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器件暗电流是反映探测器本质的特征参数,暗电流的大小决定了器件性能,包括扩散电流Idiff、产生复合电流IG-R、直接隧道电流IBBT、缺陷辅助隧道电流ITAT、碰撞电离电流IIMP和表面漏电流Isurf等类型。总的暗电流等于各项电流之和,如下式所示:
$$ {I_d} = {I_{{\rm{diff}}}} + {I_{\rm{{G - R}}}} + {I_{{\rm{BBT}}}} + {I_{{\rm{TAT}}}} + {I_{{\rm{IMP}}}} + I_{{\rm{surf}} }$$ HgCdTe器件各种暗电流中,扩散电流和产生-复合电流由材料电学性能及复合机制决定,隧道电流与材料缺陷性能有关。扩散电流是PN结空间电荷区两端载流子在电场作用下发生扩散和漂移而形成的电流,是热平衡下由空间电荷区两端少子扩散长度内的载流子所形成的电流。
载流子浓度相同的情况下,碲镉汞器件的扩散电流与少子寿命成反比,提高材料的少子寿命可降低器件扩散电流。采用非本征Au掺杂原子代替本身就为深能级复合中心的本征汞空位,有助于降低碲镉汞材料中深能级缺陷,提升P型碲镉汞材料少子寿命,降低器件暗电流,达到提升n-on-p型器件性能的目的。
昆明物理研究所采用Au掺杂技术制备的载流子浓度为1.5×1016 cm−3的Au掺杂长波碲镉汞(10.5 μm@80 K)材料,少子寿命达到0.25 μs,与目前报道的采用相同技术路线材料少子寿命最高水平相当。
图3为采用非本征Au掺杂技术与本征汞空位型长波256×256 (30 μm pitch)碲镉汞焦平面器件暗电流对比。80 K下截止波长为10.6 μm本征汞空位长波256×256碲镉汞器件暗电流为1980 pA ,而相同温度下截止波长为10.5 μm非本征Au掺杂器件暗电流仅为171 pA,采用Au掺杂技术可有效降低n-on-p型长波焦平面器件暗电流,长波器件的暗电流密度从2.2×10−4 A·cm−2降低至1.9×10−5 A·cm−2,R0A从31.3 Ω·cm2提升到了363 Ω·cm2。
图 3 256×256 (30 μm pitch) 长波碲镉汞探测器暗电流分布对比。(a)本征汞空位;(b)非本征Au掺杂
Figure 3. Dark current distribution of the 256×256 (30 μm pitch) LWIR HgCdTe detectors. (a) Intrinsic VHg doping; (b) Extrinsic Au-doping
图4为昆明物理研究所制备的Au掺杂长波器件暗电流随工作温度变化图。上下两条趋势线分别为n-on-p器件和p-on-n器件暗电流控制理论值,对比发现非本征Au掺杂器件暗电流水平明显低于本征汞空位n-on-p型器件,并且随着工作温度的升高,Au掺杂长波器件暗电流越接近Rule07 p-on-n型器件理论值,在110 K时Au掺杂长波器件暗电流控制与Rule07 p-on-n器件控制水平接近。
图 4 Au掺杂长波红外碲镉汞器件暗电流随温度变化
Figure 4. Dark current versus temperature for Au-doped LWIR HgCdTe detectors
图5为昆明物理研究所Au掺杂长波器件暗电流控制水平与国际先进水平对比图,Au掺杂长波器件R0A值较常规汞空位n-on-p型器件提升了至少一个数量级,与p-on-n型器件R0A值控制水平接近,昆明物理研究所Au掺杂长波器件暗电流控制接近国际先进水平,为高性能长波焦平面器件的研制奠定基础。
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昆明物理研究所基于Au掺杂技术对碲镉汞器件暗电流控制方面的优势,先后研制出了Au掺杂碲镉汞256×256 (30 μm pitch)、640×512 (25 μm pitch)、640×512 (15 μm pitch)等规格型号的长波器件,性能与国外报道的器件水平相当,实现了非本征Au掺杂长波碲镉汞器件系列化发展,达到了批量化的生产水平。几种器件典型性能指标如表1所示。
表 1 Au掺杂不同规格长波红外碲镉汞器件典型性能参数
Table 1. Typical performance parameters of Au-doped LWIR HgCdTe detectors with different scale
Kunming Institute of Physics Sofradir MARS VENUS SCORPIO Format 256×256 640×512 640×512 1024×768 320×256 384×288 640×512 Pixel pitch/μm 30 25 15 10 30 25 15 Cut-off wavelength/μm 10.5 10.3 9.8 9.5 9.5 9.5 9.3 Operating temperature/K 77 77 77 70 80 80 80 FOV F2 F2 F2 F3 F2 F2 F2 NETD/mK 10.4 19.1 23.1 27.7 ≤19 ≤17 ≤22 Responsivity non-uniformity 3.87% 5.45% 4.82% 4.52% - - - Average peak detectivity 2.33×1011 1.86×1011 1.62×1011 3.45×1011 - - - Array operability 99.90% 99.90% 99.87% 99.79% ≥99.70% ≥99.50% ≥99.80% -
昆明物理研究所采用非本征Au掺杂技术研制出的长波30 μm中心距256×256规格器件,F数为2时,截止波长为10.5 μm (77 K)的器件平均峰值探测率大于2.0×1011 cm·Hz1/2·W−1,NETD小于11 mK,有效像元率达到99.9%以上,响应率非均匀性小于5%,典型器件性能参数见表1,如图6(a)为组件实物图,图6(b)为器件信号响应图,图6(c)为器件NETD分布图。
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采用非本征Au掺杂技术研制出的长波25 μm中心距640×512规格器件,当F数为2时,截止波长为10.3 μm (77 K)的器件平均峰值探测率大于1.8×1011 cm·Hz1/2·W−1,NETD小于20 mK,有效像元率达到99.7%以上,响应率非均匀性小于6%,典型器件性能参数如表1所示,图7(a)为组件实物图,图7(b)为器件信号响应图,图7(c)为器件NETD分布图。
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采用非本征Au掺杂技术研制出的长波15 μm中心距640×512规格器件,当F数为2时,截止波长为9.8 μm (77 K)的器件平均峰值探测率大于1.5×1011 cm·Hz1/2·W−1,NETD小于25 mK,有效像元率达到99.7%以上,响应率非均匀性小于5%,典型器件性能参数如表1所示,图8(a)为组件实物图,图8(b)为器件信号响应图,图8(c)为器件NETD分布图。
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采用非本征Au掺杂技术研制出的长波10 μm中心距1024×768规格器件,当F数为3时,截止波长为9.5 μm (70 K)的器件平均峰值探测率大于3.0×1011 cm·Hz1/2·W−1,NETD小于30 mK,有效像元率达到99.7%以上,响应率非均匀性小于5%,典型器件性能参数如表1所示,图9(a)为组件实物图,图9 (b)为器件信号响应图,图9 (c)为器件NETD分布图。
Research of Au-doped LWIR HgCdTe detector
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摘要: 昆明物理研究所多年来持续开展了对Au掺杂碲镉汞材料、器件结构设计、可重复的工艺开发等研究,突破了Au掺杂碲镉汞材料电学可控掺杂、器件暗电流控制等关键技术,将n-on-p型碲镉汞长波器件品质因子(R0A)从31.3 Ω·cm2提升到了363 Ω·cm2(λcutoff=10.5 μm@80 K),器件暗电流较本征汞空位n-on-p型器件降低了一个数量级以上。研制的非本征Au掺杂长波探测器经历了超过7年的时间贮存,性能无明显变化,显示了良好的长期稳定性。基于Au掺杂碲镉汞探测器技术,昆明物理研究所实现了256×256 (30 μm pitch)、640×512 (25 μm pitch)、640×512 (15 μm pitch)、1024×768 (10 μm pitch)等规格的长波探测器研制和批量能力,实现了非本征Au掺杂长波碲镉汞器件系列化发展。
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关键词:
- Au掺杂 /
- 暗电流 /
- 长波红外 /
- 碲镉汞(HgCdTe) /
- 焦平面
Abstract:Significance Due to the high quantum efficiency and ultra-wide infrared wavelengths (from SWIR to VLWIR), Mercury cadmium telluride (Hg1−xCdxTe, MCT) is regarded as the preferred material for high-performance infrared focal plane arrays (FPAs). Compared with p-on-n, n-on-p FPAs have the advantages of simple and reliable manufacturing process. However, in n-on-p FPAs, P-type material with intrinsic mercury vacancy is generally used as the absorption layer. The mercury vacancy belongs to the deep-level defect, which leads to the low carrier lifetime of the absorption layer and the difficulty in controlling the dark current of the device at a low level. Replacing Hg-vacancy with Au (gold) in P-type materials is meaningful to increase minority carrier lifetime, and reduce dark current, which is the most effective way to improve the overall performance of MCT LWIR n-on-p devices. In Kunming Institute of Physics (KIP), the Au-doped MCT devices have been investigated since 2010. After years of continuous research, the key technologies including Au-doped material growth, electrical parameters control, device manufacturing and so on have been successfully broken through, which promoted the fabrication of the high-performance Au-doped n-on-p devices. In this paper, the progress of extrinsic Au-doped MCT LWIR n-on-p technologies in Kunming Institute of Physics was reported comprehensively, which was expected to pave a way for mass production of high-performance LWIR n-on-p FPAs. Progress In Kunming Institute of Physics, Te-rich liquid phase epitaxy technology was used to prepare Au-doped LW material. The mercury vacancy concentration was tuned through the heat treatment process with mercury saturation, so as to achieve effective control of electrical parameters. Through the optimization of heat treatment process, the preparation of high-quality Au-doped MCT LW materials was realized, and the carrier concentration can be controlled within 1.0-4.0×1016 cm−3. The dark current is a significant parameter that determines the performance of device. The substitution of Au atoms for mercury vacancies is efficient to reduce the deep-level defects in the MCT materials, increase the minority carrier lifetime of P-type materials, and reduce the dark current of devices. The high-performance MCT LWIR devices (10.5 μm@80 K) have been fabricated by Au-doping technology in Kunming Institute of Physics. Compared with the Hg- vacancy n-on-p device, R0A of the Au-doped LWIR n-on-p device increased from 31.3 Ω·cm2 to 363 Ω·cm2, which was close to the level of p-on-n devices (Rule07) and laid a foundation for the development of high-performance LWIR FPAs. Based on the Au-doped technology, LWIR FPAs including 256×256 (30 μm pitch), 640×512 (25 μm pitch), 640×512 (15 μm pitch) and other specifications were fabricated at Kunming Institute of Physics. The performance of these devices was comparable to those reported abroad. The series development and further mass production of non-intrinsic Au-doped MCT LWIR FPAs have been realized. Furthermore, the researches involved high and low temperature storage, high and low temperature cycle (+70-−40 ℃) and long-term storage stability were carried out, and the results show that after 7 years of long-term storage, the performance of the devices have no obvious change. Conclusions and Prospects In this paper, the development progress of extrinsic Au-doped MCT materials and devices in Kunming Institute of Physics was reported. The stability of Au-doped HgCdTe materials, dark current control and other key technologies have been broken through up to now. The merit factor (R0A) has been improved from 31.3 Ω·cm2 to 363 Ω·cm2(λcutoff=10.5 μm@80 K) for LWIR HgCdTe focal plane arrays by use of Au-doped technology. The dark current has been reduced by one order of magnitude compared with Hg-vacancy n-on-p devices. And the performance of n-on-p LWIR HgCdTe focal plane arrays has been greatly improved. The performance has not change by storage more than 7 years of the Au-doped HgCdTe device, which shown that the devices have better long-term stablity. Based on this, Kunming Institute of Physics has realized the series development of Au-doped LWIR HgCdTe with a format of 256×256 (30 μm pitch), 640×512 (25 μm pitch), 640×512 (15 μm pitch), and 1 024×768 (10 μm pitch), which has provided a foundation for the mass production of long wave HgCdTe focal plane arrays. -
Key words:
- Au-doped /
- dark current /
- long wavelength IR (LWIR) /
- HgCdTe /
- focal plane arrays (FPAs)
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表 1 Au掺杂不同规格长波红外碲镉汞器件典型性能参数
Table 1. Typical performance parameters of Au-doped LWIR HgCdTe detectors with different scale
Kunming Institute of Physics Sofradir MARS VENUS SCORPIO Format 256×256 640×512 640×512 1024×768 320×256 384×288 640×512 Pixel pitch/μm 30 25 15 10 30 25 15 Cut-off wavelength/μm 10.5 10.3 9.8 9.5 9.5 9.5 9.3 Operating temperature/K 77 77 77 70 80 80 80 FOV F2 F2 F2 F3 F2 F2 F2 NETD/mK 10.4 19.1 23.1 27.7 ≤19 ≤17 ≤22 Responsivity non-uniformity 3.87% 5.45% 4.82% 4.52% - - - Average peak detectivity 2.33×1011 1.86×1011 1.62×1011 3.45×1011 - - - Array operability 99.90% 99.90% 99.87% 99.79% ≥99.70% ≥99.50% ≥99.80% -
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