Photoelectric properties of ₂O₃-pGaSe-pInSe cascade heterostructures
Cascade heterostructure of nGa₂O₃-pGaSe-pInSe was created, and a corresponding band energy diagram was built. Electrical and photoelectric properties of this structure were investigated. Due to isotype pGaSe-pInSe heterojunction the photosensitivity spectrum of nGa₂O₃-pGaSe-pInSe heterostructure ext...
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Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України
2002
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| Zitieren: | Photoelectric properties of ₂O₃-pGaSe-pInSe cascade heterostructures / V.P. Savchyn, J.M. Stakhira, Ya.M. Fiyala, V.B. Furtak // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2002. — Т. 5, № 2. — С. 176-179. — Бібліогр.: 23 назв. — англ. |
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irk-123456789-1211922017-06-14T03:07:22Z Photoelectric properties of ₂O₃-pGaSe-pInSe cascade heterostructures Savchyn, V.P. Stakhira, J.M. Fiyala, Ya.M. Furtak, V.B. Cascade heterostructure of nGa₂O₃-pGaSe-pInSe was created, and a corresponding band energy diagram was built. Electrical and photoelectric properties of this structure were investigated. Due to isotype pGaSe-pInSe heterojunction the photosensitivity spectrum of nGa₂O₃-pGaSe-pInSe heterostructure extends up to 1.2 eV in IR range as referred to the photosensitivity spectrum of anisotype nGa₂O₃-pGaSe heterojunction. 2002 Article Photoelectric properties of ₂O₃-pGaSe-pInSe cascade heterostructures / V.P. Savchyn, J.M. Stakhira, Ya.M. Fiyala, V.B. Furtak // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2002. — Т. 5, № 2. — С. 176-179. — Бібліогр.: 23 назв. — англ. 1560-8034 PACS: 72.40, 74.40 http://dspace.nbuv.gov.ua/handle/123456789/121192 en Semiconductor Physics Quantum Electronics & Optoelectronics Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України |
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Cascade heterostructure of nGa₂O₃-pGaSe-pInSe was created, and a corresponding band energy diagram was built. Electrical and photoelectric properties of this structure were investigated. Due to isotype pGaSe-pInSe heterojunction the photosensitivity spectrum of nGa₂O₃-pGaSe-pInSe heterostructure extends up to 1.2 eV in IR range as referred to the photosensitivity spectrum of anisotype nGa₂O₃-pGaSe heterojunction. |
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Article |
| author |
Savchyn, V.P. Stakhira, J.M. Fiyala, Ya.M. Furtak, V.B. |
| spellingShingle |
Savchyn, V.P. Stakhira, J.M. Fiyala, Ya.M. Furtak, V.B. Photoelectric properties of ₂O₃-pGaSe-pInSe cascade heterostructures Semiconductor Physics Quantum Electronics & Optoelectronics |
| author_facet |
Savchyn, V.P. Stakhira, J.M. Fiyala, Ya.M. Furtak, V.B. |
| author_sort |
Savchyn, V.P. |
| title |
Photoelectric properties of ₂O₃-pGaSe-pInSe cascade heterostructures |
| title_short |
Photoelectric properties of ₂O₃-pGaSe-pInSe cascade heterostructures |
| title_full |
Photoelectric properties of ₂O₃-pGaSe-pInSe cascade heterostructures |
| title_fullStr |
Photoelectric properties of ₂O₃-pGaSe-pInSe cascade heterostructures |
| title_full_unstemmed |
Photoelectric properties of ₂O₃-pGaSe-pInSe cascade heterostructures |
| title_sort |
photoelectric properties of ₂o₃-pgase-pinse cascade heterostructures |
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Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України |
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2002 |
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http://dspace.nbuv.gov.ua/handle/123456789/121192 |
| citation_txt |
Photoelectric properties of ₂O₃-pGaSe-pInSe cascade heterostructures / V.P. Savchyn, J.M. Stakhira, Ya.M. Fiyala, V.B. Furtak // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2002. — Т. 5, № 2. — С. 176-179. — Бібліогр.: 23 назв. — англ. |
| series |
Semiconductor Physics Quantum Electronics & Optoelectronics |
| work_keys_str_mv |
AT savchynvp photoelectricpropertiesof2o3pgasepinsecascadeheterostructures AT stakhirajm photoelectricpropertiesof2o3pgasepinsecascadeheterostructures AT fiyalayam photoelectricpropertiesof2o3pgasepinsecascadeheterostructures AT furtakvb photoelectricpropertiesof2o3pgasepinsecascadeheterostructures |
| first_indexed |
2025-07-08T19:22:31Z |
| last_indexed |
2025-07-08T19:22:31Z |
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1837107829466464256 |
| fulltext |
Semiconductor Physics, Quantum Electronics & Optoelectronics. 2002. V. 5, N 2. P. 176-179.
© 2002, Institute of Semiconductor Physics, National Academy of Sciences of Ukraine176
PACS: 72.40, 74.40
Photoelectric properties of nGa2O3-pGaSe-pInSe cascade
heterostructures
V.P. Savchyn, J.M. Stakhira, Ya.M. Fiyala, V.B. Furtak
Ivan Franko National University of Lviv, 50 Dragomanov Str., 79005 Lviv, Ukraine,
e-mail: savchyn@wups.lviv.ua
Abstract. Cascade heterostructure of nGa2O3-pGaSe-pInSe was created, and a corresponding
band energy diagram was built. Electrical and photoelectric properties of this structure were
investigated. Due to isotype pGaSe-pInSe heterojunction the photosensitivity spectrum of
nGa2O3-pGaSe-pInSe heterostructure extends up to 1.2 eV in IR range as referred to the
photosensitivity spectrum of anisotype nGa2O3-pGaSe heterojunction.
Keywords: heterostructure, heterojunction, photosensitivity, indium selenide, gallium selenide,
gallium oxide.
Paper received 14.03.02; revised manuscript received 24.05.02; accepted for publication 25.06.02.
1. Introduction
As it has been shown [1-3], two materials GaSe and Ga2O3
are suitable for creating of nGa2O3-pGaSe heterostructure
(HS). The photosensitivity of such HS covers all visible
spectral range (the long-wave edge of spectrum response
is limited by the GaSe forbidden gap Eg = 2 eV) and part
of UV-range (up to 5.5 eV). Moreover, the spectral re-
sponse of photosensitivity is defined by the heterojunction
(HJ) quality, which depends on the technology condi-
tions of the oxide layer formation. In the case, if the thick-
ness of the oxide layer is comparable with the thickness
of the space-charge region, the UV-sensitivity of HJ is
not limited by the absorption edge of the oxide layer but
is extended to the higher energies than forbidden gap of
Ga2O3 [1].
Our purpose was to extend the photosensitivity of
nGa2O3-pGaSe to a longer wave range. For that the nGa2O3-
pGaSe-pInSe cascade heterostructure (CHS), in which
anisotype nGa2O3-pGaSe HJ was modified by an addition
of the isotype pInSe-pGaSe one, was created. It is necessary
to note, that properties of an isotype pInSe-pGaSe HJ require
careful study, because widely were only studied the
electrical and photoelectric properties of the anisotype
nInSe-pGaSe HJ [4-8]. In particular, it was shown that the
effective separation of photo-generated charge curriers in
a depletion layer due to an energy band diagram of such HJ
took place.
2. Experimental procedures
The preparation of nGa2O3-pGaSe-pInSe CHS was car-
ried out using both thermal oxidation of GaSe and opti-
cal contact method. The InSe and GaSe substrates with
optically specula surfaces were cleaved from single crys-
tals grown by the Bridgman method. The carrier concen-
tration of undoped pGaSe single crystals at room tem-
perature was p = 2⋅1014 cm-3 and pInSe single crystals
(p = 1⋅1014 cm-3) were doped by Cd. The GaSe substrates
are oxidized at 700°C during 0.25 h. As it was shown in
[1], under such treatment the nGa2O3 layer with electron
concentration n ≈ 1014 cm-3 at room temperature was cre-
ated and the anisotype pGaSe-nGa2O3 HJ was formed.
The plate of about 10 µm in thickness was cleaved from
an oxidized GaSe sample. Such thickness does not ex-
ceed the diffusion length Ldiff of photo-generated carri-
ers in pGaSe, which according to [9] is equal 14-18 µm.
The thickness of pInSe substrates was about 200 µm. For
optical contact formation the non-oxidized side of GaSe
plate was pressed to the pInSe substrate. The contacts
with 2 mm2 areas were formed by sputtering of
semitransparent Ni-film on the oxidized side of GaSe
and In-film on the InSe side of CHS.
The spectral response of the photosensitivity and cur-
rent-voltage (I-U) characteristics of CHS were measured
at room temperature.
V. P. Savchyn et al.: Photoelectric properties of nGa
2
O
3
-pGaSe-pInSe...
177SQO, 5(2), 2002
3. Calculation of energy band diagram
The energy band diagram of CHS was calculated with-
out taking into account interface states and using only
the following parameters of main components: pure GaSe
� mp = 0.57m0 [10], ε = 6.5 [11], χ = 3.4 eV [12]; InSe(Cd)
� mp = 0.73m0 [13], ε = 8.6 [11], χ = 4.6 eV [14]. The
Ga2O3 layer formed by thermally oxidized GaSe -
mn=0.55m0 [15], ε = 10.2 [16]. The value χ = 3.9 eV for
the Ga2O3 is calculated using the value of the bend band
for HJ created by the optical contact method [3].
The analyses of the energy band diagram of CHS shows
that under n(Ga2O3) ≤ p(GaSe) ≈ p(InSe) condition the
band bends supplement each other. It means that the
photo-EMFs in both HJs are added up, when the oxide
side of CHS is illuminated by the white light.
As shown in [1], the magnitudes of band bending and
the widths of depletion regions for anisotype nGa2O3-pGaSe
HJ depend on the conditions of GaSe-substrate thermal
oxidation. The band bending magnitude is approximated as
(1)
DV = 0.5 � 0.8 eV and the widths of the depletion region in
both HJ parts w3 ≈ w4 may be equal to 0.35-0.45 µm. As
known, the interface layer of such HJ consists of a composed
composition of a few phases (Ga2O3-Ga2Se3-GaSe) [17-20].
Due to this fact the nGa2O3-pGaSe HJ part of the
investigated CHS is a smooth junction [1] (as shown in Fig.
1).
The band bending values and the widths of the
depletion region for isotype pInSe-pGaSe HJ were
calculated using the relative concentrations of major carriers.
The magnitudes of these qualities are equal to 0.13 eV and
0.67 µm for GaSe and 0.27 eV and 0.96 µm for InSe
accordingly. The energy discontinuities of conduction DEc
and valence DEv bands for an abrupt isotype HJ are equal
to 1.2 eV and 0.4 eV correspondingly.
4. Results and discussion
The photosensitivity spectra of our CHS were measured
under illumination within a linear range of the photo-EMF
dependence on the illumination intensity. The
photosensitivity achieves 104 V/W. The positive potential
on the InSe side appears under illumination of oxide side of
CHS. The photosensitivity spectrum of CHS is calibrated
to a constant photon flux and is represented in Fig. 2.
As expected, a photosensitivity spectrum of our CHS
at hω > 2 eV consists of spectrum that is typical to
nGa2O3-pGaSe HJ prepared by thermal oxidation [1].
This spectrum is extended up to 1.2 eV because a photo-
sensitivity of the isotype pGaSe-pInSe HJ is added. Par-
ticularly, a photosensitivity spectrum of CHS in a visible
region corresponds to photosensitivity of GaSe.
As shown earlier [17-20], HJ formed by thermal oxidation
of GaSe single crystals is accompanied by inevitable arise
of additional Ga2Se3 phase on its interface as a result of Se
diffusion and Se interaction with GaSe. The CHS
photosensitivity at hω > 3 eV declines sharply due to the
light absorption in a relatively wide interface layer of
Ga2O3-GaSe HJ enriched by Ga2Se3 phase. In this inter-
face layer, an intensive recombination of photo-gener-
ated carriers prevents their separation by the depletion
layer [1]. Only at the 5 eV neighbourhood the UV-band
of a photosensitivity is observed (it is not shown in Fig.2).
It is caused by photo-generation of charge carriers in the
depletion region of the oxide film [1].
The kinetic of a photoresponse was investigated in a
short-circuit current state under GaAs-LED pulse irra-
diation (λ = 0.91 µm). The determined time of a
photocurrent relaxation is approximately 3 ms.
According to the proposed energy band diagram of CHS
charge pairs generated in the InSe can be also separated
via the recombination between the photoelectrons gathered
in a �peak� of a conduction band of InSe and the holes from
a valence band of GaSe involving intermediate states in the
interface. This is confirmed by the dependence of the
photosensitivity at λ = 0.91 µm on an additional illumi-
nation of the structure (Fig. 3). In other words, an addi-
tional illumination with a wavelength corresponding to
GaSe absorption region causes significant increase of
w
FE
w21
V D
(1 )
V D
(2 )
= 0. eV4
3.4 eV 4.6 eV
3.9 eV
hω1
hω2 hω3
w 3 w 4
n p pG a O G a Se In S e
d (1 ) d (2 )
2 3
Fig. 1. Energy band diagram of the nGa2O3-pGaSe-pInSe CHS.
1.0 1.4 1.8 2.2 2.6 3.0
10
0
10
-1
10
-2
10
-3
10
-4
hω, eV
S
ω
,
a
rb
.
u
n
.
Fig. 2. Photoresponse spectrum of the nGa2O3-pGaSe-pInSe CHS.
178 SQO, 5(2), 2002
V. P. Savchyn et al.: Photoelectric properties of nGa
2
O
3
-pGaSe-pInSe...
the photosensitivity. This increase in the spectrum range
from 2.2 to 3.3 eV, where the photosensitivity does not
change essentially (Fig. 2), correlates with GaSe absorp-
tion spectrum α(hω) [21] (Fig.3). Such behavior of the
photosensitivity at λ = 0.91 µm under an additional illu-
mination can be interpreted as follows. At hω > 2 eV,
where αd > 1, almost all light quanta are absorbed in the
GaSe layer. I. e., we can regard that αL/S light quanta
are absorbed in a unity time in a unity volume, where L is
an amount of light quanta fallen onto the area of CHS in
a unity time, S is an area of the irradiated surface. The
concentration of photo-generated holes can be determined
as δp = ναLτ/S (ν - quantum yield, τ - lifetime of photo-
generated carriers). Because d(2) = Ldiff, most of the pairs
generated in the GaSe layer are separated by the junc-
tion field, and therefore the photo-generated holes are
accumulated in the �peak� of GaSe valence band near
InSe-GaSe interface. Under intensive additional illumi-
nation of CHS, for example at L ≈ 1014 quanta/s (taking
into account ν~1 and α ~ 3 msec) the concentration of the
photo-generated holes in the �peak� of the GaSe valence
band is comparable with the concentration of equilib-
rium holes in GaSe. Consequently the recombination rate
of the photoelectrons that gather in the �peak� of InSe
conduction band, increases, and thus the charge separa-
tion is improved finally.
In contrast, the additional illumination with a wave-
length, corresponding to InSe absorption region, leads
to decrease of CHS photosensitivity at λ = 0.91 µm (Fig.
3). It is because the photoelectrons additionally are ac-
cumulated in a �peak� of the conduction band of InSe
and therefore the recombination of those electrons
generated by λ = 0.91 µm pulse irradiation becomes more
difficult.
The current-voltage (I-U) characteristics of CHS are
shown in Fig. 4. The polarity of voltage corresponds to
the polarity mark on InSe-side of CHS. Evidently, the
dark I-U characteristic of CHS illustrates a rectifying
property. The differential dark resistance of CHS ap-
proaches to the resistance of InSe substrate as a forward
bias voltage is increased. The appreciable increase of
forward current under illumination at λ = 0.8 µm (Fig.
4, curve 3) can be related to a photoconductive effect in
InSe substrate. The pinch-off voltage of forward I-U char-
acteristic is about 0.25 V and well corresponds to a band
bending in InSe part of pGaSe-pInSe HJ. Because this
band bending is a potential barrier for the holes (Fig.1),
the holes are current carriers through the isotype junc-
tion. On the other hand, a forward current through the
anisotype nGa2O3-pGaSe HJ occurs due to the interface
recombination [1]. When illuminating light is absorbed
mainly in this HJ, a significant increase of the reverse
current is observed (Fig. 4, curve 2). It means that the
reverse branch of I-U characteristic of the investigated
CHS is formed due to the processes in nGa2O3-pGaSe
HJ and, as it is shown in [1], the main mechanism of
reverse current flowing is the heat generation in the de-
pletion region.
5. Conclusions
Thus, the obtained results show the possibility of the prac-
tical use of nGa203-pGaSe-pInSe CHS due to the wide
spectral range of photosensitivity (from 1.2 to 5.0 eV). It
should be noted that nGa203-pGaSe-pInSe structure can
be formed using, for example, the Van-der-Waals epitaxy
method that as is well known [22, 23], provides high qual-
ity and stoichiometry of the epitaxial films of InSe (GaSe)
in spite of high lattice mismatch.
1.0 1.4 1.8 2.2 2.6 3.0
hω, eV
1.0
1.2
1.4
1,6
1.0
1.5
0.5
0
2.0
L , quan ta/s
2
1
10
4
10
3
10
2
10
α, cm
-1
10
12
10 10 10
13 1 4 15
S
ω
(
)
,
a
rb
.
u
n
.
S
ω
(0
)
Fig. 3. Relative photoresponse of the nGa2O3-pGaSe-pInSe CHS
at 0.91 mm versus a wavelength of an additional continues illu-
mination (Sw(l) and Sw(0) - photoresponses at an additional illu-
mination and without it correspoundly) and absorption spectrum
of GaSe single crystal [21]. Insert: relative photoresponse of CHS
at 0.91 µm versus intensity of an additional continues illumina-
tion at λ = 0.5 (1) and 0.8 µm (2).
-0.2
-0.4
-0.8
0.4 0.8 1.2
-0.6
-1.0
0.2
1.4
1.2
1.0
0.8
0.6
0.4
-1.2 -0.8 -0.4
1
2
3
U, V
I, 10 A
-6
Fig. 4. I-U characteristics of nGa2O3-pGaSe-pInSe CHS: 1 � in
dark; 2 and 3 � under illumination at λ = 0.5 µm (1013 quantum/
sec) and λ = 0.8 µm (L = 1014 quantum/sec) accordingly.
V. P. Savchyn et al.: Photoelectric properties of nGa
2
O
3
-pGaSe-pInSe...
179SQO, 5(2), 2002
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