大尺寸碲锌镉基碲镉汞材料分子束外延技术研究

针对高质量、大规模碲镉汞红外焦平面探测器需求的持续增加,本文开展了使用分子束外延方式在50 mm×50 mm(211)B碲锌镉衬底上外延碲镉汞材料技术的研究.通过对碲锌镉衬底改进湿化学腐蚀、碲锌镉衬底预处理、碲锌镉衬底缓冲层生长、碲锌镉基碲镉汞材料工艺开发等方面的研究,开发出了能够稳定获得碲锌镉基碲镉汞材料的工艺.材料...     

中国电科11所碲镉汞薄膜材料制备技术进展

碲镉汞材料具有响应速度快、量子效率高、带隙连续可调等优点,广泛应用于红外探测领域,本文报道了近年来中国电科11所在碲镉汞薄膜材料制备方面的技术进展。在碲锌镉衬底材料制备方面,已突破135mm碲锌镉晶体生长技术,碲锌镉衬底平均位错腐蚀坑密度(EPD) <1×104cm-2,具备了80mm×80mm规格碲锌镉衬底的批量生产能力。在液相外延碲镉汞薄膜制备方面,富碲水平液相外延碲镉汞薄膜平均位错腐蚀坑密度EPD<4×104cm-2,具备80mm×80mm规格碲镉汞薄膜的制备能力;富汞垂直液相外延实现高质量双层异质结碲镉汞薄膜材料批量化制备,该种材料的半峰宽(FWHM)控制在(20～40)arcsec范围内,碲镉汞薄膜厚度极差≤±06μm。在分子束外延碲镉汞薄膜方面,实现了6 in硅基碲镉汞材料制备,组分标准偏差≤00015,表面宏观缺陷密度≤100cm-2;碲锌镉基碲镉汞材料已具备50mm×50mm制备能力,组分标准偏差为0002,厚度标准偏差为0047μm。从探测器验证结果来看,基于富碲水平液相外延碲镉汞薄膜实现了1 k×1 k、2 k×2 k等规格红外焦平面探测器的工程化制备;采用双层异质结碲镉汞薄膜实现了高温工作、长波及甚长波探测器的制备;使用分子束外延制备的碲镉汞薄膜实现了27 k×27 k、54 k×54 k、8 k×8 k等规格红外焦平面探测器研制,在宇航领域有巨大的应用潜力。     

碲锌镉衬底晶面极性对水平液相外延碲镉汞薄膜的影响

研究了碲锌镉衬底（111）晶面的不同极性对水平推舟液相外延生长碲镉汞薄膜的影响。实验结果显示,（111）A面碲锌镉衬底水平液相外延生长碲镉汞薄膜材料组分和厚度均与常规（111）B面碲锌镉衬底碲镉汞薄膜材料相当;碲镉汞母液在采用（111）A面、（111）B面衬底进行液相外延生长的碲镉汞薄膜上接触角分别为（50±2）°和（30±2）°,结合微观模型分析确认碲镉汞母液在碲镉汞薄膜（111）A面存在更大的表面张力;观察并讨论了（111）A面碲镉汞与（111）B面碲镉汞薄膜材料表面微观形貌的差别;实验获得的（111）A面碲镉汞薄膜XRD半峰宽为33.1arcsec。首次报道了（111）晶面选择对母液残留的影响,研究结果表明,采用（111）A面碲锌镉衬底进行碲镉汞水平推舟液相外延生长,能够在不降低晶体质量的情况下,大幅减小薄膜表面母液残留。     

碲锌镉衬底晶向对碲镉汞薄膜表面形貌的影响

利用定向仪对原生晶片及加工后的碲锌镉衬底的晶向进行比较,观察不同晶向衬底液相外延碲镉汞薄膜的表面形貌,考察了衬底晶向偏差对液相外延碲镉汞薄膜表面形貌的影响。通过进一步的追踪碲锌镉衬底在加工过程中的晶向变化,研究衬底晶向变化的原因和解决方法。研究发现,碲锌镉晶体在初次定向切割后的加工过程中晶向会发生明显变化,而在厚度减薄较大的粗磨工艺后不会发生较大晶向偏差,因此,可将粗磨后衬底的再次定向结果作为进一步筛选碲锌镉衬底的依据,以保证液相外延碲镉汞薄膜的质量。     

液相外延碲镉汞贯穿型缺陷研究

液相外延碲镉汞材料的贯穿型缺陷会在后续器件制备中导致多个盲元的形成。采用共聚焦显微镜对该类缺陷的深度进行了表征,并对缺陷底部的成分进行了测试。使用聚焦离子束(Focused Ion Beam, FIB)将缺陷挖开后对其进行观察。对于贯穿型缺陷较多的碲锌镉衬底外延生长碲镉汞薄膜,统计后发现碲镉汞表面的贯穿型缺陷与衬底缺陷存在一定的对应关系,因此推测液相外延贯穿型缺陷起源于碲锌镉衬底缺陷。     

碲锌镉衬底重复利用技术研究

芯片制备工艺完成后,给芯片留有一定厚度的衬底,同时利用丝切割技术将多余的碲锌镉衬底取下,并对其进行重复抛光处理。碲锌镉衬底的锌值分布及半高宽(Full Width at Half Maximum, FWHM)测试结果表明,碲锌镉衬底质量较好,可以再次用来制备液相外延碲镉汞薄膜。该薄膜经过标准探测器芯片工艺后,性能合格。该研究使原本要完全去除的衬底得以重复利用,提高了碲锌镉衬底的利用率,降低了探测器的制造成本。     

3英寸Si基碲镉汞分子束外延工艺研究

随着红外焦平面阵列规模的扩大,由于尺寸和成本的限制,传统晶格匹配的碲锌镉衬底逐渐成为碲镉汞红外焦平面探测器发展的瓶颈,大尺寸、低成本硅基碲镉汞材料应运而生。本文采用分子束外延工艺生长获得了3 in Si基中波碲镉汞薄膜材料,通过采用金相显微镜、傅里叶红外光谱仪、双晶X射线衍射仪、湿化学腐蚀位错密度(EPD)法、Hall测试系统等检测手段对Si基中波碲镉汞分子束外延薄膜材料进行表面、光学、结构和电学性能表征,并采用标准平面器件工艺制备中波640×512焦平面探测阵列进行材料验证,结果表明该材料性能与国际先进水平相当。     

碲锌镉晶体的X射线衍射形貌与腐蚀形貌

碲锌镉晶体中存在着各种典型晶体缺陷,其缺陷研究一直倍受关注,X射线衍射形貌术是一种非破坏性地研究晶体材料结构完整性、均匀性的有效方法.采用反射式X射线衍射形貌术对碲锌镉衬底的质量进行了研究,并将衬底的X射线衍射形貌与Everson腐蚀形貌进行了对比分析,碲锌镉衬底的X射线衍射形貌主要有六种特征类型,分别对应不同的晶体结构或缺陷,包括均匀结构、镶嵌结构、孪晶、小角晶界、夹杂、表面划伤,对上述特征类型进行了详细的分析.目前,衬底的X射线衍射形貌主要以均匀结构类型为主,划伤和镶嵌结构缺陷基本已消除,存在的晶体缺陷主要以小角晶界为主.通过对比分析碲锌镉衬底和液相外延碲镉汞薄膜的X射线衍射形貌,发现小角晶界等晶体结构缺陷会延伸到外延层上,碲锌镉衬底质量会直接影响碲镉汞外延层的质量,晶体结构完整的衬底是制备高质量碲镉汞外延材料的基础.     

碲锌镉衬底表面在碲镉汞液相外延工艺中的热腐蚀效应

该研究以提高液相外延碲镉汞材料的质量为出发点,研究液相外延生长过程中碲锌镉衬底受到高温汞蒸气影响后的变化情况,并利用光学显微镜、白光干涉仪、能谱仪等分析测试手段对碲锌镉衬底表面进行分析.研究结果表明,液相外延生长过程中,高温汞蒸气对碲锌镉衬底中表面沉淀物尺寸无明显影响,但在衬底表面发现两种类型的腐蚀点,一种是尺寸为25μm左右的较大腐蚀点,分布较均匀;另一种是尺寸为7μm左右的圆形腐蚀点,分布不均匀.衬底经过液相外延薄膜成核生长前的温度变化过程以及高温Hg蒸气的作用,碲锌镉衬底表面形貌呈鱼鳞状,粗糙度增大了50%以上.     

碲锌镉晶片精密抛光效果的影响因素分析

碲锌镉(CZT,CdZnTe)晶片是生长红外焦平面列阵所用碲镉汞(HgCdTe)薄膜的衬底材料.为了满足碲镉汞液相外延的性能要求,采用化学机械抛光可获得平面度高、粗糙度低、无损伤层的碲锌镉晶片表面。通过对抛光结构的机械运动分析,建立了抛光过程中各参数对工艺指标的影响,通过实验优化工艺参数获得高质量的抛光效果。     

异质衬底外延碲镉汞薄膜位错抑制技术进展

分子束外延碲镉汞技术是制备第三代红外焦平面探测器的重要手段,基于异质衬底的碲镉汞材料具有尺寸大、成本低、与常规半导体设备兼容等优点,是目前低成本高性能红外探测器发展中的研究重点。对异质衬底上碲镉汞薄膜位错密度随厚度的变化规律进行了建模计算,结果显示ρ～1/h 模型与实验结果吻合度好,异质衬底上原生碲镉汞薄膜受位错反应半径制约,其位错密度无法降低至 5×10⁶cm^-2以下,难以满足长波、甚长波器件的应用需求。为了有效降低异质外延的碲镉汞材料位错密度,近年来出现了循环退火、位错阻挡和台面位错吸除等位错抑制技术,本文介绍了各技术的原理及进展,分析了后续发展趋势及重点。循环退火和位错阻挡技术突破难度大,发展潜力小,难以将碲镉汞位错密度控制在 5×10⁵cm^-2以内。台面位错吸除技术目前已经显示出了巨大的发展潜力和价值,后续与芯片工艺融合后,有望大幅促进低成本长波、中长波、甚长波器件的发展。     

Direct growth of CdZnTe/Si substrates for large-area HgCdTe infrared focal plane arrays

Direct epitaxial growth of high-quality 100lCdZnTe on 3 inch diameter vicinal {100}Si substrates has been achieved using molecular beam epitaxy (MBE); a ZnTe initial layer was used to maintain the {100} Si substrate orientation. The properties of these substrates and associated HgCdTe layers grown by liquid phase epitaxy (LPE) and subsequently processed long wavelength infrared (LWIR) detectors were compared directly with our related efforts using CdZnTe/ GaAs/Si substrates grown by metalorganic chemical vapor deposition (MOCVD). The MBE-grown CdZnTe layers are highly specular and have both excellent thickness and compositional uniformity. The x-ray full-width at half-maximum (FWHM) of the MBE-grown CdZnTe/Si increases with composition, which is a characteristic of CdZnTe grown by vapor phase epitaxy, and is essentially equivalent to our results obtained on CdZnTe/GaAs/Si. As we have previously observed, the x-ray FWHM of LPE-grown HgCdTe decreases, particularly for CdZnTe compositions near the lattice matching condition to HgCdTe; so far the best value we have achieved is 54 arc-s. Using these MBE-grown substrates, we have fabricated the first high-performance LWIR HgCdTe detectors and 256 x 256 arrays using substrates consisting of CdZnTe grown directly on Si without the use of an intermediate GaAs buffer layer. We find first that there is no significant difference between arrays fabricated on either CdZnTe/Si or CdZnTe/GaAs/Si and second that the results on these Si-based substrates are comparable with results on bulk CdZnTe substrates at 78K. Further improvements in detector performance on Si-based substrates require a decrease in the dislocation density.     

HgCdTe growth on (552) oriented CdZnTe by metalorganic vapor phase epitaxy

We report the growth of HgCdTe on (552)B CdZnTe by metalorganic vapor phase epitaxy (MOVPE). The (552) plane is obtained by 180 rotation of the (211) plane about the [111] twist axis. Both are 19.47 degrees from (111), but in opposite directions. HgCdTe grown on the (552)B-oriented CdZnTe has a growth rate similar to the (211)B, but the surface morphology is very different. The (552)B films exhibit no void defects, but do exhibit ∼40 μm size hillocks at densities of 10–50 cm⁻². The hillocks, however, are significantly flatter and shorter than those observed on (100) metalorganic vapor phase epitaxy (MOVPE) HgCdTe films. For a 12–14 μm thick film the height of the highest point on the hillock is less than 0.75 μm. No twinning was observed by back-reflection Laue x-ray diffraction for (552)B HgCdTe films and the x-ray double crystal rocking curve widths are comparable to those obtained on (211)B films grown side-by-side and with similar alloy composition. Etch pit density (EPD) measurements show EPD values in the range of (0.6–5)×10⁵ cm⁻², again very similar to those currently observed in (211)B MOVPE HgCdTe. The transport properties and ease of dopant incorporation and activation are all comparable to those obtained in (211)B HgCdTe. Mid-wave infrared (MWIR) photodiode detector arrays were fabricated on (552)B HgCdTe films grown in the P-n-N device configuration (upper case denotes layers with wider bandgaps). Radiometric characterization at T=120–160 K show that the detectors have classical spectral response with a cutoff wavelength of 5.22 μm at 120 K, quantum efficiency ∼78%, and diffusion current is the dominant dark current mechanism near zero bias voltage. Overall, the results suggest that (552)B may be the preferred orientation for MOVPE growth of HgCdTe on CdZnTe to achieve improved operability in focal plane arrays.     

Si/CdTe复合衬底HgCdTe液相外延材料的生长与性能分析

通过改进推舟液相外延技术,成功地在(211)晶向Si/CdTe复合衬底上进行了HgCdTe液相外延生长,获得了表面光亮的HgCdTe外延薄膜.测试结果表明,(211)Si/CdTe复合衬底液相外延HgCdTe材料组分及厚度的均匀性与常规(111)CdZnTe衬底HgCdTe外延材料相当;位错腐蚀坑平均密度为(5～8)×105 cm-2,比相同衬底上分子束外延材料的平均位错密度要低一个数量级;晶体的双晶半峰宽达到70″左右.研究结果表明,在发展需要低位错密度的大面积长波HgCdTe外延材料制备技术方面,Si/CdTe复合衬底HgCdTe液相外延技术可发挥重要的作用.     

CdZnTe(211)B衬底对MBE外延碲镉汞材料的影响分析

碲锌镉 CdZnTe（211）B 衬底广泛应用于碲镉汞（HgCdTe）分子束外延生长,其性能参数在很大程度上决定了碲镉汞分子束外延材料的质量。主要讨论了 CdZnTe（211）B 衬底几个关键性能参数对碲镉汞外延材料的影响,包括 Zn 组分及均匀性、缺陷（位错、孪晶及晶界和碲沉淀）以及表面状态（粗糙度和化学组成）,并且分析了对 CdZnTe（211）B 衬底进行筛分时各性能参数的评价方法和指标。     

Recent Progress in MBE Growth of CdTe and HgCdTe on (211)B GaAs Substrates

Alternate substrates for molecular beam epitaxy growth of HgCdTe including Si, Ge, and GaAs have been under development for more than a decade. MBE growth of HgCdTe on GaAs substrates was pioneered by Teledyne Imaging Sensors (TIS) in the 1980s. However, recent improvements in the layer crystal quality including improvements in both the CdTe buffer layer and the HgCdTe layer growth have resulted in GaAs emerging as a strong candidate for replacement of bulk CdZnTe substrates for certain infrared imaging applications. In this paper the current state of the art in CdTe and HgCdTe MBE growth on (211)B GaAs and (211) Si at TIS is reviewed. Recent improvements in the CdTe buffer layer quality (double crystal rocking curve full-width at half-maximum?≈?30?arcsec) with HgCdTe dislocation densities of ≤10⁶?cm^?2 are discussed and comparisons are made with historical HgCdTe on bulk CdZnTe and alternate substrate data at TIS. Material properties including the HgCdTe majority carrier mobility and dislocation density are presented as a function of the CdTe buffer layer quality.     

碲镉汞材料提纯研究

杂质是影响碲镉汞器件性能的重要因素之一.对于碲锌镉衬底晶体和窄禁带碲镉汞材料来说,杂质的影响更加显著.主要论述了碲镉汞材料中常见的杂质类型以及杂质在材料中的作用,并分析了影响器件性能的主要杂质.采用辉光放电质谱法(Glow Discharge Mass Spectrometry,GDMS)测试了材料中的杂质含量,同时通...     

Te-rich liquid phase epitaxial growth of HgCdTe on Si-based substrates

The growth of high quality (111)B oriented HgCdTe layers on CdZnTe/GaAs/Si and CdTe/Si substrates by Te-rich slider liquid phase epitaxy (LPE) is reported. Although the (111) orientation is susceptible to twinning, a reproducible process yielding twin-free layers with excellent surface morphology has been developed. The electrical properties and dislocation density in films grown on these substrates are comparable to those measured in HgCdTe layers grown on bulk CdTe substrates using the same LPE process. This is surprising in view of the large lattice mismatch that exists in these systems. We will report details of both the substrate and HgCdTe growth processes that are important to obtaining these results.     

Characterization of Dislocations in HgCdTe Heteroepitaxial Layers Using a New Substrate Removal Technique

Dislocations are known to influence the electrical and optical properties of long-wavelength infrared (LWIR) HgCdTe detectors and have been shown to limit the performance of arrays fabricated on heteroepitaxial substrates. To help better understand dislocations in HgCdTe, a new method for preparing HgCdTe diagnostic epitaxial single-crystal samples by chemically removing the supporting CdZnTe substrate has been developed. Using this new sample preparation technique, the behavior of misfit and threading dislocations in HgCdTe epitaxial layers has been investigated by using a defect etch to reveal the dislocations present in the thin HgCdTe films. In most cases etch pits on the surface of the film are spatially correlated with etch pits on the bottom of the HgCdTe film. The small displacements of the related etch pits were used to obtain crystallographic information concerning the paths followed by threading dislocations on allowed slip planes in the HgCdTe crystal. In addition, transmission electron microscopy (TEM) is used to obtain more specific information regarding the Burgers vector of the dislocation. While this new sample preparation technique is useful for studying dislocations in HgCdTe epitaxial layers, it can also be used to study stress from ohmic contacts and passivation layers. The technique can be used for both liquid-phase epitaxy (LPE)- and molecular-beam epitaxy (MBE)-grown HgCdTe on CdZnTe substrates.     

Strain Determination in Quasi-Lattice-Matched LWIR HgCdTe/CdZnTe Layers

We take advantage of the zinc distribution of (211)B CdZnTe substrates to probe the lattice-mismatch-induced stress in long-wave infrared HgCdTe layers grown by molecular beam epitaxy. High-resolution x-ray diffraction is used to accurately determine the strain-free lattice parameters of both CdZnTe and HgCdTe, together with the in-plane components of the stress tensor. By using several wafers, the stress evolution is derived over a broad range of lattice mismatch. In particular, stress relaxation is evidenced for mismatch greater than 0.02% and 0.04% for tensile and compressively strained HgCdTe, respectively. In-plane strain anisotropy, expected for the (211) orientation, is only evidenced for the compressive configuration. Strain relaxation is correlated with substrate curvature and rocking-curve peak broadening, providing indirect evidence for plastic relaxation.