Band gap and structure of single crystal BiI 3 : Resolving discrepancies in literature Nikolas J. Podraza, Wei Qiu, Beverly B. Hinojosa, Haixuan Xu (徐海譞), Michael A. Motyka, Simon R. Phillpot, James E. Baciak, Susan Trolier-McKinstry, and Juan C. Nino Citation: Journal of Applied Physics 114, 033110 (2013); doi: 10.1063/1.4813486 View online: https://doi.org/10.1063/1.4813486 View Table of Contents: http://aip.scitation.org/toc/jap/114/3 Published by the American Institute of Physics Articles you may be interested in Electronic structure and photovoltaic application of BiI 3 Applied Physics Letters 107, 131109 (2015); 10.1063/1.4932129 Synthesis, crystal structure, and properties of a perovskite-related bismuth phase, (NH 4 ) 3 Bi 2 I 9 APL Materials 4, 031101 (2016); 10.1063/1.4943680 Enhanced gamma ray sensitivity in bismuth triiodide sensors through volumetric defect control Applied Physics Letters 109, 092105 (2016); 10.1063/1.4962293 Unusual defect physics in CH 3 NH 3 PbI 3 perovskite solar cell absorber Applied Physics Letters 104, 063903 (2014); 10.1063/1.4864778 Bandgap calculations and trends of organometal halide perovskites APL Materials 2, 081514 (2014); 10.1063/1.4893495 Detailed Balance Limit of Efficiency of p-n Junction Solar Cells Journal of Applied Physics 32, 510 (1961); 10.1063/1.1736034
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Band gap and structure of single crystal BiI3: Resolving discrepancies in literatureNikolas J. Podraza, Wei Qiu, Beverly B. Hinojosa, Haixuan Xu (徐海譞), Michael A. Motyka, Simon R. Phillpot,James E. Baciak, Susan Trolier-McKinstry, and Juan C. Nino
Citation: Journal of Applied Physics 114, 033110 (2013); doi: 10.1063/1.4813486View online: https://doi.org/10.1063/1.4813486View Table of Contents: http://aip.scitation.org/toc/jap/114/3Published by the American Institute of Physics
Articles you may be interested inElectronic structure and photovoltaic application of BiI3Applied Physics Letters 107, 131109 (2015); 10.1063/1.4932129
Synthesis, crystal structure, and properties of a perovskite-related bismuth phase, (NH4)3Bi2I9APL Materials 4, 031101 (2016); 10.1063/1.4943680
Enhanced gamma ray sensitivity in bismuth triiodide sensors through volumetric defect controlApplied Physics Letters 109, 092105 (2016); 10.1063/1.4962293
Unusual defect physics in CH3NH3PbI3 perovskite solar cell absorberApplied Physics Letters 104, 063903 (2014); 10.1063/1.4864778
Bandgap calculations and trends of organometal halide perovskitesAPL Materials 2, 081514 (2014); 10.1063/1.4893495
Detailed Balance Limit of Efficiency of p-n Junction Solar CellsJournal of Applied Physics 32, 510 (1961); 10.1063/1.1736034
Band gap and structure of single crystal BiI3: Resolving discrepanciesin literature
Nikolas J. Podraza,1 Wei Qiu,2 Beverly B. Hinojosa,2 Haixuan Xu (徐海譞),2
Michael A. Motyka,3 Simon R. Phillpot,2 James E. Baciak,4 Susan Trolier-McKinstry,5
and Juan C. Nino21Department of Physics and Astronomy, University of Toledo, Toledo, Ohio 43606, USA2Department of Material Science and Engineering, University of Florida, Gainesville, Florida 32611, USA3Department of Engineering Science and Mechanics, The Pennsylvania State University, University Park,Pennsylvania 16802, USA4Department of Nuclear and Radiological Engineering, University of Florida, Gainesville,Florida 32611, USA5Department of Materials Science and Engineering, The Pennsylvania State University, University Park,Pennsylvania 16802, USA
(Received 8 February 2013; accepted 23 June 2013; published online 19 July 2013)
Bismuth tri-iodide (BiI3) is an intermediate band gap semiconductor with potential for room
temperature gamma-ray detection applications. Remarkably, very different band gap characteristics
and values of BiI3 have been reported in literature, which may be attributed to its complicated
layered structure with strongly bound BiI6 octahedra held together by weak van der Waals
interactions. Here, to resolve this discrepancy, the band gap of BiI3 was characterized through optical
and computational methods and differences among previously reported values are discussed.
Unpolarized transmittance and reflectance spectra in the visible to near ultraviolet (UV-Vis) range at
room temperature yielded an indirect band gap of 1.676 0.09 eV, while spectroscopic ellipsometry
detected a direct band gap at 1.966 0.05 eV and higher energy critical point features. The
discrepancy between the UV-Vis and ellipsometry results originates from the low optical absorption
coefficients (a� 102 cm�1) of BiI3 that renders reflection-based ellipsometry insensitive to the
indirect gap for this material. Further, electronic-structure calculations of the band structure by
density functional theory methods are also consistent with the presence of an indirect band gap of
1.55 eV in BiI3. Based on this, an indirect band gap with a value of 1.676 0.09 eV is considered to
best represent the band gap structure and value for single crystal BiI3. VC 2013 AIP Publishing LLC.[http://dx.doi.org/10.1063/1.4813486]
I. INTRODUCTION
Bismuth tri-iodide (BiI3) is a semiconductor material for
room temperature gamma-ray detection, primarily due to its
intermediate band gap, high density, and high effective
atomic number.1–3 At room temperature, BiI3 has a rhombo-
hedral crystal structure (space group R�3, No. 148) with six
formula units per unit cell (Z¼ 6).4 Within each unit cell,
BiI3 adopts a layered structure with highly ionic Bi-I bonds
in the layers and weak van der Waals bonding between
layers. The band gap energy of the semiconductor material
determines the number of electron-hole pairs generated
under the radiation, and affects the energy resolution of the
radiation detector.5 The experimentally and computationally
determined band gap energy of BiI3 has been reported with
very different values ranging from 1.43 eV to 2.2 eV, as sum-
marized in Table I. For instance, Vashchenko and Timofeev
investigated the absorption and reflection spectra of BiI3 sin-
gle crystals and reported an indirect band gap energy of
1.7306 0.005 eV at room temperature. They also observed
the temperature dependence of the band gap energy to be
�9.2� 10�4 eV/K in the 85–293K range.6,7 Jellison et al.measured the optical functions of BiI3 single crystal using
two-modulator generalized spectroscopic ellipsometry. By
modeling the complex dielectric functions, a band gap
energy of 1.9916 0.005 eV at room temperature was deter-
mined.8 Schluter et al. theoretically studied the electronic
band structure of BiI3 by the empirical pseudopotential
method.9 Their calculation indicated that BiI3 has a direct
band structure with an energy of 2.2 eV. However, recent
first-principles pseudopotential calculations by Yorikawa
and Muramatsu suggest that BiI3 has an indirect band gap
with a much smaller energy of 1.6652 eV.10 The first-
principles linearized augmented plane-wave calculations by
Singh used three different potentials and found band gaps of
1.43, 1.67, and 1.82 eV.11 Thus, there is a clear discrepancy
in the electronic structure and band gap values reported for
BiI3 in the literature. The present work investigates the band
gap energy of BiI3 single crystal by studying its optical trans-
mission and reflection spectra in the visible to near ultravio-
let (UV-Vis) spectral range and ellipsometric spectra from
the near infrared to near ultraviolet range. As a supplement
to the experimental work, the electronic band structure of
BiI3 was also studied using density functional theory (DFT).
On the basis of the present work, the nature of the discrep-
ancy on the previously reported band gap energy values is
identified and the most likely characteristics of BiI3 are
troscopic ellipsometer over a spectral range from 0.75 to
5.15 eV (Ref. 13) for three BiI3 single crystals (A, B, C).
Sample A is the smallest in area and significant incoherent
reflections are observed from the back surface, making spec-
tra below 1.78 eV unusable. Samples B and C are larger and
the back surfaces have been roughened in order to prevent
the incoherent reflections observed for sample A. The com-
plex dielectric function spectra (e¼ e1 þ ie2) and microstruc-
tural parameters were extracted using a least squares
regression analysis and a weighted error function,14 v2, to fit
the experimental ellipsometric spectra to an optical model
consisting of a semi-infinite BiI3/BiI3 þ void layer/surface
roughness/air ambient structure. When analyzing spectra col-
lected for a uniaxial material with the optic axis perpendicu-
lar to the sample surface, the measurement is primarily
sensitive to the ordinary values of e.15 Simultaneous analysis
of measurements at multiple angles of incidence can be used
to extract both the ordinary and extraordinary e, however,the presence of relatively large surface roughness and BiI3 þvoid layers prevent accurate determination of the principal
values of e in samples B and C. The large amplitude of e pre-vents accurate determination of the principal indices for sam-
ple A, even though the BiI3 þ void layer is not present and
the surface roughness is small in magnitude. Thus, only an
effective e is measured. In this work, only effective e will bediscussed, and the loss of sensitivity at low values of a is
apparent for all e extracted by reflection based spectroscopic
ellipsometry measurements of BiI3.
III. RESULTS AND DISCUSSION
A. Band gap determined by transmission andreflection spectra
The UV-Vis transmission and reflection spectra meas-
ured from 1.55 to 4.13 eV at room temperature are shown in
Fig. 1. The absorption coefficient a was determined from the
experimental spectra by16
T ¼ ð1� RÞ2e�ad
1� R2e�2ad; (1)
where T is the transmittance, R is the reflectance, and d is
the total sample thickness. The relation between the absorp-
tion coefficient a and incident photon energy (h�) near thefundamental absorption edge can be written as17,18
TABLE I. Band gap of BiI3 single crystal reported in literature.
Characterization method Band gap nature Band gap (eV) T (K) Crystal growth method Reference
EPM Direct 2.2 0 … Schluter et al.9
First-principles pseudopotential Indirect 1.6652 0 … Yorikawa and Muramatsu10
2M. Matsumoto, K. Hitomi, T. Shoji, and Y. Hiratate, IEEE Trans. Nucl.
Sci. 49, 2517 (2002).3Y. N. Dmitriev, P. R. Bennett, L. J. Cirignano, M. Klugerman, and K. S.
Shah, in SPIE Conference on Hard X-Ray, Gamma-Ray, and NeutronDetector Physics, edited by R. B. James and R. C. Schirato (1999), Vol.
3768, p. 521.4D. Nason and L. Keller, J. Cryst. Growth 156, 221 (1995).5A. Owens and A. Peacock, Nucl. Instrum. Methods Phys. Res. A 531, 18(2004).
6V. I. Vashchenko and V. B. Timofeev, Sov. Phys. Solid State 9, 1242(1967).
7V. B. Timofeev and V. I. Vashchen, Opt. Spectrosc. (Translation of
Optika i Spektroskopiya) 24, 396 (1968).8G. E. Jellison, J. O. Ramey, and L. A. Boatner, Phys. Rev. B 59, 9718(1999).
9M. Schluter, M. L. Cohen, S. E. Kohn, and C. Y. Fong, Phys. Status Solidi
B 78, 737 (1976).10H. Yorikawa and S. Muramatsu, J. Phys.: Condens. Matter 20, 325220(2008).
11D. J. Singh, Phys. Rev. B 82, 155145 (2010).12M. Schieber, T. J. Davies, W. Schnepple, P. T. Randtke, and R. C.
Carlston, J. Appl. Phys. 45, 5371 (1974).13C. Chen, I. An, G. M. Ferreira, N. J. Podraza, J. A. Zapien, and R. W.
Collins, Thin Solid Films 455–456, 14 (2004).14S. Alerovitz and B. Johs, “Multiple minima in the ellipsometric error
function,” Thin Solid Films 313–314, 124–127 (1998).15D. E. Aspnes, J. Opt. Soc. Am. 70, 1275 (1980).16P. J. Dean and D. G. Thomas, Phys. Rev. 150, 690 (1966).17J. Tauc, R. Grigorov, and A. Vancu, Phys. Status Solidi 15, 627 (1966).
18J. I. Pankove, in Optical Processes in Semiconductors (Prentice-Hall,
Englewood Cliffs, 1971), p. 38.19H. Udono, I. Kikuma, T. Okuno, Y. Masumoto, and H. Tajima, Appl.
Phys. Lett. 85, 1937 (2004).20V. M. Koshkin, V. R. Karas, and L. P. Galchine, Sov. Phys. Semicond. 3,1186 (1970).
21A. M. Elkorashy, J. Phys. Chem. Solids 47, 497 (1986).22G. E. Jellison and F. A. Modine, Appl. Phys. Lett. 69, 371 (1996); 69,2137 (1996).
23R. W. Collins and A. S. Ferlauto, in Handbook of Ellipsometry, edited by
H. G. Tompkins and E. A. Irene (William Andrew, Norwich New York,
2005), p. 125.24H. Fujiwara, J. Koh, P. I. Rovira, and R. W. Collins, Phys. Rev. B 61,10832 (2000).
25G. E. Jellison and J. S. Baba, J. Opt. Soc. Am. A 23, 468 (2006).26D. W. Berreman, J. Opt. Soc. Am. A 62, 502 (1972).27S. Kumar, D. K. Pandya, and K. L. Chopra, Thin Solid Films 164, 51(1988).
28E. Franke, M. Schubert, H. Neumann, T. E. Tiwald, D. W. Thompson,
J. A. Woollam, J. Hahn, and F. Richter, J. Appl. Phys. 82, 2906 (1997).29D. J. Kim, Y. M. Yu, Y. D. Choi, and J. W. Lee, Appl. Surf. Sci. 252,5745 (2006).
30S. Mahanty and J. Ghose, Mater. Lett. 11, 254 (1991).31P. E. Blochl, Phys. Rev. B 50, 17953 (1994).32G. Kresse and D. Joubert, Phys. Rev. B 59, 1758 (1999).33J. P. Perdew, K. Burke, and M. Ernzerhof, Phys. Rev. Lett. 77, 3865(1996).
34R. M. Martin, Electronic Structure: Basic Theory and Practical Methods(Cambridge University Press, New York, 2004).
033110-8 Podraza et al. J. Appl. Phys. 114, 033110 (2013)