Comparison of characterization techniques in p-on-n HgCdTe LWIR photodiodes technology

In this paper standard techniques for characterization of HgCdTe liquid phase epitaxial layers (LPE) were presented. The performance of long wavelength p-on-n HgCdTe photodiodes fabricated by arsenic diffusion was described. The correlation between LPE HgCdTe material parameters and properties of the infrared photodiodes was demonstrated.     

中波碲镉汞p-on-n高温工作技术研究

针对碲镉汞中波p-on-n技术进行研究,采用二次离子质谱仪分析注入后及退火后As离子在碲镉汞材料中的浓度分布,使用透射电镜表征激活退火后离子注入损伤修复状态,通过半导体参数测试仪评价pn结的IV特性,将探测器芯片装在变温杜瓦中测试其不同温度下的焦平面技术指标。研究结果表明,As离子注入后在碲镉汞体内形成大量缺陷,经过富汞退火后缺陷得到修复,同时As离子进一步向内扩散,制备的pn结工作稳定表明As离子得到有效激活,制备的中波p-on-n探测器芯片在120 K温度下有效像元率可以达到99%以上。     

碲镉汞p-on-n双层异质结材料表面缺陷研究

对碲镉汞p-on-n双层异质结材料的表面缺陷进行了研究。材料表面缺陷会对后续器件的性能产生影响。利用光学显微镜观察外延完的材料表面,发现表面不规则块状缺陷和表面孔洞缺陷较为常见。使用共聚焦显微镜、扫描电子显微镜、能谱分析等测试手段分析发现,缺陷的形成原因是p型层生长过程中镉耗尽以及n型层生长过程中产生缺陷的延伸。     

p-on-n长波、甚长波碲镉汞红外焦平面器件技术研究

As注入掺杂的p-on-n结构具有暗电流小、R₀A值高、少子寿命长等优点,是长波、甚长波碲镉汞红外焦平面器件发展的重要趋势。介绍了由昆明物理研究所研究制备的77 K温度下截止波长为9.5 μm、10.1 μm和71 K下14.97 μm 的p-on-n长波、甚长波碲镉汞红外焦平面器件,对器件的响应率、NETD、暗电流及R₀A等性能参数进行测试分析。测试结果表明,器件的有效像元率在99.78%~99.9%之间,器件的NETD均小于21 mK。实现了p-on-n长波、甚长波碲镉汞红外焦平面器件的有效制备。     

长波p-on-n碲镉汞红外焦平面器件研究进展

与n-on-p材料相比,p-on-n材料具有更低的暗电流和更高的工作温度,更适于长波以及高温工作碲镉汞红外焦平面器件。介绍了法国Sofradir公司、美国Raytheon Vision Systems公司以及国内的华北光电技术研究所和昆明物理研究所在长波p-on-n器件上的研究进展。     

MBE HgCdTe heterostructure p-on-n planar infrared photodiodes

We recently succeeded in fabricating planar Hg_1−yCd_yTe/Hg_1−xCd_xTe (x<y) heterostructure photodiodes with the p-on-n configuration. Here we discuss early results in detail and present new results on an expanded range of infrared operation. The material used for this demonstration was grown by molecular beam epitaxy on lattice-matched CdZnTe substrates. The p-on-n planar devices consist of an arsenic-doped p-type epilayer (y∼0.28) atop a long wavelength infrared n-type epilayer (x=0.22–0.23). The planar junctions were formed by selective pocket diffusion of arsenic deposited on the surface by ion implantation. Detailed analysis of the current-voltage characteristics of these diodes as a function of temperature shows that they have high performance and that their dark currents are diffusion-limited down to 52K. Low frequency noise measurements at a reverse bias voltage of 50 mV resulted in noise current values (at 1 Hz) as low as 1×10⁻¹⁴ amps/Hz^0.5 at 77K. Average R_oA values greater than 10⁶ Ω-cm² at 40K were obtained for these devices with cut-off wavelength values in the 10.6 to 12 μm range. Seventy percent of these devices have R_oA values greater than 10⁵ Ω-cm² at 40K; further studies are needed to improve device uniformity. These results represent the first demonstration that high performance long wavelength infrared devices operating at 40K can be made using HgCdTe material grown by a vapor phase epitaxy growth technique.     

碲镉汞p—on—n光伏器件优化掺杂的理论计算

从理论上考虑了碲镉汞长波光电二极管的主要电流机制，并采用合适的参数对R0A进行了计算。结果表明，由于隧道电流的限制，对于一定的衬底浓度，选择p区掺杂的浓度不宜过大，反之亦然。计算得到了优化择杂浓度与衬底浓度的关系和相应的R0A值。     

Annealing effect on the P-type carrier concentration in low-temperature processed arsenic-doped HgCdTe

We report the results of annealing effects on the As-doped alloy HgCdTe grown by molecular beam epitaxy (MBE), arsenic (As) diffusion in HgCdTe from Hg-rich solutions at low temperatures, and As ion implantation at room temperature. Hall-effect measurements, secondary ion mass spectrometry and p-on-n test photodiodes were used to characterize the As activation. High As-doping levels (10¹⁷−10¹⁹ cm⁻³) could be obtained using either MBE growth, As diffusion or As ion-implantation. Annealed below 400°C, As doping in HgCdTe shows n-type characteristics, but above 410°C demonstrates that all methods of As doping exhibit p-type characteristics independent of As incorporation techniques. For example, for samples annealed at 436°C (P_Hg≈2 atm), in addition to p-type activation, we observe a significant improvement of p/n junction characteristics independent of the As source; i.e. As doping either in situ, by diffusion, or ion implantation. A study of this As activation of As-doped MBE HgCdTe as a function of anneal temperature reveals a striking similarity to results observed for As diffusion into HgCdTe and implanted As activation as a function of temperature. The observed dependence of As activation on partial pressure of Hg at various temperatures in the range of 250 to 450°C suggests that As acts as an acceptor at high Hg pressure (>1 atm) and as a donor at low Hg pressure (<1 atm) even under Hg-rich conditions.     

Key performance-limiting defects in P-on-N HgCdTe LPE heterojunction infrared photodiodes

The operability of long-wavelength p-on-n double layer heterojunction arrays for 40K low-background applications has long been limited by the wide variation in pixel-to-pixel zero bias resistance (R_o) values. Diodes on test structures showing lower performance, with R_o values below 7 × 10⁶ ohm at 40K, usually contained gross metallurgical defects such as dislocation clusters and loops, pin holes, striations, Te inclusions, and heavy terracing. However, diodes with R_o values between 7 × 10⁶ and 1× 10⁹ ohm at 40K contained no visible defects. To study the “invisible” performance-limiting defects (i.e. defects that cannot be revealed by etching), a good correlation between the dynamic resistance at 50 mV reverse bias (R50) value at 77K and the R_o value at 40K was first established, and then used as a tool. The correlation allowed measurements of a large number of devices at 77K, rather than relying exclusively on time-consuming measurements at 40K. Interesting results regarding R_o values at 40K, such as insensitivity to low-density dislocations, mild degradation from Hg vacancies, severe degradation from Hg interstitials, and correlation with junction positioning, were obtained from specially designed experiments.     

甚长波碲镉汞红外焦平面探测器

采用砷离子注入p-on-n平面结技术制备了77 K工作温度下截止波长分别为13.23 μm和14.79 μm、像元中心距为25 μm的甚长波640×512探测器,并对其基本性能和暗电流进行了测试和分析。结果表明,对于截止波长为13.23 μm的甚长波640×512（25 μm）,器件量子效率为55%,NETD平均值为21.5 mK,有效像元率为99.81%;对于截止波长为14.79 μm的甚长波640×512（25 μm）,器件量子效率为45%,NETD平均值为34.6 mK,有效像元率为99.28%。这两个甚长波器件在液氮温度下的R₀A分别为19.8 Ω·cm²和1.56 Ω·cm²,达到了“Rule07”经验表达式的预测值,器件噪声主要受散粒噪声限制,显示出了较好的器件性能。