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Supplementary Information
Visible-blind wide-dynamic-range fast-response self-powered ultraviolet
photodetector based on CuI/In-Ga-Zn-O heterojunction
Naoomi Yamada,a, * Yuumi Kondo,a Xiang Caoa and Yoshitaka Nakanob
a Department of Applied Chemistry, Chubu University, 1200 Matsumoto, Kasugai, Aichi 487-8501, Japan
b Department of Electrical and Electronic Engineering, Chubu University, 1200 Matsumoto, Kasugai, Aichi 487-8501, Japan
* Corresponding Author. E-mail: [email protected]
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1. Elemental composition of a-IGZO
Table S1. Elemental composition of a-IGZO films in this study. The composition was obtained using scanning
electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDX).
ElementConcentration
[at%]
In 19.1 ± 0.2
Ga 19.2 ± 0.1
Zn 17.6 ± 0.3
O 44.1 ± 0.1
2. Carrier density and mobility of CuI and a-IGZO layers
Table S2. Hole density and mobility of CuI films prepared in 4 different runs. The hole density and mobility
were determined from Hall-effect measurement.
Sample No. Hole density [cm-3] Mobility [cm2 V-1 s-1]
#1 1.2 × 1018 5.8
#2 1.8 × 1018 7.0
#3 4.7 × 1018 7.0
#4 6.0 × 1018 3.8
Average 3.4 × 1018 5.9
Standard deviation 2.3 × 1018 1.5
Table S3. Electron density and mobility of a-IGZO films prepared in 4 different deposition runs. The electron
density and mobility were determined from Hall-effect measurement.
Sample No. Electron density [cm-3] Mobility [cm2 V-1 s-1]
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1
2
3
4
5
6
7
8
9
10
11
12
13
#1 1.1 × 1016 4.5
#2 1.6 × 1016 11
#3 2.8 × 1016 12
#4 7.0 × 1016 13
Average 3.1 × 1016 10
Standard deviation 2.8 × 1016 3.4
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2
3
3. Absorption coefficient of CuI
2.5 3.0 3.5 4.00
1
2
3
4
Photon energy [eV]
Abs
orpt
ion
coef
.[10
5cm
-1]
Z1,2
3.4 eV
Fig. S1. Optical absorption coefficient spectrum of CuI layer. The absorption peak (labeled by Z1,2) at the
photon energy of Ez = 3.07 eV attributed to the excitonic absorption. [1] The exciton binding energy (EBX) of
CuI is 62 meV, [2] so the bandgap energy (Eg) is estimated to be Eg = Ez + EBX = 3.1 eV. The dashed vertical
straight line denotes the photon energy used for the evaluation of the ultraviolet detectors in this study.
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4. Bandgap estimation of a-IGZO
0
20
40
60
80
100
0
20
40
60
80
100
Tran
smitt
ance
[%]
Ref
lect
ance
[%]
2.0 2.5 3.0 3.5 4.00
0.5
1.0
Abs
orpt
ion
coef
. [10
5 cm
-1]
Photon energy [eV]
3.4 eV
(a)
(b)
Fig. S2. (a) Optical transmittance and reflectance spectra for a-IGZO film deposited on glass. The open circles
represent the experimental spectra, and the solid curves are the best-fit spectra calculated by employing Tauc-
Lorentz (TL) dispersion model. The dielectric response of a-IGZO along the ultraviolet-to-visible range has
been described well with the TL dispersion model. [3] The fitting analysis provides a bandgap energy of 3.2
eV. (b) Absorption coefficient spectrum obtained from the TL fitting analysis.
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5. Optical transmittance
020406080
100
ITO/glass
020406080
100
CuI/glass
020406080
100
Tran
smitt
ance
[%]
a-IGZO/glass
2.02.53.03.54.00
20406080
100
Photon energy [eV]
Glass
(a)
(b)
(c)
(d)
Fig. S3. Optical transmittance spectra of (a) CuI/glass, (b) a-IGZO/glass, (c) ITO/glass, and (d) glass substrate.
The dotted vertical straight line denotes the photon energy used for evaluation of the ultraviolet detectors in
this study.
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6. Dark diode characteristics
(a) (c)(b)
0 0.2 0.4 0.6 0.8 1-25
-20
-15
-10
-5
| Voltage | [V]
log
(Cur
rent
)
Reverse
Forward
0 0.2 0.4 0.6 0.8 1-25
-20
-15
-10
-5
| Voltage | [V]
log
(Cur
rent
)
Reverse
Forward
0 0.2 0.4 0.6 0.8 1-25
-20
-15
-10
-5
| Voltage | [V]
log
(Cur
rent
)
Reverse
Forward
Fig. S4. Dark current–voltage (I–V) curves of CuI/a-IGZO heterojunctions with different CuI thickness: (a) 28
nm, (b) 114 nm, and (c) 148 nm. The dotted straight line shows the relationship of log I (V )=log I 0+qV
ηk B T,
where I0 is the reverse saturation current, η is the ideality factor, kB is the Boltzmann constant, and T is
temperature. The theoretical log I(V) was fitted to the experimental I–V curves using the linear least-square
method.
Table S4. Dark-diode characteristics of CuI/a-IGZO diodes with different CuI thickness. The ideality factor (η)
and reverse-saturation current (I0) were obtained from the analysis shown in Fig. S4.
CuI thickness Ideality factor, ηReverse saturation current, I0
[nA]
Rectification ratio
at ± 1 V
28 nm 2.6 15 150
114 nm 1.8 2.8 65000
178 nm 2.3 2.0 3100
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7. Thickness of Depletion Layers
In an ideal heterojunction, the depletion-layer widths in n- and p-type layers (xn and xp, respectively) at
zero bias are given by: [4]
xn=[ 2 ϵ n ϵ p ϵ02 N A V bi
qN D (ϵ n ND+ϵ p N A ) ]12,
(S1)
x p=[ 2 ϵ n ϵ p ϵ02 N DV bi
q N A ( ϵ n N D+ϵ p N A ) ]12 .
(S2)
where Vbi represents the built-in potential, ϵp (ϵn) is the static dielectric constant of the p-type (n-type) layer, NA
(ND) denotes the acceptor (donor) density of the p-type (n-type) layer, ϵ0 represents the vacuum permittivity,
and q is the elemental charge. The xp and xn values in our case were calculated from Eqs. (S1) and (S2).
The main acceptor in CuI is singly-charged copper vacancy, and thus NA is equal to its hole density (p): NA
= p. On the other hand, ND in a-IGZO is half of the electron density (n), i.e. ND = n / 2, because the main donor
is considered to be doubly-charged oxygen vacancy. We used ϵp = 9.1 for CuI [5] and ϵn = 13.5 for a-IGZO. [6]
In addition, Vbi was assumed to be ~1 eV. [7] As a result, xn ≈ 300 nm, xp ≈ 1.5 nm, and xn/xp ≈ 200 were
obtained.
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8. Photoluminescence spectrum of CuI Layer
0
20
40
60
80
100A
bsor
ptio
n [%
]
360 390 420 450Wavelength [nm]
Inte
nsity
[arb
. uni
t]
DAP
(a)
(b)
@RT
@RT
Fig. S5. (a) absorption and (b) photoluminescence spectra of CuI thin film on glass: the measurements were
performed at room temperature (~298 K).The peaks labeled by arrows in part (a) and (b) are due to excitonic
absorption and emission, respectively. The broad shoulder labeled with DAP in part (b) is ascribed to the
emission due to donor-acceptor-pair (DAP) transition.
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9. Dark current of CuI/a-IGZO
0 20 4010-13
10-12
10-11
10-10
10-9
10-8
10-7
Time [s]
| Cur
rent
| [A
]
460 480 50010-13
10-12
10-11
10-10
10-9
10-8
10-7
Dark Dark
Fig. S6. Dark current of CuI/a-IGZO: this is a magnified view of Fig. 6b around the time intervals of 0–40 s
and 460–490 s. The dark current was averaged to be 7 pA (dashed line).
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10. Transient photoresponse of CuI/a-IGZO
0.29 0.30 0.31Time [s]
Volta
ge [a
rb. u
nit]
0.80 0.85 0.90 0.95Time [s]
Rise Decay
(a) (b)
UV on
UV off
Fig. S7. Transient photovoltage response of CuI/a-IGZO for (a) rise and (b) decay processes. Both processes
consist of two components (see the solid straight lines).
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11. Comparison of Hole Mobility: CuI Polycrystalline Films vs. GaN:Mg Epilayers
1016 1017 1018 10191
5
10
50
100
Hole density [cm-3]
Hol
e m
obilit
y [c
m2
V-1 s
-1]
GaN:Mg
CuI
Fig. S8. Comparison of hole mobility as a function of hole density for CuI polycrystalline films (closed
triangles) and p-type GaN:Mg epilayers (open marks). The data for the CuI polycrystalline layers were
obtained in our previous study. [7, 8] The mobility data for the p-GaN:Mg epilayers were taken from the
literature: circles, triangles, squires, diamonds, and inverted triangles are from refs. 9, 10, 11, 12, and 13,
respectively.
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12. Photovoltage Waveforms Taken at Frequencies of 3 and 5 Hz
0 1 2 3 40
0.5
1.0
Time [s]
Pho
tovo
ltage
[ar
b. u
nit] Frequency: 3 Hz Frequency: 5 Hz
0 0.5 1.0 1.50
0.5
1.0
Time [s]
Pho
tovo
ltage
[ar
b. u
nit]
(a) (b)
Fig. S9. Photovoltage waveform under pulsed UV illumination (at 365-nm wavelength and power density of
0.7 mW cm-2) with the frequency of (a) 3 and (b) 5 Hz (the duty cycle was fixed to be 50%).
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13. Reproducibility Check
We fabricated three CuI/a-IGZO UVPDs with a CuI thickness of ~120 nm to check the reproducibility of
the performance. The UV sensing performance of these devices at zero bias is summarized in Table S4. The
UV wavelength used for the evaluations was 365 nm. In addition, the results of the alternate on/off tests and Pin
dependence of the photocurrent are shown in Fig. S9. The photovoltage wave forms under pulsed UV
illumination (at 365-nm wavelength and a power density of 0.7 mW cm -2) with a frequency of 1 Hz are also
presented in Fig. S10. From these data, good reproducibility can be confirmed.
Table S4. The performance of three CuI/a-IGZO UVPDs with a CuI thickness of ~120 nm. The three
samples were fabricated under the same conditions described in the Experimental section.
Sample No.Iph / Idark
(LDR)
Responsivity
[mA W-1]θ in Iph ∝ Pin
θ Response time [ms]
Rise Decay
#1a)4100
(72 dB)0.60 1.03
2.5 (τr1)
20 (τr2)
35 (τd1)
60 (τd2)
#24060
(72 dB)0.64 0.98
3.2 (τr1)
8.2 (τr2)
14 (τd1)
92 (τd2)
#33390
(71 dB)0.54 1.09
2.7 (τr1)
7.0 (τr2)
19 (τd1)
95 (τd2)
Average3850
(72 dB)0.59 1.03
2.8 (τr1)
0.4 (τr2)
23 (τd1)
82 (τd2)
Standard deviation 399 0.05 0.0612 (τr1)
7 (τr2)
10 (τd1)
20 (τd2)
a) The data for #1 is described in the main text.
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-40
-30
-20
-10
0
Cur
rent
[nA
]
Sample #2
0 100 200 300
-40
-30
-20
-10
0
Time [s]
Cur
rent
[nA
]
Sample #3
(a)
(b)0
-10
-20
-30
-40
-50
Pho
tocu
rren
t, I ph
[nA
] Sample #2
0 0.3 0.6 0.9 1.20
-10
-20
-30
-40
-50
Power density, Pin [mW cm-2]
Sample #3
Pho
tocu
rren
t, I ph
[nA
]
(c)
(d)
Iph ∝ Pin1.09
Iph ∝ Pin0.98
Fig. S10. Time-dependent photoresponse of samples (a) #2 and (b) #3 under alternate on/off cycles of UV
illumination (λ = 365 nm, Pin = 0.7 mW cm-2). Photocurrent of samples (c) #2 and (d) #3 under UV
illumination (λ = 365 nm) at zero bias as a function of Pin.
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5
0 10 20 30 40 500
0.5
1.0
Relative time [ms]
Pho
tovo
ltage
[ar
b. u
nit] Sample #2
(a)
0 10 20 30 40 500
0.5
1.0
Relative time [ms]
Pho
tovo
ltage
[ar
b. u
nit] Sample #3
(c)
0 50 100 150 2000
0.5
1.0
Relative time [ms]
Pho
tovo
ltage
[ar
b. u
nit] Sample #2
(b)
0 50 100 150 2000
0.5
1.0
Pho
tovo
ltage
[ar
b. u
nit]
Relative time [ms]
Sample #3
(d)
Fig. S11. (a, c) Rise and (b, d) decay parts of photovoltage waveforms for samples (a, b) #2 and (c, d). The
solid curves are the best-fit bi-exponential function described in the main text.
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