A systematic study of light dependency of persistent photoconductivity in a-InGaZnO thin-film transistors

doi:10.1088/1674-1056/abb222

中国物理B ›› 2020, Vol. 29 ›› Issue (11): 118101-.doi: 10.1088/1674-1056/abb222

Yalan Wang(王雅兰)¹, Mingxiang Wang(王明湘)¹^,†(), Dongli Zhang(张冬利)¹^,^‡(), Huaisheng Wang(王槐生)¹

收稿日期:2020-07-09 修回日期:2020-08-18 接受日期:2020-08-25 出版日期:2020-11-05 发布日期:2020-11-03

A systematic study of light dependency of persistent photoconductivity in a-InGaZnO thin-film transistors

Yalan Wang(王雅兰), Mingxiang Wang(王明湘)^†, Dongli Zhang(张冬利)^‡, and Huaisheng Wang(王槐生)

School of Electronic and Information Engineering, Soochow University, Suzhou 215006, China

Received:2020-07-09 Revised:2020-08-18 Accepted:2020-08-25 Online:2020-11-05 Published:2020-11-03
Contact: ^†Corresponding author. E-mail: mingxiang_wang@suda.edu.cn ^‡Corresponding author. E-mail: dongli_zhang@suda.edu.cn
Supported by:
Project supported in part by the National Natural Science Foundation of China (Grant Nos. 61974101 and 61971299), the State Key Laboratory of ASIC and System, Fudan University (Grant No. 2019KF007), the Natural Science Foundation of Jiangsu Province, China (Grant No. SBK2020021406), the Natural Science Foundation of the Jiangsu Higher Education Institutions of China (Grant No. 19KJB510058), and the Suzhou Science and Technology Bureau (Grant No. SYG201933).

摘要/Abstract

Abstract:

Persistent photoconductivity (PPC) effect and its light-intensity dependence of both enhancement and depletion (E-/D-) mode amorphous InGaZnO (a-IGZO) thin-film transistors (TFTs) are systematically investigated. Density of oxygen vacancy (V_O) defects of E-mode TFTs is relatively small, in which formation of the photo-induced metastable defects is thermally activated, and the activation energy (E_a) decreases continuously with increasing light-intensity. Density of V_O defects of D-mode TFTs is much larger, in which the formation of photo-induced metastable defects is found to be spontaneous instead of thermally activated. Furthermore, for the first time it is found that a threshold dose of light-exposure is required to form fully developed photo-induced metastable defects. Under low light-exposure below the threshold, only a low PPC barrier is formed and the PPC recovery is fast. With increasing the light-exposure to the threshold, the lattice relaxation of metal cations adjacent to the doubly ionized oxygen vacancies (${{\rm{V}}}_{{\rm{O}}}^{2+}$) is fully developed, and the PPC barrier increases to ∼ 0.25 eV, which remains basically unchanged under higher light-exposure. Based on the density of V_O defects in the channel and the condition of light illumination, a unified model of formation of photo-induced metastable defects in a-IGZO TFTs is proposed to explain the experimental observations.

Key words: amorphous indium-gallium-zinc oxide, thin-film transistors, persistent photoconductivity, light-intensity

Yalan Wang(王雅兰), Mingxiang Wang(王明湘), Dongli Zhang(张冬利), Huaisheng Wang(王槐生). [J]. 中国物理B, 2020, 29(11): 118101-.

Yalan Wang(王雅兰), Mingxiang Wang(王明湘), Dongli Zhang(张冬利), and Huaisheng Wang(王槐生). A systematic study of light dependency of persistent photoconductivity in a-InGaZnO thin-film transistors[J]. Chin. Phys. B, 2020, 29(11): 118101-.

图/表 13

参考文献 23

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E-mode a-IGZO TFTs
Parameters	Value	Description
N_C/cm⁻³	2.0×10¹⁹	effective DOS in CBM
N_V/cm⁻³	5×10¹⁸	effective DOS in VBM
E_g/eV	3.2	band-gap
Tail states acceptor-like DOS	g_TA(E) = N_TA exp[(E − E_C)/W_TA]
N_TA/eV⁻¹⋅cm⁻³	1.4×10¹⁸	density of tail states at E = E_C
W_TA/eV	0.36	conduction-band-tail slope
Tail states donor-like DOS	g_TD(E) = N_TDexp[(E_V − E)/W_TD]
N_TD/eV⁻¹⋅cm⁻³	4.5×10¹⁹	density of tail states at E = E_V
W_TD/eV	0.1	Valence-band-tail slope
Deep donor-like DOS	g_GD(E) = N_GD exp{−[(E − E_GD)/W_GD]²}
N_GD/eV⁻¹⋅cm⁻³	1×10¹⁷	density of donor-like at E = E_V
E_GD/eV	1	mean energy of donor-like
W_GD/eV	0.1	standard deviation of donor-like
D-mode a-IGZO TFTs
Deep donor-like DOS	g_GD(E) = N_GD exp{−[(E − E_GD)/W_GD]²}
N_GD/eV⁻¹⋅cm⁻³	5×10¹⁸	density of donor-like at E = E_V
E_GD/eV	1.3	mean energy of donor-like
W_GD/eV	0.1	standard deviation of donor-like
Shallow donor-like DOS	g_OV(E) = N_OV exp{−[(E − E_OV)/W_OV]²}
N_OV/eV⁻¹⋅cm⁻³	1×10¹⁸	peak of OV states
E_OV/eV	2.9	mean energy of OV states
W_OV/eV	0.23	standard deviation of OV states

Light-intensity	E_{a_ex}/eV	E_{a_re}/eV
0.3 mW/cm²	0.25	0.22
1 mW/cm²	0.13	0.19
5 mW/cm²	0.11	0.15

Samples		Photo-excitation				PPC recovery
Samples		I_S	β_ex	τ_ex	E_{a_ex}	β_re	τ_re	E_{a_re}
E-mode TFTs		1	↓	−1	↓	↓	−1	↓
D-mode	< D_T	1.1	−0.25	−0.28	−	−0.12	1.7	↑
TFTs	> D_T	0.16	−0.11	−0.28	−	−	slightly ↓	slightly ↓

A systematic study of light dependency of persistent photoconductivity in a-InGaZnO thin-film transistors

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