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2.
B. Asici H. C. Eroglu Y. Ergunt A. San S. Ozer 《Journal of Electronic Materials》2018,47(10):5735-5741
High quality CdZnTe substrates with 4% ZnTe mole fraction are used for epitaxial growth of HgCdTe infrared detector layers. Molecular Beam Epitaxy (MBE) growth of HgCdTe epilayers requires high quality surface layer with sub-nanometer surface roughness values as well. We report on the development of a CdZnTe substrate surface preparation process for MBE growth of high quality HgCdTe epilayers. Surface preparation processes were performed on both commercially available CdZnTe substrates and substrates obtained from in-house grown CdZnTe boules. We developed a multi-step substrate surface processing flow to achieve sub-nanometer surface roughness, low total thickness variation (TTV), and wax or slurry residue free CdZnTe substrate surfaces. Each process step was optimized with the aim of removing the subsurface damage caused by the previous process step; so that we reduce the amount of damaged layer needed to be etched prior to epitaxy. Our developed surface preparation process can be applicable to commercially available CdZnTe substrates with high surface roughness and high TTV. This process was also optimized for as-cut CdZnTe slices. We are capable of processing typically 25 mm?×?25 mm CdZnTe substrates with achievable surface roughness values (Rrms) down to below 0.5 nm. 相似文献
3.
L. A. Almeida S. Hirsch M. Martinka P. R. Boyd J. H. Dinan 《Journal of Electronic Materials》2001,30(6):608-610
We report on continuing efforts to develop a reproducible process for molecular beam epitaxy of CdZnTe on three-inch, (211)
Si wafers. Through a systematic study of growth parameters, we have significantly improved the crystalline quality and have
reduced the density of typical surface defects. Lower substrate growth temperatures (∼250–280°C) and higher CdZnTe growth
rates improved the surface morphology of the epilayers by reducing the density of triangular surface defects. Cyclic thermal
annealing was found to reduce the dislocation density. Epilayers were characterized using Nomarski microscopy, scanning electron
microscopy, x-ray diffraction, defect-decoration etching, and by their use as substrates for HgCdTe epitaxy. 相似文献
4.
Fengfeng Sheng Changhe Zhou Shiwen Sun Jianrong Yang 《Journal of Electronic Materials》2014,43(5):1397-1402
Influences of Te-rich and Cd-rich precipitates of CdZnTe substrates on the surface defects of HgCdTe epilayers grown by Te-rich liquid-phase epitaxy were investigated. The results show that HgCdTe surface defects are mainly attributable to precipitates on CdZnTe substrate surfaces. At the same time, the remelting of substrate surface layers during the liquid-phase epitaxial process also affects the number and morphology of HgCdTe surface defects. According to the morphological characteristics of surface defects, three types of surface defects were observed on the surfaces of HgCdTe epilayers. There are no obvious differences in the morphologies of the surface defects grown on Te-rich and Cd-rich substrates. However, the dislocation distributions around surface defects are different for HgCdTe epilayers grown on different substrates. 相似文献
5.
Surface Morphology and Defect Formation Mechanisms for HgCdTe (211)B Grown by Molecular Beam Epitaxy 总被引:1,自引:0,他引:1
Yong Chang C.R. Becker C.H. Grein J. Zhao C. Fulk T. Casselman R. Kiran X.J. Wang E. Robinson S.Y. An S. Mallick S. Sivananthan T. Aoki C.Z. Wang D.J. Smith S. Velicu J. Zhao J. Crocco Y. Chen G. Brill P.S. Wijewarnasuriya N. Dhar R. Sporken V. Nathan 《Journal of Electronic Materials》2008,37(9):1171-1183
The surface morphology and crystallinity of HgCdTe films grown by molecular beam epitaxy (MBE) on both CdZnTe and CdTe/Si
(211)B substrates were characterized using atomic force microscopy (AFM), as well as scanning (SEM) and transmission (TEM)
electron microscopy. Crosshatch patterns and sandy-beach-like morphologies were commonly found on MBE (211) HgCdTe epilayers
grown on both CdZnTe and CdTe/Si substrates. The patterns were oriented along the , , and directions, which were associated with the intersection between the (211) growth plane and each of the eight equivalent HgCdTe
slip planes. This was caused by strain-driven operation of slip in these systems with relative large Schmid factor, and was
accompanied by dislocation formation as well as surface strain relief. Surface crater defects were associated with relatively
high growth temperature and/or low Hg flux, whereas microtwins were associated with relatively low growth temperature and/or
high Hg flux. AFM and electron microscopy were used to reveal the formation mechanisms of these defects. HgCdTe/HgCdTe superlattices
with layer composition differences of less than 2% were grown by MBE on CdZnTe substrates in order to clarify the formation
mechanisms of void defects. The micrographs directly revealed the spiral nature of growth, hence demonstrating that the formation
of void defects could be associated with the Burton, Cabrera, and Frank (BCF) growth mode. Void defects, including microvoids
and craters, were caused by screw defect clusters, which could be triggered by Te precipitates, impurities, dust, other contamination
or flakes. Needle defects originated from screw defect clusters linearly aligned along the directions with opposite Burgers vector directions. They were visible in HgCdTe epilayers grown on interfacial superlattices.
Hillocks were generated owing to twin growth of void or needle defects on (111) planes due to low growth temperature and the
corresponding insufficient Hg movement on the growth surface. Therefore, in addition to nucleation and growth of HgCdTe in
the normal two-dimensional layer growth mode, the BCF growth mode played an important role and should be taken into account
during investigation of HgCdTe MBE growth mechanisms. 相似文献
6.
T. Aoki Y. Chang G. Badano J. Zhao C. Grein S. Sivananthan David J. Smith 《Journal of Electronic Materials》2003,32(7):703-709
Surface-void defects observed in Hg1−xCdxTe (x ∼ 0.2–0.4) alloys grown by molecular-beam epitaxy (MBE) have been investigated using scanning and high-resolution transmission-electron
microscopy (HRTEM) as well as atomic force microscopy (AFM). These surface craters, which have been attributed to Hg-deficient
growth conditions, were found to originate primarily within the HgCdTe epilayer, rather than at the CdZnTe substrate, and
they were associated with the local development of polycrystalline morphology. High-resolution observations established the
occurrence of finely spaced HgCdTe/Te intergrowths with semicoherent and incoherent grain boundaries, as well as small HgCdTe
inclusions embedded within the Te grains. This study is the first time that high-resolution electron microscopy has been used
to investigate this type of defect. 相似文献
7.
M. Martinka L. A. Almeida J. D. Benson J. H. Dinan 《Journal of Electronic Materials》2002,31(7):732-737
Because the performance of HgCdTe-based photodiodes can be significantly degraded by the presence of dislocations, we have
systematically investigated and suppressed lattice-mismatch-induced cross-hatch formation and the associated generation of
dislocations in (211)B HgCdTe/CdZnTe. A series of HgCdTe epilayers were deposited simultaneously on pairs of substrates with
differing ZnTe mole fractions. Epilayers’ CdTe mole fraction and substrates’ ZnTe mole fractions were measured using optical-transmission
spectra. Lattice mismatch and residual strain were estimated from room-temperature, x-ray diffraction, and double-crystal
rocking-curve measurements (DCRC). It was found that cross-hatch patterns were suppressed in epilayers deposited on nearly
lattice-matched substrates (|Δa/asub|<0.02%). Such epilayers exhibited excellent crystalline quality as revealed by defect-decoration etching (etch-pit density
(EPD)<105 cm−2) and x-ray diffraction (full-width at half-maximum (FWHM) ∼10 arcsec). In addition to determining the upper limits of lattice
mismatch needed to eliminate cross-hatch, we investigated the use of reticulated substrates as a means to suppress cross-hatch.
We found that growth on reticulated mesa structures (<100 μm) with edges parallel to [01-1] resulted in epilayers with substantially
reduced cross-hatch-line densities despite large lattice mismatch (Δa/asub <0.04%). The use of reticulated substrates could suppress cross-hatch because of lateral-alloy variation in large substrates
and complex multistack epilayers (e.g., multicolor detectors). 相似文献
8.
M. Carmody A. Yulius D. Edwall D. Lee E. Piquette R. Jacobs D. Benson A. Stoltz J. Markunas A. Almeida J. Arias 《Journal of Electronic Materials》2012,41(10):2719-2724
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. 相似文献
9.
J. N. Johnson L. A. Almeida J. D. Benson J. H. Dinan M. Martinka 《Journal of Electronic Materials》1998,27(6):657-660
CdZnTe wafers were inserted into a multi-chamber processing facility without prior preparation, cleaned by exposure to an
electron cyclotron resonance Ar/H2 plasma, and used as substrates for molecular beam epitaxy of HgCdTe. Changes induced in the wafer near-surface region during
the cleaning step were monitored using in situ spectroscopic ellipsometry. Ellipsometric data were subsequently modeled to provide the time evolution of the thickness of
a native overlayer. Auger electron spectra were consistent with surfaces free of residual contamination and which had the
stoichiometry of the underlying bulk. Surface roughness values of 0.4 nm were obtained ex situ using interferometric microscopy. Electron diffraction patterns of plasma prepared wafers heated to 185°C (the temperature
required for HgCdTe molecular beam epitaxy) were streaked. Structural and electrical characteristics of epilayers grown on
these substrates were found to be comparable to those deposited on wafers prepared using a conventional wet chemical process.
This demonstrates an important step in an all-vacuum approach to HgCdTe detector fabrication. 相似文献
10.
Robert Furstenberg Michael R. Papantonakis C.A. Kendziora 《Journal of Electronic Materials》2009,38(8):1533-1538
We report an infrared photo-thermal excitation imaging and spectroscopy study of CdTe and CdZnTe substrates as well as HgCdTe/CdZnTe
and HgCdTe/Si epilayers. The applicability, advantages, and limitations of the technique as a tool for both ex situ and in situ monitoring of bandgap, thickness, and growth temperature are discussed. We show that photo-thermal imaging allows for direct
visual imaging of the bandgap region of CdTe and CdZnTe substrates. We also show that photo-thermal spectroscopy can provide
epilayer thickness information independent of the dielectric function. The method is orthogonal to existing optical characterization
techniques and could be combined with them for improved accuracy. 相似文献
11.
J. N. Johnson L. A. Almeida M. Martinka J. D. Benson J. H. Dinan 《Journal of Electronic Materials》1999,28(6):817-820
Without any additional preparation, Cd1−yZnyTe (211)B (y∼3.5%) wafers were cleaned by exposure to an electron cyclotron resonance (ECR) Ar/H2 plasma and used as substrates for HgCdTe molecular beam epitaxy. Auger electron spectra were taken from as-received wafers,
conventionally prepared wafers (bromine: methanol etching, followed by heating to 330–340°C), and wafers prepared under a
variety of ECR process conditions. Surfaces of as-received wafers contained ∼1.5 monolayers of contaminants (oxygen, carbon,
and chlorine). Conventionally prepared wafers had ∼1/4 monolayer of carbon contamination, as well as excess tellurium and/or
excess zinc depending on the heating process used. Auger spectra from plasma-treated CdZnTe wafers showed surfaces free from
contamination, with the expected stoichiometry. Stoichiometry and surface cleanliness were insensitive to the duration of
plasma exposure (2–20 s) and to changes in radio frequency input power (20–100 W). Reflection high energy electron diffraction
patterns were streaked indicating microscopically smooth and ordered surfaces. The smoothness of plasma-etched CdZnTe wafers
was further confirmed ex situ using interferometric microscopy. Surface roughness values of ∼0.4 nm were measured. Characteristics of HgCdTe epilayers
deposited on wafers prepared with plasma and conventional etching were found to be comparable. For these epilayers, etch pit
densities on the order of 105 cm−2 have been achieved. ECR Ar/H2 plasma cleaning is now utilized at Night Vision and Electronic Sensors Directorate as the baseline CdZnTe surface preparation
technique. 相似文献
12.
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. 相似文献
13.
Influence of Substrate Orientation on the Growth of HgCdTe by Molecular Beam Epitaxy 总被引:1,自引:0,他引:1
An empirical study is reported, wherein HgCdTe was deposited simultaneously on multiple CdZnTe substrates of different orientations
by molecular beam epitaxy. These orientations included the following vicinal surfaces: (115)B, (113)B, (112)B, and (552)B.
Additionally, growth on (111)B was explored. Growth conditions found to be nearly optimalfor the standard (112)B orientation
were selected. Through a series of growth runs, substrate temperature was varied, and the physical properties of the resulting
HgCdTe epilayers were measured. These measurements included Nomarski microscopy, infrared transmission, x-ray diffraction,
and defect decoration etching. The properties of HgCdTe epilayers as a function of temperature were roughly similar for all
vicinal surfaces. Namely, as the temperature increased, the dislocation density decreased. At some critical temperature, the
density of void defects increased dramatically. This critical temperature varied with orientation, the (115)B exhibiting the
lowest critical temperature and the (112)B and (552)B exhibiting the highest. The (115)B, (113)B, and (112)B orientations
exhibited “needlelike” defects on the as-grown HgCdTe surface. The density of these defects decreased with increasing temperature.
The (552)B surface exhibited no such defects and growth behavior nearly identical to the (112)B growthsurface. 相似文献
14.
Heinrich Figgemeier Martin Bruder Karl-Martin Mahlein Richard Wollrab Johann Ziegler 《Journal of Electronic Materials》2003,32(7):588-591
HgCdTe detector performance and yield are strongly dependant on CdZnTe substrate and HgCdTe epilayer properties, and on key
device processes, especially for 8–12 μm application. Due to the correlation and optimization between these figures and diode
performance, AIM has developed a mature HgCdTe technology for superior detector performance and high production rate. To meet
high yield and performance for long wavelength (LW) HgCdTe diodes, dislocation densities of < 1 × 10t cm−2 both in substrate and epilayer have to be ensured. By a unique AIM substrate growth process, dislocation densities of 2 ×
104-9 × 104 cm−2 are achieved for all substrates and epilayers (100% yield). The etch pit density (EPD) on 〈111〉 epilayers is revealed by
an AIM proprietary etching procedure. One critical effect is the dislocations in the diode area, which can originate from
the substrate and epilayer growth and the subsequent device processes, respectively. Our studies have shown that device processes
can cause additional dislocations in the diode area.
Diode yield was clearly improved by a combination of wet and dry etching for diode contact etching. 相似文献
15.
J. D. Benson A. J. Stoltz J. B. Varesi L. A. Almeida E. P. G. Smith S. M. Johnson M. Martinka A. W. Kaleczyc J. K. Markunas P. R. Boyd J. H. Dinan 《Journal of Electronic Materials》2005,34(6):726-732
The surface of (211)B HgCdTe has been studied by reflection high-energy electron diffraction (RHEED) and atomic force microscopy
(AFM). RHEED analysis of the as-grown Hg-rich molecular beam epitaxy (MBE) (211)B HgCdTe suggests the surface reconstructs
by additional Hg incorporation. The plasma-etched (211)B HgCdTe surface is crystalline but stepped and facetted. RHEED analysis
indicates asymmetric pyramids (base dimensions ≈0.5×1.1 nm) are formed to minimize surface Hg concentration. The AFM examination
of plasma-etched (211)B HgCdTe reveals oriented mesoscopic features. 相似文献
16.
L. A. Almeida N. K. Dhar M. Martinka J. H. Dinan 《Journal of Electronic Materials》2000,29(6):754-759
The technique of spectroscopic ellipsometry (SE) has been utilized to monitor in real-time and precisely control the surface
temperature of Hg1−xCdxTe during molecular beam epitaxy. Due to the temperature dependence of the Hg sticking coefficient under Hg-deficient growth
conditions, the near-surface composition of an epilayer is extremely sensitive to surface temperature. SE data were acquired
in real time and modeled using a previously established library of dielectric functions of Hg1−xCdxTe as a function of composition. Utilizing SE-generated compositional profiles as a guide, substrate heating power was adjusted
in such a way as to minimize composition transients. To demonstrate the effectiveness of the technique, we have used SE to
control the temperature of HgCdTe epilayer surfaces during deposition on three-inch (211)CdZnTe/ZnTe/Si composite substrates
mounted on indium free holders. 相似文献
17.
Heteroepitaxy of HgCdTe (211)B on Ge substrates by molecular beam epitaxy for infrared detectors 总被引:3,自引:0,他引:3
J. P. Zanatta P. Ferret G. Theret A. Million M. Wolny J. P. Chamonal G. Destefanis 《Journal of Electronic Materials》1998,27(6):542-545
Epitaxial growth of (211)B CdTe/HgCdTe has been achieved on two inch germanium (Ge) by molecular beam epitaxy (MBE). Germanium
was chosen as an alternative substrate to circumvent the weaknesses of CdZnTe wafers. The ease of surface preparation makes
Ge an attractive candidate among many other alternative substrates. Best MBE CdTe growth results were obtained on (211) Ge
surfaces which were exposed to arsenic and zinc fluxes prior to the MBE growth. This surface preparation enabled CdTe growth
with B-face crystallographic polarity necessary for the HgCdTe growth. This process was reproducible, and produced a smooth
and mirror-like surface morphology. The best value of the {422} x-ray double diffraction full width at half maximum measured
from the HgCdTe layer was 68 arc-s. We present the 486 point maps of FWHM statistical values obtained from CdTe/Ge and HgCdTe/CdTe/Ge.
High resolution microscopy electron transmission and secondary ion mass spectroscopy characterization results are also presented
in this paper. High-performance middle wavelength infrared HgCdTe 32-element photodiode linear arrays, using the standard
LETI/LIR planar n-on-p ion implanted technology, were fabricated on CdTe/Ge substrates. At 78K, photodiodes exhibited very
high R0A figure of merit higher than 106 Ωcm−2 for a cutoff wavelength of 4.8 μm. Excess low frequency noise was not observed below 150K. 相似文献
18.
The growth by molecular beam epitaxy of high quality GaAs epilayers on nonmisoriented GaAs(111)B substrates is reported. Growth control of the GaAs epilayers is achieved via in situ, real time measurement of the specular beam intensity of reflection high-energy electron diffraction (RHEED). Static surface phase maps of GaAs(111)B have been generated for a variety of incident As flux and substrate temperature conditions. The dependence of GaAs(111)B to be the optimum starting surface for the latter growth of mirror-smooth epilayers. Regimes of growth conditions are optimized in terms of the static surface phase diagram and the temporal RHEED intensity oscillations. 相似文献
19.
J.D. Benson L.A. Almeida M.W. Carmody D.D. Edwall J.K. Markunas R.N. Jacobs M. Martinka U. Lee 《Journal of Electronic Materials》2007,36(8):949-957
The as-grown molecular beam epitaxy (MBE) (211)B HgCdTe surface has variable surface topography, which is primarily dependent on substrate temperature and substrate/epilayer mismatch. Nano-ripple formation and cross-hatch patterning are the predominant structural features observed. Nano-ripples preferentially form parallel to the \( [\bar {1}11] \) and are from 0 Å to 100 Å in height with a wavelength between 0.1 μm and 0.8 μm. Cross-hatch patterns result from slip dislocations in the three {111} planes intersecting the (211) growth surface. The cross-hatch step height is 4 ± 1 Å (limited data set). This indicates that only a bi-layer slip (Hg/Cd + Te) in the {111} slip plane occurs. For the deposition of MBE (211)B HgCdTe/CdTe/Si, the reorientation of multiple nano-ripples coalesced into “packets” forms cross-hatch patterns. The as-grown MBE (211)B CdTe/Si surface is highly variable but displays nano-ripples and no cross-hatch pattern. Three types of defects were observed by atomic force microscopy (AFM): needle, void/hillock, and voids. 相似文献