面向第三代红外焦平面的碲镉汞材料器件研究

文章叙述了第三代红外焦平面中所需求的碲镉汞分子束外延(MBE)的一些研究成 果。对GaAs、Si基大面积异质外延、表面缺陷抑制、p 型掺杂等MBE的主要难点问题进行了阐述。研究表明, 3 in材料的组分均匀性良好,组分x的偏差为0. 5%。晶格失配引发的孪晶缺陷可以通过合适的低温成核方法得到有效的抑制。在GaAs和Si衬底上外延的HgCdTe材料的(422) x射线衍射半峰宽( FWHM)的典型值为60～80arc·sec。大于2μm缺陷的表面密度可以控制在小于300cm- 2水平。研究发现As的表面黏附系数很低,对生长温度十分敏感,在170℃下约为1 ×10- 4。通过合适的退火,可以实现As的受主激活。采用碲镉汞多层材料已试制了长波n2on2p与p2on2n型掺杂异质结器件以及双色红外短波/中波焦平面探测器,本文报道了一些初步结果。     

碲镉汞p-on-n长波异质结探测器材料的制备研究

报道了碲镉汞p+-on-n长波双层异质结材料和异质结台面器件的研究结果,重点研究了p+-on-n型双层异质结材料制备技术。通过水平滑舟富碲液相外延生长的方法在碲锌镉衬底上原位生长In掺杂碲镉汞n型吸收层材料,然后再采用富汞垂直液相外延技术制备p型As原位掺杂的碲镉汞cap层材料,从而获得p+-on-n型双层异质结材料,并通过湿法腐蚀、台面刻蚀以及钝化等工艺得到碲镉汞 p+-on-n长波异质结台面型器件。p+-on-n异质结器件结构可以有效克服少子寿命偏低等问题,在长波及甚长波波段具有更低的暗电流和更高的R0A值,这对于解决目前长波碲镉汞红外探测器暗电流大、结阻抗低的问题,提高长波及甚长波波段碲镉汞红外焦平面器件的性能具有重要的意义。     

微电子学、集成电路

TN42005040348碲镉汞p+-on-n长波异质结探测器的研究/叶振华,吴俊,胡晓宁,巫艳,王建新,李言谨,何力(中国科学院上海技术物理研究所材料器件中心)//红外与毫米波学报.―2004,23(6).―423～426.报道了HgCdTe p+-on-n长波异质结焦平面器件的研究结果.采用由分子束外延(MBE)和原位掺杂技术生长的P+-on-n异质结材料,通过湿法腐蚀、台面钝化、台面金属化、铟柱制备和互连等工艺,得到了HgCdTe p+-on-n长波异质结焦平面器件.根据,I-V实验结果和暗电流理论,拟合计算和分析了各种暗电流机制对器件性能的影响.且获得了器件的响应光谱和探测率。图…     

甚长波碲镉汞红外探测器制备研究

报道了碲镉汞甚长波红外焦平面探测器的最新研究进展。采用水平液相外延In掺杂和垂直液相外延Ａs掺杂技术生长了高质量的p on n型双层异质结材料。并通过提高材料质量将双层异质结材料的双晶衍射半峰宽控制在30 arcsec以内。基于台面器件加工、表侧壁钝化以及In柱互连工艺,制备了640×512,25μm碲镉汞甚长波红外焦平面器件。通过进一步优化了材料生长和芯片制备工艺,在65 K的工作温度下,该器件的截止波长为1435 μｍ,有效像元率为9806,平均峰值探测率为809×1010cm·Hz1/2·W-1。     

碲镉汞p^＋-on-n长波异质结探测器的研究

报道了HgCdTe p^ -on-o长波异质结焦平面器件的研究结果．采用由分子柬外延(MBE)和原位掺杂技术生长的P^ -on-n异质结材料，通过湿法腐蚀、台面钝化、台面金属化、铟柱制备和互连等工艺，得到了HgCdTe p^ -on-o长波异质结焦平面器件．根据，I-V实验结果和暗电流理论，拟合计算和分析了各种暗电流机制对器件性能的影响．且获得了器件的响应光谱和探测率。     

碲镉汞富汞热处理技术的研究

利用自行研制的垂直开管富汞热处理设备,研究了碲镉汞（HgCdTe）富汞热处理技术。经富汞条件下3000C热处理和后续的常规N型热处理,As掺杂的Hg1-xCd,Te分子束外延材料中的As原子已被激活成P型受主,As原子激活率同石英管封管热处理试验的结果基本一致。对包括3in Si基衬底在内的材料退火前后表面形貌进行的比较显示,样品表面形貌可得到很好的保护。研究结果表明,碲镉汞开管富汞热处理技术可用于第三代碲镉汞红外焦平面技术所需大面积多层掺杂异质外延材料的制备。     

HgCdTe探测列阵干法技术的刻蚀形貌研究

首次报道了HgCdTe微台面焦平面探测列阵成形工艺的干法刻蚀技术有关刻蚀形貌的一些研究结果.从HgCdTe外延材料的特点出发,详细分析了其干法刻蚀适用的RIE(reactive ion etching)设备和刻蚀原理.采用高等离子体密度、低腔体工作压力、高均匀性和低刻蚀能量的ICP(inductively coupled plasma)增强型RIE技术,研究了不同的工艺气体配比、腔体工作压力、ICP源功率和RF源功率对HgCdTe材料刻蚀形貌的影响,并初步得到了一种稳定的、刻蚀表面清洁、光滑、图形轮廓良好、均匀性较好和刻蚀速率较高的干法刻蚀工艺.     

HgCdTe焦平面探测阵列干法技术的刻蚀速率研究

首次报道了HgCdTe焦平面探测器微台面列阵成形工艺的干法技术有关刻蚀速率的一些研究结果。从HgCdTe外延材料的特点出发,详细分析了其干法刻蚀适用的R IE(Reactive Ion Etching)设备、刻蚀原理以及刻蚀速率的影响因素。采用ICP ( Inductively Coup led Plasma)增强型R IE技术,研究了一种标准刻蚀条件的微负载效应( etch lag)对刻蚀速率的影响,以及刻蚀非线性问题,并获得刻蚀速率随时间的关系。     

分子束外延材料表面平整度的研究

分子束外延Si基HgCdTe材料的表面平整度对红外焦平面组件的制备有重要的影响.分子束外延的Si基复合衬底作为HgCdTe分子束外延的衬底材料对最终外延材料的表面平整度的影响较大.本文通过研究工艺过程中各外延因素对Si片和衬底材料表面平整度的影响,通过实验发现脱氧工艺的高温影响最大,其次是Si片自身的表面平整度和外延膜...     

HgCdTe液相外延薄膜生长及缺陷表征

液相外延是制备HgCdTe薄膜材料的一项成熟技术,大尺寸的外延薄膜是研制HgCdTe红外焦平面列阵的基础。探讨了尺寸为30mm×40mm的HgCdTe液相外延薄膜生长技术,用红外透射光谱和X光貌相技术对材料进行了评价。并对HgCdTe薄膜表面的黑点缺陷、波纹起伏等特征形貌进行了讨论,指出黑点缺陷是杂质粒子在薄膜表面形成的包裹体,而表面波纹是由生长母液中的对流引起的。     

Developments in the fabrication and performance of high-quality HgCdTe detectors grown on 4-in. Si substrates

We are continuing to develop our growth and processing capabilities for HgCdTe grown on 4-in. Si substrates by molecular beam epitaxy (MBE). Both short-wave and mid-wave infrared (SWIR and MWIR) double-layer hetero-junctions (DLHJs) have been fabricated. In order to improve the producibility of the material, we have implemented an in-situ growth composition-control system. We have explored dry etching the HgCdTe/Si wafers and seen promising results. No induced damage was observed in these samples. Detector results show that the HgCdTe/Si devices are state-of-the-art, following the diffusion-limited trend line established by other HgCdTe technologies. Focal-plane array (FPA) testing has been performed in order to assess the material over large areas. The FPA configurations range from 128×128 to 1,024×1,024, with unit cells as small as 20 μm. The MWIR responsivity and NEDT values are comparable to those of existing InSb FPAs. Pixel operabilities well in excess of 99% have been measured. We have also explored the role of growth macrodefects on diode performance and related their impact to FPA operability. The SWIR HgCdTe/Si shows similar results to the MWIR material. Short-wave IR FPA, median dark-current values of less than 0.1 e⁻/sec have been achieved.     

分子束外延生长3英寸HgCdTe晶片

报道了用分子束外延的方法制备3英寸HgCdTe薄膜的研究结果,获得的HgCdTe外延材料均匀性良好,在直径70mm圆内,组份标准偏差率为1.2%,对应80K截止波长偏差仅为0.1μm.经过生长条件的改进,表面形貌获得了大幅度改善,缺陷密刃∮00cm-2,缺陷尺寸小于10μm,可以满足大规模HgCdTe焦平面列阵的应用需求.抖     

Current status of large-area MOVPE growth of HgCdTe device heterostructures for infrared focal plane arrays

This paper reviews the current status of the growth of fully doped HgCdTe (MCT) devices by metalorganic vapor phase epitaxy (MOVPE). The current reactor system has been developed to produce 3-inch diameter epitaxial layers compatible with slice-scale processing. The new reactor system has achieved routine epitaxial growth of MCT with good morphology onto both gallium arsenide (GaAs) and GaAs on silicon (Si) wafers that were oriented (2–8°) off (100) orientation. The density of surface defects (so-called “hillocks”), typical of MOVPE growth on such orientation substrates, has been reduced to <5 cm⁻² at a sufficient yield to make the production of low cluster defect 2D arrays possible. Alternative growth experiments onto cadmium telluride (CdTe) on Si substrates with (211)B orientation have also been performed to investigate their usefulness for infrared focal plane array (IRFPA) applications. Si substrates give better thermal expansion match to the read out Si circuits (ROIC). The horizontal reactor cell design has a graphite susceptor with a rotating platen capable of using substrates up to 4-inch diameter. Work, however, has concentrated on 3-inch diameter GaAs and GaAs on Si wafers substrates in the reactor, and these reproducibly demonstrated good compositional and thickness uniformity. Cut-off wavelength and thickness uniformity maps showed that there was sufficient uniformity to produce twelve sites of large format 2D arrays (640×512 diodes on 24-μm pitch) per slice. Minority carrier lifetimes in heterostructures is an important parameter and some factors affecting this are discussed, with special emphasis on As-doped material grown under various growth conditions in an attempt to reduce Shockley-Read (S-R) trap densities. New data are presented on trap densities and theoretical fitting of lifetimes in MOVPE material. Fully doped heterostructures have been grown to investigate the device performance in the 3–5 μm medium-wave IR (MWIR) band and 8–12 μm long-wave IR (LWIR). These layers have been fabricated into mesa arrays and then indium-bumped onto Si multiplexers. A summary of the 80-K device results shows that state-of-the-art device performance has been demonstrated in MOVPE-grown device structures.     

Inductively coupled plasma etching for large format HgCdTe focal plane array fabrication

Inductively coupled plasma (ICP) using hydrogen-based gas chemistry has been developed to meet requirements for deep HgCdTe mesa etching and shallow CdTe passivation etching in large format HgCdTe infrared focal plane array (FPA) fabrication. Large format 2048×2048, 20-μm unit-cell short wavelength infrared (SWIR) and 2560×512, 25-μm unit-cell midwavelength infrared (MWIR) double-layer heterojunction (DLHJ) p-on-n HgCdTe FPAs fabricated using ICP processing exhibit >99% pixel operability. The HgCdTe FPAs are grown by molecular beam epitaxy (MBE) on Si substrates with suitable buffer layers. Midwavelength infrared detectors fabricated from 4-in. MBE-grown HgCdTe/Si substrates using ICP for mesa delineation and CdTe passivation etching demonstrate measured spectral characteristics, RoA product, and quantum efficiency comparable to detectors fabricated using wet chemical processes. Mechanical samples prepared to examine physical characteristics of ICP reveal plasma with high energy and low ion angle distribution, which is necessary for fine definition, high-aspect ratio mesa etching with accurate replication of photolithographic mask dimensions.     

应对第三代红外焦平面技术挑战的HgCdTe分子束外延

叙述了围绕第三代红外焦平面的需求所进行的HgCdTe分子束外延的一些研究结果.75mm HgCdTe薄膜材料的组分均匀性良好,80K下截止波长偏差为0.1μm.对所观察到的HgCdTe表面缺陷成核机制进行了分析讨论,获得的75mm HgCdTe材料平均表面缺陷密度低于300cm-2.研究发现As的表面黏附系数很低,对生长温度十分敏感,在170℃下约为1×10-4.计算表明,As在HgCdTe中的激活能为19.5meV,且随(Na∑Nd)1/3的增大呈线性下降关系,反比系数为3.1×10-5meV·cm.实验发现Hg饱和蒸汽压下,对应不同的温度240,380,440℃,As在HgCdTe中的扩散系数分别为(1.0±0.9)×10-16,(8±3)×10-15,(1.5±0.9)×10-13cm2/s.采用分子束外延生长的HgCdTe材料已用于红外焦平面探测器件的研制,文中报道了一些初步结果.     

Fabrication of high-performance large-format MWIR focal plane arrays from MBE-grown HgCdTe on 4″ silicon substrates

We have developed the capability to grow HgCdTe mid-wave infrared radiation double-layer heterojunctions (MWIR DLHJs) on 4″ Si wafers by molecular beam epitaxy (MBE), and fabricate devices from these wafers that are comparable to those produced by mature technologies. Test data show that the detectors, which range in cutoff wavelength over 4–7 μm, are comparable to the trendline performance of liquid phase epitaxy (LPE)-grown material. The spectral characteristics are similar, with a slight decrease in quantum efficiency attributable to the Si substrate. With respect to R₀A, the HgCdTe/Si devices are closer to the theoretical radiative-limit than LPE-grown detectors. Known defect densities in the material have been correlated to device performance through a simple model. Slight 1/f noise increases were measured in comparison to the LPE material, but the observed levels are not sufficient to significantly degrade focal plane array (FPA) performance. In addition to discrete detectors, two FPA formats were fabricated. 128×128 FPAs show MWIR sensitivity comparable to mature InSb technology, with pixel operability values in excess of 99%. A 640×480 FPA further demonstrates the high-sensitivity and high-operability capabilities of this material.     

Long wavelength infrared, molecular beam epitaxy, HgCdTe-on-Si diode performance

In the past several years, we have made significant progress in the growth of CdTe buffer layers on Si wafers using molecular beam epitaxy (MBE) as well as the growth of HgCdTe onto this substrate as an alternative to the growth of HgCdTe on bulk CdZnTe wafers. These developments have focused primarily on mid-wavelength infrared (MWIR) HgCdTe and have led to successful demonstrations of high-performance 1024×1024 focal plane arrays (FPAs) using Rockwell Scientific’s double-layer planar heterostructure (DLPH) architecture. We are currently attempting to extend the HgCdTe-on-Si technology to the long wavelength infrared (LWIR) and very long wavelength infrared (VLWIR) regimes. This is made difficult because the large lattice-parameter mismatch between Si and CdTe/HgCdTe results in a high density of threading dislocations (typically, >5E6 cm⁻²), and these dislocations act as conductive pathways for tunneling currents that reduce the R_oA and increase the dark current of the diodes. To assess the current state of the LWIR art, we fabricated a set of test diodes from LWIR HgCdTe grown on Si. Silicon wafers with either CdTe or CdSeTe buffer layers were used. Test results at both 78 K and 40 K are presented and discussed in terms of threading dislocation density. Diode characteristics are compared with LWIR HgCdTe grown on bulk CdZnTe.     

HgCdTe/Si materials for long wavelength infrared detectors

The heteroepitaxial growth of HgCdTe on large-area Si substrates is an enabling technology leading to the production of low-cost, large-format infrared focal plane arrays (FPAs). This approach will allow HgCdTe FPA technology to be scaled beyond the limitations of bulk CdZnTe substrates. We have already achieved excellent mid-wavelength infrared (MWIR) and short wavelength infrared (SWIR) detector and FPA results using HgCdTe grown on 4-in. Si substrates using molecular beam epitaxy (MBE), and this work was focused on extending these results into the long wavelength infrared (LWIR) spectral regime. A series of nine p-on-n LWIR HgCdTe double-layer heterojunction (DLHJ) detector structures were grown on 4-in. Si substrates. The HgCdTe composition uniformity was very good over the entire 4-in. wafer with a typical maximum nonuniformity of 2.2% at the very edge of the wafer; run-to-run composition reproducibility, realized with real-time feedback control using spectroscopic ellipsometry, was also very good. Both secondary ion mass spectrometry (SIMS) and Hall-effect measurements showed well-behaved doping and majority carrier properties, respectively. Preliminary detector results were promising for this initial work and good broad-band spectral response was demonstrated; 61% quantum efficiency was measured, which is very good compared to a maximum allowed value of 70% for a non-antireflection-coated Si surface. The R₀A products for HgCdTe/Si detectors in the 9.6-μm and 12-μm cutoff range were at least one order of magnitude below typical results for detectors fabricated on bulk CdZnTe substrates. This lower performance was attributed to an elevated dislocation density, which is in the mid-10⁶ cm⁻² range. The dislocation density in HgCdTe/Si needs to be reduced to <10⁶ cm⁻² to make high-performance LWIR detectors, and multiple approaches are being tried across the infrared community to achieve this result because the technological payoff is significant.     

High-quality large-area MBE HgCdTe/Si

HgCdTe offers significant advantages over other similar semiconductors, which has made it the most widely utilized variable-gap material in infrared (IR) focal plane array (FPA) technology. HgCdTe hybrid FPAs consisting of two-dimensional detector arrays that are hybridized to Si readout circuits (ROIC) are the dominant technology for second-generation infrared systems. However, one of the main limitations of the HgCdTe materials system has been the size of lattice-matched bulk CdZnTe substrates, used for epitaxially grown HgCdTe, which have been limited to 30 cm² in production. This size limitation does not adequately support the increasing demand for larger FPA formats which now require sizes up to 2048×2048, and only a single die can be printed per wafer. Heteroepitaxial Si-based substrates offer a cost-effective technology that can be scaled to large wafer sizes and further offer a thermal-expansion-matched hybrid structure that is suitable for large format FPAs. This paper presents data on molecular-beam epitaxy (MBE)-grown HgCdTe/Si wafers with much improved materials characteristics than previously reported. We will present data on 4- and 6-in diameter HgCdTe both with extremely uniform composition and extremely low defects. Large-diameter HgCdTe/Si with nearly perfect compositional uniformity and ultra low defect density is essential for meeting the demanding specifications of large format FPAs.     

Analysis of Mesa Dislocation Gettering in HgCdTe/CdTe/Si(211) by Scanning Transmission Electron Microscopy

Due to its strong infrared absorption and variable band-gap, HgCdTe is the ideal detector material for high-performance infrared focal-plane arrays (IRFPAs). Next-generation IRFPAs will utilize dual-color high-definition formats on large-area substrates such as Si or GaAs. However, heteroepitaxial growth on these substrates is plagued by high densities of lattice-mismatch-induced threading dislocations (TDs) that ultimately reduce IRFPA operability. Previously we demonstrated a postgrowth technique with the potential to eliminate or move TDs such that they have less impact on detector operability. In this technique, highly reticulated mesa structures are produced in as-grown HgCdTe epilayers, and then subjected to thermal cycle annealing. To fully exploit this technique, better understanding of the inherent mechanism is required. In this work, we employ scanning transmission electron microscopy (STEM) analysis of HgCdTe/CdTe/Si(211) samples prepared by focused ion beam milling. A key factor is the use of defect-decorated samples, which allows for a correlation of etch pits observed on the surface with underlying dislocation segments viewed in cross-section STEM images. We perform an analysis of these dislocations in terms of the general distribution, density, and mobility at various locations within the mesa structures. Based on our observations, we suggest factors that contribute to the underlying mechanism for dislocation gettering.