potential for radiation measurement applications

Authors

Go Okada,Noriaki Ikenaga,Yasuhiro Koguchi,Takayuki Yanagida,Safa Kasap,Hidehito Nanto

Journal

Materials Research Bulletin

Published Date

2023/3/1

In Sm3+-doped Li2CaSiO4, the Sm3+ ion is reduced to the Sm2+ state by X-ray irradiation. The valence change was confirmed by the difference in their photoluminescence spectra, measured before and after irradiation. Only luminescence peaks due to the 4f-4f transitions of Sm3+ are observed before the irradiation while an additional luminescence band is observed at 900 nm due to the 5d-4f transition of Sm2+. The reaction is that a fraction of X-ray generated electrons is captured by Sm3+ ions, which convert to the Sm2+ state. The generated Sm2+ state is fairly stable while it is effectively reversed back to the Sm3+ state by a heat treatment at an elevated temperature. A numerical approximation revealed the activation energy to be 0.40 and 0.52 eV. Even after the heat-treatment, the reduction of Sm3+ to Sm2+ is reproducible multiple times, which shows good potential for using radiation measurement applications.

Roadmap on chalcogenide photonics

Authors

Behrad Gholipour,Stephen R Elliott,Maximilian J Müller,Matthias Wuttig,Daniel W Hewak,Brian E Hayden,Yifei Li,Seong Soon Jo,Rafael Jaramillo,Robert E Simpson,Junji Tominaga,Yihao Cui,Avik Mandal,Benjamin J Eggleton,Martin Rochette,Mohsen Rezaei,Imtiaz Alamgir,Hosne Mobarok Shamim,Robi Kormokar,Arslan Anjum,Gebrehiwot Tesfay Zeweldi,Tushar Sanjay Karnik,Juejun Hu,Safa O Kasap,George Belev,Alla Reznik

Journal

Journal of Physics: Photonics

Published Date

2023/1/23

Alloys of sulphur, selenium and tellurium, often referred to as chalcogenide semiconductors offer a highly versatile, compositionally-controllable material platform for a variety of passive and active photonic applications. They are optically nonlinear, photoconductive materials with wide transmission windows that present various high-and low-index dielectric, low-epsilon and plasmonic properties across ultra-violet, visible and infrared frequencies, in addition to an ultra-fast, non-volatile, electrically-/optically-induced switching capability between phase states with markedly different electromagnetic properties. This roadmap collection presents an in-depth account of the critical role that chalcogenide semiconductors play within various traditional and emerging photonic technology platforms. The potential of this field going forward is demonstrated by presenting context and outlook on selected socio-economically …

Recent advances in radiophotoluminescence materials for luminescence dosimetry

Authors

Go Okada,Yasuhiro Koguchi,Takayuki Yanagida,Safa Kasap,Hidehito Nanto

Published Date

2022/11/22

Radiophotoluminescence (RPL) is a phenomenon in which a luminescence centre is formed in a medium upon interaction with ionizing radiation. The RPL is observed by a conventional photoluminescence (PL) technique, and the PL intensity is proportional to the dose. With the latter feature, the RPL has found successful applications in personnel and environmental dosimetry. However, the conventional materials considered for radiation measurements may be limited to Ag-doped phosphate glass, LiF, and Al 2 O 3: C, Mg. The recent research works, however, have found a number of additional RPL materials for luminescence dosimetry. The aim of the present paper is to review the series of newly reported RPL materials and potential applications in dosimetry.

Direct conversion X-ray detectors with 70 pA cm− 2 dark currents coated from an alcohol-based perovskite ink

Authors

Yunlong Li,Emmanuel Adeagbo,Cyril Koughia,Blaine Simonson,Richard D Pettipas,Anastasiia Mishchenko,Salman M Arnab,Luc Laperrière,George Belev,Amy L Stevens,Safa O Kasap,Timothy L Kelly

Journal

Journal of Materials Chemistry C

Published Date

2022

Direct conversion X-ray image detectors offer higher spatial resolution than their indirect counterparts. Organic–inorganic hybrid perovskites are among the most sensitive X-ray photoconductors for these detectors; however, high dark currents make it difficult for perovskites to compete with commercial amorphous selenium (a-Se) technology. Here we report a simple perovskite ink formulation that uses environmentally friendly 85% ethanol as the solvent. The ink was used to blade-coat thick perovskite films, which when combined with poly(methyl methacrylate) (PMMA) blocking layers, produce direct conversion detectors with dark currents ∼70 pA cm−2. These dark currents are two to three orders of magnitude lower than those of other perovskite-based detectors and are comparable to those of commercial a-Se devices. Other device figures-of-merit, including X-ray sensitivity and mobility-lifetime (μτ) product, are …

Time‐of‐flight transient photoconductivity technique

Authors

Safa O Kasap

Published Date

2022/7/6

Time‐of‐flight (TOF) transient photoconductivity technique and its variations have been widely used in the characterization of charge transport in a vast range inorganic and organic material systems. A short pulse of photoexcitation (such as a laser pulse or an electron beam pulse) generates carriers very near the semitransparent electrode of a sample that is sandwiched between two opposite electrodes. Under small signals, the photoinjected charge is much less than the charge on the electrode ( CV ), and the field in the sample is taken to be uniform. The carriers with the opposite sign to the bias on the semitransparent electrode become immediately neutralized, whereas those with the opposite polarity become drifted along the direction of the external force (charge × field) imposed by the applied field. The external photocurrent …

X-ray detectors

Authors

Safa Kasap,Zahangir Kabir

Published Date

2022/11/11

The basic principle of operation of an x-ray detector is described through the Shockley-Ramo theorem, and the ionization energy, i.e., electron and hole pair creation energy, is introduced and used in formulating the responsivity of the detector. Typical detector materials and structures are also described. The spectroscopic detector operation is explained and its resolution is discussed. One of the most extensive modern applications of semiconductor detectors is in medical x-ray imaging. Flat panel x-ray imagers (FPXIs) are described in detail due to their extensive use in imaging. In direct conversion (DC) FPXIs, the absorbed x-ray photons are directly converted to charges in the pixel’s photoconductor. The applied field then drifts them to the collecting electrodes of the pixel. These FPXIs use either a thin-film transistor (TFT) active matrix array (AMA) on a glass substrate, based on a-Si:H technology or, in a smaller …

Fluctuations in the collected charge in integrating photoconductive detectors under small and large signals: the variance problem

Authors

Kieran O Ramaswami,Richard J Curry,Ian Hinder,Robert E Johanson,Safa O Kasap

Journal

Journal of Physics D: Applied Physics

Published Date

2022/6/9

Charge collection efficiency (CE) η 0 under small signal conditions, corresponding to a uniform field in the detector medium, has been widely used in evaluating the performance of photoconductive detectors. The present paper answers the question,'What is the variance of the collected charge in an integrating detector as a function of photoinjection level and what are the errors if we continue to use the small signal equations?'The variance in η 0 under small signals has been theoretically derived in the literature and has been a key factor in the detective quantum efficiency modeling of integrating detectors based on various semiconductors. is a noise source and can degrade the detector performance under incomplete charge collection. The statistical variance in the CE η 0, under small signals and the variance in the CE η r under an arbitrary injection level r (injected charge divided by charge on the electrodes) have been studied using the Monte …

Effect of Substrate Temperature on the Structural, Optical and Electrical Properties of DC Magnetron Sputtered VO2 Thin Films

Authors

Azianty Saroni,Saadah Abdul Rahman,Boon Tong Goh

Journal

Materials Today: Proceedings

Published Date

2018/1/1

In2O3/InN nanostructure composites were grown by nitrogen plasma assisted in-situ thermal annealing at different substrate temperatures, Ts. At Ts = 200 °C a cauliflower like morphology of In2O3/InN nanostructure composites with a grain size (∼100-200 nm) were formed. Higher substrate temperature leads to larger grain size (∼400-500 nm). The composite grown at Ts = 200 °C showed a promising In2O3/InN with a visible optical band gap of 2.63 eV. This composite exhibited a high photocurrent density response which more than 50 % (equivalent to 795 μA/cm2) upon illumination of visible light compared to the dark condition (< 10 μA/cm2) at 1 VAg/AgCl. Moreover, the formation of In2O3/InN nanostructure composite suppresses the electron/hole recombination leading to the enhancement of the photoelectrochemical processes

RPL properties of samarium-doped CaSO4

Authors

Go Okada,Wakako Shinozaki,Satoshi Ueno,Yasuhiro Koguchi,Kazuki Hirasawa,Francesco d’Errico,Takayuki Yanagida,Safa Kasap,Hidehito Nanto

Journal

Japanese Journal of Applied Physics

Published Date

2022/2/2

Radiophotoluminescence (RPL) properties of Sm-doped CaSO 4 for radiation dosimetry applications are reported. The samples with varying Sm concentrations are prepared via the solid-state reaction process. The as-prepared samples show photoluminescence due to typical 4f–f transitions of Sm 3+ whereas, after X-ray irradiation, additional emission features appear with a broad band peaking at 630 nm as well as a set of multiple sharp lines across 680–820 nm, which are attributed to the 5d–4f and 4f–4f transitions of Sm 2+, respectively. Therefore, the RPL in the present material system relies on the generation of Sm 2+ centers. The sensitivity is about 3 times lower than that of Ag-doped phosphate glass, but no fading and build-up of signal are evident even immediately after the irradiation. The signal is reversible by heat-treatment at 500 C, and is reproducible even after the thermal erasure, especially when …

The Effect of Fractionation during the Vacuum Deposition of Stabilized Amorphous Selenium Alloy Photoconductors on the Overall Charge Collection Efficiency

Authors

Safa Kasap

Journal

Sensors

Published Date

2022/9/20

The general fabrication process for stabilized amorphous selenium (a-Se) detectors is vacuum deposition. The evaporant alloy is typically selenium alloyed with 0.3–0.5%As to stabilize it against crystallization. During the evaporation, fractionation leads to the formation of a deposited film that is rich in As near the surface and rich in Se near the substrate. The As content is invariably not uniform across the film thickness. This paper examines the effect of non-uniform As content on the charge collection efficiency (CE). The model for the actual CE calculation is based on the generalized CE equation under small signals; it involves the integration of the reciprocal range-field product (the schubweg) and the photogeneration profile. The data for the model input were extracted from the literature on the dependence of charge carrier drift mobilities and lifetimes on the As content in a-Se1−xAsx alloys to generate the spatial variation of hole and electron ranges across the photoconductor film. This range variation is then used to calculate the actual CE in the integral equation as a function of the applied field. The carrier ranges corresponding to the average composition in the film are also used in the standard CE equation under uniform ranges to examine whether one can simply use the average As content to calculate the CE. The standard equation is also used with ranges from the spatial average and average inverse. Errors are then compared and quantified from the use of various averages. The particular choice for averaging depends on the polarity of the radiation-receiving electrode and the spatial variation of the carrier ranges.

radiophotoluminescence (RPL)

Authors

Go Okada,Takayuki Yanagida,Hidehito Nanto,Safa Kasap

Journal

Phosphors for Radiation Detectors

Published Date

2022/1/21

This chapter covers a wide range of radio‐photoluminescence (RPL) technologies, from fundamentals to applications. It presents the definition of the term of RPL and distinguishes it from thermally‐stimulated luminescence and optically‐stimulated luminescence as a different type of dosimetric technique using a phosphor medium. RPL is a very powerful tool when the measurement environment requires exposure to light or heat. The chapter introduces a list of RPL materials and their fundamental properties, as reported in the literature. The RPL center is typically very stable and the resulting luminescence is due to electronic transitions within the RPL center. The chapter also introduces the principal properties as well as applications of four selected RPL materials with many illustrative materials. These include: Ag‐doped sodium‐aluminophosphate glasses, Al …

Doped and Stabilized Amorphous Selenium Single and Multilayer Photoconductive Layers for X‐Ray Imaging Detector Applications

Authors

Safa O Kasap

Journal

Photoconductivity and Photoconductive Materials: Fundamentals, Techniques and Applications

Published Date

2022/7/6

Stabilized amorphous selenium (a‐Se) refers to a‐Se that has been stabilized against crystallization by alloying it with As. Generally, the As content is below 1%, but it can be as high as 6% when the stabilized a‐Se film constitutes the n‐layer in a pin‐type X‐ray detector. The stabilized a‐Se layer that constitutes the i‐layer typically consists of 0.3% As with Cl doping at the ppm level. This chapter describes how a‐Se multilayers are used in modern flat panel X‐ray imagers and examines the major factors that control the sensitivity of a‐Se alloy‐based photoconductors, that is, the X‐ray attenuation coefficient, the ionization energy (the electron and hole pair creation energy), charge transport and trapping, and dark current. Empirical equations are provided for the linear attenuation and energy absorption coefficients. Recent data on the dependence of the ionization energy on the …

The formation of a one-dimensional van der Waals selenium crystal from the three-dimensional amorphous phase: A spectroscopic signature of van der Waals bonding

Authors

Milos Krbal,Alexander V Kolobov,Paul Fons,Yuta Saito,George Belev,Safa Kasap

Journal

Applied Physics Letters

Published Date

2022/1/17

Trigonal selenium is a prototypical one-dimensional (1D) van der Waals (vdW) solid, where covalently bonded helical chains are held together by weaker vdW forces. In this work, we have studied structural transformation from a three-dimensional amorphous phase of non-interacting Se chains into a 1D vdW crystal using x-ray absorption spectroscopy. The crystallization process and establishment of vdW interaction are accompanied by elongation and weakening of covalent Se-Se bonds. We have found a unique signature in the x-ray absorption near-edge structure spectrum that is associated with vdW bonds and can be used to identify the formation of the latter. We believe that a similar approach can be used to study other 1D vdW solids, such as transition-metal trichalcogenides, and particularly stress the usefulness of x-ray absorption spectroscopy to identify vdW bonds.

Photoconductivity: Fundamental Concepts

Authors

Safa O Kasap

Journal

Photoconductivity and Photoconductive Materials: Fundamentals, Techniques and Applications

Published Date

2022/7/6

Photoconductivity is defined, and the importance of electrical contacts are highlighted by examining the origin of the dark current flowing through a photoconductor. The Shockley–Ramo theorem is explained and the photoconductive gain and the necessary prerequisites for its manifestation are discussed. Major recombination kinetics are addressed, including the Shockley–Read–Hall statistics, Simmons–Taylor formulation, and Langevin recombination, and their main features are highlighted. Photoconductivity experiments have been extensively used by numerous researchers to characterize various semiconductor materials. Principles of steady‐state and modulated photoconductivity (frequency‐resolved photoconductivity) are introduced along with their main features in extracting material characteristics such as the density of states in the bandgap. The effects of traps on transient …

Improved optical quantum efficiency and temporal performance of a flat-panel imager with avalanche gain

Authors

Corey Orlik,Adrian F Howansky,Sébastien Léveillé,Anastasiia Mishchenko,Safa Kasap,Jann Stavro,Amir H Goldan,James R Scheuermann,Wei Zhao

Published Date

2021/2/15

Active matrix flat panel imagers (AMFPIs) with thin film transistor (TFT) arrays are becoming the standard for digital x-ray imaging due to their high image quality and real time readout capabilities. However, in low dose applications their performance is degraded by electronic noise. A promising solution to this limitation is the Scintillator High-Gain Avalanche Rushing Photoconductor AMFPI (SHARP-AMFPI), an indirect detector that utilizes avalanche amorphous selenium (a-Se) to amplify optical signal from the scintillator prior to readout. We previously demonstrated the feasibility of a large area SHARP-AMFPI, however there are several areas of desired improvement. In this work, we present a newly fabricated SHARP-AMFPI prototype detector with the following developments: metal oxide hole blocking layer (HBL) with improved electron transport, transparent bias electrode for increased optical coupling, and …

Correction: Thickness dependence of electron transport in pure a-Se photoconductive films

Authors

Derek Mortensen,George Belev,Kirill Koughia,Robert E Johanson,Safa O Kasap

Journal

Canadian Journal of Physics

Published Date

2021

The equation shown in fig. 5 in the original paper has a typographical error. The last three terms are supposed to be Gaussian functions but the square in each is missing. As stated and discussed in the text, the model uses one exponential and three Gaussian peaks and the corrected equation is

Self-heating-induced electrical and optical switching in high quality VO2 films controlled with current pulses

Authors

Ozan Gunes,Cyril Koughia,Chunzi Zhang,George Belev,Shi-Jie Wen,Qiaoqin Yang,Safa O Kasap

Journal

Journal of Materials Science: Materials in Electronics

Published Date

2021/10

Self-heating (SH)-induced electrical and optical switching in high quality VO2 films grown by magnetron sputtering on a c-cut sapphire substrate has been investigated under various applied constant current pulses (ID). The effect of SH on the behavior of electrical conductivity (σ), optical transmittance (, and film temperature (T) examined by applying a constant current pulse of various magnitudes with a pulse duration of five seconds (Δt = 5 s) in VO2 films which were pre-heated to and stabilized at 57 °C, at the brink of insulator-to-metal transition (IMT). The SH effect that arose from the application of constant ID pulses led to a significant increase in T and substantial changes in σ and . Observations showed that, depending on the magnitude of ID, the σ and demonstrate strikingly different temporal behavior not only during the SH-induced IMT but also after the removal of ID. The observed …

See List of Professors in Safa Kasap University(University of Saskatchewan)

Safa Kasap FAQs

What is Safa Kasap's h-index at University of Saskatchewan?

The h-index of Safa Kasap has been 29 since 2020 and 49 in total.

What are Safa Kasap's top articles?

The articles with the titles of

29 December 2023 Professor Patrick McNally Dublin City University, Ireland Former Deputy Editor-in-Chief

Improved temporal performance and optical quantum efficiency of avalanche amorphous selenium for low dose medical imaging

The effect of excited-state absorption on up-conversion photoluminescence behavior in erbium-ion doped gallium lanthanum sulphide-oxide glasses

X-ray induced reduction of Sm3+ into Sm2+ in Li2CaSiO4 and its potential for radiation measurement applications

Roadmap on chalcogenide photonics

Recent advances in radiophotoluminescence materials for luminescence dosimetry

Direct conversion X-ray detectors with 70 pA cm− 2 dark currents coated from an alcohol-based perovskite ink

Time‐of‐flight transient photoconductivity technique

...

are the top articles of Safa Kasap at University of Saskatchewan.

What are Safa Kasap's research interests?

The research interests of Safa Kasap are: electronic materials, optoelectronic and photonic materials, devices, detectors, photoconductors

What is Safa Kasap's total number of citations?

Safa Kasap has 15,744 citations in total.

What are the co-authors of Safa Kasap?

The co-authors of Safa Kasap are Setsuhisa Tanabe, Dean Chapman, Timothy L. Kelly, Maria Mitkova, Richard J Curry, Go Okada.

Co-Authors

H-index: 68
Setsuhisa  Tanabe

Setsuhisa Tanabe

Kyoto University

H-index: 43
Dean Chapman

Dean Chapman

University of Saskatchewan

H-index: 37
Timothy L. Kelly

Timothy L. Kelly

University of Saskatchewan

H-index: 36
Maria Mitkova

Maria Mitkova

Boise State University

H-index: 35
Richard J Curry

Richard J Curry

Manchester University

H-index: 33
Go Okada

Go Okada

Kanazawa Institute of Technology

academic-engine