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15.  Thin film transistors with wurtzite ZnO channels grown on Si3N4/SiO2/Si (111) substrates by pulsed laser deposition
D.J. Rogers; V.E. Sandana; F. Hosseini Teherani; M. Razeghi
Proc. SPIE 7603, Oxide-based Materials and Devices, 760318 (March 02, 2010)-- March 7, 2010 ...[Visit Journal]
Thin Film Transistors (TFT) were made by growing ZnO on Si3N4/SiO2/Si (111) substrates by pulsed laser deposition. X-ray diffraction and scanning electron microscope studies revealed the ZnO to have a polycrystalline wurtzite structure with a smooth surface, good crystallographic quality and a strong preferential c-axis orientation. Transmission studies in similar ZnO layers on glass substrates showed high transmission over the whole visible spectrum. Electrical measurements of a back gate geometry FET showed an enhancement-mode response with hard saturation, mA range Id and a VON ∼ 0V. When scaled down, such TFTs may be of interest for high frequency applications. [reprint (PDF)]
 
15.  Persistent photoconductivity in Ga0.49In0.51P/GaAs heterojunctions
S. Ben Amor; L. Dmowski; J. C. Portal; N. J. Pulsford; R. J. Nicholas; J. Singleton; M. Razeghi
J. Appl. Phys. 65, 2756–2760 (1989-- November 18, 1988 ...[Visit Journal]
We have studied the persistent photoconductivity (PPC) effect in Ga0.49 Ino. sl P IGaAs heterostructures. Through time- and temperature-dependent Hall effect, we observe very small relaxation rates and the PPC remains observable at room temperature. Optical experiments show an optical energy threshold of 1.15 e V and an infrared quenching of the ppc. Thermal cycling of the samples strongly affects the PPC and the quenching temperature. The center responsible for the observed PPC, therefore, appears related to defects, Most of our observations are qualitatively understood in a large lattice relaxation DX-like center approach. However, the origin of the high quenching temperature remains to be explained. [reprint (PDF)]
 
15.  Recent advances of terahertz quantum cascade lasers
Manijeh Razeghi
Proc. SPIE 8119, Terahertz Emitters, Receivers, and Applications II, 81190D (September 07, 2011)-- November 7, 2011 ...[Visit Journal]
In the past decade, tremendous development has been made in GaAs/AlGaAs based THz quantum cascade laser (QCLs), however, the maximum operating temperature is still limited below 200 K (without magnetic field). THz QCL based on difference frequency generation (DFG) represents a viable technology for room temperature operation. Recently, we have demonstrated room temperature THz emission (∼ 4 THz) up to 8.5 μW with a power conversion efficiency of 10 μW/W². A dual-period distributed feedback grating is used to filter the mid-infrared spectra in favor of an extremely narrow THz linewidth of 6.6 GHz. [reprint (PDF)]
 
15.  Recent Advances in InAs/GaSb Superlattices for Very Long Wavelength Infrared Detection
G.J. Brown, F. Szmulowicz, K. Mahalingam, S. Houston, Y. Wei, A. Gin and M. Razeghi
SPIE Conference, San Jose, CA, Vol. 4999, pp. 457-- January 27, 2003 ...[Visit Journal]
New infrared (IR) detector materials with high sensitivity, multi-spectral capability, improved uniformity and lower manufacturing costs are required for numerous long and very long wavelength infrared imaging applications. One materials system has shown great theoretical and, more recently, experimental promise for these applications: InAs/InxGa1-xSb type-II superlattices. In the past few years, excellent results have been obtained on photoconductive and photodiode samples designed for infrared detection beyond 15 microns. The infrared properties of various compositions and designs of these type-II superlattices have been studied. The infrared photoresponse spectra are combined with quantum mechanical modeling of predicted absorption spectra to provide insight into the underlying physics behind the quantum sensing in these materials. Results for superlattice photodiodes with cut-off wavelengths as long as 25 microns are presented. [reprint (PDF)]
 
15.  Geiger-mode operation of back-illuminated GaN avalanche photodiodes
J. L. Pau, R. McClintock, K. Minder, C. Bayram, P. Kung, M. Razeghi, E. Muñoz, and D. Silversmith
Applied Physics Letters, Vol. 91, No. 04, p. 041104 -1-- July 23, 2007 ...[Visit Journal]
We report the Geiger-mode operation of back-illuminated GaN avalanche photodiodes fabricated on transparent AlN templates specifically for back illumination in order to enhance hole-initiated multiplication. The spectral response in Geiger-mode operation was analyzed under low photon fluxes. Single photon detection capabilities were demonstrated in devices with areas ranging from 225 to 14,063 µm2. Single photon detection efficiency of 20% and dark count rate < 10 kHz were achieved in the smallest devices. [reprint (PDF)]
 
15.  Ultrafast Pulse Generation from Quantum Cascade Lasers
Feihu Wang, Xiaoqiong Qi, Zhichao Chen, Manijeh Razeghi, and Sukhdeep Dhillon
Wang, F.; Qi, X.; Chen, Z.; Razeghi, M.; Dhillon, S. Ultrafast Pulse Generation from Quantum Cascade Lasers. Micromachines 2022, 13, 2063. https://doi.org/10.3390/ mi13122063 ...[Visit Journal]
Quantum cascade lasers (QCLs) have broken the spectral barriers of semiconductor lasers and enabled a range of applications in the mid-infrared (MIR) and terahertz (THz) regimes. However, until recently, generating ultrashort and intense pulses from QCLs has been difficult. This would be useful to study ultrafast processes in MIR and THz using the targeted wavelength-by-design properties of QCLs. Since the first demonstration in 2009, mode-locking of QCLs has undergone considerable development in the past decade, which includes revealing the underlying mechanism of pulse formation, the development of an ultrafast THz detection technique, and the invention of novel pulse compression technology, etc. Here, we review the history and recent progress of ultrafast pulse generation from QCLs in both the THz and MIR regimes. [reprint (PDF)]
 
15.  Graphene versus oxides for transparent electrode applications
Sandana, V. E.; Rogers, D. J.; Teherani, F. Hosseini; Bove, P.; Razeghi, M.
Proc. SPIE 8626, Oxide-based Materials and Devices IV, 862603 (March 18, 2013)-- March 18, 2013 ...[Visit Journal]
Due to their combination of good electrical conductivity and optical transparency, Transparent Conducting Oxides (TCOs) are the most common choice as transparent electrodes for optoelectronics applications. In particular, devices, such as LEDs, LCDs, touch screens and solar cells typically employ indium tin oxide. However, indium has some significant drawbacks, including toxicity issues (which are hampering manufacturing), an increasing rarefication (due to a combination of relative scarcity and increasing demand [1]) and resulting price increases. Moreover, there is no satisfactory option at the moment for use as a p-type transparent contact. Thus alternative materials solutions are actively being sought. This review will compare the performance and perspectives of graphene with respect to TCOs for use in transparent conductor applications. [reprint (PDF)]
 
15.  Development of material quality and structural design for high performance type-II InAs/GaSb superlattice photodiodes and focal plane arrays
M. Razeghi, B.M. Nguyen, D. Hoffman, P.Y. Delaunay, E.K. Huang, M.Z. Tidrow and V. Nathan
SPIE Porceedings, Vol. 7082, San Diego, CA 2008, p. 708204-- August 11, 2008 ...[Visit Journal]
Recent progress made in the structure design, growth and processing of Type-II InAs/GaSb superlattice photo-detectors lifted both the quantum efficiency and the R0A product of the detectors. Type-II superlattice demonstrated its ability to perform imaging in the Mid-Wave Infrared (MWIR)and Long-Wave Infrared (LWIR) ranges, becoming a potential competitor for technologies such as Quantum Well Infrared Photo-detectors (QWIP) and Mercury Cadmium Telluride (MCT). Using an empirical tight-binding model, we developed superlattices designs that were nearly lattice-matched to the GaSb substrates and presented cutoff wavelengths of 5 and 11 μm. We demonstrated high quality material growth with X-ray FWHM below 30 arcsec and an AFM rms roughness of 1.5 Å over an area of 20x20 μm2. The detectors with a 5 μm cutoff, capable of operating at room temperature, showed a R0A of 1.25 106 Ω.cm2 at 77K, and a quantum efficiency of 32%. In the long wavelength infrared, we demonstrated high quantum efficiencies above 50% with high R0A products of 12 Ω.cm2 by increasing the thickness of the active region. Using the novel M-structure superlattice design, more than one order of magnitude improvement has been observed for electrical performance of the devices. Focal plane arrays in the middle and long infrared range, hybridized to an Indigo read out integrated circuit, exhibited high quality imaging. [reprint (PDF)]
 
15.  Development of Quantum Well Infrared Photodetectors at the Center for Quantum Devices
M. Razeghi, M. Erdtmann, C. Jelen, J. Diaz, F. Guastavino, G.J. Brown, and Y.S. Park
Infrared Physics and Technology 42 (3-5)-- January 1, 2001 ...[Visit Journal]
Results of detector characterization are presented for quantum well infrared photodetectors (QWIPs) fabricated from a variety of III-V material systems lattice-matched to GaAs or InP substrate, p-Type GaAs/GaInP QWIPs show background limited performance up to temperatures of 120 K, while p-type GaInAsP/GaInAsP QWIPs exhibit broadband response from lambda = 2.5-10 mum. n-Type GaAs/GaInP QWIPs are sensitive deep into the VLWIR with very low dark current. Extremely large responsivities of 33.2 AW(-1) were obtained from n-type GaInAs/InP QWIPs operating at lambda = 9 mum. Devices made from n-type AlGaInAs/InP and GaInAs/AlInAs have also been realized that extend the wavelength range of sensitivity from 3 mum out to 20 mum while remaining lattice-matched to InP. Lattice-matched multispectral detectors are demonstrated for sensitivity at both 4 and 8.5 mum Localized epitaxy of GaInAs/InP superlattice structures lattice-matched to InP was performed on Si substrate for the purpose of monolithic integration of III-V QWIPs with Si-based read-out integrated circuitry. [reprint (PDF)]
 
14.  Room-temperature continuous-wave operation of quantum-cascade lasers at λ ~ 4 µm
J.S. Yu, S.R. Darvish, A. Evans, J. Nguyen, S. Slivken, and M. Razeghi
Applied Physics Letters 88 (4)-- January 23, 2006 ...[Visit Journal]
High-power cw λ~4 μm quantum-cascade lasers (QCLs) are demonstrated. The effect of different cavity length and laser die bonding is also investigated. For a high-reflectivity-coated 11-μm-wide and 4-mm-long epilayer-down bonded QCL, cw output powers as high as 1.6 W at 80 K and 160 mW at 298 K are obtained, and the cw operation is achieved up to 313 K with 12 mW. [reprint (PDF)]
 
14.  UV photodetectors based on AlxGa1-xN grown by MOCVD
A. Saxler, D. Walker, X. Zhang, P. Kung, J. Xu, and M. Razeghi
SPIE Photonics West '96 Photodetectors: Materials and Devices; Proceedings 2685-- January 27, 1996 ...[Visit Journal]
Metalorganic chemical vapor deposition was used to deposit AlxGa1-xN active layers with varying aluminum compositions on basal plane sapphire substrate. AlxGa1-xN (x < 0.5) ultraviolet photodetectors have been fabricated and characterized with cut-off wavelengths as short as 260 nm. Carrier lifetimes on the order of 10 milliseconds were estimated from frequency dependent measurements of the responsivity. [reprint (PDF)]
 
14.  Fabrication of Indium Bumps for Hybrid Infrared Focal Plane Array Applications
J. Jiang, S. Tsao, T. O'Sullivan, M. Razeghi, and G.J. Brown
Infrared Physics and Technology, 45 (2)-- March 1, 2004 ...[Visit Journal]
Hybrid infrared focal plane arrays (FPAs) have found many applications. In hybrid IR FPAs, FPA and Si read out integrated circuits (ROICs) are bonded together with indium bumps by flip-chip bonding. Taller and higher uniformity indium bumps are always being pursued in FPA fabrication. In this paper, two indium bump fabrication processes based on evaporation and electroplating techniques are developed. Issues related to each fabrication technique are addressed in detail. The evaporation technique is based on a unique positive lithography process. The electroplating method achieves taller indium bumps with a high aspect ratio by a unique “multi-stack” technique. This technique could potentially benefit the fabrication of multi-color FPAs. Finally, a proposed low-cost indium bump fabrication technique, the “bump transfer”, is given as a future technology for hybrid IR FPA fabrication. [reprint (PDF)]
 
14.  Long-Wavelength InAsSb Photoconductors Operated at Near Room Temperatures (200-300 K)
J.D. Kim, D. Wu, J. Wojkowski, J. Piotrowski, J. Xu, and M. Razeghi
Applied Physics Letters., 68 (1),-- January 1, 1996 ...[Visit Journal]
Long-wavelength InAs1−xSbx photoconductors operated without cryogenic cooling are reported. The devices are based on p-InAs1−xSbx/p-InSb heterostructures grown on (100) semi-insulating GaAs substrates by low pressure metalorganic chemical vapor deposition (LP‐MOCVD). Photoreponse up to 14 μm has been obtained in a sample with x=0.77 at 300 K, which is in good agreement with the measured infrared absorption spectra. The corresponding effective lifetime of ≊0.14 ns at 300 K has been derived from stationary photoconductivity. The Johnson noise limited detectivity at λ=10.6 μm is estimated to be about 3.27×107 cm· Hz½/W at 300 K. [reprint (PDF)]
 
14.  Room temperature operation of InxGa1-xSb/InAs type-II quantum well infrared photodetectors grown by MOCVD
D. H. Wu, Y. Y. Zhang, and M. Razeghi
Applied Physics Letters 112, 111103-- March 14, 2018 ...[Visit Journal]
We demonstrate room temperature operation of In0.5Ga0.5Sb/InAs type-II quantum well photodetectors on InAs substrate grown by metal-organic chemical vapor deposition. At 300 K, the detector exhibits a dark current density of 0.12 A/cm2, peak responsivity of 0.72 A/W corresponding to a quantum efficiency of 23.3%, with calculated specific detectivity of 2.4×109 cm.Hz1/2/W at 3.81 μm. [reprint (PDF)]
 
14.  Room temperature terahertz quantum cascade laser sources with 215 μW output power through epilayer-down mounting
Q. Y. Lu, N. Bandyopadhyay, S. Slivken, Y. Bai, and M. Razeghi
Appl. Phys. Lett. 103, 011101 (2013)-- July 1, 2013 ...[Visit Journal]
We report room temperature terahertz (THz) quantum cascade laser sources with high power based on difference frequency generation. The device is Čerenkov phase matched and spectrally purified with an integrated dual-period distributed-feedback grating. Symmetric current injection and epilayer-down mounting of the device onto a patterned submount are used to improve the electrical uniformity and heat removal, respectively. The epilayer-down mounting also allows for THz anti-reflective coating to enhance the THz outcoupling efficiency. Single mode emission at 3.5 THz with a side-mode suppression ratio and output power up to 30 dB and 215  μW are obtained, respectively. [reprint (PDF)]
 
14.  Minority electron unipolar photodetectors based on Type-II InAs/GaSb/AlSb superlattices for very long wavelength infrared detection
B.M. Nguyen, S. Bogdanov, S. Abdollahi Pour, and M. Razeghi
Applied Physics Letters, Vol. 95, No. 18, p. 183502-- November 2, 2009 ...[Visit Journal]
We present a hybrid photodetector design that inherits the advantages of traditional photoconductive and photovoltaic devices. The structure consists of a barrier layer blocking the transport of majority holes in a p-type semiconductor, resulting in an electrical transport due to minority carriers with low current density. By using the M-structure superlattice as a barrier region, the band alignments can be experimentally controlled, allowing for the efficient extraction of the photosignal with less than 50 mV bias. At 77 K, a 14 µm cutoff detector exhibits a dark current 3.3 mA·cm−2, a photoresponsivity of 1.4 A/W, and the associated shot noise detectivity of 4×1010 Jones. [reprint (PDF)]
 
14.  Semiconductor ultraviolet detectors
M. Razeghi and A. Rogalski
Journal of Applied Physics Applied Physics Review 79 (10)-- May 15, 1996 ...[Visit Journal]
In this review article a comprehensive analysis of the developments in ultraviolet (UV) detector technology is described. At the beginning, the classification of UV detectors and general requirements imposed on these detectors are presented. Further considerations are restricted to modern semiconductor UV detectors, so the basic theory of photoconductive and photovoltaic detectors is presented in a uniform way convenient for various detector materials. Next, the current state of the art of different types of semiconductor UV detectors is presented. Hitherto, the semiconductor UV detectors have been mainly fabricated using Si. Industries such as the aerospace, automotive, petroleum, and others have continuously provided the impetus pushing the development of fringe technologies which are tolerant of increasingly high temperatures and hostile environments. As a result, the main efforts are currently directed to a new generation of UV detectors fabricated from wide band-gap semiconductors the most promising of which are diamond and AlGaN. The latest progress in development of AlGaN UV detectors is finally described in detail. [reprint (PDF)]
 
14.  Photoluminescence characteristics of polar and nonpolar AlGaN/GaN superlattices
Z. Vashaei, C. Bayram, P. Lavenus, and M. Razeghi
Applied Physics Letters, Vol. 97, No. 12, p. 121918-1-- September 20, 2010 ...[Visit Journal]
High quality Al0.2Ga0.8N/GaN superlattices (SLs) with various (GaN) well widths (1.6 to 6.4 nm) have been grown on polar c-plane and nonpolar m-plane freestanding GaN substrates by metal-organic chemical vapor deposition. Atomic force microscopy, high resolution x-ray diffraction, and photoluminescence (PL) studies of SLs have been carried out to determine and correlate effects of well width and polarization field on the room-temperature PL characteristics. A theoretical model was applied to explain PL energy-dependency on well width and crystalline orientation taking into account internal electric field for polar substrate. Absence of induced-internal electric field in nonpolar SLs was confirmed by stable PL peak energy and stronger PL intensity as a function of excitation power density than polar ones. [reprint (PDF)]
 
14.  Comparison of type-II superlattice and HgCdTe infrared detector technologies
Jagmohan Bajaj; Gerry Sullivan; Don Lee; Ed Aifer; Manijeh Razeghi
Proc. SPIE 6542, Infrared Technology and Applications XXXIII, 65420B (May 14, 2007)-- May 14, 2007 ...[Visit Journal]
Performance of HgCdTe detector technology surpasses all others in the mid-wave and long-wave infrared spectrum. This technology is relatively mature with current effort focused on improving uniformity, and demonstrating increased focal plane array (FPA) functionality. Type-II superlattice (InAs-GaSb and related alloys) detector technology has seen rapid progress over the past few years. The merits of the superlattice material system rest on predictions of even higher performance than HgCdTe and of engineering advantages. While no one has demonstrated Type-II superlattice detectors with performance superior to HgCdTe detectors, the difference in performance between these two technologies is decreasing. In this paper, we review the status and highlight relative merits of both HgCdTe and Type-II superlattice based detector technologies. [reprint (PDF)]
 
14.  High magnetic field studies of the two‐dimensional electron gas in GaInAs‐InP superlattices
J. C. Portal; R. J. Nicholas; M. A. Brummell; M. Razeghi; M. A. Poisson
J. C. Portal, R. J. Nicholas, M. A. Brummell, M. Razeghi, M. A. Poisson; High magnetic field studies of the two‐dimensional electron gas in GaInAs‐InP superlattices. Appl. Phys. Lett. 1 August 1983; 43 (3): 293–295.-- August 1, 1983 ...[Visit Journal]
We report the observation of Shubnikov–de Haas oscillations in superlattices of GaInAs and InP, showing evidence of two‐dimensional behavior. The electron g‐factor is deduced from both the criteria for resolution of a spin splitting by comparison with the broadening parameter Γ, and from the tilted field method, and is shown to increase with increasing resolution of the Landau levels in a manner consistent with the theory of Ando and Uemura. In the ultraquantum limit, structure at ν=1/2 and ν=1/3 is observed. [reprint (PDF)]
 
14.  Optical losses of Al-free lasers for λ = 0.808 and 0.98 μm
H. Yi, J. Diaz, B. Lane, and M. Razeghi
Applied Physics Letters 69 (20)-- November 11, 1996 ...[Visit Journal]
In this work, we study the origin of the optical losses in Al‐free InGaAsP/GaAs (λ=0.808 μm) and InGaAs/GaAs/InGaP (λ=0.980 μm) lasers. Theoretical modeling and the experimental results indicate that the scattering of the laser beam by refractive index fluctuation in the alloys is the dominant loss in our lasers, and the loss due to the free‐carrier absorption and scattering by interface roughness are negligible. [reprint (PDF)]
 
14.  High-power high-wall plug efficiency mid-infrared quantum cascade lasers based on InP/GaInAs/InAlAs material system
M. Razeghi
SPIE Proceedings, San Jose, CA Volume 7230-11-- January 26, 2009 ...[Visit Journal]
The latest result at the Center for Quantum Devices about high power, high wall plug efficiency, mid-infrared quantum cascade lasers (QCLs) is presented. At an emitting wavelength of 4.8 µm, an output power of 3.4 W and a wall plug efficiency of 16.5% are demonstrated from a single device operating in continuous wave at room temperature. At a longer wavelength of 10.2 µm, average power as high as 2.2 W is demonstrated at room temperature. Gas-source molecular beam epitaxy is used to grow the QCL core in an InP/GaInAs/InAlAs material system. Fe-doped semiinsulating regrowth is performed by metal organic chemical vapor deposition for efficient heat removal and low waveguide loss. This accomplishment marks an important milestone in the development of high performance midinfrared QCLs. [reprint (PDF)]
 
14.  Highly Conductive Co-Doped Ga2O3Si-In Grown by MOCVD
Junhee Lee, Honghyuk Kim, Lakshay Gautam and Manijeh Razeghi
Coatings 2021, 11(3), 287; https://doi.org/10.3390/coatings11030287 ...[Visit Journal]
We report a highly conductive gallium oxide doped with both silicon and indium grown on c-plane sapphire substrate by MOCVD. From a superlattice structure of indium oxide and gallium oxide doped with silicon, we obtained a highly conductive material with an electron hall mobility up to 150 cm2/V·s with the carrier concentration near 2 × 1017 cm−3. However, if not doped with silicon, both Ga2O3:In and Ga2O3 are highly resistive. Optical and structural characterization techniques such as X-ray, transmission electron microscope, and photoluminescence, reveal no significant incorporation of indium into the superlattice materials, which suggests the indium plays a role of a surfactant passivating electron trapping defect levels. [reprint (PDF)]
 
14.  1-5 jim ROOM-TEMPERATURE PULSED OPERATION OF GalnAsP/lnP DOUBLE HETEROSTRUCTURE GROWN BY LP MOCVD
Manijeh Razeghi, P. Hirtz, J.P. Larivain, R. Blondeau, B. de Crémoux, J.P. Duchemin,
ELECTRONICS LETTERS, vol. 17, no.18-- September 3, 1981 ...[Visit Journal]
The letter reports the first successful room-temperature pulsed operation of a broad-area contact laser of GaInAsP/InP double heterostructure, grown by LP MOCVD, emitting at 1.5 μm. Pulsed thresholds as low as 2.5 kA/cm2 have been obtained for 1.5 μm, for an active layer thickness of 0.48 μm. This is equal to a current density per micrometre of 5.2 kA cm−2 μm−1. InxGa1−xAsyP1−y, III, III, V, V alloys are of great interest for use in infra-red devices. They can be grown lattice matched on InP over a wide range of compositions. The resulting bandgap (1.35–0.75 eV) covers a spectral range which contains the region of lowest losses and lowest dispersion in modern optical fibres. This property makes In1−xGaxASyP1−y, very attractive as a semiconductor laser and detector material for future fibre communication systems. [reprint (PDF)]
 
14.  Low pressure metalorganic chemical vapor deposition of high quality AlN and GaN thin films on sapphire and silicon substrates
P. Kung, X. Zhang, E. Bigan, and M. Razeghi
Optoelectronic Integrated Circuit Materials, Physics and Devices, SPIE Conference, San Jose, CA; Proceedings, Vol. 2397-- February 6, 1995 ...[Visit Journal]
High quality AlN and GaN epilayers have been grown on basal plane sapphire by low pressure metalorganic chemical vapor deposition. The X-ray rocking curve linewidth of the AlN and GaN films were about 100 and 30 arcsecs respectively. Sharp absorption edges were determined at 6.1 and 3.4 eV respectively. Successful donor-bound excitonic luminescence emissions were detected for GaN films grown on sapphire and silicon. Two additional lines at 3.37 and 3.31 eV were observed on GaN on sapphire and assumed to be impurity-related. Doping of GaN layers was achieved with magnesium. Mg-related photoluminescence emissions were successfully detected on as-grown samples, without any post-growth treatment. [reprint (PDF)]
 

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