ARTICLE IN PRESS

Physica B 376–377 (2006) 249–252
www.elsevier.com/locate/physb

A web-based database for EPR centers in semiconductors
T. Umeda, S. Hagiwara, M. Katagiri, N. Mizuochi, J. Isoya
Graduate School of Library, Information, and Media Studies, Research Center for Knowledge Communities,
University of Tsukuba, Tsukuba 305-8550, Japan

Abstract
We develop a web-based database system for electron paramagnetic resonance (EPR) centers in semiconductors. This database isavailable to anyone at http://www.kc.tsukuba.ac.jp/div-media/epr/. It currently has more than 300 records of the spin-Hamiltonianparameters for major known EPR centers. One can upload own new records to the database or can use simulation tools powered by
EPR–NMRr. Here, we describe the features and objectives of this database, and mention some future plans.
r 2005 Elsevier B.V. All rights reserved.
Keywords: EPR; Database; Semiconductor; Defect

1. Introduction
Electron paramagnetic resonance (EPR) or electron spinresonance (ESR) spectroscopy is widely used to study
defects and impurities in semiconductors. Its ﬁrst application to semiconductors was reported in 1953 for Si [1].
Since then, more than 410 EPR centers in Si have beenreported [2]. In addition, Ge, diamond, GaAs, and recently
GaN, SiC, ZnO, and other new semiconductors have beenstudied using EPR, resulting in a large accumulation of
EPR data so far. EPR spectroscopy provides uniqueinformation about the wave function of a paramagnetic
center, which can be directly compared with the results ofﬁrst-principles calculations, leading to a number of
conﬁdent identiﬁcations of defects and impurities. With
this valuable feature, it will be continually applied to
semiconductors in the future.
However, a troublesome problem with EPR for semiconductors is that, unlike in other spectrographic techniques, the spectroscopic data can not be simply describedbased on where resonant peaks are observed with thescanning of the excitation energy. This is because the EPR
spectrum is drastically changed by a crystal orientation
with respect to the applied magnetic ﬁeld. Furthermore,
there are many duplicate peaks in the spectrum due to theCorresponding author. Tel/Fax: +81 29 859 1307.

E-mail address: umeda@slis.tsukuba.ac.jp (T. Umeda).
0921-4526/$ - see front matter r 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.physb.2005.12.065

presence of symmetry-related sites in a crystal. Traditionally, EPR data have been described in terms of a set of thespin-Hamiltonian (SH) parameter tensors, from which we
can simulate a set of peak positions for a certain
experimental condition. Of course, this simulation process
requires special software as well as a deep understanding of
the SH calculation.
Due to these problems, even EPR specialists often ﬁnd it
difﬁcult to accurately compare EPR spectra. This has
become a barrier to EPR studies, and the barrier is getting
higher as the number of reports increases. Thus, tominimize this barrier and establish a more efﬁcient andconvenient system for accumulating EPR data, we havedeveloped a web (world wide web)-based database, named
EPR in Semiconductors [3]. This database is now accessible
to anyone from anywhere via the Internet.
2. Two foresightful works
Before we introduce EPR in Semiconductors, we mustmention two foresightful projects that guided us indesigning the database.
One is the big web-based database for EPR named theSpin Trap DataBase (STDB) [4]. The STDB contains morethan 10,000 records of spin traps that are used extensively
in chemical, medical, and biological science. To collect sucha large number of records, many contributors are
absolutely necessary. For this purpose, it is important toARTICLE IN PRESS
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T. Umeda et al. / Physica B 376–377 (2006) 249–252

design a simple and ﬂexible electronic format for EPR
data, one that can be handled easily by any experimentalist.
In STDB, this issue is less important because of theisotropic nature of spin traps in liquid. Deﬁning a spin trap
only requires a set of the g and hyperﬁne (HF) constants.
For semiconductors, however, one must deﬁne not only a
set of SH tensors but also symmetry-related sites of therelevant crystal.
The other is the new Landort–Börnstein series whichmakes a great effort to accumulate all the reported SH
parameters for semiconductors (Fig. 1). We believe that
this is the most sophisticated and knowledgeable compilation of EPR centers in semiconductors. However, the ways
the SH tensors are described are not unique even in thisexcellent reference. For example, as shown in Fig. 1(a), thetensors for diamond are expressed by principal values andprincipal axes [5], while for Si [Fig. 1(b)] the principal
values and a characteristic angle (y) are given instead [2].
Furthermore, these axes or angles have to be changed when
we choose a different coordinate for a spin system. This
complication also appears in ofﬁcial journals, where the SH
parameters are expressed in a variety of formats orcoordinates. We should also point out that, even using
the well-deﬁned data like in Fig. 1, there remains thecomplicated problem of calculating a set of peak positions,as we mentioned already.
Accordingly, the best way to accumulate EPR data is toelectronically store the SH parameters in a web-based
database like the STDB. We could use them to simulate a
set of peak positions for any experimental conditions wedesire. For this purpose, we need (1) an appropriate
electronic format for EPR data, (2) an appropriate
simulator that can handle the above format, and (3) an

Fig. 1. The new Landort–Börnstein series for EPR centers in (a) diamondand (b) Si, after Refs. [5] and [2], respectively. Note that both pages
summarize EPR centers of monoclinic-I symmetry, while their expressions
are apparently different.

appropriate web-based interface to offer the services of thedatabase.
3. The web-based database: EPR in Semiconductors
To satisfy the above requirements, we adopted thesimulation program EPR–NMRr, which was developedby the group of Profs. Weil (University of Saskatchewan,
Canada) and Mombourquette (Queen’s University, Canada) [6]. One of us (J. Isoya) contributed to the development
ROADMAP, EPRFD, ECHO,(1)PRTPROPAR, EULER, ↵PLOT=1, FREQ=9452.0,
AUTONUC,NSITE=12, NN=1 ↵↵Label:G6(Six2)↵(2)
Author:T. Umeda↵
Reference:J.W. Corbett, G.D.
Watkins, Phys.Rev.Lett. 7, 314(1961);G.D.Watkins, J.W. Corbett,Phys. Rev.138, A543(1965).↵
Origin:V2(+)↵
Sample:low-resistivityp-Si
irradiatedby 1.5-MeV electrons.↵
Symmetry:Monoclinic-I↵
Temperature:20K↵
Coordinate:x=[100],y=[011],z=[011]↵
RelativeIntensity:0.0934↵
OtherRemarks:Generation
rate=0.008defects/cm3 perelectron/cm2, strongly
temperature-dependent.↵
↵
0.5↵
(3)
si29↵
↵
2.0041 2.0004 2.0020↵(4)-62.4 00↵↵72.53 42.79 42.79↵
-55
0
0↵
↵
1, 1↵
↵
1 0 0↵
0 1 0↵
0 0 1↵↵-1 0 0↵0 0 -1↵
0 -1 0↵↵1 0 0↵
0 -1 0↵0 0 -1↵↵-1 0 0↵0 0 1↵
0 1 0↵↵
0-0.707107
0.707107 -0.5
0.707107 0.5↵
00.707107-0.707107 -0.5
-0.707107 0.5↵
0-0.707107-0.707107 0.5-0.707107 -0.5↵00.707107
0.707107 0.5
0.707107 -0.5↵(5)0.707107↵
-0.5↵
0.5↵
-0.707107↵
-0.5↵
0.5↵
0.707107↵
0.5↵
-0.5↵
-0.707107↵
0.5↵
-0.5↵

0
0.707107 0.707107↵-0.707107 -0.5
0.5↵
0.707107 -0.5
0.5↵ (5)↵0-0.707107 -0.707107↵
0.707107 -0.5
0.5↵
-0.707107 -0.5
0.5↵↵
0-0.707107 -0.707107↵-0.5↵-0.707107 0.5
0.707107 0.5
-0.5↵
↵
0
0.707107 0.707107↵
0.707107 0.5
-0.5↵
-0.5↵
-0.707107 0.5↵
0.0, 0.0, 90.0, 0.0↵
(6)
0.0, 90.0, 2.0↵
↵
2↵
2, 3↵
1, 4↵
(7)
↵
2↵
2, 3↵
1, 4↵
↵
2↵
2, 3↵
1, 4↵
↵
2↵
2, 3↵
1, 4↵
↵
2↵
2, 3↵
1, 4↵
↵
2↵
2, 3↵
1, 4↵
↵
2↵
2, 3↵
1, 4↵
↵
2↵
2, 3↵
1, 4↵
↵
2↵
2, 3↵
1, 4↵
↵
2↵
2, 3↵
1, 4↵
↵
2↵
2, 3↵
1, 4↵
↵
2↵
2, 3↵
1, 4↵

Fig. 2. Record ﬁle format for the EPR in Semiconductors database. This
example deﬁnes the famous G6 center (þ1 divacancy) in Si. In general,
only highlighted parts have to be changed to prepare a record ﬁle. There
are seven sections: (1) commands to execute the EPR–NMRr simulator,(2) comment lines to supply helpful information regarding this record, (3)electron spins (S) and nuclear spins (I) (for this case S ¼ 12 and I ¼ 12 of
29Si), (4) SH parameter tensors (here, a g tensor and a 29Si HF tensor), (5)12 rotation matrices for a diamond-type crystal, (6) angular parameters tospecify a crystal rotation, and (7) a transition table. Further details can befound in Ref. [3].

ARTICLE IN PRESS
T. Umeda et al. / Physica B 376–377 (2006) 249–252

of this program. We believe that it is one of the mostpowerful simulation tools for EPR specialists, and it iscertainly one of the most popular. Using the format of thisprogram, many experimentalists will be able to prepare
new record ﬁles by themselves. With the ofﬁcial permissionof Prof. Weil and Prof. Mombourquette, we have joined
EPR–NMRr to our web service program.
The record format for the database is shown in Fig. 2.
This format is basically the same as used for a ‘‘ROADMAP’’ simulation of EPR–NMRr, which calculates anangular map of the resonant ﬁelds with respect to a
crystal’s rotation. In principle, one record is deﬁned by one
text ﬁle. The ﬁle consists of Sections (1)–(7). In Section (4),two SH tensors are deﬁned by a set of three principal
values and three Euler angles. A simple matrix expressionis also available. Although the expressions of these tensors
are changed by the choice of coordinate, consistent
simulated results can always be obtained regardless of theexpressions or coordinate. To create a new record as easily

251

as possible, please reuse a similar record in the databaseand modify the highlighted parts only. It is also quitepossible to deﬁne very complicated spin systems, such as
high-spin systems, multi-nuclei systems, and spin systems
involving higher-order SH terms. More details about how
to prepare new record ﬁles can be found in our web pages(see the Help pages) or in the original EPR–NMRr
manual.
The database system is composed mainly of thecomponents shown in Figs. 3(a)–(e). Their functions andinstructions are as follows.
(a) Outputs: Users can obtain their desired outputs bysimply clicking on the Spin-Hamiltonian Parameter List
[Fig. 3(b)]. One can download original record ﬁles or one
can simulate angular map or EPR spectrum or energy level,
as shown in Fig. 3(a). Three types of simulations can be
executed for any experimental conditions, making it
possible to directly compare your experimental data withthe recorded ones. Or using the original ﬁles, one canFig. 3. The whole EPR in Semiconductors system [3].

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T. Umeda et al. / Physica B 376–377 (2006) 249–252

execute higher-grade simulations on own computer. Whena user executes a simulation, three text ﬁles will be returnedto the user. One ﬁle (.out) contains the principal values andaxes of each SH tensor in terms of various expressions,which greatly helps in understanding. The print ﬁle (.plt)
contains plot data for creating original graphs.
(b) Spin-Hamiltonian Parameter List: This is the maininterface of the database, and allows anyone to easily selectrecords and obtain various outputs as shown in Fig. 3(a).
The database is classiﬁed into six categories: Si, GaAs,
GaN, SiC, Diamond, and Others. Using this interface,authorized users, who have registered the Registration
Form [Fig. 3(e)], can edit or delete their own record ﬁles.
For each record, the updated version is automaticallygiven, as shown in the Figure. To ensure the reliability andsecurity of the database, no one can modify record ﬁlesthat have been uploaded by others. Therefore, if a center isstill controversial, there may exist two or more folders/ﬁlesthat have been uploaded by different groups for the center.
Users themselves judge which is the better one.
(c) Search Form: Both numerical search and keyword
search are available. Using this form, the desired EPR data
can quickly be found in the database.
(d) Upload Form: New records (text ﬁles) can be
uploaded to the database from here. Firstly our server
checks whether the uploaded ﬁles have a valid
EPR–NMRr format. If the check is okay, then an author
who uploaded the ﬁles will receive angular-map simulation
results (see Fig. 3(a)) so that the author can conﬁrm
visually whether those ﬁles have been correctly prepared.
Finally, the records are listed in the Spin-Hamiltonian
Parameter List [Fig. 3(b)].
(e) Registration Form: This authorizes a user to upload
new ﬁles to the database. Simply enter account name andpassword, together with personal information (name and email address), and our server automatically registers theuser. The personal information is used only for noncommercial communication from us to the registeredperson.
At present, the database contains about 300 records ofthe major known defects reported from the 1960s to the
1980s. For more recent EPR results, we plan to directly ask
researchers to upload their works to the database. Hopefully, this database will contribute to an efﬁcient accumu-

lation, maintenance, and reuse of knowledge about EPR
centers in semiconductors. We can of course help the
preparation of record ﬁles when someone contacts us (seethe contact page [3]).
Lastly, we should clarify the important relationshipbetween the journals and this database. The database does
not include a screening system. Therefore, the publicationof EPR data in an ofﬁcial journal is absolutely necessary
for their complete authorization. When one publishes any
SH parameters recorded in the database, please cite theoriginal references. If one publishes any outputs (e.g.,simulated results) generated by the database system, pleasecite this database.
4. Conclusion
We have developed a web-based database for EPR
centers in semiconductors. The database offers very useful
simulation services powered by EPR–NMRr, whichmakes it quite easy to compare one’s EPR data with theothers. Please try the database and please upload new data.
In doing so, an up-to-date and continuously expanding
database of EPR centers will be formed, which expectedly
contributes to further progress in the EPR research ofdefects in semiconductors.
Acknowledgements
We greatly acknowledge Prof. J.A. Weil and Prof. M.J.
Mombourquette for permitting us to use their program forusers of the database free of charge.
References[1] A.M. Portis, A.F. Kip, C. Kittel, W.H. Brattain, Phys. Rev. 90 (1953)
988.
[2] C.A.J. Ammerlaan, Landort–Börnstein new series, group III, vol.
41A2a, pp. 244–308.
[3] EPR in Semiconductors, http://www.kc.tsukuba.ac.jp/div-media/epr/.
[4] STDB (Spin Trap DataBase), http://epr.niehs.nih.gov/stdb.html.
[5] C.A.J. Ammerlaan, Landort–Börnstein new series, group III,
vol. 41A2, pp. 6–76.
[6] The EPR–NMRr program is available at http://www.chem.queensu.
ca/eprnmr/.