This document reports on an x-ray spectroscopy study of two groups of semiconductor compounds, investigating their electronic band structures through analysis of x-ray emission and absorption spectra of sulfur and phosphorus. Comparisons are made between compounds with similar crystal structures and chemical formulas to understand how small differences in structure affect the electronic properties. Key results include determination of band gaps and identification of features corresponding to different atomic orbitals in the emission spectra.

1. / PHIS. W FRANCE 7 (1997)
Colloque C2, Supplément au Journal de Physique III d'avril 1997 C2-285
Abstract With the x-ray spectroscopy method two groups of semiconducting compounds are investigated. The first group
consists of: CdhtiSi (spinel type structure; p 4 3m _ o I ), CdGa2S4 and HgGaA ( the "defective" chalcopyrite; / 4 _ s )• To
the second group belong: Tl3TaS4 (that is made of coordinative tetrahedra [TaSJ and of structure units [TlSs]; / 4 3m _ t? )
and isostructural compounds TI3PS4 and TI3ASS4 (the structural type K3PS4; F -d")- flnore
scent K-emission bands
and absorption K-spectra (XANES) of sulphur in compounds investigated are received with the resolution about 0.2 eV. The
primary L23-emission bands of S have been studied using RSM-500 sjth resolution 0.4 eV. The electron energy structure of
the valence bands are similar in isoelectronic compounds Cdln2S.f, CdGa2S,i and HgGa2S4 that follows from the likeness of the
forms of the x-ray emission bands in these compounds. At the same time the absorption SK-spectra (XANES) are alike only for
CdGa2S4 and HgGa2 S4 and differ significantly with SK-spectrum of Cdlh2S4, that is due to the difference of S-atom
sorroundings in these compounds. The similarity of the forms of all x-ray spectra in isostructural and isoelectronic compounds
TI3PS4 and TI3ASS4 proves the likeness of the electron-energy structure in these compounds and of the environment of S-atom
in these compounds. The emission and absorption spectra of S in Tt3TaS4 differ from ones of TI3PS4 and TI3ASS4, that is due to
the fact, that Ta-atom is not isoelectronic to atoms of P and As, that results in the difference of S-atom surroundings and the
electron-energy structure.
The two groups of semiconductor compounds of the type A" (CdGa2S4, HgGa2S<i, CdIn2S4> and of the type TI3AS4
(A=Ta, As, P) are very perspective to be used in quantum electronics [1,2]. For all these compounds the fluorescent K-bands
and K-absorption spectra of sulphur and phosphorus were recorded using the Ioharm spectrograph DRS-2 (Rowland circle
radius 250 mm) in the first order reflection of a quartz crystal (10 i t ) with resolution » 0.2 eV, and primary L^-bands of
sulphur were recorded using
CdGa2 S4
figure 1
grating spectrometer RSM-500
(grating radius 2000 mm) with
resolution * 0.4 eV. The
sulphur K- and L-spectra were
matched by energy to common
scale vising the energy of S K,,,-
line. The same procedure was
used for the K- and L-spectra of
phosphorus. To determine the
common energy scale for the x-
ray spectra of S and P in TI3PS4
the energies of the inner 2p
level of S and P in this
compound were measured using
the x-ray electron spectrometer.
Deconvolution of the K spectra
has been carried out to
eliminate the smearing due to
the inner K level and the
spectrometer window widths.
The short-wave part (tail) of the
corrected emission S K-band
curve was approximated by a
straight line. The latter crosses
the axis of abscissae at
X-Ray Spectroscopic Studies of some Compounds with the same Chemical
Formula and Different Crystal Structure
A.A. Lavrentyev, I.Ya. Nikiforov and B.V. Gabrelian
Department of Physics, Don State Technical University, Gagarin sq. 1, Rostov-on-Don 344010, Russia
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jp4/1997203

2. C2-286 JOURNAL DE PHYSIQUE IV
the energy E , , which was taken as a zero of
the energy scale; it is the top of the valence
band. The experimental uncorrected x-ray
spectra for S and P are shown in figures 1-2.
The K-band of S represents the energy
distribution of the partial S p-states, whereas
S Ly-band gives a direct picture of the
density of the S s-states [3] (Fig. 1-2).
For CdGa2 S4 , HgGa2 S4 and CdIn2S4 the
S K-band consists of three subtends A, B, and
C. On the x-ray K- and Lybands of S for
CdIn2 S4 , matched in Fig. 1, there are seen the
structure features B on a distance » 3.7 eV
apart from Ey.
Somewhat deeper, at the distance of » 9.5
eV from E, a narrow Cd d-band is situated
according to the data presented in [4] and on
the S K-band it has the œrresrwnding small
maximum D, indicative of some S p-states
admixture to Cd d-states. On the S Ly-band
of CdIn2 S4 there is a feature D. We interprète
the feature D as an admixture of S s-states to
Cd d-states.
The compounds investigated in the first
group have different crystal structures and the
nearest surrounding of S atoms is different
too. CdIn2 S4 is normal spinel with an S atom
surrounded by three In atoms and one Cd
atom, this surrounding represents a distorted
tetrahedron with the S atom awrdination
number being four. CdGa2 S4 and HgGaA
belong to the defect chalcopyrite structure, having an S atom surrounded by two Ga atoms and one Cd (Hg) atom, the
coordination number of the S atom being three. Nevertheless, S K-bands of these compounds sufficiently resemble each other.
From the above said it follows that local partial density of states and total density of states in usual and defect lattices for this
class of compounds differ only slightly.
The x-ray absorption spectra are possibly more sensible to changes of the compound crystal structure. The range nearest
to the absorption edge (of the order of magnitude of some eV) is determined by the density of states near the conduction baud
bottom, and the more distant range - by scattering of photoelectrons on atoms of the nearest surrounding. As is seen from
Fig. 1 the absorption spectra are considerably different. Only the absorption spectra resemblance of CdGa2 S4 and HgGaA is
noticeable. Both these compounds have the defect chalcopyrite structure.
For the compound TI3PS4 one can see the similarity between the corresponding x-ray spectra for S and P (Fig. 2). The
analysis of these spectra shows that the top of the valence band in Tl3PS4 is formed from S p-states (maximum A of the S K-
band), and the electron p-states of P (maximum B of the P K-band) situated at the energy 3.5 eV. The lower part of the
valence band in Tl3PS4 is formed from the electron s-states of S (maximum F of the Ly-band). The electron s-states ofP are
situated 2.5 eV deeper than the S s-states and form the bottom of the valence band
The forms of the x-ray spectra and density of states of isoelectronic compounds with the same type of crystal structure are
nearly always alike. This is confirmed by comparision of the x-ray K- and L-spectra of S in TI3PS4 and Tl3AsS4 (Fig. 2). Tbe
chemical formula of the compounds TI3AsS4 and Ti3TaS4 are nearly the same, but their crystal lattices are different [5], which
results in different forms of the x-ray K-absorption spectra of S in Tl3 TaS4 and Tl3AsS4 (Fig. 2).
Using corrected S K-spectra, the energy gaps E g between the emission ending and absorption beginning were determined
for the compounds investigated with experimental errors of 0.2 eV: CdGa2 S4 - 3.5 eV; HgGa2 S4 - 2.9 eV; CdIn2S4 - 2.2 eV;
Tl3 TaS4 -1.8 eV; Tl3 AsS4 -1.8 eV; TI3PS4- 2.0 eV.
References
[ 1] Physicochemical properties of semiconducting materials, ed. Novosjolova A.N. and Lazarev V.B. (Nauka, Moscow, 1979)
[2] Slivka V.Yu., Voroshilov Yu.V. and Chepur D.V. Kvant. Electron. 20 (1981) 74-93.
[3] Meisel A., Leonhardt G. and Sargan R. Rontgenspektren und chemische Bindung (Académie, Leipzig, 1977)
[4] Lotz W. J. Optical Soc. Amer. 60 (1970) 206-210.
[5] Voroshilov Yu.V. and Slivka V.Yu. Kvant. Electron. 19 (1980) 38-60.