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1.
Krishna C. Mandal Sung Hoon Kang Michael Choi Jiuan Wei Lili Zheng Hui Zhang Gerald E. Jellison Michael Groza Arnold Burger 《Journal of Electronic Materials》2007,36(8):1013-1020
Spectrometer-grade CdTe single crystals with resistivities higher than 109 Ω cm have been grown by the modified Bridgman method using zone-refined precursor materials (Cd and Te) under a Cd overpressure.
The grown CdTe crystals had good charge-transport properties (μτ
e = 2 × 10−3 cm2 V−1, μτ
h = 8 × 10−5 cm2 V−1) and significantly reduced Te precipitates compared with crystals grown without Cd overpressure. The crystal growth conditions
for the Bridgman system were optimized by computer modeling and simulation, using modified MASTRAPP program, and applied to
crystal diameters of 14 mm (0.55′′), 38 mm (1.5′′), and 76 mm (3′′). Details of the CdTe crystal growth operation, structural,
electrical, and optical characterization measurements, detector fabrication, and testing using 241Am (60 keV) and 137Cs (662 keV) sources are presented. 相似文献
2.
Krishna C. Mandal Sung Hoon Kang Michael Choi Job Bello Lili Zheng Hui Zhang Michael Groza Utpal N. Roy Arnold Burger Gerald E. Jellison David E. Holcomb Gomez W. Wright Joseph A. Williams 《Journal of Electronic Materials》2006,35(6):1251-1256
High-quality, large (10 cm long and 2.5 cm diameter), nuclear spectrometer grade Cd0.9Zn0.1Te (CZT) single crystals have been grown by a controlled vertical Bridgman technique using in-house zone refined precursor
materials (Cd, Zn, and Te). A state-of-the-art computer model, multizone adaptive scheme for transport and phase-change processes
(MASTRAP), is used to model heat and mass transfer in the Bridgman growth system and to predict the stress distribution in
the as-grown CZT crystal and optimize the thermal profile. The model accounts for heat transfer in the multiphase system,
convection in the melt, and interface dynamics. The grown semi-insulating (SI) CZT crystals have demonstrated promising results
for high-resolution room-temperature radiation detectors due to their high dark resistivity (ρ≈2.8 × 1011 Θ cm), good charge-transport properties [electron and hole mobility-life-time product, μτe≈(2–5)×10−3 and μτh≈(3–5)×10−5 respectively, and low cost of production. Spectroscopic ellipsometry and optical transmission measurements were carried out
on the grown CZT crystals using two-modulator generalized ellipsometry (2-MGE). The refractive index n and extinction coefficient
k were determined by mathematically eliminating the ∼3-nm surface roughness layer. Nuclear detection measurements on the single-element
CZT detectors with 241Am and 137Cs clearly detected 59.6 and 662 keV energies with energy resolution (FWHM) of 2.4 keV (4.0%) and 9.2 keV (1.4%), respectively. 相似文献
3.
A. Hossain Y. Cui A.E. Bolotnikov G.S. Camarda G. Yang D. Kochanowska M. Witkowska-Baran A. Mycielski R.B. James 《Journal of Electronic Materials》2009,38(8):1593-1599
CdMnTe offers several potential advantages over CdZnTe as a room- temperature gamma-ray detector, but many drawbacks in its
growth process impede the production of large, defect-free single crystals with high electrical resistivity and high electron
lifetimes. Here, we report our findings of the defects in several vanadium-doped as-grown as well as annealed Cd1−x
Mn
x
Te crystals, using etch pit techniques. We carefully selected single crystals from the raw wafer to fabricate and test as
a gamma-ray detector. We describe the quality of the processed Cd1−x
Mn
x
Te surfaces, and compare them with similarly treated CdZnTe crystals. We discuss the characterization experiments aimed at
clarifying the electrical properties of fabricated detectors, and evaluate their performance as gamma-ray spectrometers. 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.
S. Perkowitz 《Journal of Electronic Materials》1985,14(5):551-562
Far infrared (10 to 250 cm−1) reflection and transmission spectroscopy is used to characterize the free-carrier and alloy properties of the leading infrared
detector material Hg1-xCdxTe and the substrate materials CdTe and CdZnTe. The data yield values for carrier concentration and mobility, the compositional
parameter x and film thickness which generally agree with other determinations. The advantages of this contactless nondestructive
technique are described. Applications to the newly proposed infrared detector material Hg1-xMnxTe are briefly reviewed. 相似文献
6.
As-grown CdZnTe usually contains defects, such as twins, subgrain boundaries, dislocations, and Te precipitates. It is always
important to anneal CdZnTe slices in Cd vapor to eliminate these defects, especially Te precipitates. The exchange of Zn atoms
between the slices and the vapor plays an important role during the annealing process. In this paper, the effects of Zn partial
pressure on the properties of the annealed slices are studied carefully by measuring the concentration profiles, the infrared
(IR) transmission spectra, and the x-ray rocking curves. It was found that a surface layer with different compositions and
possibly different structure from the bulk crystal formed during the annealing of CdZnTe samples in the saturated Zn vapor.
The accumulation of excess Te in the surface layer helps to increase the IR permeability of the bulk crystal greatly. To improve
the crystallization quality, a lower Zn-pressure annealing should be used following the high Zn-pressure annealing. The diffusion
of Zn in the bulk crystal has also been analyzed at the temperatures of 700°C and 500°C. Calculations determined that DZn (700°C)=4.02 × 10−12 cm2s−1 and DZn (500°C)=1.22 × 10−13 cm2s−1. 相似文献
7.
D. Brellier E. Gout G. Gaude D. Pelenc P. Ballet T. Miguet M. C. Manzato 《Journal of Electronic Materials》2014,43(8):2901-2907
We report the bulk growth of single-crystal CdZnTe and characterization of material associated with large-area wafers produced from the CdZnTe ingots. Our experimental vertical gradient freeze set-up enables accurate detection of the beginning and end of the crystallization step by careful monitoring of the thermal cycle. Single crystal, (111)-oriented ingots with a diameter of 80 mm were routinely obtained without grain boundary or twin. The size of the CdZnTe ingots was extended to 115 mm in diameter, enabling production of large-dimension substrates suitable for infrared focal-plane arrays with megapixel-resolution. Crystal quality was investigated by double-crystal x-ray rocking curve mapping and by chemical revelation of etch pits. Typical mean values for the rocking curve full width at half maximum were in the range 20–40 arcs. Evaluation of etch pit density on the (111)Te face furnished values in the low 104/cm2. 相似文献
8.
S. Terterian M. Chu D. Ting L. C. Wu C. C. Wang M. Szawlowski G. Vissor P. N. Luke 《Journal of Electronic Materials》2003,32(7):796-802
A large number of room-temperature detectors have been produced from CdZnTe crystals grown with 10% Zn and 1.5% excess tellurium
by the low-pressure, vertical-Bridgman technique. Radiation spectra obtained by these crystals using a 241Am source reveal the characteristic 59.5-keV line as well as the six low-energy peaks, which include the Cd and Te escape
peaks. Similarly, 57Co spectra obtained also show a very well-defined 122-keV peak with a 3:1 peak-to-valley ratio. Seven CdZnTe crystals have
been grown for reproducibility studies. Four of these crystals have resistivities over 1E9 Ω-cm. Considering that the indiumdoping
level is on the order of 2E15 cm−3, the reproducibility is excellent. The theoretical basis of the high-resistivity phenomenon in CdZnTe is discussed in reference
to a previous paper. The uniformity of these 6-in.-long CdZnTe crystals is studied, and various measurements are carried out,
both laterally and vertically, along the boule. It is determined that, in general, roughly a 3.5-in. section near the middle
of the 6-in. boule has sufficient resistivity for producing radiation detectors. This nonuniformity along the vertical direction
is caused mostly by the composition change of Cd, Zn, Te, and In-doping level in the growth melt caused by differences in
the segregation coefficients of these elements. Although, variations in resistivity are seen across some of the wafer slices,
most show very good uniformity with high breakdown voltage. Some of the variations are attributed to the different grains
within the boule. Similar results are seen in the measured radiation spectra obtain on 4 mm × 4 mm × 2 mm samples from different
locations across the wafer, where some samples show well-resolved secondary peaks, while others display only the primary spectral
lines. 相似文献
9.
Theodore C. Harman 《Journal of Electronic Materials》1993,22(9):1165-1172
A Te-rich liquid-phase-epitaxial growth process is reported whereby reproducible Sb-doped layers are prepared with hole concentrations
and hole mobilities ranging from 1.8×1016 to 1.3×1019 cm−3 and 280 to 29 cm2/V s, respectively, at 77K for x-values ranging from 0.23 to 0.29. An effective electronic distribution coefficient for Sb
of 0.01 is calculated from the hole concentration at 77K and the concentration of Sb in the growth solution. The process for
group Va doping of low-x Hg1−x Cdx Te from Te-rich solutions and the procedure for the growth of a CdZnTe buffer layer on a CdTeSe substrate are described.
For Te-rich Cd−Zn−Te growth solutions the distribution coefficient of Zn was found to be 18. The growth of a structure consisting
of an Sb-doped HgCdTe epilayer on a CdZnTe buffer layer lattice matched (Δa/a<10−4) to a CdSeTe substrate has been demonstrated. 相似文献
10.
Thermomigration of tellurium precipitates in CdZnTe crystals grown by vertical bridgman method 总被引:1,自引:0,他引:1
T. S. Lee J. W. Park Y. T. Jeoung H. K. Kim C. H. Chun J. M. Kim I. H. Park J. M. Chang S. U. Kim M. J. Park 《Journal of Electronic Materials》1995,24(9):1053-1056
Te precipitates in CdZnTe have been characterized by x-ray diffraction at room and higher temperatures. From the x-ray results
at room temperature, it has been confirmed that Te precipitates in CdZnTe have the same structural phase as observed in elemental
Te under high pressure. The x-ray results at higher temperature indicate that Te precipitates melt around 440°C. CdZnTe samples
containing Te precipitates have been annealed at temperatures below and above 440°C with thermal gradient of ∼70°C/cm. Results
of the observation with infrared microscope before and after the annealings indicate distinct occurrence of thermomigration
of Te precipitates in samples annealed at temperature above 440°C compared with ones annealed at temperature below 440°C.
Thermomigration velocity obtained from these results is ∼50 μm/h. The average value for the effective diffusion coefficient
of the metallic atoms in Te precipitates calculated by using the thermomigration velocity is ∼3 x 10−5 cm2/s. 相似文献
11.
E. C. Piquette M. Zandian D. D. Edwall J. M. Arias 《Journal of Electronic Materials》2001,30(6):627-631
A semi-empirical constraint to the thermodynamical model for growth of Hg1−xCdxTe (MCT) by molecular beam epitaxy is described. This constraint, derived by forcing the population of Hg atoms in a surface
layer to be proportional to the HgTe fractional growth rate, can determine an optimal total growth rate for specific beam
fluxes and substrate temperature. Utilizing improved growth conditions determined by this model has resulted in MCT layers
with consistently lower visible defect density (e.g., voids). The majority of recent layers grown using the constrained conditions
has achieved defect densities limited by the CdZnTe substrate. On the highest quality substrates, total defect densities have
consistently been reduced to the 100–200 cm−2 range using the improved conditions for compositions x=0.2 to x=0.6. On more typical substrates, the total defect density
is 1000–1500 cm−2. This compares with densities of 3000–5000+ cm−2 for old layers grown under non-optimized conditions. The density of voids has remained about the same upon using the improved
conditions, and is determined primarily by the Te precipitate content of the substrate, but microdefect (hillock) density
has been reduced by almost a factor of ten. 相似文献
12.
Majid Zandian J. D. Garnett R. E. Dewames M. Carmody J. G. Pasko M. Farris C. A. Cabelli D. E. Cooper G. Hildebrandt J. Chow J. M. Arias K. Vural Donald N. B. Hall 《Journal of Electronic Materials》2003,32(7):803-809
We report on Hg1−xCdxTe mid-wavelength infrared (MWIR) detectors grown by molecular-beam epitaxy (MBE) on CdZnTe substrates. Current-voltage (I-V)
characteristics of HgCdTe-MWIR devices and temperature dependence of focal-plane array (FPA) dark current have been investigated
and compared with the most recent InSb published data. These MWIR p-on-n Hg1−xCdxTe/CdZnTe heterostructure detectors give outstanding performance, and at 68 K, they are limited by diffusion currents. For
temperatures lower than 68 K, in the near small-bias region, another current is dominant. This current has lower sensitivity
to temperature and most likely is of tunneling origin. High-performance MWIR devices and arrays were fabricated with median
RoA values of 3.96 × 1010 Ω-cm2 at 78 K and 1.27 × 1012 Ω-cm2 at 60 K; the quantum efficiency (QE) without an antireflection (AR) coating was 73% for a cutoff wavelength of 5.3 μm at
78 K. The QE measurement was performed with a narrow pass filter centered at 3.5 μm. Many large-format MWIR 1024 × 1024 FPAs
were fabricated and tested as a function of temperature to confirm the ultra-low dark currents observed in individual devices.
For these MWIR FPAs, dark current as low as 0.01 e−/pixel/sec at 58 K for 18 × 18 μm pixels was measured. The 1024 × 1024 array operability and AR-coated QE at 78 K were 99.48%
and 88.3%, respectively. A comparison of these results with the state-of-the-art InSb-detector data suggests MWIR-HgCdTe devices
have significantly higher performance in the 30–120 K temperature range. The InSb detectors are dominated by generation-recombination
(G-R) currents in the 60–120 K temperature range because of a defect center in the energy gap, whereas MWIR-HgCdTe detectors
do not exhibit G-R-type currents in this temperature range and are limited by diffusion currents. 相似文献
13.
J. K. Markunas L. A. Almeida R. N. Jacobs J. Pellegrino S. B. Qadri N. Mahadik J. Sanghera 《Journal of Electronic Materials》2010,39(6):738-742
Large-area high-quality Hg1–x
Cd
x
Te sensing layers for infrared imaging in the 8 μm to 12 μm spectral region are typically grown on bulk Cd1–x
Zn
x
Te substrates. Alternatively, epitaxial CdTe grown on Si or Ge has been used as a buffer layer for high-quality epitaxial
HgCdTe growth. In this paper, x-ray topographs and rocking-curve full-width at half-maximum (FWHM) data will be presented
for recent high-quality bulk CdZnTe grown by the vertical gradient freeze (VGF) method, previous bulk CdZnTe grown by the
vertical Bridgman technique, epitaxial CdTe buffer layers on Si and Ge, and a HgCdTe layer epitaxially grown on bulk VGF CdZnTe. 相似文献
14.
Jason MacKenzie Francis Joseph Kumar Henry Chen 《Journal of Electronic Materials》2013,42(11):3129-3132
The focus of this work is to evaluate the suitability and substrate potential of Cd0.9Zn0.1Te and Cd0.96Zn0.04Te crystals grown by the traveling heater method (THM). THM-grown Cd0.9Zn0.1Te crystals used for gamma spectroscopy have shown very good spectral performance owing partly to the very low concentration of Te inclusions and precipitates. Inspection in the infrared (IR) of annealed THM-grown CdZnTe wafers reveals no inclusions >3 μm, and Fourier-transform infrared measurements show IR transmission values in excess of 60%. Wafer etch pit density values are typically less than 4 × 10?4 pits/cm2, and double-crystal x-ray rocking-curve measurements show full-width at half-maximum values approaching 40 arcsec. 〈211〉 wafers have been produced with off orientation within 0.3°. (111)-Oriented, seeded THM growth runs have the ability to provide 10 60 mm × 60 mm × 2 mm wafers from a 75-mm-diameter boule or 20 90 mm × 90 mm × 2 mm wafers from a 100-mm-diameter boule. 相似文献
15.
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
16.
D. D. Edwall 《Journal of Electronic Materials》1993,22(8):847-851
Etch pit density and spatial compositional uniformity data are presented for organometallic vapor phase epitaxial Hg1−x Cdx Te grown by the direct alloy and interdiffused growth methods. For alloy growth, composition variation is as low as Δx=0.004
and 0.02 over 2- and 3-in diam areas, respectively; while for growth on CdZnTe substrates, etch pit density values lower than
2×105 cm−2 have been achieved. For interdiffused growth on CdZnTe, etch pit density values lower than 5×105 cm−2 have been obtained, while the composition variation is usually Δx≤0.004 and 0.014 over 2- and 3-in diam areas, respectively.
Data demonstrate that the choice of particular CdZnTe substrate strongly affects the subsequent etch pit density measured
in the layer. Reasonably uniform n-type doping over 3-in diam area using the source triethylgallium is also reported for both
growth methods. 相似文献
17.
F. Aqariden P.D. Dreiske M.A. Kinch P.K. Liao T. Murphy H.F. Schaake T.A. Shafer H.D. Shih T.H. Teherani 《Journal of Electronic Materials》2007,36(8):900-904
Hg1−x
Cd
x
Te samples of x ~ 0.3 (in the midwave infrared, or MWIR, spectral band) were prepared by molecular beam epitaxy (MBE) for fabrication into
30-μm-pitch, 256 × 256, front-side-illuminated, high-density vertically-integrated photodiode (HDVIP) focal plane arrays (FPAs).
These MBE Hg1−x
Cd
x
Te samples were grown on CdZnTe(211) substrates prepared in this laboratory; they were ~10-μm thick and were doped with indium to ~5 × 1014 cm−3. Standard HDVIP process flow was employed for array fabrication. Excellent array performance data were obtained from these
MWIR arrays with MBE HgCdTe material. The noise-equivalent differential flux (NEΔΦ) operability of the best array is 99.76%,
comparable to the best array obtained from liquid-phase epitaxy (LPE) material prepared in this laboratory. 相似文献
18.
Epitaxial layers of Hg1−xCdx Te were grown on CdTe substrates by the chemical vapor transport technique using Hgl2 as a transport agent. The epilayers were of nearly uniform composition both laterally and to a depth of about one-half of
the layer thickness. By comparison, the composition varied continuously throughout the depth of the layer for epilayers grown
by the physical vapor transport technique. Layers were grown both p- and n-type with carrier concentrations on the order of
1017 cm−3. Low-temperature annealing was used to convert the p-type layers into n-type. The room-temperature carrier mobilities of
as-grown and converted n-type layers ranged from 103 to 104 cm2/V-s depending on the composition and are comparable to previous literature values for undoped Hg1−xCdxTe crystals. 相似文献
19.
Wayne Lo 《Journal of Electronic Materials》1977,6(1):39-48
Single crystals of Pb1−x Snx Te (0.06<x<0.08) have been grown by using an ingot-nucleation technique from a Te-rich source. The as-grown crystals have
a p-type carrier concentration around 1019 cm−3 and dislocation density as low as 103 cm−2. Diode lasers fabricated from these crystals have contact resistances of 2×10−5 Ω-cm2 and a single-mode single-ended output power of 750 μW at heat sink temperatures around 15 K. 相似文献
20.
K. Chattopadhyay K. M. Pour S. U. Egarievwe J. O. Ndap H. Chen X. Ma S. Morgan A. Burger 《Journal of Electronic Materials》1999,28(6):666-669
A large photorefractive effect was measured in CdS0.8Se0.2:V and Cd0.55Mn0.45Te:V ternary crystals which shows promise for many device applications such as optical signal processing and optical limiting.
In this study, we compared the results obtained from two-wave mixing experiments with Cd0.55Mn0.45Te:V and CdS0.8Se0.2:V crystals at the 633 nm wavelength. As the signal to pump beam ratio was varied from 10−1 to 10−4, Cd0.55MN0.45Te:V and CdS0.8Se0.2:V showed a maximum photorefractive gain of 0.17 and 0.20 cm−1, respectively. The grating formation time of both the crystals were measured to be in the milli-second range at an incident
intensity of 200 mW/cm2. 相似文献