Properties and Applications of Silicon Carbide Part 1 pdf

Identification and Kinetic Properties of the Photosensitive Impurities and Defects in High-Purity Semi-Insulating Silicon Carbide 3D.. Identification and Kinetic Properties of the Photos

ProPerties and aPPlications of silicon carbideEdited by rosario Gerhardt

Properties and Applications of Silicon Carbide

Edited by Rosario Gerhardt

Published by InTech

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referencing or personal use of the work must explicitly identify the original source.Statements and opinions expressed in the chapters are these of the individual contributors and not necessarily those of the editors or publisher No responsibility is accepted for the accuracy of information contained in the published articles The publisher

assumes no responsibility for any damage or injury to persons or property arising out

of the use of any materials, instructions, methods or ideas contained in the book

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First published March, 2011

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Properties and Applications of Silicon Carbide, Edited by Rosario Gerhardt

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Identification and Kinetic Properties of the Photosensitive Impurities and Defects in High-Purity Semi-Insulating Silicon Carbide 3

D V Savchenko, B D Shanina and E N Kalabukhova

One-dimensional Models for Diffusion and Segregation of Boron and for Ion Implantation

of Aluminum in 4H-Silicon Carbide 29

Yasuto Hijikata Hiroyuki Yaguchi and Sadafumi Yoshida

Magnetic Properties of Transition-Metal-Doped Silicon Carbide Diluted Magnetic Semiconductors 89

Andrei Los and Victor Los

Electrodynamical Modelling of Open Cylindrical and Rectangular Silicon Carbide Waveguides 115

L Nickelson, S Asmontas and T Gric

Silicon Carbide Based Transit Time Devices:

The New Frontier in High-power THz Electronics 143

Moumita MukherjeeContents

VI

Contact Formation on Silicon Carbide by Use of Nickel and Tantalum from a Materials Science Point of View 171

Yu Cao and Lars Nyborg

Other applications: Electrical, Structural and Biomedical 195

Properties and Applications of Ceramic Composites Containing Silicon Carbide Whiskers 197

Brian D Bertram and Rosario A Gerhardt

Spectroscopic properties of carbon fibre reinforced silicon carbide composites for aerospace applications 231

Davide Alfano

Effect of Self-Healing on Fatigue Behaviour

of Structural Ceramics and Influence Factors

on Fatigue Strength of Healed Ceramics 251

Wataru Nakao

Contribution to the Evaluation of Silicon Carbide Surge Arresters 259

Arnaldo Gakiya Kanashiro and Milton Zanotti Jr

Silicon Carbide Neutron Detectors 275

Fausto Franceschini and Frank H Ruddy

Fundamentals of biomedical applications of biomorphic SiC 297

Mahboobeh Mahmoodi and Lida Ghazanfari

Silicon Carbide Whisker-mediated Plant Transformation 345

Shaheen Asad and Muhammad Arshad

Bulk Processing, Phase Equilibria and Machining 359

Silicon Carbide: Synthesis and Properties 361

Houyem Abderrazak and Emna Selmane Bel Hadj Hmida

Combustion Synthesis of Silicon Carbide 389

Alexander S Mukasyan

In Situ Synthesis of Silicon-Silicon Carbide Composites from SiO2-C-Mg System via Self-Propagating High-Temperature Synthesis 411

Contents VII

High Reliability Alumina-Silicon Carbide

Laminated Composites by Spark Plasma Sintering 427

Vincenzo M Sglavo and Francesca De Genua

High Temperature Phase Equilibrium

of SiC-Based Ceramic Systems 445

Yuhong Chen, Laner Wu ,Wenzhou Sun,

Youjun Lu and Zhenkun Huang

Liquid Phase Sintering of Silicon

Carbide with AlN-Re2O3 Additives 457

Laner Wu, Yuhong Chen ,Yong Jiang,

Youjun Lu and Zhenkun Huang

Investigations on Jet Footprint Geometry and its

Characteristics for Complex Shape Machining with

Abrasive Waterjets in Silicon Carbide Ceramic Material 469

S Srinivasu D and A Axinte D

Ductile Mode Micro Laser Assisted

Machining of Silicon Carbide (SiC) 505

Deepak Ravindra, Saurabh Virkar and John Patten

Silicon carbide (SiC) is an interesting material that has found application in a variety of industries The two best known applications of this material are its use as an abrasive material and its more recent use as a wide band gap semiconductor for high power, high temperature electronic devices The high hardness of this material, known for many years, led to its use in machining tools and in other structural applications Us-age of SiC in semiconductor devices only became possible in the last twenty years, when commercially available SiC single crystals became available Thin films and nanoparticles of SiC are still rare, but monolithic SiC and composites containing SiC have been available much longer One of the challenges of working with this material is that it can crystallize into many different polymorphs, the most common being the 3C (β-SiC), and the hexagonal (α-SiC): 2H, 4H and 6H phases Because of its high melting point, achieving reasonable bulk densities in polycrystalline materials is difficult In addition, the semiconducting material forms Schottky barriers with most metals, while the formation of its native oxide, SiO2, can pose additional issues when used in oxidiz-ing atmospheres However, the scientific community has shown ingenuity in turning some of the pitfalls into decided advantages for a variety of applications.

In this book, we explore an eclectic mix of articles that highlight some new potential applications of SiC and different ways to achieve specific properties Some articles de-scribe well-established processing methods, while others highlight phase equilibria or machining methods A resurgence of interest in the structural arena is evident, while new ways to utilize the interesting electromagnetic properties of SiC continue to in-crease The reader is encouraged to explore the vast literature in this field, ranging from 40,000 up to 150,000 articles depending on which database one chooses to search

in, but several gems may be found among the chapters in this book

Preface

X

The articles have been grouped according to the following three categories: Part A: Thin Films and Electromagnetic Applications Part B: Other Applications: Electri-cal, Structural and Biomedical Part C: Bulk Processing Methods, Phase Stability and Machining

Katarina Lovrecic, the publishing process manager, deserves much credit for this work She initiated contact with the various authors and kept everyone on task throughout this process I would like to also acknowledge the assistance of my graduate students, Brian D Bertram and Timothy L Pruyn, who helped proofread the chapters and make suggestions to the authors The final editing of all materials was conducted by In-Tech publications

Rosario A Gerhardt

Professor of Materials Science and Engineering

Georgia Institute of Technology

Atlanta, USA

Thin Films and Electromagnetic Applications

Part 1 Thin Films and Electromagnetic Applications

Identification and Kinetic Properties of the Photosensitive

Impurities and Defects in High-Purity Semi-Insulating Silicon Carbide 3

Identification and Kinetic Properties of the Photosensitive Impurities and Defects in High-Purity Semi-Insulating Silicon Carbide

D V Savchenko, B D Shanina and E N Kalabukhova

X

Identification and Kinetic Properties of the

Photosensitive Impurities and Defects in

High-Purity Semi-Insulating Silicon Carbide

D V Savchenko, B D Shanina and E N Kalabukhova

V.E Lashkaryov Institute of Semiconductor Physics,

National Academy of Science of Ukraine

Ukraine

1 Introduction

Semi-insulating (SI) silicon carbide substrates are required for high power microwave

devices and circuits based on SiC and GaN SI properties of SiC can be achieved by

introducing deep levels from either impurities or intrinsic defects into the material to

compensate shallow donors and acceptors and pin the Fermi level near the middle of the

bandgap Intrinsic defects with deep levels are believed to be responsible for the SI

properties of undoped material Most of the intrinsic defects studied in SI 4H-SiC grown by

physical vapour transport (PVT) and high temperature chemical vapour deposition

(HTCVD), referred to as high purity semi-insulating (HPSI) material, have energies ranging

from 0.85 eV to 1.8 eV below the conduction band (Müller et al., 2003; Son et al., 2004)

However, not all of these defects are temperature stable and desirable for SI SiC Among the

defects, which are stable after annealing at 1600 0C – 1800 0C and believed to be responsible

for SI properties of HPSI 4H-SiC are the ID and SI-5 defects ID defect with energy level of

1.79 eV below the conduction band which occupies quasi-cubic (ID1) and hexagonal (ID2)

lattice sites were observed in both HTCVD and PVT p-type HPSI wafers and identified as

the carbon vacancy in the single positive charge state, 

SI-5 defect with energy level of 1.2  1.5 eV below the conduction band (EC) is found to be a

dominating defect among a series of other defects (SI1-SI9) observed in HTCVD and PVT

HPSI 4H-SiC substrates in the dark and under light illumination with different photon

energies (Son et al 2004) The HEI4 center with the g-values similar to those found for SI-5

defect was observed in electron irradiated n-type 4H-SiC samples but with the concentration

higher than that in HPSI samples which was sufficient to observe the hyperfine (HF)

structure of the defect (a Umeda et al., 2006) As a result, based on the analysis of the HF

structures of 29Si and 13C and first principles calculations, the SI-5 center was identified to be

1

Properties and Applications of Silicon Carbide4

originated from the negatively charged carbon antisite-vacancy (AV) pair (CSiV ) C

(b Umeda et al., 2006) The energy level of the SI-5 center obtained from the photo-EPR

studies of the electron irradiated n-type 4H-SiC samples amounts to 1.1 eV below the

conduction band and coincides with the ionization levels (EC – 1.0 eV and EC – 0.9 eV)

calculated from the first principles for the (0–) and (–2–) charge states of the CSiVC,

respectively (Bockstedte et al., 2006) According to theory the Fermi level EF is pinned at

 EC – 1.1 eV or lower due to CSiVC in SiC Thus, the single vacancies as well as the carbon

AV pairs are found to be the dominant defects responsible for the SI property of SiC

The presented review indicates that the investigation of the SI SiC material mainly was

focused on the identification of the intrinsic defects responsible for the SI properties of SiC

At the same time, investigation of the role, which they play in the trapping, recombination,

and ionization of non-equilibrium charge carriers, processes of paramount importance for

semiconducting materials, has not received proper attention HPSI 4H-SiC samples have a

specific feature of the so-called persistent relaxation (PR) of the photo-response and

persistent photoconductivity (PPC), which originate from a very long (over 30 h)

low-temperature lifetime of photo-carriers trapped into defect and impurity levels (Kalabukhova

et al., 2006)

In this chapter we present the results of identification of the intrinsic defects observed in

EPR spectrum of HPSI 4H and 6H-SiC wafers in the dark and under photo-excitation and

investigation of the PR and PPC which form in HPSI 4H-SiC samples at low temperatures

after termination of photo-excitation

The existence of very long lifetime of photo-carriers (PR of the photo-response) in

semiconductors is reported since the 1930s (Sheinkman & Shik, 1976) The phenomenon of

the PPC has been observed for a wide set of binary (Queisser & Theodorou, 1986;

Dissanayake, et al., 1991; Evwaraye et al., 1995) and amorphous semiconductor materials

(Kakalios & Fritzsche, 1984)

The main specifications of PPC are the following: 1) the type of semiconductor and it’s state

(mono- or poly-crystal, or amorphous, or powder) is not important; 2) the wavelength of

photo-excitation does not mean; 3) the photo-response time has a temperature dependence

proportional to exp(Erec/kT), where Erec is the recombination barrier, which depends on a

time; 4) residual photoconductivity can achieve a large value PPC >> 0, where 0 is a

conductivity before photo-excitation Two main models have been proposed for the

explanation of the PPC In the first model, the reason of PPC existence is a significant

concentration of traps, which serve as the recombination centres for electrons and holes and

have enough high activation energy for ionization (Litton & Reynolds, 1964) The second

model is the so called a ‘barrier model’, which supposes the space separation of

photo-carriers due to an appearance of the electrical barriers, which are potential barriers for the

recombination of carriers Macroscopic potential barriers may arise at surfaces, interfaces,

junctions, around doping inhomogeneities Microscopic barriers against recombination may

arise due to impurity atoms with large lattice relaxations (Lang & Logan, 1977; Dissanayake

& Jiang, 1992) The second model was considered in (Shik A.Ya., 1976; Ryvkin & Shlimak,

1973) as the main mechanism of PPC in CdS The height of the barriers was determined to

be equal to 105 V/cm

To distinguish between the models responsible for the PR and PPC in HPSI 4H-SiC we have

studied kinetic properties of the photosensitive paramagnetic impurities (nitrogen and

boron centers) and deep defects observed in HPSI 4H SiC, using EPR, photo EPR methods

and optical admittance spectroscopy It was expected that in the case of ‘barrier model’ electrostatic potential fluctuations will cause the noticeable shift of the g-factor of nitrogen donor centers with respect to that measured in the dark or broadening of their spectral lines

as long as 4HSiC does not have the center of inversion symmetry Otherwise, we have to reject this model and consider the role played in PR and PPC by deep traps

2 Samples and experimental technique

The nature of the intrinsic defects in HPSI 4H and 6H-SiC was studied on the samples grown up by the PVT method at the Cree Research Inc and Bandgap Technologies Inc., respectively, by EPR and photo-EPR methods The nature of PR of the photo-response and

of PPC in HPSI 4H-SiC material was studied on the samples grown by PVT method at the Cree Research Inc by photo-EPR and optical admittance spectroscopy The HPSI material was purposefully undoped SiC with a residual impurity concentration of the order of

1015 cm–3, which has a high room-temperature electrical resistivity (on the order of

1010 Ωcm) Before carrying out experiments, the samples were annealed in an inert atmosphere at T = 1800 0C to remove surface intrinsic defects which are known to be always present in a SI SiC material before its annealing and characterized by an EPR signal with isotropic g-factor g = g = 2.0025 (Macfarlane & Zvanut, 1999; Kalabukhova et al., 2001)

A study of the temperature dependence of charge carrier concentration performed on the same HPSI 4H-SiC samples on which the EPR measurements were carried out revealed that the samples were n-type, and that the Fermi level was localized in the upper half of the band gap The activation energy, derived from the slope of the dependence of charge carrier concentration on 1/T, turned out to be 1.1 eV The charge carrier concentration determined

at the highest temperature of the experiment was about 1×1015 cm–3 (Kalabukhova et al., 2004)

The EPR and photo-EPR spectra were measured in an X-band (9 GHz) and Q-band (37 GHz) EPR spectrometers in the temperature range of 4.2 K – 140 K Photo-excitation of samples by interband light was provided by a 250-W high-pressure mercury vapor lamp equipped with interference filters for wavelengths from 365 nm to 380 nm To illuminate a sample with impurity light, a 100-W xenon and halogen incandescent lamps were used in combination with either an UM-2 prism monochromator or the interference or glass filters, which enabled us to carry out photo experiments in the wavelength range from 380 nm to 1000 nm Light focused by a short-focus doubleconvex quartz lens was coupled into the resonator through a light guide, with the sample of about 1.7 x 4 mm2 in size fixed to its end face oriented such that the c axis of the crystal was perpendicular to the direction of the external magnetic field The thickness of the illuminated sample was about 35 m, which was thin enough for the light to illuminate the total sample

The PPC data obtained by optical admittance spectroscopy at T = 300 K were taken from (Kalabukhova et al., 2006) The technique employed in optical admittance spectroscopy measurements was described in considerable detail in (Evwaraye et al., 1995)

The EPR spectra were simulated with the help of an Easyspin toolbox (Stoll & Schweiger, 2005) The EPR lineshape was Gaussian The determination error of the g-factor was

 0.0002 The determination error for the defect and impurity energy levels was approximately  0.06 eV

Identification and Kinetic Properties of the Photosensitive Impurities and Defects in High-Purity Semi-Insulating Silicon Carbide 5

originated from the negatively charged carbon antisite-vacancy (AV) pair (CSiV ) C

(b Umeda et al., 2006) The energy level of the SI-5 center obtained from the photo-EPR

studies of the electron irradiated n-type 4H-SiC samples amounts to 1.1 eV below the

conduction band and coincides with the ionization levels (EC – 1.0 eV and EC – 0.9 eV)

calculated from the first principles for the (0–) and (–2–) charge states of the CSiVC,

respectively (Bockstedte et al., 2006) According to theory the Fermi level EF is pinned at

 EC – 1.1 eV or lower due to CSiVC in SiC Thus, the single vacancies as well as the carbon

AV pairs are found to be the dominant defects responsible for the SI property of SiC

The presented review indicates that the investigation of the SI SiC material mainly was

focused on the identification of the intrinsic defects responsible for the SI properties of SiC

At the same time, investigation of the role, which they play in the trapping, recombination,

and ionization of non-equilibrium charge carriers, processes of paramount importance for

semiconducting materials, has not received proper attention HPSI 4H-SiC samples have a

specific feature of the so-called persistent relaxation (PR) of the photo-response and

persistent photoconductivity (PPC), which originate from a very long (over 30 h)

low-temperature lifetime of photo-carriers trapped into defect and impurity levels (Kalabukhova

et al., 2006)

In this chapter we present the results of identification of the intrinsic defects observed in

EPR spectrum of HPSI 4H and 6H-SiC wafers in the dark and under photo-excitation and

investigation of the PR and PPC which form in HPSI 4H-SiC samples at low temperatures

after termination of photo-excitation

The existence of very long lifetime of photo-carriers (PR of the photo-response) in

semiconductors is reported since the 1930s (Sheinkman & Shik, 1976) The phenomenon of

the PPC has been observed for a wide set of binary (Queisser & Theodorou, 1986;

Dissanayake, et al., 1991; Evwaraye et al., 1995) and amorphous semiconductor materials

(Kakalios & Fritzsche, 1984)

The main specifications of PPC are the following: 1) the type of semiconductor and it’s state

(mono- or poly-crystal, or amorphous, or powder) is not important; 2) the wavelength of

photo-excitation does not mean; 3) the photo-response time has a temperature dependence

proportional to exp(Erec/kT), where Erec is the recombination barrier, which depends on a

time; 4) residual photoconductivity can achieve a large value PPC >> 0, where 0 is a

conductivity before photo-excitation Two main models have been proposed for the

explanation of the PPC In the first model, the reason of PPC existence is a significant

concentration of traps, which serve as the recombination centres for electrons and holes and

have enough high activation energy for ionization (Litton & Reynolds, 1964) The second

model is the so called a ‘barrier model’, which supposes the space separation of

photo-carriers due to an appearance of the electrical barriers, which are potential barriers for the

recombination of carriers Macroscopic potential barriers may arise at surfaces, interfaces,

junctions, around doping inhomogeneities Microscopic barriers against recombination may

arise due to impurity atoms with large lattice relaxations (Lang & Logan, 1977; Dissanayake

& Jiang, 1992) The second model was considered in (Shik A.Ya., 1976; Ryvkin & Shlimak,

1973) as the main mechanism of PPC in CdS The height of the barriers was determined to

be equal to 105 V/cm

To distinguish between the models responsible for the PR and PPC in HPSI 4H-SiC we have

studied kinetic properties of the photosensitive paramagnetic impurities (nitrogen and

boron centers) and deep defects observed in HPSI 4H SiC, using EPR, photo EPR methods

and optical admittance spectroscopy It was expected that in the case of ‘barrier model’ electrostatic potential fluctuations will cause the noticeable shift of the g-factor of nitrogen donor centers with respect to that measured in the dark or broadening of their spectral lines

as long as 4HSiC does not have the center of inversion symmetry Otherwise, we have to reject this model and consider the role played in PR and PPC by deep traps

2 Samples and experimental technique

The nature of the intrinsic defects in HPSI 4H and 6H-SiC was studied on the samples grown up by the PVT method at the Cree Research Inc and Bandgap Technologies Inc., respectively, by EPR and photo-EPR methods The nature of PR of the photo-response and

of PPC in HPSI 4H-SiC material was studied on the samples grown by PVT method at the Cree Research Inc by photo-EPR and optical admittance spectroscopy The HPSI material was purposefully undoped SiC with a residual impurity concentration of the order of

1015 cm–3, which has a high room-temperature electrical resistivity (on the order of

1010 Ωcm) Before carrying out experiments, the samples were annealed in an inert atmosphere at T = 1800 0C to remove surface intrinsic defects which are known to be always present in a SI SiC material before its annealing and characterized by an EPR signal with isotropic g-factor g = g = 2.0025 (Macfarlane & Zvanut, 1999; Kalabukhova et al., 2001)

A study of the temperature dependence of charge carrier concentration performed on the same HPSI 4H-SiC samples on which the EPR measurements were carried out revealed that the samples were n-type, and that the Fermi level was localized in the upper half of the band gap The activation energy, derived from the slope of the dependence of charge carrier concentration on 1/T, turned out to be 1.1 eV The charge carrier concentration determined

at the highest temperature of the experiment was about 1×1015 cm–3 (Kalabukhova et al., 2004)

The EPR and photo-EPR spectra were measured in an X-band (9 GHz) and Q-band (37 GHz) EPR spectrometers in the temperature range of 4.2 K – 140 K Photo-excitation of samples by interband light was provided by a 250-W high-pressure mercury vapor lamp equipped with interference filters for wavelengths from 365 nm to 380 nm To illuminate a sample with impurity light, a 100-W xenon and halogen incandescent lamps were used in combination with either an UM-2 prism monochromator or the interference or glass filters, which enabled us to carry out photo experiments in the wavelength range from 380 nm to 1000 nm Light focused by a short-focus doubleconvex quartz lens was coupled into the resonator through a light guide, with the sample of about 1.7 x 4 mm2 in size fixed to its end face oriented such that the c axis of the crystal was perpendicular to the direction of the external magnetic field The thickness of the illuminated sample was about 35 m, which was thin enough for the light to illuminate the total sample

The PPC data obtained by optical admittance spectroscopy at T = 300 K were taken from (Kalabukhova et al., 2006) The technique employed in optical admittance spectroscopy measurements was described in considerable detail in (Evwaraye et al., 1995)

The EPR spectra were simulated with the help of an Easyspin toolbox (Stoll & Schweiger, 2005) The EPR lineshape was Gaussian The determination error of the g-factor was

 0.0002 The determination error for the defect and impurity energy levels was approximately  0.06 eV