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晶界是限制CdZnTe核辐射成像探测器大面积应用的主要缺陷之一. 为了探究改善晶界附近电场分布特性的方式, 本文采用Silvaco TCAD从理论上研究了亚禁带光照对于含晶界CdZnTe探测器内电场分布的影响. 仿真结果表明, 在无偏压下, 亚禁带光照能使得晶界势垒降低, 从而减小对载流子传输的阻碍作用. 在外加偏压下, 亚禁带光照使得晶界引起的电场死区消失, 使其电场分布趋向于线性分布. 同时研究了不同波长和不同强度的亚禁带光照对于晶界电场分布的影响, 结果表明光强低于1×10 –9W/cm 2时, 亚禁带光照对于CdZnTe晶体的电场无调节作用. 而在波长850 nm, 光强1×10 –7W/cm 2的亚禁带光照下, 实现了更平坦地电场分布, 因此可有效地提高器件的载流子收集效率. 仿真结果为调节晶界电场分布提供了理论指导.
Grain boundary is one of the main defects, limiting the large-area application of CdZnTe nuclear radiation imaging detectors. In order to explore the ways to improve the electric field distribution properties near grain boundary, the effect of sub-bandgap illumination on the electric field distribution in CdZnTe detector with grain boundary is studied by Silvaco TCAD simulation technique. The grain boundary potential barrier and electric field dead zone are found in simulation results that significantly affect the carrier transport process in CdZnTe detector. The electric field dead zone caused by the grain boundary disappears under the bias of sub-bandgap illumination. Thus the electric field distribution tends to be linear. Meanwhile, the effects of different wavelengths and intensities of sub-bandgap illumination on the electric field distribution at the grain boundary are also investigated. The results show that the electric field of CdZnTe is distorted by sub-bandgap illumination at an intensity lower than 1×10 –9W/cm 2. In contrast, a flatter electric field distribution is achieved at a wavelength of 850 nm and an intensity of 1×10 –7W/cm 2. The carriers can be transported by drifting, reducing the probability of being captured or recombined by defects during transport, thus improving the charge collection efficiency of the detector. In addition, the microscopic mechanism of the modulation of the electric field distribution by sub-bandgap illumination and the energy band model of CdZnTe crystal containing grain boundary are proposed. Owing to the existence of the grain boundary, two space charge regions are formed near the grain boundary. The energy band at the grain boundary is bent upward. Meanwhile, the metal-semiconductor contact forms a Schottky barrier, and the energy band near the electrode is bent upward. When the bias voltage is applied, the energy band structure of the CdZnTe tends to tilt from the cathode to the anode. The sub-bandgap illumination can lower the energy band barrier at the grain boundary and regulate the energy band on both sides of the grain boundary. It is believed that this discussion will also make some contributions to understanding of the effects of illumination and grain boundary in other types of optoelectronic devices, especially the applications of thin films in solar cells and detectors. -
Keywords:
- CdZnTe/
- grain boundary/
- silvaco/
- sub-bandgap illumination
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Parameters Value Parameters Value Band gap/eV 1.6 Dielectric constant 10.9 Conduction band density/cm–3 9.14×1017 Optical recombination rate/(cm3·s–1) 1.5×10–10 Valence band density/cm–3 5.19×1018 Electronic auger coefficient/(cm6·s–1) 5×10–30 Electron mobility/cm2/(V·s) 1000 Hole Auger coefficient/(cm6·s–1) 1×10–31 Hole mobility/cm2/(V·s) 100 Acceptor band tail state/(cm–3·eV–1) 7.5×1014 Donor band tail state/(cm–3·eV–1) 7.5×1014 
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Level position
/eVType Density
/cm–3Electron capture cross section/cm2 Hole capture cross section/cm2 EV+0.86 Donor 5×1011 3×10–14 3×10–15 下载:
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Level
position
/eVType Density
/cm–3Electron
capture cross
section/cm2Hole capture
cross section/cm2EC– 0.10 Donor 1×1012 1.2×10–15 1.2×10–16 EV+ 0.14 Acceptor 1×1012 2.5×10–15 2.5×10–16 EV+ 0.75 Acceptor 5×1012 3×10–14 3×10–15 下载:
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Wavelength/nm Extinction coefficientk Refractive indexn Absorption coefficient/cm–1 890 1.417×10–4 2.9196 10 下载:
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Wavelength/nm Extinction coefficientk Refractive index/n Absorption coefficient/cm–1 850 2.707×10–4 2.9511 40 890 1.417×10–4 2.9196 10 940 3.540×10–5 2.8796 5 下载:
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[1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19] [20] [21] [22] [23] [24] [25] [26] [27] [28] [29] [30] [31] [32] [33] [34] [35] [36] [37] [38]
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