X-ray irradiation induced changes in electron transport in stabilized a-Se photoconductors

Walornyj, M.; Kasap, S. O.

doi:10.1063/1.4839935

Cited by 13 publications

(3 citation statements)

References 39 publications

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“…We note that the measurements we report herein obviously apply to a-Se films that have not been exposed to any radiation. The irradiation of stabilized a-Se photoconductors with heavy doses of X-rays leads to the reduction of both hole and electron lifetimes, but the drift mobilities are unchanged [23,24]. Both lifetimes recover with time through relaxation processes to their equilibrium values.…”

Section: Resultsmentioning

confidence: 94%

Temperature dependence of charge carrier ranges in stabilized a-Se photoconductors

FogalBud

KasapSafa

2014

Can. J. Phys.

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Using time-of-flight (TOF) and interrupted-field TOF we have measured the electron and hole drift mobilities, e and h , lifetimes, e and h , and hence carrier ranges, e e and h h , in stabilized a-Se as a function of temperature from −25 to 45°C. Above room temperature, e e and h h show a slight increase with temperature and peak around 31 and 35°C, respectively. The e e at 35°C and h h at 40°C are approximately the same as room temperature values. Below room temperature, down to −25°C, both e and h decrease with decreasing temperature with activation energies E e and E h that are 0.38 and 0.21 eV. The electron and hole lifetimes, e and h , are also thermally activated but they increase with decreasing temperature with activation energies E e and E h that are 0.31 and 0.18 eV. These are quite close to corresponding activation energies for the drift mobilities within experimental errors. The electron and hole ranges, e e and h h , therefore exhibit only a weak temperature dependence, both increase slightly with temperature. These observations are consistent with shallow trap controlled transport in the presence of a set of deep traps. The X-ray sensitivity of a photoconductor, among other factors, depends on the charge collection efficiency, which depends on electron and hole ranges, e e and h h . Because these carrier ranges do not show any significant temperature dependence, one can conclude that the X-ray sensitivity of stabilized a-Se over the temperature range from −25 to 40°C should not be affected by changes in the collection efficiency. Résumé: En utilisant des techniques de temps de vol (TOF), non et interrompu, nous mesurons les mobilités de dérive des électrons et des trous, e et h , les temps de vie, e et h , et donc la portée des porteurs de charge, e e et h h , dans du a-Se stabilisé en fonction de la température, de −25 à 45°C. Au dessus de la température de la salle, e e et h h augmentent légèrement avec la température avec un maximum à 31 et 35°C respectivement. On voit que e e à 35°C et h h à 40°C ont même valeur qu'à la température de la salle. Sous la température de la salle jusqu'à −25°C, à la fois e et h diminuent avec la température, avec des énergies d'activation E e ϭ 0.38 eV et E h ϭ 0.21 eV. Par contre, les temps de vie e et h croissent avec une baisse de la température, avec des énergies d'activation E e = 0.31 eV et E h = 0.18 eV. Aux erreurs de mesure près, ces énergies sont proches de celles pour la mobilité. Il s'ensuit que les portées e e et h h n'ont qu'une faible dépendance en température, les deux augmentant légèrement avec la température. Ces résultats sont cohérents avec ceux obtenus par transport contrôlé par pièges peu profonds en présence de pièges profonds. La sensibilité X d'un photoconducteur, parmi d'autres facteurs, dépend de l'efficacité à collecter des charges, qui, elle, dépend des portées e e et h h . Puisque ces portées ne montrent pas de dépendance significative en température, nous pouvons conclure que la sensibilité X du a-Se stabilisé ne devrait pas être affec...

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Section: Resultsmentioning

confidence: 94%

Temperature dependence of charge carrier ranges in stabilized a-Se photoconductors

FogalBud

KasapSafa

2014

Can. J. Phys.

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“…The work herein addresses the question "Do electron lifetime measurements reported on a-Se films, as in ref. 10, for example, represent true deep trapping effects, or do lifetime measurements have a different interpretation?" This is the fundamental issue we address.…”

Section: Introductionmentioning

confidence: 98%

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

et al. 2014

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Electron transport in vacuum-deposited a-Se films with thicknesses varying from 13 to 501 m has been investigated by conventional time-of-flight (TOF) and interrupted field TOF experiments. To separate the influences of electric field and the thickness, all TOF experiments were performed at a constant electric field. It has been found that the electron mobility is relatively constant in thick films (L > 50 m) and increases in thinner films (L < 50 m) with decreasing thickness. On the other hand, the electron lifetime is relatively thickness independent in films with thickness L > 50 m, but drops sharply in thin films when L < 50 m. These observations can be explained based on the density of states model that includes three types of traps forming Gaussian-like distributions within the mobility gap as reported in Koughia et al. (J. Appl. Phys. 97, 033706 (2005)).Résumé : Nous étudions, par temps de vol (TOF) sans et avec interruption, le transport d'électrons dans des films de a-Se déposés sous vide et d'épaisseur allant de 13 à 501 m. Afin de séparer l'influence du champ électrique de celle de l'épaisseur, toutes les mesures sont faites à champ électrique constant. Nous trouvons que la mobilité électronique est relativement constante dans les films épais (L > 50 m) et augmente dans les films minces (L < 50 m) lorsque l'épaisseur décroît. D'autre part, le temps de vie des électrons est relativement indépendant de l'épaisseur si L > 50 m, mais décroît rapidement lorsque L diminue sous les 50 m. Ces observations s'expliquent sur la base du modèle de densité d'états qui inclut trois types de pièges formant une distribution de type gaussien à l'intérieur du gap de mobilité, tel que rapporté par Koughia et al. (J. Appl. Phys. 97, 033706 (2005)).

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“…Third, since carrier–lattice interaction is effectively weaker in the supersonic state, it seems that fewer structural defects are produced under high electric fields. Or, we may predict that defect‐generation behaviors depend upon the applied electric field and charge separation processes, in which stronger electron–lattice interaction could play major roles. For further explorations of the avalanche mechanism, photoluminescence measurements under high fields will be valuable.…”

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confidence: 99%

A Polaronic View of Impact Ionization in Amorphous Se Films

Tanaka

2017

Physica Rapid Research Ltrs

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In this letter, it is proposed that the impact ionization in amorphous Se films, which triggers avalanche carrier multiplications, occurs through transformations of electron and hole motions from polaronic to supersonic states, the situation resembling those envisaged for semiconducting one-dimensional organic polymers. However, reflecting unique origins of the conduction and the valence band in Se, the electron-lattice interaction appears stronger than the hole-lattice interaction, which seems to be responsible for characteristic properties such as less efficient electron multiplication. The idea is consistent with the fact that a-Si:H having three-dimensional structures exhibits no corresponding phenomena.

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X-ray irradiation induced changes in electron transport in stabilized a-Se photoconductors

Cited by 13 publications

References 39 publications

Temperature dependence of charge carrier ranges in stabilized a-Se photoconductors

Temperature dependence of charge carrier ranges in stabilized a-Se photoconductors

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

A Polaronic View of Impact Ionization in Amorphous Se Films

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