Supplemental Material
Gate-Tunable Photocurrent in ZnO Nanowires Mediated By Nanowire-Substrate Interface
States
Liangliang Yang, Qiaoming Wang, Xin Tao, Shelby P. Taylor, and Yi Gu
Department of Physics and Astronomy, Washington State University, Pullman, WA 99164
Figure S1
Examples of (a) ID vs VG and IPC vs VG relations under the (b) 325 nm and (c) 517
nm laser illuminations with the extended VG range.
Figure S1 (a) shows that the ID increases by 6 orders of magnitude, as VG changes from below –
40 V to 20 V. The lowest value of ID is ~ 1 pA, representing the “OFF” state of the channel.
Under the above-bandgap excitation (325 nm laser emission), IPC exhibits little variations with
VG [Figure S1 (b)], consistent with the results shown in the main text. As demonstrated in Figs.
S1 (c) and S3, under the 517 nm illumination, IPC saturates with VG increasing beyond ~ 30 – 40
V. This saturation is likely due to the movement of the Fermi level above the conduction band
edge, with all interface states populated by electrons (see also the main text).
Table S1 lists the material parameters used in the calculations for Fig. 4 in the main text. For
calculations shown in Fig. 3, where there are no interface traps, a donor density of 1.4 × 1018 cm3
and an electron mobility of 250 cm2/Vs were used. Figure S1 shows, in the presence of the
nanowire/substrate interface states, the reasonable agreement between the experimental and
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calculated ID vs VG and ID vs VDS results. We note that, the change of ID with the varying VG, i.e.
∆ID/∆VG, is mostly determined by the electron mobility.
Table S1 Materials parameters used in calculations
ZnO
Electron mobility
(cm2/Vs)
Hole mobility (cm2/Vs)
Dielectric Constant
Band Gap (eV)
Donor density (cm-3)
N0 (cm-2)
Electron Affinity (eV)
Donor Level (eV)
Si3N4
400
34
8.66
3.385
2 × 1018
7.5
5
7 × 1012
6
0.046 (From the
conduction Band)
1.9
E0 = 2.56 eV (From the
conduction Band)
Es = 0.51 eV
Gaussian Energy Distribution
Electron Trap (eV)
Electron effective mass
Hole effective Mass
ZnO/Si3N4 Interface
0.24
0.8
Figure S2
Experimental (solid line) and calculated (dashed line) of (a) ID vs VDS and
(b) ID vs VG results, with the nanowire/substrate interface states taken into account in the
calculations.
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Figure S3 shows IPC vs VG relations under the 517 nm
illumination before and after the annealing at 250 oC in
the Ar atmosphere. The annealing did not lead to the
passivation of the interface states, as the magnitude of IPC
after the annealing remains relatively unchanged. There
are some variations in the IPC vs VG relations, possibly
due to the decrease of the surface water coverage (which
can modify the gate coupling) as a result of the annealing.
Figure S3
IPC vs VG relations before
and after the annealing at 250 oC in the
Ar atmosphere.
However, the general trend of the IPC vs VG relation appears to be independent of the annealing.
We note that the range of the gate voltage sweep shown here is much larger than that in the
original manuscript (see also below).
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