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Many
Derek W Palmer
Identity and Semiconductor-Related Publications


        E-Mail: d.w.palmer@semiconductors.co.uk

I was previously a Senior Lecturer in Physics in the School of Physics and Astronomy of the University of Sussex in Brighton, UK. My research there comprised experimental studies of the properties & structures of lattice defects in semiconductors (Ge, Si and III-V materials) & bcc metals, electron & ion irradiation-damage processes and ion implantation. The lattice defects were investigated by electrical methods (electrical resistivity, Hall effect and majority-carrier & minority-carrier DLTS)
and by light-ion-channelling / Rutherford Back-Scattering / nuclear reactions.
At present I am an Honorary University Fellow at the University of Exeter in Devon, UK,
associated there with the "Quantum Solids and Nanostructures" research group in the School of Physics   WebSite


Some of my semiconductor-related research publications are listed below.
If you would like a pdf copy of any those publications, please send your request to my e-mail address stated above.
With your request, please include the name and address of your academic or industrial organisation.


  Photograph of Derek W Palmer

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Electronic Energy Levels in Group-III Nitrides
Derek W Palmer
in
The Elsevier Encyclopedia entitled
"Comprehensive Semiconductor Science and Technology"
(2011), Volume 4, pp. 390–447
(Elsevier Publishers, Amsterdam) - Editors: Bhattacharya P, Fornari R and Kamimura H
Encyclopedia Details

SYNOPSIS
This Chapter, "Electronic Energy Levels in Group-III Nitrides", of the Encyclopedia is a detailed review of the published information concerning the electronic energy levels created within the valence-band to conduction-band energy gap of crystalline boron nitride, aluminum nitride, gallium nitride and indium nitride by the presence of lattice defects and impurities. Knowledge and understanding of the bandgap levels that can occur in these III-Nitride semiconductors are essential for producing effective p-type and n-type doping and for optimization of their properties, including electrical conductivity, carrier mobilities and optical luminescence, for their many electronic and optoelectronic applications. Theoretical and experimental data for the zinc-blende and wurtzite structures are considered in detail, and certainties and uncertainties concerning the energy levels and their likely impurity or defect identities are assessed.

Please send me a pdf copy of this paper.


First principles studies of the effect of (001) surface terminations on the electronic properties
of the negatively charged nitrogen-vacancy defect in diamon
H Pinto, D W Palmer, R Jones, J P Goss, Amit K Tiwari, P R Briddon, Nick G Wright, Alton B Horsfall, M J Rayson and S Öberg

Physical Review B 86 (2012) 045313 (eight pages)

Density functional calculations have been carried out on (001)-orientated slabs of diamond with different surface terminations. A negatively charged nitrogen-vacancy defect (NV^-) is placed in the middle of the slab approximately 1 nm from each surface and the effect of the surface on the internal optical transition in NV is investigated. The calculations show that the chemical nature of the surface is important. We find that although the clean surface does not lead to charge transfer between the defect and the surface, there is a splitting of the empty excited state, the final state in optical absorption, arising from a strong hybridization of the surface and defect bands. This leads to a broadening of the 1.945-eV transition of the NV^- defect. OH- and F-terminated surfaces have no surface states in the band gap and again charge transfer between the defect and surface does not occur. The splitting of the e levels responsible for the optical transitions for OH or F termination is similar to that found in periodic boundary condition simulations for bulk diamond where the defects are separated by 1 nm, and thus the calculations show that hydroxylated or fluorinated surfaces give favorable optical properties.



Ab-Initio Studies of Fluorine Passivation on the Electronic Structure of the NV- Defect in Nanodiamond
H Pinto, D W Palmer, R Jones, J P Goss, P R Briddon and S Öberg

Journal of Nanoscience and Nanotechnology 12 (2012) 1–5
(Proceedings of the E-MRS Meeting held in Strasbourg, France in May 2011)

We have investigated using density functional theory the effect of fluorine termination of a (001) diamond surface on the electronic energy levels of an NV- centre buried beneath the surface. We find that, like OH termination, fluorine passivates the surface and reduces the influence of the surface on the electronic properties of the NV- centre. The results have significance for the optical properties of NV- defects in nanodiamonds.



On the diffusion of NV defects in diamond
H Pinto, R Jones, D W Palmer, J P Goss, P R Briddon and S Öberg

Phys Stat Solidi-A 1-4 (29 May 2012) ...
(Proceedings of the Hasselt Diamond Workshop, 14-16 March 2012)

Besides their importance for quantum information processing, NV defects are crucial agents for the diffusion and aggregation of nitrogen in diamond. In the absence of transition metals, it is thought that the first stage of nitrogen aggregation,where close neighbour nitrogen pairs are formed, is mediated by NV defects. Here we use density functional theory to explore the barriers to NV diffusion. We conclude that the barrier is around 5 eV when there is a ready source of vacancies and that this barrier is weakly dependent on pressure.



Ab-initio study of the diffusion of NV defects in diamond
H Pinto, D W Palmer, R Jones, J P Goss, P R Briddon and S Oberg

Presented at the 63rd Diamond Conference, Univ of Warwick, 09-12 July 2012
The Conference Book includes the extended abstract of the paper.

 



A theoretical study of the diffusion of nitrogen-vacancy defect in diamond
H Pinto, D W Palmer, R Jones, J P Goss, P R Briddon and S Oberg

Presented at the NanoTP-Theory Meeting, Aveiro, Portugal, June 2012 ..

Nitrogen is a prominent impurity in diamond. Indeed, diamond can be categorized according to the concentration of nitrogen present, type I when signifleant concentrations are present and type II otherwise. Type I diamond can be further divided regarding the type of defect present. In type Ib diamonds, it exists mainly as an amphoteric substitutional imparity N, while, in type la diamonds, it exists mainly in complexes such as pairs of neighbouring N defects labelled A centres, vacancy-nitrogen centres VNj with j running from 1 to 4, as well as nitrogen interstitial defects. The binding energy of nitrogen to the vacancy increases with the number of nitrogen atoms and so, in natural diamonds which have been exposed to high temperatures for millennia, the main nitrogen defects are A centres and B centres which are VN4. Of interest here is the diffusion mechanism by which these multi-nitrogen defects are created. Besides their importance for quantum information processing, the NV defects are believed to be crucial agents for the diffusion and aggregation of nitrogen in diamond. In the absence of transition metals, it is thought that the first stage of nitrogen aggregation is mediated by NV defects. In this paper, using local-density functional theory, we investigate the migration and re-orientation barriers of NV. We found that the reorientation and the diffusion have very similar barriers of around 5 eV in agreement with barriers found experimentally for the formation of A centres in HPHT diamond as well as IN previous theoretical calculations. Moreover we discuss the influence of pressure and we conclude that the diffusion of NV is almost independent of pressure.



Ab-initio studies of different surface terminations on the electronic properties of NV-
in diamond

H Pinto, D W Palmer, R Jones, J P Goss, P R Briddon and S Öberg
NanoteC11 Conference, Nantes, France, 31 August - 03 Sept 2011

We have studied, using large scale ab-initio DFT-LDA calculations, the influences of different surface terminations of the (001) surface on the electronic properties of the NV- centre (the nitrogen-vacancy lattice defect in its negative charge state) in diamond. The calculations predict that when the surface is OH or F terminated there is a minimum interaction between the defect and the surface, while the bare surface produces splitting of the e-level involved in the NV luminescence, and therefore would be expected to produce broadening of the luminescence.



Surface effects on the luminescence of the NV- defect in diamond
H Pinto, D W Palmer, R Jones, J P Goss, P R Briddon and S Öberg
Presented at the 62nd Diamond Conference, University of Warwick, UK, 04-07 July 2011

In this work we have investigated for nanodiamond the influence of the bare (001) diamond surface, and also hydroxylated and fluorinated (001) diamond surfaces, on the electronic band structure of the NV- centre when it lies between 1 nm and 2 nm from the surface. The results indicate that when the (001) diamond surface is OH or F terminated there is a minimum interaction between the defect and the surface, while the bare (001) diamond surface produces splitting of the E-level involved in the NV- 1.945 eV zero-phonon luminescence line and therefore would be expected to produce broadening of that luminescence line.




Ab-initio studies of surface-fluorination effect on the electronic structure of the NV- defect in nanodiamond
H Pinto, D W Palmer, R Jones, J P Goss, P R Briddon and S Öberg
E-MRS Spring Meeting, Nice, France, 09-11 May 2011: to be published in the Meeting Proceedings

We have investigated, using density functional theory, the effect of fluorine termination of a (001) diamond surface on the electronic energy levels of an NV- centre buried beneath the surface. We find that, like OH termination, fluorine passivates the surface and has less influence on the electronic properties of the NV- centre. The results have significance for the optical properties of NV- defects in nanodiamonds.




Theory of the surface effects on the luminescence of the NV- defect in nanodiamond
H Pinto, R Jones, D W Palmer, J P Goss, P R Briddon and S Öberg
Hasselt Diamond Workshop (SBDD XVI), Hasselt, Belgium, 21-23 February 2011,
to be published in the Proceedings, Phys. Status Solidi A, 2011

A vacancy with one of the carbon neighbours replaced by a nitrogen atom in diamond (the NV centre) is a defect of particular interest due to its many potential applications. In the negatively charged state, the defect is paramagnetic with spin 1 and under optical excitation it exhibits an intense luminescence with a zero-phonon line at 1.945 eV. This fluorescence is found in nanodiamonds even as small as 5 nm and an important question is the effect of the surface of the nanodiamond on the optical emission of NV- defects in nanodiamonds. Density functional calculations have been used in this work to investigate the effect of the (001) and (001)-OH diamond surfaces on the electronic structure of NV- defects in nanodiamonds. We show that the (001)-OH diamond surface has the minimum interaction with the defect and is the ideal terminating surface of nanodiamonds, while the (001) diamond clean surface has a strong effect on broadening the emission.




Kinetics of the electronically stimulated formation of a boron-oxygen complex in crystalline silicon
Derek W Palmer, Karsten Bothe and Jan Schmidt
Physical Review B 76 (2007) 035210-1 to -6

We present new experimental data relating to the slow stage of the illumination-induced or electron-injection-induced generation, in crystalline p-type silicon, of the carrier-recombination center believed to be the defect complex (BsO2i)+ formed by diffusion of oxygen interstitial dimers O2i++ to substitutional boron atoms Bs-, and, taking account of those data, we consider a detailed theoretical model for the kinetics of the diffusion reaction. The model proposes that the generation rate of the (BsO2i)+ defects is controlled by capture of a majority-carrier hole by the dimer following capture of a minority-carrier electron, and by the Coulomb attraction of the O2i++ to the Bs- atom, and leads to predictions for the defect generation rate that are in excellent quantitative agreement with experiment.       Full Paper





Electronically Stimulated Degradation of Silicon Solar Cells
J Schmidt, K Bothe, D Macdonald, J Adey, R Jones, and D W Palmer

J. Mater. Res. 21 (2006) 5-12 (published as an "Outstanding Paper" of the MRS 2005 Spring Meeting)
Carrier lifetime degradation in crystalline silicon solar cells under illumination with white light is a frequently observed phenomenon. Two main causes of such degradation effects have been identified in the past, both of them being electronically driven and both are related to the most common acceptor element, boron, in silicon: (i) the dissociation of iron-boron pairs and (ii) the formation of recombination-active boron-oxygen complexes. While the first mechanism is particularly relevant in metal-contaminated solar-grade multicrystalline silicon materials, the latter process is important in monocrystalline Czochralski-grown silicon, rich in oxygen. This paper starts with a short review of the characteristic features of both processes. We then briefly address the effect of iron-boron dissociation on solar cell parameters. Regarding the boron-oxygen-related degradation, the current status of the physical understanding of the defect formation process and the defect structure are presented. Finally, we discuss different strategies for effectively avoiding the degradation.



E Center in Silicon Has a Donor Level in the Band Gap
A Nylandsted Larsen, A Mesli, K Bonde Nielsen, H Kortegaard Nielsen, L Dobaczewski, J Adey, R Jones,
D W Palmer, P R Briddon and S O¨berg

Phys Rev Lett 97 (2006) 106402

It has been an accepted fact for more than 40 years that the E center in Si (the group-V impurity— vacancy pair)—one of the most studied defects in semiconductors—has only one energy level in the band gap: namely, the acceptor level at about 0.45 eV below the conduction band. We now demonstrate that it has a second level, situated in the lower half of the band gap at 0.27 eV above the valence band. The existence of this level, having a donor character, is disclosed by a combination of different transientcapacitance techniques and electronic-structure calculations. The finding seriously questions some diffusion-modeling approaches performed in the past. (DOI: 10.1103)




Mechanisms of Light-Induced Degradation in Mono- and Multi-Crystalline Silicon Solar Cells
J Schmidt, K Bothe, D Macdonald, J Adey, R Jones and D W Palmer,
Proceedings, 20th European Photo-Voltaic Conference, 06-10 June 2005, Barcelona, Spain,

Light-induced degradation of crystalline silicon solar cells is a frequently observed phenomenon. Two main causes of such degradation effects have been identified in the past, both of them being electronically driven and both related to the most common acceptor element, boron, in silicon: (i) the dissociation of iron-boron pairs and (ii) the formation of recombination-active boron-oxygen complexes. While the first mechanism is particularly relevant in metal-contaminated solar-grade multicrystalline silicon materials, the latter process is important in monocrystalline Czochralski-grown silicon, rich in oxygen. This paper starts with a short review of the characteristic features of the two processes. We then briefly address the effect of iron-boron dissociation on solar cell parameters. Regarding the boron-oxygen-related degradation, the current status of the physical understanding of the defect formation process and the defect structure are presented. Finally, we discuss different strategies for effectively avoiding the degradation.




Theory of Boron-Vacancy Complexes in Silicon
J Adey, R Jones, D W Palmer, P R Briddon and S Öberg
Phys Rev B 71 (2005) 165211-1 to -6,

The substitutional boron-vacancy BsV complex in silicon is investigated using the local density functional theory. These theoretical results give an explanation of the experimentally reported, well established metastability of the boron-related defect observed in p-type silicon irradiated at low temperature and of the two hole transitions that are observed to be associated with one of the configurations of the metastable defect.   BsV is found to have several stable configurations, depending on charge state.  In the positive charge state the second nearest neighbor configuration with C1 symmetry is almost degenerate with the second nearest neighbor configuration that has C1h symmetry since the bond reconstruction is weakened by the removal of electrons from the center. A third nearest neighbor configuration of BsV has the lowest energy in the negative charge state.  An assignment of the three energy levels associated with BsV is made.  The experimentally observed Ev + 0.31 eV and Ev + 0.37 eV levels are related to the donor levels of second nearest neighbor BsV with C1 and C1h symmetry respectively. The observed Ev + 0.11 eV level is assigned to the vertical donor level of the third nearest neighbor configuration. The boron-divacancy complex BsV2 is also studied and is found to be stable with a binding energy between V2 and Bs of around 0.2 eV. Its energy levels lie close to those of the V2.  However, the defect is likely to be an important defect only in heavily doped material.




Electronically Stimulated Degradation of Crystalline Silicon Solar Cells
J Schmidt, K Bothe, D Macdonald, J Adey, R Jones, and D W Palmer,
MRS Spring Meeting, 28 March - 01 April 2005, San Francisco, California, USA,

Carrier lifetime degradation in crystalline silicon solar cells under illumination with white light is a frequently observed phenomenon. Two main causes of such degradation effects have been identified in the past, both of them being electronically driven and both are related to the most common acceptor element, boron, in silicon: (i) the dissociation of interstitial ironsubstitutional boron (FeiBs) pairs and (ii) the formation of recombination-active boron-oxygen complexes. In solar-grade multicrystalline silicon (mc-Si), the first mechanism is most relevant. This well-known process, which is linked to the degree of iron contamination in the material, can also be observed in single- crystalline iron-contaminated B-doped float-zone (FZ) and Czochralski (Cz) silicon and is not restricted to mc-Si. The second carrier lifetime degradation effect can be observed in metal-impurity-free B-doped Cz-Si rich in oxygen. This effect is attributed to the simultaneous presence of Bs and interstitial oxygen (Oi). Interestingly, as for the FeiBs dissociation, this degradation effect also occurs in the dark when minority-carriers are injected (e.g., by a forward-biased pn junction), leading to the conclusion that the degradation is caused by the presence of minority-carriers and that photons are not directly involved. However, in contrast to the FeiBs-related lifetime degradation, which also occurs during annealing above ~100°C, the latter degradation effect is fully reversible by annealing above ~200°C, i.e., the degraded lifetime recovers during low temperature annealing, making it relatively easy to distinguish between the two effects. Recently, much research has been devoted to the boron-oxygen-related degradation problem, which is presently the main obstacle for making single-crystalline Cz-Si an ideal cost-saving material for high-efficiency solar cells. This contribution reviews the present physical understanding of both degradation effects and discusses different approaches for reducing or even completely avoiding them. Special attention is paid to a recently proposed defect reaction model [J. Schmidt and K. Bothe, Phys. Rev. B 69, 024107 (2004)] of the boron-oxygen degradation, in which a fast-diffusing oxygen dimer (O2i) is trapped by Bs to form a BsO2i complex, acting as a highly effective recombination center. Results of theoretical calculations using density functional theory show that BsO2i is a bistable defect with a donor level in the upper half of the silicon band gap, in good agreement with the results of temperature- and injection- dependent lifetime measurements. Calculated activation energies for the dissociation and association of the BsO2i complex are also in excellent agreement with the barrier energies determined experimentally on lifetime samples and solar cells.




Mechanisms of Light-Induced Degradation in c-Si Solar Cells
J Schmidt, K Bothe, D Macdonald, J Adey, R Jones and D W Palmer
Proceedings, Fourth Internat. Symposium on Advanced Science & Technology of Silicon Materials
22-26 November 2004, Kona, Hawaii, USA

Light-induced degradation of crystalline silicon solar cells is a frequently observed phenomenon. Two main causes of such degradation effects have been identified in the past, both of them being electronically driven and both are related to the most common acceptor element, boron, in silicon: (i) the dissociation of iron-boron pairs and (ii) the formation of recombination-active boron-oxygen complexes. While the first mechanism is particularly relevant in metal-contaminated solar-grade multicrystalline silicon materials, the latter process is important in monocrystalline Czochralski-grown silicon rich in oxygen. This paper starts with a short review of the characteristic features of both processes. We then briefly address the effect of iron-boron dissociation on solar cell parameters. Regarding the boron-oxygen-related degradation, the current status of the physical understanding of the defect formation process and the defect structure are presented. Finally, we discuss different strategies for effectively avoiding the degradation




Degradation of Boron-Doped Czochralski-Grown Silicon Solar Cells
J Adey, R Jones, D W Palmer, P R Briddon and S Öberg
Phys Rev Lett 93 (2004) 055504-1 to -4

The formation mechanism and properties of the boron-oxygen center responsible for the degradation of Czochralski-grown Si(B) solar cells during operation is investigated using density functional calculations.We find that boron traps an oxygen dimer to form a bistable defect with a donor level in the upper half of the band gap. The activation energy for its dissociation is found to be 1.2 eV. The formation of the defect from mobile oxygen dimers, which are shown to migrate by a Bourgoin mechanism under minority carrier injection, has a calculated activation energy of 0.3 eV. These energies and the dependence of the generation rate of the recombination center on boron concentration are in good agreement with observations.
See also Erratum (printing error in a figure caption) in Phys Rev Lett 93 (2004) 169904




Investigation of the Anomalous Signature of the (Ec-0.19eV) Defect produced in Proton-Implanted n-GaAs
W O Siyanbola and D W Palmer
Materials Engineering 13 (2002) 179-186

The nature and the anomalous emission characteristics reported for an electron trap PE5 induced by proton implantation in n-GaAs have been investigated. Using conventional majority-carrier Deep Level Transient Spectroscopy (DLTS), the signature of the defect level was determined after 1.0 MeV proton and 2.0 MeV helium ion irradiations respectively. No evidence of the reported anomalous emission property was observed. In contrast, we found that the defect exhibited the usual emission characteristics with apparent electronic energy level at (0.19±0.02) eV and a capture cross-section of (1.93±0.3)xl0-13 cm2. Our analyses further suggested that the defect is not necessarily hydrogen-impurity related as previously proposed and that it seems likely to arise from initial atomic displacement.




Production Rate of the Electron Trap E3 in Proton-Irradiated n-GaAs Schottky Diodes
W O Siyanbola and D W Palmer
Materials Engineering 13 (2002) 89-97

By the use of Deep Level Transient Spectroscopy (DLTS) and capacitance-voltage profiling we have studied the production rate of the well known electron trap E3 in 1.0 MeV proton- irradiated n-GaAs Schottky diodes fabricated from VPE and MBE grown layers. In VPE-grown layers irradiated at room temperature to cumulative doses of 5.55 x 1011 cm-2, the trap E3 production rate was found to be 302±30cm-1, while in the MBE-grown layer irradiated to a total dose of 8.0 x 1012 cm-2, the defect production rate was evaluated to be 285±15 cm-1. A comparison of these results with those obtained elsewhere in proton-irradiated LPE grown layers showed no significant sample dependence of E3 production rate; consistent with published work in electron-irradiated n-GaAs. The implication of these results concerning the nature of the E3 defect is also discussed.



Point Defects and Non-Doping Impurities in Semiconductors and Their Characterisation by Electrical Techniques
D W Palmer
in 'Crystal Growth of Materials for Energy Production and Energy Saving Applications'
(R Fornari and L Sorba (Editors): Edizioni ETS, Italy, 2001), pages 148-171
Proceedings, International Study School, ICTP Trieste, 05-10 March 2001

The presence of lattice point defects at non-equilibrium concentrations and of non-doping impurities can never be completely prevented in the growth and processing of semiconductors, and such imperfections can have serious effects, often deleterious but sometimes beneficial, on the electrical properties of the semiconductor and on the electronic devices manufactured therefrom. It is therefore essential to be able to detect and understand those imperfections. Appropriate electrical measurements on semiconductors - conductivity & Hall coefficient in homogeneous structures, and current-voltage, thermally-stimulated capacitance & current, photo-capacitance & deep level transient spectroscopy (including under applied uniaxial stress) in diode structures - as described in detail with up-to-date examples in this paper, lead not only to knowledge and understanding of the imperfections themselves, but also provide information on the properties of the imperfections that affect the electronic and opto-electronic behaviour of the semiconductor.



Characterization of Electroluminescent Structures
based on Gallium Arsenide Ion-Implanted with Ytterbium and Oxygen

D W Palmer, V A Dravin, V M Konnov, E A Bobrova, N N LoÏko, S G Chernook and A A Gippius
Semiconductors 35 (2001) 325-330
(Translated from Fizika i Tekhnika Poluprovodnikov, Vol. 35, No. 3, 2001, pp. 339-344)

Light-emitting diodes based on GaAs crystals ion-implanted with ytterbium and oxygen were fabricated. The current-voltage and capacitance-voltage characteristics of these diodes were analyzed. The deep level centers were studied by the deep-level transient spectroscopy. The electro-luminescence spectra of the structures include the emission lines related to optical transitions within the 4 shell of Yb3+ ions.



Characterisation of Semiconductor Heterostructures by Capacitance Methods
D W Palmer
Microelectronics Journal 30 (1999) 665-672
Proceedings, MADICA'98 Conference, 09-11 November 1998, Monastir, Tunisia

Investigations of the steady-state and transient electrical capacitance properties of semiconductor heterostructures allow determination of the conduction-band and valence-band energy offsets that occur at the interfaces between materials of different band-gaps and of the presence of carrier-trapping states both in the materials and at the interfaces. For determination of band offsets, the main technique is C-V measurement, ie of the steady-state small-signal (differential) capacitance as a function of applied voltage, and this paper outlines the C-V Intercept and C-V Charge-Profile Methods. Concerning electron and hole trapping in heterostructures including in quantum well structures, the presence, concentrations and energy levels of such carrier trapping states can be effectively determined by the C-V-T and DLTS techniques. This paper outlines the principles of these techniques for studying heterostructures, and gives examples of data and results.



Uniaxial Stress-Symmetry Studies on the E1, E2 and E3 Irradiation-Induced Defects in Gallium Arsenide
S J Hartnett and D W Palmer
Materials Science Forum 258-263 (1997) 1027-1032
Proceedings of the 19th International Conference on Defects in Semiconductors (ICDS-19),
21-25 July 1997, Aveiro, Portugal

To obtain information on the crystallographic symmetries of the El, E2 and E3 irradiation- induced defects in n-GaAs we have investigated the effects of uniaxial-stress upto 0.4 GPa on the DLTS spectra of epitaxial n-GaAs irradiated by 1.0 MeV protons. We find that for each of those three defect levels, uniaxial stress applied along a <100> direction of the GaAs caused increase but no broadening of the DLTS-measured electron ionisation energy, but that <110> applied stress produced both broadening of the DLTS peaks and increase in the mean ionisation energy of each defect. For the El defect the effect of 0.4 GPa <110> stress was to produce clearly observable splitting of its peak into two peaks. By detailed analysis of the DLTS peak shapes we deduce that <110> stress causes splitting of each of the El, E2 and E3 electronic energy levels into two levels of equal populations. These data strongly suggest that the El, E2 and E3 defects each have C3v (trigonal) crystallographic symmetry, ie that each is an atomic arrangement that contains a single <111> symmetry axis. The data do not support the identification of the El and E2 defects as simple arsenic vacancies of Td symmetry, but are consistent with a previous proposal that E3 defects are arsenic Frenkel pairs. We believe these to be the first uniaxial-stress studies on any irradiation-induced defect in GaAs.



A Sharp Defect-Annealing Stage Below Room Temperature in Irradiated N-Type Indium Phosphide
A Canimoglu and D W Palmer
Materials Science Forum 258-263 (1997) 837-842
Proceedings of the 19th International Conference on Defects in Semiconductors (ICDS-19),
21-25 July 1997, Aveiro, Portugal

We have irradiated n-type InP Schottky diodes at 85K using 1.0 MeV protons and have investigated the irradiation-induced defects by in-situ DLTS measurements between 85K and 350K. It is expected that in such irradiation most of the radiation-damage collisions produce rather simple lattice defects. We find that the DLTS spectrum shows strong lattice-defect peaks centred near 115K, 205K and 315K, of which the 115K peak is removed during the first DLTS measurement to room temperature. In isochronal heatings performed at steady zero applied bias the latter defect disappears in a sharp annealing stage centred near 197K for 30-minute heatings, and isothermal heatings in the same bias condition indicate defect annealing by first-order reaction kinetics. The isochronal data are consistent with an annealing activation energy and a pre-factor of approximately 0.65 eV and 1x1013 s-1 respectively. This pre-factor value indicates that the annealing involves a small number of defect jumps, and therefore strongly suggests that the annealing stage near 197K is due to interstitial-vacancy combination within a close Frenkel-pair structure of indium or phosphorus; it seems likely to be the former. By standard DLTS procedures we find the thermal ionisation energy and electron-capture cross-section of the defect to be 0.20 eV and 2 x 10-15 cm2.










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