共查询到20条相似文献,搜索用时 15 毫秒
1.
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
2.
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
3.
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
4.
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
5.
We study the adsorption of Hg on CdTe(211)B using an 88-wavelength spectroscopic ellipsometer mounted on a commercial, molecular
beam epitaxy (MBE) chamber. A detailed analysis of the pseudo-dielectric function shows that Hg is present at the surface
both in chemisorbed and physisorbed form. Effective medium models for a mixture of chemisorbed and physisorbed Hg on the microscopically
rough CdTe surface could not fit our data. However, a proposed model in which a partial layer of physisorbed Hg sits on top
of a partial layer of chemisorbed Hg fits the measured pseudo-dielectric function well and yields precise values for the thicknesses
of the chemisorbed and the physisorbed Hg layers. These values change in the expected manner as a function of Hg flux, temperature,
and Te coverage. An analysis of the uncertainty in the measured thicknesses is carried out in detail, and a study of the limitations
of the ellipsometer used for this study is presented. The effects of these limitations on the precision and accuracy of in-situ
data are enumerated. 相似文献
6.
We study the plasma-assisted molecular beam epitaxy of cubic GaN on GaAs(OOl) substrates by means ofin-situ reflection high-energy electron diffraction. The epilayers are characterized by x-ray diffraction, photoluminescence, and
Hall measurements, and it is found that the overall best films are grown under a N/Ga ratio close to one. For anin-situ determination of the N/Ga ratio, the growth kinetics is studied via surface reconstruction transitions. The effective N flux
giving rise to growth is measured using the transient behavior of the half-order diffraction streak intensity for various
plasma operating conditions. 相似文献
7.
G. Brill S. Velicu P. Boieriu Y. Chen N. K. Dhar T. S. Lee Y. Selamet S. Sivananthan 《Journal of Electronic Materials》2001,30(6):717-722
The traditional substrate of choice for HgCdTe material growth has been lattice matched bulk CdZnTe material. However, as
larger array sizes are required for future devices, it is evident that current size limitations of bulk substrates will become
an issue and therefore large area Si substrates will become a requirement for HgCdTe growth in order to maintain the cost-efficiency
of future systems. As a result, traditional substrate mounting methods that use chemical compounds to adhere the substrate
to the substrate holder may pose significant technical challenges to the growth and fabrication of HgCdTe on large area Si
substrates. For these reasons, non-contact (indium-free) substrate mounting was used to grow mid-wave infrared (MWIR) HgCdTe
material on 3″ CdTe/Si substrates. In order to maintain a constant tepilayer temperature during HgCdTe nucleation, reflection
high-energy electron diffraction (RHEED) was implemented to develop a substrate temperature ramping profile for HgCdTe nucleation.
The layers were characterized ex-situ using Fourier transform infrared (FTIR) and etch pit density measurements to determine
structural characteristics. Dislocation densities typically measured in the 9 106 cm−2 to 1 107 cm−2 range and showed a strong correlation between ramping profile and Cd composition, indicating the uniqueness of the ramping
profiles. Hall and photoconductive decay measurements were used to characterize the electrical properties of the layers. Additionally,
both single element and 32 32 photovoltaic devices were fabricated from these layers. A RA value of 1.8 106-cm2 measured at −40 mV was obtained for MWIR material, which is comparable to HgCdTe grown on bulk CdZnTe substrates. 相似文献
8.
R. H. Sewell C. A. Musca J. M. Dell L. Faraone B. F. Usher T. Dieing 《Journal of Electronic Materials》2005,34(6):795-803
Lattice mismatch between substrates and epitaxial layers of different molefractions can create a variety of distortions and
defects in Hg(1−x)Cd(x)Te epilayers, thus degrading the performance of infrared detectors fabricated from this material. X-ray diffraction is a sensitive
nondestructive technique, which allows in-depth characterization of the crystal lattice prior to detector fabrication. We
present results of triple-axis diffractometry performed on single- and double-layer HgCdTe films grown on (211)B CdZnTe substrates
by molecular beam epitaxy (MBE). In this study, both the ω and 2θ diffraction angles have been recorded absolutely so that
the diffraction peaks in the RSMs can be positioned directly in reciprocal space, without requiring reference to a substrate
peak. The positions of both surface-symmetric and asymmetric diffraction peaks have been used to extract lattice spacings
parallel and perpendicular to the (211) growth direction. The relaxed lattice parameter of each epilayer has been calculated
assuming that the layers are elastically strained. The low symmetry of the (211) growth direction, coupled with the anisotropic
elasticity of zinc-blende semiconductors, results in monoclinic distortion of the lattice, as observed in these samples. In
double-layer samples, the mosaicity of both layers is greater than that observed in single epilayers. Layers subjected to
a Hg-saturated anneal show greater lattice distortion than as-grown samples. 相似文献
9.
We have constructed an optical microscopy system to automatically locate, count, and determine the size of polycrystalline
“void” defects on epitaxial layers of HgCdTe grown on CdZnTe or Si substrates. Void macrodefects are readily imaged because
their polycrystalline surface is rough, and consequently they scatter light out of the image under specular reflection imaging
conditions. Using a computer-controlled stage to move the wafer, a succession of individual, contiguous bright-field images
is recorded over the entire wafer. Each image is analyzed by software to locate and characterize all the light-scattering
objects present in the frame. Several different representations of the spatial distribution and size of defects are generated,
and these can be presented either as false-color density maps or dot-location maps. In addition, various types of statistics
on the defect population and size distributions are also available. These data not only convey overall information on the
quality of a given wafer, and as such are quite useful for screening to determine which wafers are suitable for array fabrication,
but they also allow inferences to be made concerning the origin or root cause of different classes of defects. Several examples
are presented to illustrate the use of full-wafer defect mapping to identify macrodefect problems in HgCdTe growth on CdZnTe
that can arise from substrate temperature lateral nonuniformity, nonmatched source flux angular distributions, substrate contamination,
and intrinsic substrate imperfections. 相似文献
10.
HgCdTe材料的表面缺陷是造成探测器性能下降的主要原因之一。采用聚焦离子束(Focused Ion Beam, FIB)、扫描电子显微镜(Scanning Electron Microscope, SEM)和能量色散X射线光谱仪(Energy Dispersive X-ray Spectrometer, EDX)研究了碲锌镉(CdZnTe)基HgCdTe外延层的表面缺陷。通过分析不同类型缺陷形成的原因,确定缺陷起源于HgCdTe材料生长过程。缺陷的形状与生长条件关系密切。凹坑及火山口状缺陷与Hg缺乏/稍高生长温度、分子束源坩埚中材料形状变化造成的不稳定束流有关。金刚石状缺陷和火山口状/金刚石状复合缺陷的产生与Hg/Te高束流比、低生长温度相关。在5 cm×5 cm大小的CdZnTe(211)B衬底表面上生长出了组分为0.216、厚度约为6.06~7 μm的高质量HgCdTe外延层。同时还建立了缺陷类型与HgCdTe薄膜生长工艺的关系。该研究对于制备高质量HgCdTe/CdZnTe外延层具有参考意义。 相似文献
11.
M. Reddy J. M. Peterson S. M. Johnson T. Vang J. A. Franklin E. A. Patten W. A. Radford J. W. Bangs D. D. Lofgreen 《Journal of Electronic Materials》2009,38(8):1764-1770
This paper presents the progress in the molecular beam epitaxy (MBE) growth of HgCdTe on large-area Si and CdZnTe substrates
at Raytheon Vision Systems. We report a very high-quality HgCdTe growth, for the first time, on an 8 cm × 8 cm CdZnTe substrate.
This paper also describes the excellent HgCdTe growth repeatability on multiple 7 cm × 7 cm CdZnTe substrates. In order to
study the percentage wafer area yield and its consistency from run to run, small lots of dual-band long-wave infrared/long-wave
infrared triple-layer heterojunction (TLHJ) layers on 5 cm × 5 cm CdZnTe substrates and single-color double-layer heterojunction
(DLHJ) layers on 6-inch Si substrates were grown and tested for cutoff wavelength uniformity and micro- and macrovoid defect
density and uniformity. The results show that the entire lot of 12 DLHJ-HgCdTe layers on 6-inch Si wafers meet the testing
criterion of cutoff wavelength within the range 4.76 ± 0.1 μm at 130 K and micro- and macrovoid defect density of ≤50 cm−2 and 5 cm−2, respectively. Likewise, five out of six dual-band TLHJ-HgCdTe layers on 5 cm × 5 cm CdZnTe substrates meet the testing criterion
of cutoff wavelength within the range 6.3 ± 0.1 μm at 300 K and micro- and macrovoid defect density of ≤2000 cm−2 and 500 cm−2, respectively, on the entire wafer area. Overall we have found that scaling our HgCdTe MBE process to a 10-inch MBE system
has provided significant benefits in terms of both wafer uniformity and quality. 相似文献
12.
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
13.
Molecular beam epitaxy HgCdTe growth-induced void defects and their effect on infrared photodiodes 总被引:3,自引:0,他引:3
J. M. Arias M. Zandian J. Bajaj J. G. Pasko L. O. Bubulac S. H. Shin R. E. De Wames 《Journal of Electronic Materials》1995,24(5):521-524
We have carried out a study and identified that MBE HgCdTe growth-induced void defects are detrimental to long wavelength
infrared photodiode performance. These defects were induced during nucleation by having surface growth conditions deficient
in Hg. Precise control and reproducibility of the CdZnTe surface temperature and beam fluxes are required to minimize such
defects. Device quality material with void defect concentration values in the low 102 cm2 range were demonstrated. 相似文献
14.
A. J. Stoltz M. Jaime-Vasquez J. D. Benson J. B. Varesi M. Martinka 《Journal of Electronic Materials》2006,35(6):1461-1464
High-density argon-hydrogen plasmas have been demonstrated to be very effective as etchants of CdTe, CdZnTe, and HgCdTe materials
for focal plane array applications. Understanding the physical, chemical, and electrical characteristics of these surfaces
is critical in elucidating the mechanisms of processing Hg1−xCdxTe. The ways in which these plasmas interact with HgCdTe, such as etch rates and loading, have been studied.1–11 However, little is known on how these plasmas affect the first few atomic layers of HgCdTe. In this study, the effects of
high-density plasmas on the surface of HgCdTe were examined. The combination of argon and hydrogen plasma etch leaves a well-ordered,
near-stoichiometric surface determined by both x-ray photoelectron spectroscopy and reflection high-energy electron diffraction
(RHEED). Starting with Hg0.78Cd0.22Te, we were able to produce surfaces with x=0.4 and a RHEED pattern sharp enough to measure 2×1 reconstruction. 相似文献
15.
16.
Physical structure of molecular-beam epitaxy growth defects in HgCdTe and their impact on two-color detector performance 总被引:1,自引:0,他引:1
A. A. Buell L. T. Pham M. D. Newton G. M. Venzor E. M. Norton E. P. Smith J. B. Varesi V. B. Harper S. M. Johnson R. A. Coussa T. De Leon J. A. Roth J. E. Jensen 《Journal of Electronic Materials》2004,33(6):662-666
The flexible nature of molecular-beam epitaxy (MBE) growth is beneficial for HgCdTe infrared-detector design and allows for
tailored growths at lower costs and larger focal-plane array (FPA) formats. Control of growth dynamics gives the MBE process
a distinct advantage in the production of multicolor devices, although opportunities for device improvement still exist. Growth
defects can inhibit pixel performance and reduce the operability in FPAs, so it is important to understand and evaluate their
properties and impact on detector performance. The object of this paper is to understand and correlate the effects of macrodefects
on two-color detector performance. We observed the location of single-crystal and polycrystalline regions on planar and cross-sectioned
surfaces of two-color device structures when void defects were viewed by scanning electron microscopy (SEM). Compositional
analysis via energy dispersive x-ray analysis (EDXA) of voids in the cross section showed elevated Te and reduced Hg when
compared to defect-free growth areas. The second portion of this study examined the correlation of macrodefects with pixel
operability and diode current-voltage (I–V) characteristics in mid-wavelength infrared (MWIR)/MWIR (M/M) and long wavelength
infrared (LWIR)/LWIR (L/L) two-color devices. The probability of diode failure when a void is present is 98% for M/M and 100%
for L/L. Voids in two-color detectors also impact diodes neighboring their location; the impact is higher for L/L detectors
than M/M detectors. All void-containing diodes showed early breakdown in the I–V characteristics in one or both bands. High
dislocation densities were observed surrounding voids; the high density spread further from the void for L/L detectors compared
to M/M detectors. 相似文献
17.
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
18.
Lijie Zhao J. S. Speck R. Rajavel J. Jensen D. Leonard T. Strand W. Hamilton 《Journal of Electronic Materials》2000,29(6):732-735
Transmission electron microscopy (TEM) was used to evaluate the microstructure of molecular beam epitaxy (MBE) grown (211)B
oriented HgCdTe films. TEM analysis of in-situ doped p-on-n and n-p-n device structures will be presented. Under fully optimized
growth conditions the substrate-epilayer interface is free of threading dislocations and twins, and a high degree of structural
integrity is retained throughout the entire device structure. However, under non-optimal growth conditions that employ high
Hg/Te flux ratios, twins can be generated in the p-type layer of p-on-n device structure, resulting in roughness and facetting
of the film surface. We propose a mechanism for twin formation that is associated with surface facetting. TEM evaluation of
voids, threading dislocations and Te-precipitates in HgCdTe films are also discussed. 相似文献
19.
This paper describes our progress to improve the material quality, reproducibility, and flexibility of molecular beam epitaxial
(MBE) growth of HgCdTe. Data, statistics, and yields according to defined screen criteria are presented for n-type layer carrier
concentration and mobility, void defect density, and dislocation density for more than 100 layers. Minority carrier lifetime
data are also presented. Continued improvements in impurity reductiont have allowed us to achieve, for the first time, reproducible,
low n-type carrier concentration in the mid-1014 cnr−3 range with high electron mobility. Data are presented that show that low dislocation density films are obtained for growth
on CdZnTe substrates with a wide range of Zn concentration. Results are presented from a nine-growth run first pass success
demonstration run to further assess material quality reproducibility and flexibility of wavelength band tuning. These results
demonstrate the promising potential of MBE growth for flexible manufacturing of HgCdTe for infrared focal plane arrays. 相似文献
20.
J.G.A. Wehner R.H. Sewell C.A. Musca J.M. Dell L. Faraone 《Journal of Electronic Materials》2007,36(8):877-883
Investigation into resonant-cavity-enhanced (RCE) HgCdTe detectors has revealed a discrepancy in the refractive index of the
CdTe layers grown by molecular beam epitaxy (MBE) for the detectors, compared with the reported value for crystalline CdTe.
The refractive index of the CdTe grown for RCE detectors was measured using ellipsometry and matches that of CdTe with an
inclusion of approximately 10% voids. X-ray measurements confirm that the sample is crystalline and strained to match the
lattice spacing of the underlying Hg(1−x)Cd(x)Te, while electron diffraction patterns observed during growth indicate that the CdTe layers exhibit some three-dimensional
structure. Secondary ion mass spectroscopy results further indicate that there is enhanced interdiffusion at the interface
between Hg(1−x)Cd(x)Te and CdTe when the Hg(1−x)Cd(x)Te is grown on CdTe, suggesting that the defects are nucleated within the CdTe layers. 相似文献