Supplementary Information for
Ultra-broadband and high-responsive photodetectors based on the bismuth film
at room temperature
J. D. Yao, J. M. Shao, G. W. Yang
1
S1. Ohmic contact between the electrodes and the Bi film
The current-voltage (I-V) characteristics of the Bi photodetector are shown in
Fig. S1. The good linearity of the curve reveals good ohmic contact between the
electrodes and the Bi film.
6
Current (mA)
4
2
0
-2
-4
-6
-1.0
-0.5
0.0
0.5
1.0
Voltage (V)
Figure S1. The current-voltage (I-V) characteristics of the Bi photodetector.
2
S2. EDS analysis of the PLD-grown Bi film
EDS analysis suggests that the film only possess Bi atoms, indicative of its high
purity.
Figure S2. EDS analysis of the PLD-grown Bi film.
3
S3. Dynamic response of the Bi photodetector
The temporal photoresponse is depicted in Fig. S3. The time dependent photoresponse
can be described by the following equations.
For the rise,
I (t )  I 0  A0 [exp(t /  rise )] ,
and for the decay,
I (t )  I 0  A0 [exp( t /  decay )] ,
Where  rise is the response time,  decay is the recovery time, I0 is the dark current,
and A0 is a constant. The response time and recovery time is calculated to be 0.9 s and
1.9 s, respectively.
4
3.0
(a)
2.5
light on
light on
Photocurrent (A)
2.0
1.5
1.0
0.5
0.0
light off
-0.5
0
10
20
30
40
50
60
Time (s)
(b)
Photocurrent (A)
2.0
1.5
1.0
rise= 0.9 s
0.5
experimental data
fitting
0.0
40
41
42
43
44
45
Time (s)
(c)
Photocurrent (A)
2.20
experiment data
fitting
1.65
decay= 1.9 s
1.10
0.55
0.00
17
18
19
20
21
22
Time (s)
Figure S3. The rising and falling times of the Bi photodetector. (a) A temporal
photoresponse. The enlarged (b) rising and (c) falling edge of the data in (a).
Source-drain bias: 0.05 V. Device size: 2 mm  1.2 mm .
5
S4. Switching behavior of the Bi photodetector under illumination with
wavelength from ultraviolet to infrared.
Fig. S4 plots the switching behavior of the Bi photodetector under periodic
illuminations. The result exhibits an excellent long-term reproducibility for all
wavelengths, from ultraviolet to near-infrared, indicating its great potential for
broadband photodetection.
1.6
16
370 nm
532 nm
1.2
12
light on
Photocurrent (uA)
Photocurrent (uA)
light on
0.8
0.4
0.0
8
4
0
light off
light off
-0.4
-4
0
20
40
60
80
0
50
Time (s)
100
150
5
20
1550 nm
1064 nm
4
15
light on
3
Photocurrent (uA)
Photocurrent (uA)
200
Time (s)
2
1
0
light on
10
5
0
light off
light off
-1
0
50
100
150
200
0
Time (s)
100
200
300
400
Time (s)
Figure S4. Switching behavior of the Bi photodetector under illumination with
wavelength of (a) 370 nm, (b) 532 nm, (c) 1064 nm, (d) 1550 nm. Source-drain bias:
0.05 V. Device area: 2 mm  1.2 mm.
6
S5. XRD diffraction patterns of the Bi films with different thickness
400
60 nm
(a)
(003)
Intensity (a.u.)
300
200
(006)
(104)
100
0
10
20
30
40
50
60
2 (deg)
2.0k
(b)
(003)
1.5k
Intensity (a.u.)
120 nm
1.0k
(006)
(012)
500.0
(104)
0.0
10
20
30
40
50
60
2 (deg)
6k
180 nm
(c)
5k
(003)
(006)
Intensity (a.u.)
4k
3k
2k
(012)
1k
(014)
(202)
0
10
20
30
40
50
60
2 (deg)
Figure S5. XRD diffraction peaks of the Bi films with the thickness of (a) 60 nm, (b)
120 nm, (c) 180 nm.
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S6. Two channel model for the Bi TI film
The schematic diagram of the two channel model is illustrated in Fig. S4. The total
conductance of the film is given by(1)
Gtotal  GS  GB  GS   B
Wd B
,
L
Gtotal , GB and GS are the total, bulk and surface conductance,  B is the
conductivity of the bulk; dB, W, L are the thickness, width and length, depicted in
detail in Fig. S4. Considering that the surface channel is metallic while the bulk is
insulating, i.e. GS  GB , the total conductance can be express as:
Gtotal  GS .
GS has no relationship with the film thickness, therefore the total conductance show
little relationship with the film thickness.
Under certain bias U, the current can be expressed as
I  I S  I B  I S   S ES 
nS eSUWd S
.
L
On light illumination,
IP 
nSp eSUWd S
,
L
The photocurrent
I  I P  I 
nS eSUWd S
, n S =nSP  nS .
L
Here, IS and IB are the surface and bulk current, E is the Electric field intensity along
the channel,  S , S and dS are the surface conductivity, mobility and thickness,
respectively. n S and nSP are the surface carrier density in dark and under illumination.
Therefore, the photocurrent is positively correlated with the number of effective
8
photogenerated carriers.
L
W
I
dS
dB
Figure S4. The schematic diagram of the two channel model for the TI Bi film.
Reference
1. S. Xiao, D. Wei, X. Jin, Bi(111) Thin Film with Insulating Interior but Metallic
Surfaces. Phys Rev Lett 109, 166805 (2012).
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