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M. Reddy,
J. M. Peterson,
T. Vang,
J. A. Franklin,
M. F. Vilela,
K. Olsson,
E. A. Patten,
W. A. Radford,
J. W. Bangs,
L. Melkonian,
E. P. G. Smith, D. D. Lofgreen,
S. M. Johnson
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ABSTRACT: This paper presents the status of HgCdTe growth on large-area Si and CdZnTe substrates at Raytheon Vision Systems (RVS). The
different technological tools that were used to scale up the growth from 4inch to 6inch diameter on Si and from 4cm×4cm
to 8cm×8cm on CdZnTe without sacrificing the quality of the layers are described. Extremely high compositional uniformity
and low macrodefect density were achieved for single- and two-color HgCdTe layers on both Si and CdZnTe substrates. Finally,
a few examples of detector and focal-plane array results are included to highlight the importance of high compositional uniformity
and uniformly low macrodefect density of the epitaxial layers in obtaining high operability and low cluster outages in single-
and two-color focal-plane arrays (FPAs).
KeywordsHgCdTe–IR detector–two-color–dual-band–MBE–molecular beam epitaxy–large-area substrates–FPAs
Journal of Electronic Materials 05/2012; 40(8):1706-1716. · 1.47 Impact Factor
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ABSTRACT: Raytheon Vision Systems (RVS) continues to further its capability to deliver state-of-the-art high-performance, large-format,
HgCdTe focal-plane arrays (FPAs) for dual-band long-wavelength infrared (L/LWIR) detection. Specific improvements have recently
been implemented at RVS in molecular-beam epitaxy (MBE) growth and wafer fabrication and are reported in this paper. The aim
of the improvements is to establish producible processes for 512×512 30-μm-unit-cell L/LWIR FPAs, which has resulted in: the growth of triple-layer heterojunction (TLHJ) HgCdTe back-to-back photodiode
detector designs on 6cm×6cm CdZnTe substrates with 300-K Fourier-transform infrared (FTIR) cutoff wavelength uniformity
of ±0.1μm across the entire wafer; demonstration of detector dark-current performance for the longer-wavelength detector band approaching
that of single-color liquid-phase epitaxy (LPE) LWIR detectors; and uniform, high-operability, 512×512 30-μm-unit-cell FPA performance in both LWIR bands.
KeywordsHgCdTe–infrared detectors–molecular-beam epitaxy (MBE)–dual-band long-wavelength infrared (L/LWIR)
Journal of Electronic Materials 05/2012; 40(8):1630-1636. · 1.47 Impact Factor
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ABSTRACT: In this paper, we show the versatility of using molecular-beam epitaxy (MBE) for the growth of the mercury cadmium telluride
(HgCdTe) system. Abrupt composition profiles, changes in doping levels or switching doping types are easily performed. It
is shown that high-quality material is achieved with Hg(1–x)Cd
x
Te grown by MBE from a cadmium mole fraction of x=0.15 to x=0.72. Doping elements incorporation as low as 1015cm−3 for both n-type and p-type material as well as high incorporation levels >1018cm−3 for both carrier types were achieved. X-ray curves, secondary-ion mass spectrometry (SIMS) data, Hall data, the influence
of doping incorporation with cadmium content and growth rate, etch pit density (EPD), composition uniformity determined from
Fourier-transform infrared (FTIR) transmission spectro- scopy, and surface defect maps from low to high x values are presented to illustrate the versatility and quality of HgCdTe material grown by MBE. All data presented in this
work are from layers grown on silicon (112) substrate.
Journal of Electronic Materials 05/2012; 38(8):1755-1763. · 1.47 Impact Factor
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ABSTRACT: HgCdTe grown on large-area Si substrates allows for larger array formats and potentially reduced focal-plane array (FPA) cost
compared with smaller, more expensive CdZnTe substrates. The goal of this work is to evaluate the use of HgCdTe/Si for mid-wavelength/long-wavelength
infrared (MWIR/LWIR) dual-band FPAs. A series of MWIR/LWIR dual-band HgCdTe triple-layer n-P-n heterojunction (TLHJ) device structures were grown by molecular-beam epitaxy (MBE) on 100-mm (211)Si substrates. The wafers
showed low macrodefect density (<300cm−2) and was processed into 20-μm-unit-cell 640×480 detector arrays which were mated to dual-band readout integrated circuits (ROICs) to produce FPAs. The
measured 80-K cutoff wavelengths were 5.5μm for MWIR and 9.4μm for LWIR, respectively. The FPAs exhibited high pixel operabilities in each band, with noise equivalent differential temperature
(NEDT) operabilities of 99.98% for the MWIR band and 99.6% for the LWIR band demonstrated at 84K.
KeywordsHgCdTe-dual band-FPAs-Si substrates-infrared detectors-molecular-beam epitaxy (MBE)
Journal of Electronic Materials 04/2012; 39(10):2215-2219. · 1.47 Impact Factor
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[show abstract]
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ABSTRACT: This paper describes molecular-beam epitaxy growth of mid-wavelength infrared (MWIR) and long-wavelength infrared (LWIR) dual-band
device structures on large-area (6cm×6cm) CdZnTe substrates. Wafer-level composition and defect mapping techniques were
used to investigate the limiting mechanisms in improving the cutoff wavelength (λ
c) uniformity and reducing the defect density. Structural quality of epitaxial layers was monitored using etch pit density
(EPD) measurements at various depths in the epitaxial layers. Finally, 640×480, 20-μm-pixel-pitch dual-band focal-plane arrays (FPAs) were fabricated to demonstrate the overall maturity of growth and fabrication
processes of epitaxial layers. The MWIR/LWIR dual-band layers, at optimized growth conditions, show a λ
c variation of ±0.15μm across a 6cm×6cm CdZnTe substrate, a uniform low macrodefect density with an average of 1000cm−2, and an average EPD of 1.5×105cm−2. FPAs fabricated using these layers show band1 (MWIR) noise equivalent temperature difference (NETD) operability of 99.94%
and band2 (LWIR) NETD operability of 99.2%, which are among the highest reported to date.
KeywordsCrystal growth-defects-detector-molecular-beam epitaxy-optical characterization-optoelectronic materials-photovoltaic materials-II-VI semiconductors-CdZnTe-HgCdTe
Journal of Electronic Materials 04/2012; 39(7):974-980. · 1.47 Impact Factor
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J. D. Benson,
L. O. Bubulac,
P. J. Smith,
R. N. Jacobs,
J. K. Markunas,
M. Jaime-Vasquez,
L. A. Almeida,
A. J. Stoltz,
P. S. Wijewarnasuriya,
G. Brill,
Y. Chen,
U. Lee,
M. F. Vilela,
J. Peterson,
S. M. Johnson, D. D. Lofgreen,
D. Rhiger,
E. A. Patten,
P. M. Goetz
[show abstract]
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ABSTRACT: The electrical performance of HgCdTe/Si photodiodes is shown not to have a direct relationship with the dislocation density
as revealed by defect etching. This has led to an equivalent circuit model to explain the relationship of the dislocation
density and the electrical test data. A new (112)B HgCdTe/CdTe/Si and CdTe/Si etch pit density (EPD) etch has been demonstrated.
The new etch has been used to look for distinctive features which may be responsible for the poor electrical performance of
individual diode pixels. The new etch chemistry also reduces the surface roughness of the etched epilayer and makes EPD determination
less problematic. The new (to HgCdTe) technique of electrostatic force microscopy has also been used to analyze the electrical
properties of dislocations.
KeywordsHgCdTe/CdTe/Si-molecular beam epitaxy-atomic force microscopy-electrostatic force microscopy-etch pit density
Journal of Electronic Materials 04/2012; 39(7):1080-1086. · 1.47 Impact Factor
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ABSTRACT: Molecular beam epitaxy (MBE) growth of HgCdTe on large-size Si (211) and CdZnTe (211)B substrates is critical to meet the
demands of extremely uniform and highly functional third-generation infrared (IR) focal-panel arrays (FPAs). We have described
here the importance of wafer maps of HgCdTe thickness, composition, and the macrodefects across the wafer not only to qualify
material properties against design specifications but also to diagnose and classify the MBE-growth-related issues on large-area
wafers. The paper presents HgCdTe growth with exceptionally uniform composition and thickness and record low macrodefect density
on large Si wafers up to 6-in in diameter for the detection of short-wave (SW), mid-wave (MW), and long-wave (LW) IR radiation.
We have also proposed a cost-effective approach to use the growth of HgCdTe on low-cost Si substrates to isolate the growth-
and substrate-related problems that one occasionally comes across with the CdZnTe substrates and tune the growth parameters
such as growth rate, cutoff wavelength (λ
cutoff) and doping parameters before proceeding with the growth on costly large-area CdZnTe substrates. In this way, we demonstrated
HgCdTe growth on large CdZnTe substrates of size 7cm×7cm with excellent uniformity and low macrodefect density.
Journal of Electronic Materials 08/2008; 37(9):1274-1282. · 1.47 Impact Factor
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M.F. Vilela, D.D. Lofgreen,
E.P.G. Smith,
M.D. Newton,
G.M. Venzor,
J.M. Peterson,
J.J. Franklin,
M. Reddy,
Y. Thai,
E.A. Patten,
S.M. Johnson,
M.Z. Tidrow
[show abstract]
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ABSTRACT: Long-wavelength infrared (LWIR) HgCdTe p-on-n double-layer heterojunctions (DLHJs) for infrared detector applications have been grown on 100mm Ge (112) substrates by
molecular beam epitaxy (MBE). The objective of this current work was to grow our baseline p-on-n DLHJ detector structure (used earlier on Si substrates) on 100mm Ge substrates in the 10μm to 11μm LWIR spectral region, evaluate the material properties, and obtain some preliminary detector performance data. Material
characterization techniques included are X-ray rocking curves, etch pit density (EPD) measurements, compositional uniformity
determined from Fourier-transform infrared (FTIR) transmission, and doping concentrations determined from secondary-ion mass
spectroscopy (SIMS). Detector properties include resistance-area product (RoA), spectral response, and quantum efficiency.
Results of LWIR HgCdTe detectors and test structure arrays (TSA) fabricated on both Ge and silicon (Si) substrates are presented
and compared. Material properties demonstrated include X-ray full-width of half-maximum (FWHM) as low as 77 arcsec, typical
etch pit densities in mid 106cm−2 and wavelength cutoff maximum/minimum variation <2% across the full wafer. Detector characteristics were found to be nearly
identical for HgCdTe grown on either Ge or Si substrates.
Journal of Electronic Materials 08/2008; 37(9):1465-1470. · 1.47 Impact Factor
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[show abstract]
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ABSTRACT: The ability to accurately predict HgCdTe focal plane array (FPA) performance using nondestructive, postgrowth wafer analysis
is of great importance. These predictions, if accurate, reduce costs by screening the wafers prior to processing, and selecting
only those wafers that are most likely to yield FPAs that meet program specifications. In this paper, we examine the use of
a macrodefect inspection tool, the NSX 1255, from August Technology. This inspection tool has the ability to measure defects
0.5 μm and larger and store the location and size data to a file. We have then, through the use of custom written software, been
able to analyze these data on a wafer by wafer basis. We have also incorporated the use of a thin film transmission matrix
model to analyze room-temperature Fourier transform infrared spectroscopy (FTIR) transmission spectra. This technique, which
is applied to the entire wafer surface, can be used to determine the individual layer thicknesses as well as their compositions.
Then, using analytical expressions for bandgap, absorption, and index of refraction, we can predict responsivity and quantum
efficiency. Through the use of these two inspection tools and our analysis software, we are able to overlay FPA die information
and perform statistics on a die-per-die basis. This allows us to effectively “pass” or “fail” each FPA based on the program
specifications. We are then able to set a minimum criterion for the number of FPAs that pass on any given wafer. That wafer
is then sent off to processing if it meets this criterion. Furthermore, knowing why a wafer fails before it reaches processing
allows for real time feedback to the epilayer growth process. This allows for run-to-run adjustments in order to keep as many
wafers within specifications as possible and increases yield overall.
Journal of Electronic Materials 01/2007; 36(8):958-962. · 1.47 Impact Factor
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[show abstract]
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ABSTRACT: The ability to achieve high-yield focal plane arrays from Hg1−xCdxTe molecular beam epitaxy material depends strongly on postgrowth wafer analysis. Nondestructive analysis that can determine
layer thicknesses as well as alloy compositions is critical in providing run-to-run consistency. In this paper, we incorporate
the use of a thin film transmission matrix model to analyze Fourier transform infrared (FTIR) transmission spectra. Our model
uses a genetic algorithm along with a multidimensional, nonlinear minimization Nelder-Mead algorithm to determine the composition
and thickness of each layer in the measured epitaxial structure. Once a solution has been found, the software is able to predict
detector performance such as quantum efficiency and spectral response. We have verified our model by comparing detector spectral
data to our predicted spectral data derived from the room-temperature FTIR transmission data. Furthermore, the model can be
used to generate design curves for detectors with varying absorber thicknesses and/or different operating temperatures. The
consequence of this are reduced cycle times and reduced design variations.
Journal of Electronic Materials 01/2006; 35(6):1487-1490. · 1.47 Impact Factor
