nanomaterials
Review
The Advent of Indium Selenide: Synthesis, Electronic
Properties, Ambient Stability and Applications
Danil W. Boukhvalov 1,2 , Bekir Gürbulak 3 , Songül Duman 4 , Lin Wang 5,6 ,
Antonio Politano 7, * ID , Lorenzo S. Caputi 8 , Gennaro Chiarello 8 and Anna Cupolillo 8, *
1
2
3
4
5
6
7
8
*
Department of Chemistry, Haiyang University, 17 Haengdang-dong, Seongdong-gu, Seoul 133-791, Korea;
danil@hanyang.ac.kr
Theoretical Physics and Applied Mathematics Department, Ural Federal University, Mira Street 19,
620002 Ekaterinburg, Russia
Department of Physics, Faculty of Sciences, Atatürk University, 25240 Erzurum, Turkey;
gurbulak@atauni.edu.tr
Department of Basic Sciences, Faculty of Sciences, Erzurum Technical University, 25050 Erzurum, Turkey;
songul.duman@erzurum.edu.tr
National Laboratory for Infrared Physics, Shanghai Institute of Technical Physics, Chinese Academy of
Sciences, Shanghai 200083, China; wanglin@mail.sitp.ac.cn
Synergetic Innovation Center of Quantum Information & Quantum Physics, University of Science and
Technology of China, Hefei 230026, China
Graphene Labs, Fondazione Istituto Italiano di Tecnologia, Via Morego 30, 16163 Genoa, Italy
Department of Physics, University of Calabria, via ponte Bucci, cubo 31/C, 87036 Rende, Italy;
lorenzo.caputi@fis.unical.it (L.S.C.); gennaro.chiarello@fis.unical.it (G.C.)
Correspondence: antonio.politano@iit.it (A.P.); anna.cupolillo@fis.unical.it (A.C.);
Tel.: +39-010-7178-1882 (A.P.); +39-0984-496-160 (A.C.)
Received: 17 October 2017; Accepted: 28 October 2017; Published: 5 November 2017
Abstract: Among the various two-dimensional semiconductors, indium selenide has recently
triggered the interest of scientific community, due to its band gap matching the visible region of the
electromagnetic spectrum, with subsequent potential applications in optoelectronics and especially
in photodetection. In this feature article, we discuss the main issues in the synthesis, the ambient
stability and the application capabilities of this novel class of two-dimensional semiconductors,
by evidencing open challenges and pitfalls. In particular, we evidence how the growth of single
crystals with reduced amount of Se vacancies is crucial in the road map for the exploitation of
indium selenide in technology through ambient-stable nanodevices with outstanding values of both
mobility of charge carriers and ON/OFF ratio. The surface chemical reactivity of the InSe surface,
as well as applications in the fields of broadband photodetection, flexible electronics and solar energy
conversion are also discussed.
Keywords: indium selenide; exfoliation; Bridgman-Stockbarger growth; chemical reactivity;
angle-resolved photoemission spectroscopy; nanodevices
1. Introduction
The recent interest toward layered semiconductors [1–5] is motivated by their potential impact
in nanoelectronics [6–9], due to the joint presence of finite values of band gaps [10,11] and
flexibility [12,13]. In particular, while graphene does not have a band gap [14–17], van der Waals
semiconductors enable the devising of nanodevices with outstanding values for the ON/OFF ratio [6].
Moreover, by reducing the thickness, in some cases, the band gap becomes direct, with implications
for optoelectronics [18] and photodetection.
Nanomaterials 2017, 7, 372; doi:10.3390/nano7110372
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Indium selenide represents an intriguing candidate for nanoelectronics [19], since it is an
ambient-stable [20], flexible [21–23] semiconductor with high values of mobility of charge carriers [24].
Moreover, by exfoliating the bulk crystal, it is possible to attain nanosheets with a highly crystalline
–
quality [25–27].
InSe is made of stacked
layers of Se-In-In-Se atoms with van der Waals bonding between
–
quadruple layers [28,29]. Recently, several researchers have reported the outstanding efficiency
of InSe-based optoelectronic devices [30–32]. Field-effect transistors (FETs) with an active channel
of few layers of InSe are characterized– by values of electron mobility at room temperature as
high as 103 cm2 /(V·s) [30]. Furthermore, InSe has good prospects for applications in the field of
photovoltaics [22], strain engineering [33], and nonlinear optics [34].
Depending on the different stacking sequences of layers, different polytypes of layered materials
exist. Three highly distinct polytypes of the InSe crystal have been identified [35,36] (β, ε, and γ,
(β, ε
dγ
4 )
see Figure 1), in which In and Se atoms are differently arranged. The β (space group symmetry
D6h
4
The
β
(space
group
symmetry
𝐷
6ℎ
1
and ε polytypes
(space group symmetry𝐷1D3h ) are characterized by a hexagonal lattice consisting of
ε
3ℎ
eight atoms in the unit cell, and their extension over two layers [37].
Rhombohedral
γ polytype
(space
. Rhombohedral
γ polytype
(space
5
5
group symmetry C3v ) contains
two cations and two anions distributed on four adjacent layers [35,38].
𝐶3𝑣
Figure 1. Geometrical structure of the three polytypes of InSe. C0 and a0 represent the lattice parameters
along the perpendicular to layers and in the layer plane, respectively. Reproduced from Ref. [39].
While ε-InSe
both
hile ε has an indirect band gap of 1.4 eV [36],
, both
β βandand
γ γ-InSe have a direct band
eV,
respectively).
Accordingly,
only β and
gap [36] with closely matching values (1.28 eV [37] and 1.29 eV [40], respectively).
Accordingly,
only β
γ
phases
of
InSe
could
and γ phases of InSe could supposedly be employed in optoelectronics, for which finite and direct
band gaps are beneficial [41]. Exfoliated samplesγof γ-InSe host quantization effects, which enable
near-infrared photoluminescence emission [26].
2. Growth
Several growth techniques have been used for growing indium-selenide compounds: vacuum
evaporation [42], molecular beam epitaxy (MBE) [43], colloidal methods [44,45], flash evaporation [46],
chemical vapour deposition [47], van der Waals epitaxy [48], radiofrequency sputtering [49],
Czochralski [50] and the Bridgman-Stockbarger technique [37,51,52].
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Among these methods, the Bridgman-Stockbarger growth is the most suitable for the large-scale
production of high-quality bulk InSe semiconductors for device applications, with a typical time
requirement ranging from 5 to 35 days for an ingot. The quite long time needed is also a
consequence of some technical difficulties that need to be overcome during the growth process.
The Bridgman-Stockbarger method involves starting from high-purity In and Se elements, which are
sealed in quartz ampoules, heated in vacuum in a furnace at temperatures as high as 950 ◦ C. Figure 2
shows the typical temperature profile at which the furnace should be kept during the growth
process. However, selenium has a high vapor pressure value at temperatures higher than 600 ◦ C [53],
with possible fractures on the bulbs being used for growth. This problem can be avoided by decreasing
the reaction rate, increasing the growth time, and/or by decreasing the growth temperature with a
subsequent slower growth rate. Successively, the crucible is suspended in the middle of the vertical
furnace with two designated zones. The temperature of the lower zone of the furnace is reduced to
~250 ◦ C at a rate typically of around 1.5 ◦ C/h. Both furnace zones are cooled to 250 ◦ C over ~75 h.
The solidified ingot is then cooled to room temperature over ~50 h.
Figure 2. Temperature profile of the furnace in a typical Bridgman-Stockbarger growth of InSe single
crystals [37]. In the inset an InSe single-crystal ingot grown by the Bridgman/Stockbarger method
is displayed.
Using the Bridgman-Stockbarger method, InSe single crystals can be grown as both n- and
– Doping can be achieved by the
p-type depending on growth conditions and dopant elements [54].
direct addition of the dopant elements to the growth ampoules [55–67]. To introduce dopants in a
homogeneously distributed fashion, during the growth it is necessary to rotate the growth furnace,
kept at about 50 ◦ C above the melting point, around its own axis for many hours, at a particularly
slow rate. In the choice of the dopant, one has to consider that the atomic radius of the doped
elements should match that of the replaced atoms. In general, the grown crystals of InSe inevitably
contain numerous defects, which act as deep trap levels. We reiterate that defects and impurities in
semiconductors are associated with the energy levels in the forbidden gap. Thus, the presence of Se
vacancies, i.e., anion vacancies, in InSe crystals leads to deep energy levels in the band gap. By doping
InSe with transition metals, the localized levels originating from the vacancies disappear [37].
3. Exfoliation
The ingots of InSe, obtained by Bridgman-Stockberger technique, have no cracks and voids at the
surface. Due to the extreme weakness of the interlayer van der Waals bond, the ingots can be easily
cleaved along the (001) planes. Flakes with outstanding flatness and bright surfaces can be exfoliated
from the parental bulk single-crystal ingot without chemical etching or mechanical polishing processes.
To date, only mechanical exfoliation [23,26] (the ordinary scotch tape method) has been used to obtain
Nanomaterials 2017, 7, 372
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atomically thick flakes of InSe. It is expected that liquid-phase exfoliation could be also achieved in
future works on InSe. This achievement would boost the technological exploitation of InSe.
4. Electronic Properties
tronic
band
structure
ββ
The electronic
band
structure
ofofof
β-InSe
has been measured by angle-resolved photoemission
tronic
band
structure
spectroscopy (ARPES) only in the case of bulk crystals [68] (Figure 3).
Experimental
structure
β
Figure 3. Experimental
bandband
structure
ofof
β-InSe
along the high-symmetry directions. The energy scale
was set to zero
at valence-band
maximum
Experimental
band structure
of β(VBM). Reproduced with permission from Ref. [68].
The orbital components of the different bands experimentally revealed by ARPES are indicated by
projections to 5p (panel a of Figure 4) and 5s (panel b) states of In and to 4p (panel c) and 4s (panel d)
states of Se along the whole Brillouin zone.
Figure 4. Theoretical band structure projected to (a) In-5p; (b) In-5s; (c) Se-4p; and (d) Se-4s atomic
orbitals. The intensity of the various bands is reported in a color scale, whose legend is displayed in
the right part of panels (a,b) and between panels (c,d). Reproduced with permission from Ref. [68].
Nanomaterials 2017, 7, 372
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The
valence-band
maximumoriginate
(VBM) is mainly derived from 5pz states of In. The crossing of
bands
at ~1.6
eV at Γ principally
bandsat
at~1.6
~1.6 eV
eV at
at ΓΓ principally
principally originates
originate from the Se-4p and In-5s states, whereas states at 4.5 eV
bands
predominantly
arise
Concerning
γ from In-5s.
Concerningγ-InSe,
γ
Concerning
density functional theory has evidenced a transition from direct to indirect
band gap semiconductor, which occurs by reducingthe
the band
number
of layersof[69],
structure
γ as also manifest from the
the
band
structure
of
analysis of Figure 5, where the behavior of the band structure of γ-InSe as aγfunction of the thickness is
shown. Figure 6 displays the dependence of the photoluminescence spectra, acquired with micrometric
spatial resolution, as a function of thickness; by reducing the thickness, a shift of the maximum toward
higher photon energies occurs.
γ
Figure 5. Band structure of γ-InSe
with a number of layers L = 1, 5 and 10 layers. Reproduced with
γ
permission from Ref. [69].
Figure 6. Normalized microphotoluminescence spectra forγ γ-InSe nanosheets with L = 4, 10 and
γ
24 layers. Reproduced with permission from Ref. [69].
5. Ambient Stability
The stability of the performances of nanodevices in ambient conditions is an essential requisite in
order to devise applications based on InSe. The ambient stability of FETs with an active channel of
InSe has been demonstrated in Ref. [20]. However, therein, it was also shown that FETs with an active
Nanomaterials 2017, 7, 372
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channel of uncapped InSe exhibit a p-type transport, while ambipolar transport was achieved only in
the presence of a capping layer (Figure 7).
Figure 7. (a) Optical image of typical InSe back-gate transistor devices: in one device the channel
is capped with a flake of hexagonal boron nitride (h-BN), whereas the other channel is exposed to
atmosphere. (b) Behavior of the drain current as a function of the gate voltage for the cases of capped
and uncapped InSe-based transistors. The uncapped device shows dominant p-type transport (even if
with notable hysteresis), while the capped device noticeably displays ambipolar transport. Reproduced
with permission from Ref. [20]. Copyright Royal Society of Chemistry, 2016.
Nevertheless, even the uncapped InSe nanodevices are stable in air without any perceptible
modification in the I-V curves measured again after two weeks (Figure 8). Consequently, one can affirm
that no fast degradation occurs for InSe, contrary to the cases of Bi2 Se3 [70] and black phosphorus [71].
Figure 8. IDS -V G curve of uncapped InSe-based transistors freshly fabricated (red curve) and after
two weeks (blue curve). Reproduced with permission from Ref. [20]. Copyright Royal Society of
Chemistry, 2016.
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For the case of InSe, the origin of the p-type doping of ambient-stable InSe-based FETs was
unveiled in Ref. [20], where the authors investigated the correlation between the surface chemical
reactivity, the environmental doping and the effects induced by defects in InSe (Figure 9).
The interaction of ambient gases (H2 O, CO, CO2 , N2 , O2 ) with InSe was assessed for two
adsorption sites on undefected InSe: over Se atoms, which are the outermost surface atoms of the InSe
monolayer (top position, Figure 9a,b), and over the middles of hexagons (hole position, Figure 9c,d).
Theoretical results (Table 1) clarify that for all examined molecules the preferential adsorption site is
that over holes.
Table 1. Adsorption energies of different ambient species over the hole and on-top with respect to Se
atoms. Reproduced with permission from Ref. [20]. Copyright Royal Society of Chemistry, 2016.
Species/Adsorption Site
Hole (eV)
H2 O
CO
CO2
N2
O2
−0.139
0.014
0.244
0.097
0.705
−
Top (eV)
0.69
2.75
2.05
1.15
3.67
Figure 9. Top and side views of the geometrical structure of InSe monolayer in the case of adsorption
of H2 O (a,c) and CO (b,d) molecules over hole sites (a,b) and top sites (c,d) with respect to Se atoms.
Reproduced with permission from Ref. [20]. Copyright Royal Society of Chemistry, 2016.
According to the values of adsorption energies calculated in Table 1, only the adsorption of H2 O
on hole sites is energetically favorable at room temperature, with a charge transfer of 0.01 electrons per
each molecule. As a result, the InSe surface is only slightly p-doped. Therefore, among ambient gases,
only water is able to form stable bonds with InSe at room temperature with manifest displacement of
Se atoms from their positions in the pristine InSe (Figure 9c,d). These theoretical predictions have been
Nanomaterials 2017, 7, 372
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confirmed by vibrational experiments, which also indicated that the adsorption of water molecules
on InSe at room temperature is entirely dissociative. The vibrational spectrum of water-dosed
InSe (Figure 10) exhibits an intense band at 450 meV, which constitutes a fingerprint of the water
decomposition that occurred. As a matter of fact, this mode is due to the O–H stretching vibration in –
–
–OH groups [72], while molecular
water would display O–H stretching energy in the 400–425 meV–
–
range [73].
Figure 10. Vibrational spectrum of InSe exposed to water molecules at room temperature. Reproduced
with permission from Ref. [20]. Copyright Royal Society of Chemistry, 2016.
Similarly, other recent theoretical works have recently reported positive adsorption energy of
water molecules on Se vacancies [74] and almost zero adsorption energies for the physical adsorption
of oxygen over various adsorption sites of the InSe surface [75]. Other theoretical works [76,77] Have
reported rather large (0.1~0.3 eV) negative values of adsorption energies, but disagree with each other
about type of doping from NH3 and about the values of the transferred charge from InSe substrate
to molecules. In particular, results in Ref. [77] point to stable adsorption of molecules from air for all
adsorption sites of InSe and, according to these theoretical predictions, InSe should be much more
heavily doped under ambient conditions. However, it is quite evident that the theoretical model by
Ma et al. [77] disagrees with experiments.
In InSe, extreme sensitivity of adsorption properties to local distortions is expected. Figure 9
depicts how adsorption on different sites provides different distortions of the atomic structure of InSe
substrate. Molecular dynamic simulations also demonstrate the influence of the water layer on the
structure of the InSe monolayer [78]. The optimization of both atomic positions and lattice constants
provides a different magnitude of local distortions and, as a result, charge distribution, adsorption
energies and charge transfer are subsequently modified.
It is worth reporting that two computational studies (both using the Vienna Ab initio
simulation package- VASP- code) have recently reported contradictory results on the change of
the lattice parameter when the InSe thickness is reduced down to the monolayer regime [79,80].
This disagreement between theoretical models highlights the noticeable dependence of results of the
calculations on various usually unimportant and technical parameters. Moreover, the dependence
of the energetics of adsorption from distortions permits the manipulation of chemical and electric
properties of monolayer InSe by strain [32,77] or by distortion of scaffold, as previously reported for
graphene [78,79]. Thickness-dependent changes of vibrational spectra of InSe [36] and GaSe [81]
also prove the sensitivity of lattice properties of these compounds on the number of layers.
Further theoretical investigation of the role of various substrates, ripples and strain on doping of InSe
surface is ongoing.
Nanomaterials 2017, 7, 372
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The calculation of the energy cost of dissociation of water molecules in both defect-free and
defective InSe monolayer for the various kinds of defects (single In and Se vacancies, the combined
existence of single In and Se vacancies, and Stone-Wales defects) indicates that water dissociation
over undefected InSe is not energetically favored. In detail, the energetic cost is ~2 eV (Figure 11a).
Analogously to the case of graphene [82], the presence of defects noticeably reduces the energy cost
of chemisorption by a value depending on the type of defect. The presence of In vacancies reduces
the energy cost for water decomposition to 1.85 eV (Figure 11b). Water decomposition is particularly
favorable on Se vacancies, over which the energy cost is only 0.29 eV (Figure 11c). For the case of
the joint presence of single In and Se vacancies, the energy cost for decomposition is about 1 eV
(Figure 11d), while it is ~0.7 eV for the case of Stone-Wales defects (Figure 11e).
Figure 11. Atomic structure of pristine (a) and defective (b–e)
– InSe monolayer before (left) and after
(right) the decomposition of the water molecules. The indicated values represent the energy cost of
the dissociation of water molecules for each specific case. Reproduced with permission from Ref. [20].
Copyright Royal Society of Chemistry, 2016.
Based on the relationship between calculated DFT energies and temperatures of reactions [83],
it can be concluded that reactions with energies below 0.5 eV, e.g., in the case of water decomposition
at Se vacancies, occur at room temperature at a rather high rate [20]. Calculations by Shi et al. [74]
also indicate favorability of water decomposition on Se vacancies, and suggest a possible solution
for this problem by reparation of the vacancies through substitution of missing Se atoms by S with a
Nanomaterials 2017, 7, 372
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treatment of InSe surface in CH3 SH. It is worth noticing that the substitution of Se with S and also
the formation of local In2 O3 -like structures resulting from the penetration of oxygen atoms into the
InSe monolayer [75] do not provide any visible changes in the band structure of InSe. These results
suggest the routes toward healing of defects in InSe surfaces, but further modeling is required to find
realistic methods.
6. Applications
Compared with other group IIIA-VIA layered (MX, M = Ga and In, X = S, Se and Te), InSe has
a narrower bandgap, which overlaps well with the solar spectrum and offers efficient solar energy
–
conversion. Several works [84–88]
have already demonstrated that InSe is an alternative candidate
to thin-film cells, due to its high mechanical flexibility [21,23]. Tamalampudi et al. [23] have
demonstrated that photodetectors with an active channel of a few layers of InSe show broadband
–
efficiency from the visible to the near-infrared range (450–785
nm). InSe-based photodetectors
have been fabricated on (i) a rigid SiO2 /Si substrate, and (ii) a flexible polyethylene terephthalate
−1 12.3 A·W−1 at 450 nm (on SiO /Si) and
−1
3.9 A·W−1
(PET) film [23]. Photoresponsivities as high as
2
at 633 nm (on PET) have been measured [23], and with an order of magnitude improvement
by simply sweeping the gate voltage above threshold of the transfer characteristic for electron
conduction. The responsivity of InSe-based photodetectors in Figure 12−1goes up to 7 A·W−1 at
−2
power intensity− lower
λ than 0.07 W·cm (λ~633 nm), and this value is substantially higher than that of
−4 A·W−1 ) based photodetectors. Thus, InSe-based
graphene(5 × 10−4 A·W−1 )−and MoS
−
−1
−1 2 - (4.2 × 10
photodetectors are the most efficient among those realized with two-dimensional materials, including
graphene and transition-metal dichalcogenides [7]. Their response time is only a few tens of ms
and, moreover, they show long-term stability in photoswitching [23]. Remarkably, the bending
of the InSe-based device fabricated on the flexible PET substrate does not significantly reduce its
performances [23]. Therefore, the stretchable nature of InSe represents an ideal candidate for advanced
optoelectronic applications.
Figure 12. (left panel) Sketch of a InSe-based FETfor optoelectronics; (middle panel) Behavior of the
responsivity as a function of the power and of the drain-source voltage; (right panel): The photocurrent
of the InSe device on PET film (shown in the inset in the bent geometry) acquired when the device
was in planar geometry with 633 nm illumination of 22.74, 8.67, 4.46, 2.85, 0.70, and 0.29 mW·cm−2 for
purple, blue, green, yellow, orange, and red curves, respectively. Reproduced with permission from
−2
Ref. [23]. Copyright American Chemical Society, 2014.
With such excellent optoelectronic merits, layered InSe nanosheets will become not only
outstanding candidates for optical sensing applications, but also promising components for configuring
2D heterostructure devices for high-performance photodetectors and emitters [89]. Owing to
the low-density interface states, InSe-based hetero-junctions can be used for tailoring the device
characteristics [90]. A graphene/few-layer InSe heterostructure photodetector has been reported with
an external quantum efficiency of over 2 × 105 %, which represents a spectacular improvement with
respect to the homostructural few-layer InSe device [32]. An absolute power conversion efficiency
–
ν
Nanomaterials 2017, 7, 372
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of about 18% for wavelengths of 1.10–1.25 µm has been reported for solar cells exploiting crystalline
InSe as a window layer in heterostructure diodes [91]. Homojunction diodes formed from layers of
p- and n-type InSe exhibit electroluminescence of exciton recombination at hν~1.23 eV. A ~20 meV
redshift with respect to the photoluminance peak (1.25 eV) is observed. This redshift is attributed to
the reabsorption of photons by the top InSe layer [92]. Conversely, heterojunction diodes formed by
combining layers of p-type GaSe and n-type InSe emit photons at lower energies, due to the generation
of spatially indirect excitons and a staggered valence band lineup for the holes at the GaSe/InSe
interface [93].
Finally, in the prospect of a technological employment of atomically thin InSe nanosheets,
it is worth mentioning that, by means of morphological nano-manipulation procedures such as
nanotexturing, it is possible to enhance light absorption, bandwidth and the luminescent response [94].
7. Conclusions
In this feature article, we have discussed the main features of the science and technology
based on InSe. Single crystals of InSe can be grown by different techniques, among which
Bridgman-Stockbarger is the most suitable for up-scaling. As a matter of fact, it allows the production
of large-scale, high-quality single crystals, which can be easily exfoliated to atomic thickness. To date,
only mechanical exfoliation has been used, but we suggest that liquid-phase exfoliation would allow
deeper employment of InSe in technology.
Nanodevices with flakes of InSe as active channels are characterized by high mobility of charge
carriers and very high ON/OFF ratios. By reducing the thickness of the flakes, the band gap energy
increases and a direct-to-indirect transition occurs, while electron and exciton effective masses are
substantially constant with thickness. Concerning potential applications of InSe, highly performing
broadband photodetectors and solar cells have been realized. The flexibility of InSe makes it a solid
candidate for flexible electronics.
Ambient stability is one of the most valuable properties of InSe. However, the presence of Se
vacancies enables water decomposition at room temperature, with the introduction of a p-type doping
in InSe exposed to ambient air humidity. Therefore, the minimization of defects is the most important
challenge in the growth of InSe compounds.
Author Contributions: The general structure of the Feature Article was conceived by Antonio Politano and
Anna Cupolillo, who have also coordinated the various contributions. Each author has equally contributed to
the draft taking in charge a part of the manuscript. In details, the paragraph on synthesis has been written by
Bekir Gürbulak and Songül Duman. The section on electronic properties has been written by Anna Cupolillo,
Antonio Politano, and Lorenzo S. Caputi. The paragraph on physical chemistry with InSe has been mostly written
by Danil W. Boukhvalov, with contribution of Antonio Politano and Gennaro Chiarello for the review of existing
vibrational studies. The paragraph on applications has been written by Lin Wang for InSe-based photodetectors
and by Bekir Gürbulak and Songül Duman for InSe-based diodes.
Conflicts of Interest: The authors declare no conflict of interest.
References
1.
2.
3.
4.
5.
Buscema, M.; Island, J.O.; Groenendijk, D.J.; Blanter, S.I.; Steele, G.A.; van der Zant, H.S.J.;
Castellanos-Gomez, A. Photocurrent generation with two-dimensional van der Waals semiconductors.
Chem. Soc. Rev. 2015, 44, 3691–3718. [CrossRef] [PubMed]
Roldán, R.; Castellanos-Gomez, A.; Cappelluti, E.; Guinea, F. Strain engineering in semiconducting
two-dimensional crystals. J. Phys. Condens. Matter 2015, 27. [CrossRef] [PubMed]
Scholz, A.; Stauber, T.; Schliemann, J. Plasmons and screening in a monolayer of MoS2 . Phys. Rev. B 2013, 88.
[CrossRef]
Stauber, T.; Gómez-Santos, G. Plasmons in layered structures including graphene. New J. Phys. 2012, 14.
[CrossRef]
Lee, T.H.; Kim, S.Y.; Jang, H.W. Black phosphorus: Critical review and potential for water splitting
photocatalyst. Nanomaterials 2016, 6, 194. [CrossRef] [PubMed]
Nanomaterials 2017, 7, 372
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.
20.
21.
22.
23.
24.
25.
12 of 16
Fiori, G.; Bonaccorso, F.; Iannaccone, G.; Palacios, T.; Neumaier, D.; Seabaugh, A.; Banerjee, S.K.; Colombo, L.
Electronics based on two-dimensional materials. Nat. Nanotechnol. 2014, 9, 768–779. [CrossRef] [PubMed]
Koppens, F.H.L.; Mueller, T.; Avouris, P.; Ferrari, A.C.; Vitiello, M.S.; Polini, M. Photodetectors based
on graphene, other two-dimensional materials and hybrid systems. Nat. Nanotechnol. 2014, 9, 780–793.
[CrossRef] [PubMed]
Lee, J.Y.; Shin, J.H.; Lee, G.H.; Lee, C.H. Two-dimensional semiconductor optoelectronics based on van der
Waals heterostructures. Nanomaterials 2016, 6, 193. [CrossRef] [PubMed]
Yang, H.; Qin, S.; Zheng, X.; Wang, G.; Tan, Y.; Peng, G.; Zhang, X. An Al2 O3 Gating Substrate for the Greater
Performance of Field Effect Transistors Based on Two-Dimensional Materials. Nanomaterials 2017, 7, 286.
[CrossRef] [PubMed]
Miro, P.; Audiffred, M.; Heine, T. An atlas of two-dimensional materials. Chem. Soc. Rev. 2014, 43, 6537–6554.
[CrossRef] [PubMed]
Bhimanapati, G.R.; Lin, Z.; Meunier, V.; Jung, Y.; Cha, J.; Das, S.; Xiao, D.; Son, Y.; Strano, M.S.; Cooper, V.R.;
et al. Recent Advances in Two-Dimensional Materials beyond Graphene. ACS Nano 2015, 9, 11509–11539.
[CrossRef] [PubMed]
Akinwande, D.; Petrone, N.; Hone, J. Two-dimensional flexible nanoelectronics. Nat. Commun. 2014, 5.
[CrossRef] [PubMed]
Zhu, W.; Yogeesh, M.N.; Yang, S.; Aldave, S.H.; Kim, J.-S.; Sonde, S.; Tao, L.; Lu, N.; Akinwande, D. Flexible
Black Phosphorus Ambipolar Transistors, Circuits and AM Demodulator. Nano Lett. 2015, 15, 1883–1890.
[CrossRef] [PubMed]
Novoselov, K. Graphene: Mind the gap. Nat. Mater. 2007, 6, 720–721. [CrossRef] [PubMed]
Giubileo, F.; Di Bartolomeo, A.; Martucciello, N.; Romeo, F.; Iemmo, L.; Romano, P.; Passacantando, M.
Contact resistance and channel conductance of graphene field-effect transistors under low-energy electron
irradiation. Nanomaterials 2016, 6, 206. [CrossRef] [PubMed]
Luongo, G.; Giubileo, F.; Genovese, L.; Iemmo, L.; Martucciello, N.; Di Bartolomeo, A. I-V and C-V
Characterization of a High-Responsivity Graphene/Silicon Photodiode with Embedded MOS Capacitor.
Nanomaterials 2017, 7, 158. [CrossRef] [PubMed]
Jin, K.; Zhou, X.; Liu, Z. Graphene/sulfur/carbon nanocomposite for high performance lithium-sulfur
batteries. Nanomaterials 2015, 5, 1481–1492. [CrossRef] [PubMed]
Wang, X.; Huang, L.; Peng, Y.; Huo, N.; Wu, K.; Xia, C.; Wei, Z.; Tongay, S.; Li, J. Enhanced rectification,
transport property and photocurrent generation of multilayer ReSe2 /MoS2 p–n heterojunctions. Nano Res.
2015, 9, 507–516. [CrossRef]
Bandurin, D.A.; Tyurnina, A.V.; Yu, G.L.; Mishchenko, A.; Zolyomi, V.; Morozov, S.V.; Kumar, R.K.;
Gorbachev, R.V.; Kudrynskyi, Z.R.; Pezzini, S.; et al. High electron mobility, quantum Hall effect and
anomalous optical response in atomically thin InSe. Nat. Nanotechnol. 2017, 12, 223–227. [CrossRef]
[PubMed]
Politano, A.; Chiarello, G.; Samnakay, R.; Liu, G.; Gurbulak, B.; Duman, S.; Balandin, A.A.; Boukhvalov, D.W.
The influence of chemical reactivity of surface defects on ambient-stable InSe-based nanodevices. Nanoscale
2016, 8, 8474–8479. [CrossRef] [PubMed]
Mosca, D.H.; Mattoso, N.; Lepienski, C.M.; Veiga, W.; Mazzaro, I.; Etgens, V.H.; Eddrief, M. Mechanical
properties of layered InSe and GaSe single crystals. J. Appl. Phys. 2002, 91, 140–144. [CrossRef]
Ho, C.-H.; Chu, Y.-J. Bending Photoluminescence and Surface Photovoltaic Effect on Multilayer InSe 2D
Microplate Crystals. Adv. Opt. Mater. 2015, 3, 1750–1758. [CrossRef]
Tamalampudi, S.R.; Lu, Y.Y.; Kumar, R.; Sankar, R.; Liao, C.D.; Moorthy, K.; Cheng, C.H.; Chou, F.C.;
Chen, Y.T. High performance and bendable few-layered InSe photodetectors with broad spectral response.
Nano Lett. 2014, 14, 2800–2806. [CrossRef] [PubMed]
Ho, P.-H.; Chang, Y.-R.; Chu, Y.-C.; Li, M.-K.; Tsai, C.-A.; Wang, W.-H.; Ho, C.-H.; Chen, C.-W.; Chiu, P.-W.
High-Mobility InSe Transistors: The Role of Surface Oxides. ACS Nano 2017, 11, 7362–7370. [CrossRef]
[PubMed]
Mudd, G.W.; Svatek, S.A.; Hague, L.; Makarovsky, O.; Kudrynskyi, Z.R.; Mellor, C.J.; Beton, P.H.; Eaves, L.;
Novoselov, K.S.; Kovalyuk, Z.D.; et al. High Broad-Band Photoresponsivity of Mechanically Formed
InSe–Graphene van der Waals Heterostructures. Adv. Mater. 2015, 27, 3760–3766. [CrossRef] [PubMed]
Nanomaterials 2017, 7, 372
26.
27.
28.
29.
30.
31.
32.
33.
34.
35.
36.
37.
38.
39.
40.
41.
42.
43.
44.
45.
46.
13 of 16
Mudd, G.W.; Svatek, S.A.; Ren, T.; Patanè, A.; Makarovsky, O.; Eaves, L.; Beton, P.H.; Kovalyuk, Z.D.;
Lashkarev, G.V.; Kudrynskyi, Z.R.; et al. Tuning the bandgap of exfoliated InSe nanosheets by quantum
confinement. Adv. Mater. 2013, 25, 5714–5718. [CrossRef] [PubMed]
Lin, Z.; Karthik, P.S.; Hada, M.; Nishikawa, T.; Hayashi, Y. Simple technique of exfoliation and dispersion
of multilayer graphene from natural graphite by ozone-assisted sonication. Nanomaterials 2017, 7, 125.
[CrossRef] [PubMed]
Sánchez-Royo, J.F.; Muñoz-Matutano, G.; Brotons-Gisbert, M.; Martínez-Pastor, J.P.; Segura, A.; Cantarero, A.;
Mata, R.; Canet-Ferrer, J.; Tobias, G.; Canadell, E.; et al. Electronic structure, optical properties, and lattice
dynamics in atomically thin indium selenide flakes. Nano Res. 2014, 7, 1556–1568. [CrossRef]
Ho, C.-H. Thickness-dependent carrier transport and optically enhanced transconductance gain in III–VI
multilayer InSe. 2D Mater. 2016, 3. [CrossRef]
Sucharitakul, S.; Goble, N.J.; Kumar, U.R.; Sankar, R.; Bogorad, Z.A.; Chou, F.-C.; Chen, Y.-T.; Gao, X.P.A.
Intrinsic Electron Mobility Exceeding 103 cm2 /(V·s) in Multilayer InSe FETs. Nano Lett. 2015, 15, 3815–3819.
[CrossRef] [PubMed]
Lei, S.; Wen, F.; Ge, L.; Najmaei, S.; George, A.; Gong, Y.; Gao, W.; Jin, Z.; Li, B.; Lou, J.; et al. An Atomically
Layered InSe Avalanche Photodetector. Nano Lett. 2015, 15, 3048–3055. [CrossRef] [PubMed]
Chen, Z.; Biscaras, J.; Shukla, A. A high performance graphene/few-layer InSe photo-detector. Nanoscale
2015, 7, 5981–5986. [CrossRef] [PubMed]
Ma, Y.; Dai, Y.; Yu, L.; Niu, C.; Huang, B. Engineering a topological phase transition in β-InSe via strain.
New J. Phys. 2013, 15. [CrossRef]
Yüksek, M.; Yaglioglu, H.G.; Elmali, A.; Aydin, E.M.; Kürüm, U.; Ateş, A. Nonlinear and saturable absorption
characteristics of Ho doped InSe crystals. Opt. Commun. 2014, 310, 100–103. [CrossRef]
Han, G.; Chen, Z.-G.; Drennan, J.; Zou, J. Indium Selenides: Structural Characteristics, Synthesis and Their
Thermoelectric Performances. Small 2014, 10, 2747–2765. [CrossRef] [PubMed]
Lei, S.; Ge, L.; Najmaei, S.; George, A.; Kappera, R.; Lou, J.; Chhowalla, M.; Yamaguchi, H.; Gupta, G.;
Vajtai, R.; et al. Evolution of the Electronic Band Structure and Efficient Photo-Detection in Atomic Layers of
InSe. ACS Nano 2014, 8, 1263–1272. [CrossRef] [PubMed]
Gürbulak, B.; Şata, M.; Dogan, S.; Duman, S.; Ashkhasi, A.; Keskenler, E.F. Structural characterizations
and optical properties of InSe and InSe: Ag semiconductors grown by Bridgman/Stockbarger technique.
Physica E 2014, 64, 106–111. [CrossRef]
Mudd, G.W.; Patanè, A.; Kudrynskyi, Z.R.; Fay, M.W.; Makarovsky, O.; Eaves, L.; Kovalyuk, Z.D.; Zólyomi, V.;
Falko, V. Quantum confined acceptors and donors in InSe nanosheets. Appl. Phys. Lett. 2014, 105. [CrossRef]
Zhirko, Y.; Trachevsky, V.; Kovalyuk, Z. On the Possibility of Layered Crystals Application for Solid State
Hydrogen Storages—InSe and GaSe Crystals. In Hydrogen Storage; InTech: Rijeka, Croatia, 2012.
Julien, C.M.; Balkanski, M. Lithium reactivity with III–VI layered compounds. Mater. Sci. Eng. B 2003, 100,
263–270. [CrossRef]
Viti, L.; Hu, J.; Coquillat, D.; Knap, W.; Tredicucci, A.; Politano, A.; Vitiello, M.S. Black Phosphorus Terahertz
Photodetectors. Adv. Mater. 2015, 27, 5567–5572. [CrossRef] [PubMed]
El-Sayed, S. Optical investigations of the indium selenide glasses. Vacuum 2003, 72, 169–175. [CrossRef]
Emery, J.Y.; Brahim-Ostmane, L.; Hirlimann, C.; Chevy, A. Reflection high-energy electron diffraction studies
of InSe and GaSe layered compounds grown by molecular beam epitaxy. J. Appl. Phys. 1992, 71, 3256–3259.
[CrossRef]
Lauth, J.; Kulkarni, A.; Spoor, F.C.M.; Renaud, N.; Grozema, F.C.; Houtepen, A.J.; Schins, J.M.; Kinge, S.;
Siebbeles, L.D.A. Photogeneration and Mobility of Charge Carriers in Atomically Thin Colloidal InSe
Nanosheets Probed by Ultrafast Terahertz Spectroscopy. J. Phys. Chem. Lett. 2016, 7, 4191–4196. [CrossRef]
[PubMed]
Lauth, J.; Gorris, F.E.S.; Samadi Khoshkhoo, M.; Chassé, T.; Friedrich, W.; Lebedeva, V.; Meyer, A.;
Klinke, C.; Kornowski, A.; Scheele, M.; et al. Solution-Processed Two-Dimensional Ultrathin InSe Nanosheets.
Chem. Mater. 2016, 28, 1728–1736. [CrossRef]
Julien, C.; Samaras, I.; Tsakiri, M.; Dzwonkowski, P.; Balkanski, M. Lithium insertion in InSe films and
applications in microbatteries. Mater. Sci. Eng. B 1989, 3, 25–29. [CrossRef]
Nanomaterials 2017, 7, 372
47.
48.
49.
50.
51.
52.
53.
54.
55.
56.
57.
58.
59.
60.
61.
62.
63.
64.
65.
66.
67.
68.
69.
14 of 16
Park, J.-H.; Afzaal, M.; Helliwell, M.; Malik, M.A.; O’Brien, P.; Raftery, J. Chemical vapor deposition of indium
selenide and gallium selenide thin films from mixed alkyl/dialkylselenophosphorylamides. Chem. Mater.
2003, 15, 4205–4210. [CrossRef]
Lang, O.; Klein, A.; Schlaf, R.; Löher, T.; Pettenkofer, C.; Jaegermann, W.; Chevy, A. InSeGaSe heterointerfaces
prepared by Van der Waals epitaxy. J. Cryst. Growth 1995, 146, 439–443. [CrossRef]
Shigetomi, S.; Ikari, T. Crystalline InSe films prepared by RF-sputtering technique. Jpn. J. Appl. Phys. 1991,
30, L2127. [CrossRef]
Chevy, A.; Gouskov, A.; Besson, J. Growth of crystalline slabs of layered InSe by the Czochralski method.
J. Cryst. Growth 1978, 43, 756–759. [CrossRef]
De Blasi, C.; Micocci, G.; Mongelli, S.; Tepore, A. Large InSe single crystals grown from stoichiometric and
non-stoichiometric melts. J. Cryst. Growth 1982, 57, 482–486. [CrossRef]
Chevy, A. Improvement of growth parameters for Bridgman-grown InSe crystals. J. Cryst. Growth 1984, 67,
119–124. [CrossRef]
Hoshino, H.; Schmutzler, R.W.; Hensel, F. The High Temperature Vapour Pressure Curve and the Critical
Point of Liquid Selenium. Ber. Bunsenges. Phys. Chem. 1976, 80, 27–31. [CrossRef]
Shigetomi, S.; Ikari, T. Electrical and optical properties of n- and p-InSe doped with Sn and As. J. Appl. Phys.
2003, 93, 2301–2303. [CrossRef]
Duman, S.; Elkoca, Z.; Gurbulak, B.; Bahtiyari Tekle, T.; Dogan, S. Metal/p-InSe:Mn Schottky barrier diodes.
J. Optoelectron. Adv. Mater. 2012, 14, 693–698.
Duman, S.; Gürbulak, B.; Doǧan, S.; Türüt, A. Electrical characteristics and inhomogeneous barrier analysis
of Au–Be/p-InSe:Cd Schottky barrier diodes. Microelectron. Eng. 2009, 86, 106–110. [CrossRef]
Duman, S.; Gurbulak, B.; Turut, A. Temperature-dependent optical absorption measurements and Schottky
contact behavior in layered semiconductor n-type InSe(:Sn). Appl. Surf. Sci. 2007, 253, 3899–3905. [CrossRef]
Gürbulak, B.; Kundakçi, M.; Ateş, A.; Yildirim, M. Electric field influence on exciton absorption of Er doped
and undoped InSe single crystals. Phys. Scr. 2007, 75, 424–430. [CrossRef]
Gürbulak, B. Urbach tail and optical investigations of Gd doped and undoped InSe single crystals. Phys. Scr.
2004, 70, 197–201. [CrossRef]
Ateş, A.; Yildirim, M.; Gürbulak, B. Investigation of the electrical properties of Ho-doped InSe single crystal.
Physica E 2004, 21, 85–90. [CrossRef]
Shigetomi, S.; Ikari, T. Impurity levels in layered semiconductor n-InSe doped with Ge. Phys. Status Solidi B
2003, 236, 135–142. [CrossRef]
Shigetomi, S.; Ikari, T. Optical and Electrical Characteristics of Layered Semiconductor p-InSe Doped with
Sb. Jpn. J. Appl. Phys. Part 1 2003, 42, 6951–6954. [CrossRef]
Shigetomi, S.; Ikari, T. Optical and electrical properties of layer semiconductor n-InSe doped with Sn. Jpn. J.
Appl. Phys. Part 1 2002, 41, 5565–5566. [CrossRef]
Shigetomi, S.; Ikari, T. Annealing behavior of layer semiconductor p-InSe doped with Hg. Jpn. J. Appl. Phys.
Part 1 2000, 39, 1184–1185. [CrossRef]
Gürbulak, B.; Yildirim, M.; Ateç, A.; Doǧan, S.; Yoǧurtçu, Y.K. Growth and Temperature Dependence of
Optical Properties of Er Doped and Undoped n-Type InSe. Jpn. J. Appl. Phys. Part 1 1999, 38, 5133–5136.
[CrossRef]
Gürbulak, B. Growth and optical properties of Dy doped and undoped n-type InSe single crystal.
Solid State Commun. 1999, 109, 665–669. [CrossRef]
Shigetomi, S.; Ikari, T.; Nakashima, H. Impurity levels in p-type layered semiconductor InSe doped with Hg.
Phys. Status Solidi B 1998, 209, 93–99. [CrossRef]
Politano, A.; Campi, D.; Cattelan, M.; Ben Amara, I.; Jaziri, S.; Mazzotti, A.; Barinov, A.; Gürbulak, B.;
Duman, S.; Agnoli, S.; et al. Indium selenide: An insight on electronic band structure and surface excitations.
Sci. Rep. 2017, 7. [CrossRef] [PubMed]
Mudd, G.W.; Molas, M.R.; Chen, X.; Zólyomi, V.; Nogajewski, K.; Kudrynskyi, Z.R.; Kovalyuk, Z.D.; Yusa, G.;
Makarovsky, O.; Eaves, L.; et al. The direct-to-indirect band gap crossover in two-dimensional van der Waals
Indium Selenide crystals. Sci. Rep. 2016, 6. [CrossRef] [PubMed]
Nanomaterials 2017, 7, 372
70.
71.
72.
73.
74.
75.
76.
77.
78.
79.
80.
81.
82.
83.
84.
85.
86.
87.
88.
89.
90.
91.
15 of 16
Kong, D.; Cha, J.J.; Lai, K.; Peng, H.; Analytis, J.G.; Meister, S.; Chen, Y.; Zhang, H.J.; Fisher, I.R.; Shen, Z.X.;
Cui, Y. Rapid surface oxidation as a source of surface degradation factor for Bi2 Se3 . ACS Nano 2011, 5,
4698–4703. [CrossRef] [PubMed]
Island, J.O.; Steele, G.A.; van der Zant, H.S.J.; Castellanos-Gomez, A. Environmental instability of few-layer
black phosphorus. 2D Mater. 2015, 2. [CrossRef]
Politano, A.; Chiarello, G. Enhancement of hydrolysis in alkali ultrathin layers on metal substrates in the
presence of electron confinement. Chem. Phys. Lett. 2010, 494, 84–87. [CrossRef]
Henderson, M.A. The interaction of water with solid surfaces: Fundamental aspects revisited. Surf. Sci. Rep.
2002, 46, 1–308. [CrossRef]
Shi, L.; Zhou, Q.; Zhao, Y.; Ouyang, Y.; Ling, C.; Li, Q.; Wang, J. Oxidation mechanism and protection
strategy of ultrathin Indium Selenide: Insight from Theory. J. Phys. Chem. Lett. 2017, 8, 4368–4373. [CrossRef]
[PubMed]
Xiao, K.; Carvalho, A.; Neto, A.C. Defects and oxidation resilience in InSe. Phys. Rev. B 2017, 96. [CrossRef]
Cai, Y.; Zhang, G.; Zhang, Y.-W. Charge Transfer and Functionalization of Monolayer InSe by Physisorption
of Small Molecules for Gas Sensing. J. Phys. Chem. C 2017, 121, 10182–10193. [CrossRef]
Ma, D.; Ju, W.; Tang, Y.; Chen, Y. First-principles study of the small molecule adsorption on the InSe
monolayer. Appl. Surf. Sci. 2017, 426, 244–252. [CrossRef]
Peng, Q.; Xiong, R.; Sa, B.; Zhou, J.; Wen, C.; Wu, B.; Anpo, M.; Sun, Z. Computational mining
of photocatalysts for water splitting hydrogen production: Two-Dimensional InSe-family monolayers.
Catal. Sci. Technol. 2017, 7, 2744–2752. [CrossRef]
Guo, Y.; Zhou, S.; Bai, Y.; Zhao, J. Enhanced piezoelectric effect in Janus group-III chalcogenide monolayers.
Appl. Phys. Lett. 2017, 110, 163102. [CrossRef]
Jin, H.; Li, J.; Dai, Y.; Wei, Y. Engineering the electronic and optoelectronic properties of InX (X = S, Se, Te)
monolayers via strain. Phys. Chem. Chem. Phys. 2017, 19, 4855–4860. [CrossRef] [PubMed]
Quan, L.; Song, Y.; Lin, Y.; Zhang, G.; Dai, Y.; Wu, Y.; Jin, K.; Ding, H.; Pan, N.; Luo, Y. The Raman
enhancement effect on a thin GaSe flake and its thickness dependence. J. Mater. Chem. C 2015, 3, 11129–11134.
[CrossRef]
Boukhvalov, D.W.; Katsnelson, M.I. Chemical Functionalization of Graphene with Defects. Nano Lett. 2008,
8, 4373–4379. [CrossRef] [PubMed]
Boukhvalov, D.W.; Dreyer, D.R.; Bielawski, C.W.; Son, Y.-W. A Computational Investigation of the Catalytic
Properties of Graphene Oxide: Exploring Mechanisms by using DFT Methods. ChemCatChem 2012, 4,
1844–1849. [CrossRef]
Gordillo, G.; Calderón, C. CIS thin film solar cells with evaporated InSe buffer layers. Sol. Energy Mater.
Sol. Cells 2003, 77, 163–173. [CrossRef]
Segura, A.; Chevy, A.; Guesdon, J.P.; Besson, J.M. Photovoltaic efficiency of InSe solar cells. Sol. Energy Mater.
1979, 2, 159–165. [CrossRef]
Damodara Das, V.; Sathyanarayanan, J.; Damodare, L. Effect of annealing and surface treatment on the
efficiency of photoelectrochemical (PEC) solar cells with vacuum-deposited n-InSe thin film electrode.
Surf. Coat. Technol. 1997, 94–95, 669–671.
Kovalyuk, Z.; Katerynchuk, V.; Savchuk, A.; Sydor, O. Intrinsic conductive oxide–p-InSe solar cells. Mater. Sci.
Eng. B 2004, 109, 252–255. [CrossRef]
Darwish, A.; Hanafy, T.; Attia, A.; Habashy, D.; El-Bakry, M.; El-Nahass, M. Optoelectronic performance
and artificial neural networks (ANNs) modeling of n-InSe/p-Si solar cell. Superlattices Microstruct. 2015, 83,
299–309. [CrossRef]
Mandal, K.C.; Das, S. Fabrication and characterization of improved p-GaTe/n-InSe heterojunction solar cells.
In Proceedings of the 2012 38th IEEE Photovoltaic Specialists Conference (PVSC), Austin, TX, USA, 3–8 June
2012; pp. 000177–000180.
Mönch, W. Interface States. In Semiconductor Surfaces and Interfaces; Springer: Berlin, Germany, 2013;
Volume 26, pp. 81–103.
Ando, K.; Katsui, A. Optical properties and photovoltaic device applications of InSe films. Thin Solid Films
1981, 76, 141–148. [CrossRef]
Nanomaterials 2017, 7, 372
92.
93.
94.
16 of 16
Balakrishnan, N.; Kudrynskyi, Z.R.; Fay, M.W.; Mudd, G.W.; Svatek, S.A.; Makarovsky, O.; Kovalyuk, Z.D.;
Eaves, L.; Beton, P.H.; Patanè, A. Room Temperature Electroluminescence from Mechanically Formed van
der Waals III-VI Homojunctions and Heterojunctions. Adv. Opt. Mater. 2014, 2, 1064–1069. [CrossRef]
Chen, X.B.; Kelley, D.F. Photophysics of GaSe/InSe nanoparticle heterojunctions. J. Phys. Chem. B 2006, 110,
25259–25265. [CrossRef] [PubMed]
Brotons-Gisbert, M.; Andres-Penares, D.; Suh, J.; Hidalgo, F.; Abargues, R.; Rodríguez-Cantó, P.J.; Segura, A.;
Cros, A.; Tobias, G.; Canadell, E. Nanotexturing to enhance photoluminescent response of atomically thin
indium selenide with highly tunable band gap. Nano Lett. 2016, 16, 3221–3229. [CrossRef] [PubMed]
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