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: n-yamada@isc.chubu.ac.jp

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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]

2

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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3

4

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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References

[1] M. Grundmann, F. -L. Schein, M. Lorenz, T. Böntgen, J. Lenzner, H. von Wenckstern, Phys Status Solidi A

210 (2013) 1671–1703.

[2] C. I. Yu, T. Goto, M. Ueta, J. Phys. Soc. Jpn. 34 (1973) 693–698.

[3] T. Kamiya, K. Nomura, H. Hosono, Physica Status Solidi A 206 (2009) 860–867.

[4] S. M. Sze, Physics of Semiconductor Devices, Wiley, New York, USA, 1981.

[5] S. B. Sharma, S. C. Sharma, B. S. Sharma, S. S. Bedi, J. Phys. Chem. Solids 53 (1992) 329–335.

[6] D. H. Lee, K. Nomura, T. Kamiya, H. Hosono, ECS Solid State Lett. 1 (2012) Q8–Q10.

[7] N. Yamada, R. Ino, H. Tomura, Y. Kondo, Y. Ninomiya, Adv. Electron. Mater. 3 (2017) 1700298.

[8] N. Yamada, Y. Kondo, R. Ino, Phys. Status Solidi A (2018) DOI:10.1002/pssa.201700782.

[9] D. K. Gaskill, L.B. Rowland, K. Doverspike, Electrical transport properties of AlN, GaN and AlGaN, in: J.

H. Edger (Ed.), Properties of Group III Nitrides, EMIS Data Reviews Series No. 11, Inspec, London, UK

1994, p. 108.

[10] Y. Arakawa, K. Ueno, A. Kobayashi, J. Ohta, H. Fujioka, APL Mater. 4 (2016) 086103.

[11] M. G. Cheong, K. S. Kim, C. S. Kim, R. J. Choi, H. S. Yoon, N. W. Namgung, E. K. Suh, H. J. Lee, Appl.

Phys. Lett. 80 (2002) 1001–1003.

[12] P. Kozodoy, S. P. DenBaars, U. K. Mishra, J. Appl. Phys. 87 (2000) 770–775.

[13] P. Kozodoy, S. Keller, S. P. DenBaars, U. K. Mishra, J. Cryst. Growth 195 (1998) 265–269.

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