Anna Cavallini - Academia.edu (original) (raw)

Papers by Anna Cavallini

Research paper thumbnail of Quantification of roughness and spatial distribution of dislocations in MBE and MOVPE grown LED heterostructures

A combination of nanoscale imaging techniques such as atomic force microscopy and scanning electr... more A combination of nanoscale imaging techniques such as atomic force microscopy and scanning electron microscopy are used to investigate the relationship between surface morphology and height statistics of GaN cap layers in InGaN/GaN light emitting diode heterostructures. The investigated samples were grown in two very different growth regimes which lead to distinct characteristic superficial landscapes. We also report here on the introduction of a new methodological approach that adapt the concept of height-height correlation function, a well known statistical tool in the field of studies on rough surfaces. We evaluate to which extent the geometrical properties of the constitutive 'bricks' (hillocks for ammonia assisted molecular beam epitaxial film) and structural defects (dislocation pits for metal organic vapor phase epitaxial film) affects the statistical properties of heights of these GaN surfaces. Finally, we have studied the spatial distribution of dislocation pits in both the samples to assess the quantitative differences between these heterostructures of very distinct surface morphology.

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Research paper thumbnail of Ge clustering effects in Ge doped CdTe: Electrical and structural properties

Journal of Applied Physics, 2011

ABSTRACT High resistivity CdTe can be achieved by introducing impurities that create deep levels ... more ABSTRACT High resistivity CdTe can be achieved by introducing impurities that create deep levels which, in turn, control the electronic transport properties of the material via a compensation process. We have characterized the effects of thermal annealing of high resistivity CdTe: Ge under either Te- or Cd-rich atmosphere to understand how modifications in the structure of Ge-related defective states and their electrical activity affect the material transport properties. We have investigated the transport properties with current-voltage analyses, the electrically active deep traps by photoinduced current transient spectroscopy and the local environment of Ge atoms by x-ray absorption spectroscopy. By correlating the modifications observed, we determined the occurrence of Ge clustering effects and associated them to the formation of electrically active deep donor traps, one located at E(C)-0.31 eV and the other one at midgap, with an activation energy of 0.82 eV. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3626048]

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Research paper thumbnail of Electrical properties of extended defects in III-nitrides

Acta Materialia, 2015

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Research paper thumbnail of Recovery of radiation damage in CdTe and CdZnTe Detectors

IEEE Symposium Conference Record Nuclear Science 2004., 2000

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Research paper thumbnail of Deep levels and irradiation effects in n-GaN

J Phys Condens Matter, 2000

The electrical activity of defects was investigated in hydride vapour phase epitaxy n-type galliu... more The electrical activity of defects was investigated in hydride vapour phase epitaxy n-type gallium nitride (GaN) grown on sapphire by deep level transient spectroscopy, iso-thermal current spectroscopy, photoconductivity decay measurements and the electron beam induced current (EBIC) method. In order to identify the defect origin, the epilayers were irradiated by high energy protons, and their characteristics before and after irradiation were compared. Irradiation generates two new deep levels and significantly increases the electron carrier concentration of the as-grown epilayer levels. The photocurrent decay is characterized by a stretched exponential law, the slope and time constant of which dramatically decrease after irradiation. The results are discussed in terms of carrier capture at deep levels. EBIC analyses, according to the DLTS findings, revealed an increase in recombination, and also a different distribution of the recombining centres.

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Research paper thumbnail of Experimental/numerical investigation of the physical mechanisms behind high-field degradation of power HFETs and their implications on device design

2001 GaAs Reliability Workshop. Proceedings (IEEE Cat. No.01TH8602), 2001

In a previous paper we showed how simple drift-diffusion simulations backed up the hypothesis of ... more In a previous paper we showed how simple drift-diffusion simulations backed up the hypothesis of electron trapping at the device surface between gate and drain as a mechanism able to consistently explain all of the experimentally observed degradation modes following a high-field (hot carrier) stress. This paper expands on such previous findings by showing: (i) simulation results of HFETs with

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Research paper thumbnail of CREEP BEHAVIOUR OF COMPOSITE BONE CEMENT

ABSTRACT

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Research paper thumbnail of Advances in Optics Design and Precision Manufacturing Technologies

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Research paper thumbnail of Analyses of compensation related defects in II-VI semiconductors

... P.Siffert Mat Sci.Eng. B16, 223 (1993). 7. P.Blood and JWOrton, The Electrical Characterizati... more ... P.Siffert Mat Sci.Eng. B16, 223 (1993). 7. P.Blood and JWOrton, The Electrical Characterization of Semiconductors: Majority Carriers and Electron States, (Academic Press, UK, 1992). 8. PMMooney J.Appl.Phys. 54, 208 (1983). 9. E.Lopez-Cruz, J.Gonzalez-Hemandez, DDAllred ...

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Research paper thumbnail of SI LEC GaAs nuclear detectors: characterization, performance and applications

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Research paper thumbnail of Gallium Arsenide charged particle detectors: deep levels effects

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Research paper thumbnail of INFLUENCE OF DEFECTS ON DIFFUSION LENGTH INHOMOGENEITY IN GAAS-TE WAFERS

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Research paper thumbnail of PAPERS PRESENTED AT THE 3RD INTERNATIONAL WORKSHOP ON BEAM-INJECTION-ASSESSMENT-OF-DEFECTS-IN-SEMICONDUCTORS (BIADS-93) - A NATO ADVANCED RESEARCH WORKSHOP - AUGUST 30 - SEPTEMBER 2, 1993, BOLOGNA, ITALY - FOREWORD

Materials Science and Engineering B

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Research paper thumbnail of Electronic levels in silicon MaWCE nanowires: evidence of a limited diffusion of Ag

Nanotechnology, 2015

Deep level transient spectroscopy (DLTS) was performed on lowly n-doped silicon nanowires grown b... more Deep level transient spectroscopy (DLTS) was performed on lowly n-doped silicon nanowires grown by metal-assisted wet chemical etching (MaWCE) with silver as the catalyst in order to investigate the energetic scheme inside the bandgap. To observe the possible diffusion of atoms into the bulk, DLTS investigation was also performed on the samples after removing the nanowires. Two of the four energy levels observed in the nanowires were also detected inside the substrate. Based on these results and on literature data about deep levels in bulk silicon, some hypotheses are advanced regarding the identification of the defects responsible for the energy levels revealed.

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Research paper thumbnail of Neutron and proton irradiation: effects on the active layer width and electric field distribution in semi-insulating GaAs Schottky diodes

Semiconducting and Insulating Materials 1998. Proceedings of the 10th Conference on Semiconducting and Insulating Materials (SIMC-X) (Cat. No.98CH36159), 1998

ABSTRACT Irradiation (with neutrons or protons) markedly changes the values of the active layer w... more ABSTRACT Irradiation (with neutrons or protons) markedly changes the values of the active layer width as well as the electric field distribution of Schottky diodes made on semi-insulating GaAs. However, the behaviour of both of them as a function of the reverse biasing is almost the same as before irradiation, when either neutrons or protons are used. Spectroscopic measurements revealed that not only the dominant defect EL2 increases in density but also other shallower level traps, which must be accounted for to explain the observed changes of both active layer width and electric field

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Research paper thumbnail of Special Issue containing papers presented at the Conference on Extended Defects in Semiconductors - 2002 (EDS 2002), Bologna, Italy, 1-6 June 2002 - Preface

Journal of Physics Condensed Matter

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Research paper thumbnail of Defective states in semi-insulating gallium arsenide substrates

Semi-insulating gallium arsenide substrates are widely used for microwave discrete devices and in... more Semi-insulating gallium arsenide substrates are widely used for microwave discrete devices and integrated circuits. However, the performance of the above devices may be significantly affected by the substrate quality, i.e. crystal defects and related deep levels. Consequently, a careful characterization of substrates is mandatory to improve both device performance and production yields. In this work we have investigated gallium arsenide substrates from different suppliers and/or differently processed. To these substrates we have applied, discussed and compared different methodologies (current-voltage and capacitance-voltage characteristics as well as spectroscopic methods) to characterize the many deep levels which are either present in as-received semi-insulating substrates or induced by device processing such as ion implantation and the subsequent thermal annealing.

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Research paper thumbnail of Role of surface trap states on two-dimensional electron gas density in InAlN/AlN/GaN heterostructures

Applied Physics Letters

In order to clarify the effect of charged dislocations and surface donor states on the transport ... more In order to clarify the effect of charged dislocations and surface donor states on the transport mechanisms in polar AlInN/AlN/GaN heterostructures, we have studied the current-voltage characteristics of Schottky junctions fabricated on AlInN/AlN/GaN heterostructures. The reverse-bias leakage current behaviour has been interpreted with a Poole-Frenkel emission of electrons from trap states near the metal-semiconductor junction to dislocation induced states. The variation of the Schottky barrier height as a function of the AlN layer thickness has been measured and discussed, considering the role of the surface states in the formation of the two dimensional electron gas at AlN/GaN interface.

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Research paper thumbnail of Breakdown and low-temperature anomalous effects in 6H SiC JFETs

International Electron Devices Meeting 1998. Technical Digest (Cat. No.98CH36217), 1998

Dipartimento di Elettronica e Informatica and INFM, University of Padova, via Gradenigo 6/A, 1-35... more Dipartimento di Elettronica e Informatica and INFM, University of Padova, via Gradenigo 6/A, 1-35 13 1 Padova, Italy, Tel. +39-049-8277658; Fax +39-49-8277699; e-mad: zanoni@dei.unipd.it ($) Dipartimento di Ingegneria dei Materiali, University of Trento, via ...

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Research paper thumbnail of Influence of surface pre-treatment on the electronic levels in silicon MaWCE nanowires

Nanotechnology, 2015

Deep level transient spectroscopy (DLTS) was performed on n-doped silicon nanowires grown by meta... more Deep level transient spectroscopy (DLTS) was performed on n-doped silicon nanowires grown by metal-assisted wet chemical etching (MaWCE) with gold as the catalyst in order to investigate the energetic scheme inside the bandgap. To observe the possible dependence of the level scheme on the processing temperature, DLTS measurements were performed on the nanowires grown on a non-treated Au/Si surface and on a thermally pre-treated Au/Si surface. A noticeable modification of the configuration of the energy levels was observed, induced by the annealing process. Based on our results on these MaWCE nanowires and on literature data about deep levels in bulk silicon, some hypotheses were advanced regarding the identification of the defects responsible of the energy levels revealed.

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Research paper thumbnail of Quantification of roughness and spatial distribution of dislocations in MBE and MOVPE grown LED heterostructures

A combination of nanoscale imaging techniques such as atomic force microscopy and scanning electr... more A combination of nanoscale imaging techniques such as atomic force microscopy and scanning electron microscopy are used to investigate the relationship between surface morphology and height statistics of GaN cap layers in InGaN/GaN light emitting diode heterostructures. The investigated samples were grown in two very different growth regimes which lead to distinct characteristic superficial landscapes. We also report here on the introduction of a new methodological approach that adapt the concept of height-height correlation function, a well known statistical tool in the field of studies on rough surfaces. We evaluate to which extent the geometrical properties of the constitutive 'bricks' (hillocks for ammonia assisted molecular beam epitaxial film) and structural defects (dislocation pits for metal organic vapor phase epitaxial film) affects the statistical properties of heights of these GaN surfaces. Finally, we have studied the spatial distribution of dislocation pits in both the samples to assess the quantitative differences between these heterostructures of very distinct surface morphology.

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Ge clustering effects in Ge doped CdTe: Electrical and structural properties

Journal of Applied Physics, 2011

ABSTRACT High resistivity CdTe can be achieved by introducing impurities that create deep levels ... more ABSTRACT High resistivity CdTe can be achieved by introducing impurities that create deep levels which, in turn, control the electronic transport properties of the material via a compensation process. We have characterized the effects of thermal annealing of high resistivity CdTe: Ge under either Te- or Cd-rich atmosphere to understand how modifications in the structure of Ge-related defective states and their electrical activity affect the material transport properties. We have investigated the transport properties with current-voltage analyses, the electrically active deep traps by photoinduced current transient spectroscopy and the local environment of Ge atoms by x-ray absorption spectroscopy. By correlating the modifications observed, we determined the occurrence of Ge clustering effects and associated them to the formation of electrically active deep donor traps, one located at E(C)-0.31 eV and the other one at midgap, with an activation energy of 0.82 eV. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3626048]

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Research paper thumbnail of Electrical properties of extended defects in III-nitrides

Acta Materialia, 2015

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Recovery of radiation damage in CdTe and CdZnTe Detectors

IEEE Symposium Conference Record Nuclear Science 2004., 2000

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Research paper thumbnail of Deep levels and irradiation effects in n-GaN

J Phys Condens Matter, 2000

The electrical activity of defects was investigated in hydride vapour phase epitaxy n-type galliu... more The electrical activity of defects was investigated in hydride vapour phase epitaxy n-type gallium nitride (GaN) grown on sapphire by deep level transient spectroscopy, iso-thermal current spectroscopy, photoconductivity decay measurements and the electron beam induced current (EBIC) method. In order to identify the defect origin, the epilayers were irradiated by high energy protons, and their characteristics before and after irradiation were compared. Irradiation generates two new deep levels and significantly increases the electron carrier concentration of the as-grown epilayer levels. The photocurrent decay is characterized by a stretched exponential law, the slope and time constant of which dramatically decrease after irradiation. The results are discussed in terms of carrier capture at deep levels. EBIC analyses, according to the DLTS findings, revealed an increase in recombination, and also a different distribution of the recombining centres.

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Experimental/numerical investigation of the physical mechanisms behind high-field degradation of power HFETs and their implications on device design

2001 GaAs Reliability Workshop. Proceedings (IEEE Cat. No.01TH8602), 2001

In a previous paper we showed how simple drift-diffusion simulations backed up the hypothesis of ... more In a previous paper we showed how simple drift-diffusion simulations backed up the hypothesis of electron trapping at the device surface between gate and drain as a mechanism able to consistently explain all of the experimentally observed degradation modes following a high-field (hot carrier) stress. This paper expands on such previous findings by showing: (i) simulation results of HFETs with

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Research paper thumbnail of CREEP BEHAVIOUR OF COMPOSITE BONE CEMENT

ABSTRACT

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Advances in Optics Design and Precision Manufacturing Technologies

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Analyses of compensation related defects in II-VI semiconductors

... P.Siffert Mat Sci.Eng. B16, 223 (1993). 7. P.Blood and JWOrton, The Electrical Characterizati... more ... P.Siffert Mat Sci.Eng. B16, 223 (1993). 7. P.Blood and JWOrton, The Electrical Characterization of Semiconductors: Majority Carriers and Electron States, (Academic Press, UK, 1992). 8. PMMooney J.Appl.Phys. 54, 208 (1983). 9. E.Lopez-Cruz, J.Gonzalez-Hemandez, DDAllred ...

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Research paper thumbnail of SI LEC GaAs nuclear detectors: characterization, performance and applications

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Gallium Arsenide charged particle detectors: deep levels effects

Bookmarks Related papers MentionsView impact

Research paper thumbnail of INFLUENCE OF DEFECTS ON DIFFUSION LENGTH INHOMOGENEITY IN GAAS-TE WAFERS

Bookmarks Related papers MentionsView impact

Research paper thumbnail of PAPERS PRESENTED AT THE 3RD INTERNATIONAL WORKSHOP ON BEAM-INJECTION-ASSESSMENT-OF-DEFECTS-IN-SEMICONDUCTORS (BIADS-93) - A NATO ADVANCED RESEARCH WORKSHOP - AUGUST 30 - SEPTEMBER 2, 1993, BOLOGNA, ITALY - FOREWORD

Materials Science and Engineering B

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Research paper thumbnail of Electronic levels in silicon MaWCE nanowires: evidence of a limited diffusion of Ag

Nanotechnology, 2015

Deep level transient spectroscopy (DLTS) was performed on lowly n-doped silicon nanowires grown b... more Deep level transient spectroscopy (DLTS) was performed on lowly n-doped silicon nanowires grown by metal-assisted wet chemical etching (MaWCE) with silver as the catalyst in order to investigate the energetic scheme inside the bandgap. To observe the possible diffusion of atoms into the bulk, DLTS investigation was also performed on the samples after removing the nanowires. Two of the four energy levels observed in the nanowires were also detected inside the substrate. Based on these results and on literature data about deep levels in bulk silicon, some hypotheses are advanced regarding the identification of the defects responsible for the energy levels revealed.

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Neutron and proton irradiation: effects on the active layer width and electric field distribution in semi-insulating GaAs Schottky diodes

Semiconducting and Insulating Materials 1998. Proceedings of the 10th Conference on Semiconducting and Insulating Materials (SIMC-X) (Cat. No.98CH36159), 1998

ABSTRACT Irradiation (with neutrons or protons) markedly changes the values of the active layer w... more ABSTRACT Irradiation (with neutrons or protons) markedly changes the values of the active layer width as well as the electric field distribution of Schottky diodes made on semi-insulating GaAs. However, the behaviour of both of them as a function of the reverse biasing is almost the same as before irradiation, when either neutrons or protons are used. Spectroscopic measurements revealed that not only the dominant defect EL2 increases in density but also other shallower level traps, which must be accounted for to explain the observed changes of both active layer width and electric field

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Special Issue containing papers presented at the Conference on Extended Defects in Semiconductors - 2002 (EDS 2002), Bologna, Italy, 1-6 June 2002 - Preface

Journal of Physics Condensed Matter

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Defective states in semi-insulating gallium arsenide substrates

Semi-insulating gallium arsenide substrates are widely used for microwave discrete devices and in... more Semi-insulating gallium arsenide substrates are widely used for microwave discrete devices and integrated circuits. However, the performance of the above devices may be significantly affected by the substrate quality, i.e. crystal defects and related deep levels. Consequently, a careful characterization of substrates is mandatory to improve both device performance and production yields. In this work we have investigated gallium arsenide substrates from different suppliers and/or differently processed. To these substrates we have applied, discussed and compared different methodologies (current-voltage and capacitance-voltage characteristics as well as spectroscopic methods) to characterize the many deep levels which are either present in as-received semi-insulating substrates or induced by device processing such as ion implantation and the subsequent thermal annealing.

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Role of surface trap states on two-dimensional electron gas density in InAlN/AlN/GaN heterostructures

Applied Physics Letters

In order to clarify the effect of charged dislocations and surface donor states on the transport ... more In order to clarify the effect of charged dislocations and surface donor states on the transport mechanisms in polar AlInN/AlN/GaN heterostructures, we have studied the current-voltage characteristics of Schottky junctions fabricated on AlInN/AlN/GaN heterostructures. The reverse-bias leakage current behaviour has been interpreted with a Poole-Frenkel emission of electrons from trap states near the metal-semiconductor junction to dislocation induced states. The variation of the Schottky barrier height as a function of the AlN layer thickness has been measured and discussed, considering the role of the surface states in the formation of the two dimensional electron gas at AlN/GaN interface.

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Research paper thumbnail of Breakdown and low-temperature anomalous effects in 6H SiC JFETs

International Electron Devices Meeting 1998. Technical Digest (Cat. No.98CH36217), 1998

Dipartimento di Elettronica e Informatica and INFM, University of Padova, via Gradenigo 6/A, 1-35... more Dipartimento di Elettronica e Informatica and INFM, University of Padova, via Gradenigo 6/A, 1-35 13 1 Padova, Italy, Tel. +39-049-8277658; Fax +39-49-8277699; e-mad: zanoni@dei.unipd.it ($) Dipartimento di Ingegneria dei Materiali, University of Trento, via ...

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Research paper thumbnail of Influence of surface pre-treatment on the electronic levels in silicon MaWCE nanowires

Nanotechnology, 2015

Deep level transient spectroscopy (DLTS) was performed on n-doped silicon nanowires grown by meta... more Deep level transient spectroscopy (DLTS) was performed on n-doped silicon nanowires grown by metal-assisted wet chemical etching (MaWCE) with gold as the catalyst in order to investigate the energetic scheme inside the bandgap. To observe the possible dependence of the level scheme on the processing temperature, DLTS measurements were performed on the nanowires grown on a non-treated Au/Si surface and on a thermally pre-treated Au/Si surface. A noticeable modification of the configuration of the energy levels was observed, induced by the annealing process. Based on our results on these MaWCE nanowires and on literature data about deep levels in bulk silicon, some hypotheses were advanced regarding the identification of the defects responsible of the energy levels revealed.

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