Steve Sque - Report on the ICDS-22

Introduction

The 22^nd International Conference on Defects in Semiconductors (ICDS) was held on campus at the University of Århus in Denmark, from 28^th July to 1^st August 2003. The conference covered work on a wide range of semiconductor materials, including the nitrides (e.g., AlN and GaN), group-IV based semiconductors: Si, Ge, diamond, SiC and their alloys, and III-V and II-VI semiconductors. Furthermore, defects in oxides, magnetic semiconductors, and defects related to nanocrystals were among the topics discussed. The ICDS was attended by ∼280 delegates with a wide variety of nationalities.

The conference adopted the following general structure. In the morning there would be a plenary session, followed by a break and then two oral sessions running in parallel. Lunch would follow, and the afternoon would contain poster sessions, further parallel oral sessions, and on Wednesday the conference excursion.

Session A: Defects in Diamond

The oral session of primary interest to the U.K. Diamond Research Network was held on the first day of the conference and consisted of an invited lecture and four contributed talks.

Konstantin Iakoubovskii (Catholic University of Leuven, Belgium) presented his invited keynote address on the topic of the annealing of vacancies and interstitials in diamond, and in particular he detailed the role of nitrogen in the production and annealing of such defects. The concentration of single interstitials vs. annealing temperature was measured, naturally for different types of diamond, as it is the nitrogen content that defines these types. Konstantin suggested the dominant forms that nitrogen takes in the different types of diamond, and associated these with the concentrations of vacancies and carbon interstitials at varying annealing temperatures.
Alison Mainwood (King's College London, U.K.) spoke on the interaction of hydrogen-implantation with boron in diamond — specifically the passivation of boron by hydrogen and the damage to the lattice caused by the implantation. Cathodoluminescence (CL) was used to investigate different depths into samples of differing boron concentrations, and the annealing behaviour of the samples was investigated. The results were dominated by damage caused to the lattice by the implantation, and neither H nor B–H complexes were satisfactorily detected, although it was clear that the boron was passivated by hydrogen even outside of the range of implantation. The main conclusion was that implantation causes damage that is not removed by reasonable annealing, and that it is therefore a poor method for doping.
Rolf Sauer (University of Ulm, Germany) was next to speak, and did so regarding bound exciton luminescence related to phosphorus donors in CVD diamond. He reported results from low-temperature CL measurements on phosphorus-doped grown chemical-vapour-deposited (CVD) diamond, and detailed an observed phosphorus bound-exciton spectrum including a novel CL spectrum at high photon energies. The origin of this spectrum was discussed, and it was concluded that it was most likely due to isoelectronic traps consisting of a boron atom and a phosphorus atom on close-by lattice sites.
Next, work by Matthew Watkins (King's College London, U.K.) on transition metals in diamond was presented by Alison Mainwood. She described two models for the electronic structure of transition metals (TMs) in diamond, and showed that ab-initio Hartree-Fock calculations suggest the two models represent extremes that are not met in practice. In particular, the electronic structures of TMs change from being best described by the Ludwig-Woodbury model to being better described by the vacancy model as the atomic number of the TM increases.
My own presentation was next, in which I spoke on the electrical activity of chalcogen and pnictogen hydrogen defects in diamond. I described my ab-initio density-functional-theory (DFT) calculations of the electrical levels of substitutional chalcogen (S, Se, and Te) and pnictogen (N, P, As, and Sb) defects in diamond, and of their single-hydrogen complexes. My main finding was that both arsenic and antimony are shallower donors than phosphorus, which so far is the most successful donor found experimentally, and I presented the case for the inclusion of arsenic into diamond.

Corbett Session

A session of particular interest to PhD students in the U.K. Diamond Research Network might have been the Corbett Session, in which PhD students gave oral presentations in the hope of winning the prestigious Corbett Prize for the best student presentation, as voted for by the audience. The session consisted of six 15-minute talks.

Atsushi Koizumi (Nagoya University, Japan) started the session with his talk about the effects of GaAs:Er,O active layer thickness on luminescence properties of GaInP/Er,O-co-doped GaAs/GaInP injection-type double heterostructure light-emitting diodes. His main findings were that the emitted light intensity increases with increasing active layer thickness, although the excitation cross-section shows a concurrent decrease, so that there is a compromise to be met.
Hisaomi Iwata (Luleå University of Technology, Sweden) spoke next on stacking faults in silicon carbide. After introducing stacking faults (SFs), Hisaomi told how they can introduce new electrical levels localised at the SF, and showed that they give rise to a split-off band in the bandstructure. He also spoke on the validity of modelling SFs as simple rectangular quantum wells.
Naoki Fukata (University of Tsukuba, Japan) presented his work on the in-situ spectroscopic measurement of defect formation in SiO₂ induced by femtosecond laser radiation. He included a movie showing how the colour of laser light transmitted through SiO₂ changes as the sample undergoes structural changes. It was found that the irradiation produces self-trapped excitons, followed by oxygen vacancies. The measurement technique allows the study of the structural change of SiO₂ during irradiation.
Hannah Smith (King's College London, U.K.) spoke next, about mapping the energy levels of the self-interstitial in diamond. Stress was applied in different crystallographic directions in order to investigate the effect on the energy levels of the ⟨001⟩ split-interstitial in diamond. It was found that the uniaxial stress perturbations led to optical transitions that are not predicted by theory.
Natalia Martsinovich (University of Sussex, U.K.) described her DFT calculations on hydrogen-defect complexes in silicon. The stability of various structures of small hydrogen aggregates in silicon was investigated. She found that several of the H₂^* di-hydrogen defect can aggregate along the (110) direction, and lead to the formation of so-called ‘H-induced platelets’ in silicon. Natalia also investigated the role of a stable OH₂ complex in H-enhanced oxygen diffusion in silicon.
Last to speak was Michael Scarpulla (University of California, Berkeley, U.S.A.), and he presented work on diluted magnetic semiconductors formed by ion implantation and pulsed-laser melting. In Ga(Mn)As and Ga(Mn)P, manganese (in concentrations of ∼3–6%) supplies magnetic ions and holes to the system, and single-crystal Ga(Mn)P can be grown with ∼60% of Mn on Ga substitutional sites. Now, the presence of Te helps increase the substitutional Mn fraction to ∼80%, but can quench the ferromagnetism. A higher substitutional Mn fraction will, however, raise the Curie temperature.

The winner of the Corbett Prize was announced at the conference banquet on Thursday night - Naoki Fukata of the University of Tsukuba, Japan. He received a ‘diploma’, a cash prize, and of course a hearty round of applause.

Poster Session

Two poster sessions were held over the course of the conference, the first session having an area dedicated to posters regarding work on diamond.

L. V. C. Assali (University of São Paulo, Brazil) presented R. Larico's work on the structural and electronic properties of Ni-related active centres in diamond.
Krish Bharuth-Ram (University of Natal, South Africa) presented a poster on implantation sites of Cu atoms in diamond.
Steen Dannefaer (University of Winnipeg, Canada) displayed a poster regarding the application of the positron annihilation technique in the detection of vacancies in brown diamonds.
J. F. Justo (University of São Paulo, Brazil) presented L. V. C. Assali's work describing a comparative study on titanium impurities in silicon, diamond, and silicon carbide.
Alexander Nizovtsev (National Academy of Sciences, Minsk, Belarus) gave a poster on NV centres in diamond: spin-selective photokinetics.
Luis Rino (University of Aveiro, Portugal) defended a poster on work regarding nickel-nitrogen complexes in synthetic diamond: the 1.660 eV luminescence system.

General

The ICDS-22 was a great success, with a large number of works presented orally and in poster presentations. Unfortunately, the field of diamond research constituted only a very small part of the conference, although what was presented was of good value, and as always, there was much to be learnt from contemporaneous research into other semiconductor materials. The next ICDS will be held in 2005 at Awaji Island in Japan, under the chairmanship of Hiroshi Katayama-Yoshida.