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| 14. | Conduction‐ and valence‐band offsets in GaAs/Ga0.51In0.49P single quantum wells grown by metalorganic chemical vapor deposition D. Biswas; N. Debbar; P. Bhattacharya; M. Razeghi; M. Defour; F. Omnes Appl. Phys. Lett. 56, 833–835 (1990)-- February 26, 1990 ...[Visit Journal] We have independently estimated the conduction- and valence-band offsets D.Ec and D.Ev in
GaAs/Gao .
51 Ino49 P quantum wells by measuring the capacitance transient resulting from
thermal emission of carriers from the respective wens. The heterostructure samples were
grown by low-pressure metalorganic chemical vapor deposition. The band offsets are
extrapolated from the emission activation energies with appropriate corrections. The estimated
values of AEc and AEv are 0.198 and 0.285 eV, respectively. [reprint (PDF)] |
| 14. | Ultraviolet Detectors for AstroPhysics Present and Future M. Ulmer, M. Razeghi, and E. Bigan Optoelectronic Integrated Circuit Materials, Physics and Devices, SPIE Conference, San Jose, CA; Proceedings, Vol. 239-- February 6, 1995 ...[Visit Journal] Astronomical instruments for the study of UV astronomy have been developed for NASA missions such as the Hubble Space Telescope. The systems that are `blind to the visible' (`solar-blind') yet sensitive to the UV that have been flown in satellites have detective efficiencies of about 10 to 20%, although typically electron bombardment charge coupled devices are higher at 30 - 40% and ordinary CCDs achieve 1 - 5%. Therefore, there is a large payoff still to be gained by further improvements in the performance of solar blind UV detectors. We provide a brief review of some aspects of UV astronomy, UV detector development, and possible technologies for the future. We suggest that a particularly promising future technology is one based on the ability of investigators to produce high quality films made of wide bandgap III-V semiconductors. [reprint (PDF)] |
| 14. | Recent advances in LWIR type-II InAs/GaSb superlattice photodetectors and focal plane arrays at the Center for Quantum Devices M. Razeghi, D. Hoffman, B.M. Nguyen, P.Y. Delaunay, E.K. Huang, and M.Z. Tidrow SPIE Porceedings, Vol. 6940, Orlando, FL 2008, p. 694009-- March 17, 2008 ...[Visit Journal] In recent years, Type-II InAs/GaSb superlattice photo-detectors have experienced significant improvements in material quality, structural designs, and imaging applications. They now appear to be a possible alternative to the state-of-the-art
HgCdTe (MCT) technology in the long and very long wavelength infrared regimes. At the Center for Quantum Devices,we have successfully realized very high quantum efficiency, very high dynamic differential resistance R0A - product LWIR Type – II InAs/GaSb superlattice photodiodes with efficient surface passivation techniques. The demonstration of high quality LWIR Focal Plane Arrays that were 100 % fabricated in - house reaffirms the pioneer position of this university-based laboratory. [reprint (PDF)] |
| 14. | Metalorganic chemical vapor deposition of monocrystalline GaN thin films on β-LiGaO2substrates P. Kung, A. Saxler, X. Zhang, D. Walker, R. Lavado, and M. Razeghi Applied Physics Letters 69 (14)-- September 30, 1996 ...[Visit Journal] We report the metalorganic chemical vapor deposition growth and characterization of monocrystalline GaN thin films on β-LiGaO2 substrates. The influence of the growth temperature on the crystal quality was studied. The structural, electrical, and optical properties of the films were assessed through scanning electron microscopy, x-ray diffraction, Hall measurements, optical transmission, photoluminescence. [reprint (PDF)] |
| 14. | Scale-up of the Chemical Lift-off of (In)GaN-based p-i-n Junctions from Sapphire Substrates Using Sacrificial ZnO Template Layers D. J. Rogers, S. Sundaram, Y. El Gmili, F. Hosseini Teherani, P. Bove, V. Sandana, P. L. Voss, A. Ougazzaden, A. Rajan, K.A. Prior, R. McClintock, & M. Razeghi Proc. SPIE 9364, Oxide-based Materials and Devices VI, 936424 -- March 24, 2015 ...[Visit Journal] (In)GaN p-i-n structures were grown by MOVPE on both GaN- and ZnO-coated c-sapphire substrates. XRD studies of the as-grown layers revealed that a strongly c-axis oriented wurtzite crystal structure was obtained on both templates and that there was a slight compressive strain in the ZnO underlayer which increased after GaN overgrowth. The InGaN
peak position gave an estimate of 13.6at% for the indium content in the active layer. SEM and AFM revealed that the top surface morphologies were similar for both substrates, with an RMS roughness (5 μm x 5 μm) of about 10 nm. Granularity appeared slightly coarser (40nm for the device grown on ZnO vs 30nm for the device grown on the GaN template) however. CL revealed a weaker GaN near band edge UV emission peak and a stronger broad defect-related
visible emission band for the structure grown on the GaN template. Only a strong ZnO NBE UV emission was observed for the sample grown on the ZnO template. Quarter-wafer chemical lift-off (CLO) of the InGaN-based p-i-n structures from the sapphire substrate was achieved by temporary-bonding the GaN surface to rigid glass support with wax and then selectively dissolving the ZnO in 0.1M HCl. XRD studies revealed that the epitaxial nature and strong preferential c-axis orientation of the layers had been maintained after lift-off. This demonstration of CLO scale-up, without compromising the crystallographic integrity of the (In)GaN p-i-n structure opens up the perspective of transferring GaN based devices off of sapphire substrates industrially. [reprint (PDF)] |
| 14. | III-Nitride Optoelectronic Devices: From ultraviolet detectors and visible emitters towards terahertz intersubband devices M. Razeghi, C. Bayram, Z. Vashaei, E. Cicek and R. McClintock IEEE Photonics Society 23rd Annual Meeting, November 7-10, 2010, Denver, CO, Proceedings, p. 351-352-- January 20, 2011 ...[Visit Journal] III-nitride optoelectronic devices are discussed. Ultraviolet detectors and visible emitters towards terahertz intersubband devices are reported. Demonstration of single photon detection efficiencies of 33% in the ultraviolet regime, intersubband energy level as low as in the mid-infrared regime, and GaN-based resonant tunneling diodes with negative resistance of 67 Ω are demonstrated. [reprint (PDF)] |
| 14. | High Power 3-12 μm Infrared Lasers: Recent Improvements and Future Trends M. Razeghi, S. Slivken, A. Tahraoui, A. Matlis, and Y.S. Park Physica E: Low-Dimensional Systems and Nanostructures 11 (2-3)-- October 1, 2001 ...[Visit Journal] In this paper, we discuss the progress of quantum cascade lasers (QCLs) grown by gas-source molecular beam epitaxy. Room temperature QCL operation has been reported for lasers emitting between 5-11 μm, with 9-11 μm lasers operating up to 425 K. Laser technology for the 3-5 μm range takes advantage of a strain-balanced active layer design. We also demonstrate record room temperature peak output powers at 9 and 11 μm (2.5 and 1 W, respectively) as well as record low 80K threshold current densities (250 A/cm²) for some laser designs. Preliminary distributed feedback (DFB) results are also presented and exhibit single mode operation for 9 μm lasers at room temperature. [reprint (PDF)] |
| 14. | III-Nitride Optoelectronic Devices: From Ultraviolet Toward Terahertz M. Razeghi IEEE Photonics Journal-Breakthroughs in Photonics 2010, Vol. 3, No. 2, p. 263-267-- April 26, 2011 ...[Visit Journal] We review III-Nitride optoelectronic device technologies with an emphasis on recent breakthroughs. We start with a brief summary of historical accomplishments and then report the state-of-the-art in three key spectral regimes: (1) Ultraviolet (AlGaN-based avalanche photodiodes, single photon detectors, focal plane arrays, and light emitting diodes), (2) Visible (InGaN-based solid state lighting, lasers, and solar cells), and (3) Near-, mid-infrared, and terahertz (AlGaN/GaN-based gap-engineered intersubband devices). We also describe future trends in III-Nitride optoelectronic devices. [reprint (PDF)] |
| 14. | Mid-infrared quantum cascade lasers with high wall plug efficiency Y. Bai, B. Gokden, S. Slivken, S.R. Darvish, S.A. Pour, and M. Razeghi SPIE Proceedings, San Jose, CA Volume 7222-0O-- January 26, 2009 ...[Visit Journal] We demonstrate optimization of continuous wave (cw) operation of 4.6 µm quantum cascade lasers (QCLs). A 19.7 µm by 5 mm, double channel processed device exhibits 33% cw WPE at 80 K. Room temperature cw WPE as high as 12.5% is obtained from a 10.6 µm by 4.8 mm device, epilayer-down bonded on a diamond submount. With the semi-insulating regrowth in a buried ridge geometry, 15% WPE is obtained with 2.8 W total output power in cw mode at room temperature. This accomplishment is achieved by systematically decreasing the parasitic voltage drop, reducing the waveguide loss and improving the thermal management. [reprint (PDF)] |
| 14. | Advances in antimonide-based Type-II superlattices for infrared detection and imaging at center for quantum devices M. Razeghi, A. Haddadi, A.M. Hoang, E.K. Huang, G. Chen, S. Bogdanov, S.R. Darvish, F. Callewaert, R. McClintock Infrared Physics & Technology, Volume 59, Pages 41-52 (2013)-- July 1, 2013 ...[Visit Journal] Type-II InAs/GaSb superlattices (T2SLs), a system of multi-interacting quantum wells, was introduced by Nobel Laureate L. Esaki in the 1970s. Since then, this material system has drawn a lot of attention especially for infrared detection. In recent years, T2SL material system has experienced incredible improvements in material quality, device structure designs and device fabrication process which elevated the performances of T2SL-based photo-detectors to a comparable level to the state-of-the-art material systems for infrared detection such as Mercury Cadmium Telluride (MCT). In this paper, we will present the current status of T2SL-based photo-detectors and focal plane arrays for imaging in different infrared regions, from SWIR to VLWIR, and the future outlook of this material system. [reprint (PDF)] |
| 14. | Recent progress of widely tunable, CW THz sources based QCLs at room temperature Manijeh Razeghi Terahertz Science and Technology, Vol.10, No.4, pp. 87-151-- December 7, 2017 ...[Visit Journal] The THz spectral region is of significant interest to the scientific community, but is one of the hardest regions to access with conventional technology. A wide range of compelling new applications are initiating a new revolution in THz technology, especially with regard to the development of compact and versatile devices for THz emission and detection. In this article, recent advances with regard to III-V semiconductor optoelectronics are explored with emphasis on how these advances will lead to the next generation of THz component technology [reprint (PDF)] |
| 14. | Very High Average Power at Room Temperature from λ ~ 5.9 μm Quantum Cascade Lasers J.S. Yu, S. Slivken, A. Evans, J. David and M. Razeghi Virtual Journal of Nanoscale Science & Technology 26-- May 26, 2003 ...[Visit Journal][reprint (PDF)] |
| 14. | New frontiers in InP based quantum devices Manijeh Razeghi Indium Phosphide and Related Materials, 2008. IPRM 2008. 20th International Conference on, pp.1,4, (2008)-- May 29, 2008 ...[Visit Journal] Recent research activities taking place at center for quantum devices (CQD) based on InP material system, especially the exploration and demonstration of the state-of-art high performance quantum cascade lasers (QCL), greatly facilitate the understanding of the underlining physical principles governing the device operation. Thanks to the endless effort putting into the semiconductor epitaxy technologies, including the Molecular Beam Epitaxy (MBE) and low pressure metal organic chemical vapor deposition (LP-MOCVD), the world has seen a close approaching to the ultimate band gap engineering. Highly sophisticated man-made heterostructure, which incorporates hundreds of alternating layers of GaInAs/AlInAs with each layer thickness and composition specifically designed, can be created within a single growth. The material quality is evidenced by the atomically abrupt interfaces. The versatility of the band gap engineering is greatly enhanced by the strain-balanced technique, which allows for growing structures with continuously tunable conduction band offset with little defects. As a result, the room temperature continuous wave (CW) wall plug efficiency (WPE) and the maximum achievable output optical power from a single device have been constantly improving. Novel waveguide incorporating the photonic crystal distributed feedback (PCDFB) mechanism is also investigated with satisfactory preliminary results. [reprint (PDF)] |
| 14. | High Temperature Continuous Wave Operation of ~8 μm Quantum Cascade Lasers S. Slivken, A. Matlis, C. Jelen, A. Rybaltowski, J. Diaz, and M. Razeghi Applied Physics Letters 74 (2)-- January 11, 1999 ...[Visit Journal] We report single-mode continuous-wave operation of a λ∼8 μm quantum cascade laser at 140 K. The threshold current density is 4.2 kA/cm² at 300 K in pulsed mode and 2.5 kA/cm² at 140 K in continuous wave for 2 mm long index-guided laser cavities of 20 μm width. Wide stripe (W ∼ 100 μm), index-guided lasers from the same wafer in pulsed operation demonstrate an average T0 of 210 K with other wafers demonstrating a T0 as high as 290 K for temperatures from 80 to 300 K. This improvement in high-temperature performance is a direct result of three factors: excellent material quality, a low-loss waveguide design, and a low-leakage index-guided laser geometry. [reprint (PDF)] |
| 14. | Geiger-mode operation of ultraviolet avalanche photodiodes grown on sapphire and free-standing GaN substrates E. Cicek, Z. Vashaei, R. McClintock, C. Bayram, and M. Razeghi Applied Physics Letters, Vol. 96, No. 26, p. 261107 (2010);-- June 28, 2010 ...[Visit Journal] GaN avalanche photodiodes (APDs) were grown on both conventional sapphire and low dislocation density free-standing (FS) c-plane GaN substrates. Leakage current, gain, and single photon detection efficiency (SPDE) of these APDs were compared. At a reverse-bias of 70 V, APDs grown on sapphire substrates exhibited a dark current density of 2.7×10−4 A/cm² whereas APDs grown on FS-GaN substrates had a significantly lower dark current density of 2.1×10−6 A/cm². Under linear-mode operation, APDs grown on FS-GaN achieved avalanche gain as high as 14 000. Geiger-mode operation conditions were studied for enhanced SPDE. Under front-illumination the 625 μm² area APD yielded a SPDE of 13% when grown on sapphire substrates compared to more than 24% when grown on FS-GaN. The SPDE of the same APD on sapphire substrate increased to 30% under back-illumination—the FS-GaN APDs were only tested under front illumination due to the thick absorbing GaN substrate. [reprint (PDF)] |
| 14. | Tight-binding theory for the thermal evolution of optical band gaps in semiconductors and superlattices S. Abdollahi Pour, B. Movaghar, and M. Razeghi American Physical Review, Vol. 83, No. 11, p. 115331-1-- March 15, 2011 ...[Visit Journal] A method to handle the variation of the band gap with temperature in direct band-gap III–V semiconductors and superlattices using an empirical tight-binding method has been developed. The approach follows closely established procedures and allows parameter variations which give rise to perfect fits to the experimental data. We also apply the tight-binding method to the far more complex problem of band structures in Type-II infrared superlattices for which we have access to original experimental data recently acquired by our group. Given the close packing of bands in small band-gap Type-II designs, k·p methods become difficult to handle, and it turns out that the sp3s* tight-binding scheme is a practical and powerful asset. Other approaches to band-gap shrinkage explored in the past are discussed, scrutinized, and compared. This includes the lattice expansion term, the phonon softening mechanism, and the electron-phonon polaronic shifts calculated in perturbation theory. [reprint (PDF)] |
| 14. | Demonstration of Zn-Diffused Planar Long-Wavelength Infrared Photodetector Based on Type-II Superlattice Grown by MBE Rajendra K. Saroj, Van Hoang Nguyen, Steven Slivken, Gail J. Brown and Manijeh Razeghi IEEE Journal of Quantum Electronics ...[Visit Journal] We report on a planar long-wavelength infrared photodetector based on InAs/InAs1−xSbx type-II superlattice with zinc diffusion. The superlattice structures were grown by molecular beam epitaxy, followed by a post-growth Zinc diffusion process in a metal-organic chemical vapor deposition reactor. The planar photodetectors showed a peak responsivity of 2.18 A/W, under an applied bias of −20 mV, with a corresponding quantum efficiency of 44.5%, without any anti-reflection coating, and had a 100% cut-off wavelength of 8.5 μm at 77 K temperature. These photodetectors exhibit a specific peak detectivity of 3.0×10^12 cm.Hz^1/2/W, with a dark current density of 1.5 × 10−5 A/cm2 and the differential-resistance-area product of ∼8.6 × 10−1 Ω.cm2, under an applied bias of −20 mV at 77 K. A comparative study between the planar and conventional mesa isolated photodetectors was also carried out. [reprint (PDF)] |
| 14. | Current status and potential of high power mid-infrared intersubband lasers S. Slivken, Y. Bai, B. Gokden, S.R. Darvish and M. Razeghi SPIE Proceedings, San Francisco, CA (January 22-28, 2010), Vol. 7608, p. 76080B-1-- January 22, 2010 ...[Visit Journal] Some of the recent advances in high power quantum cascade laser development will be reviewed in this paper. Research areas explored include short wavelength (λ <4 µm) lasers, high performance strain-balanced heterostructures, and high power long wavelength (7< λ< 16 µm) lasers. Near λ=4.5 µm, highlights include demonstration of 18% continuous wave wallplug efficiency at room temperature, 53% pulsed wallplug efficiency at 40 K, and 120 W of peak power output from a single device at room temperature. Near λ ~10 µm, up to 0.6 W of continuous output power at room temperature has also been demonstrated, with pulsed efficiencies up to 9%. [reprint (PDF)] |
| 14. | Photoluminescence study of InAsSb/InAsSbP heterostructures grown by low-pressure metalorganic chemical vapor deposition S. Kim, M. Erdtmann, D. Wu, E. Kaas, H. Yi, J. Diaz, and M. Razeghi Applied Physics Letters 69 (11)-- September 9, 1996 ...[Visit Journal] Photoluminescence has been measured for double‐ and separate‐confinement InAsSb/InAsSbP heterostructures grown by low‐pressure metalorganic vapor deposition. A measurement of the integrated luminescence intensity at the temperature range of 77–300 K shows that over a wide range of excitation level (1–5×10² W/cm²) the radiative transitions are the dominant. mechanism below T∼170 K. Auger recombination coefficient C=C0 exp(−Ea/kT) with C0≊5×10−27 cm6/s and Ea≊40 meV has been estimated. [reprint (PDF)] |
| 14. | High power, electrically tunable quantum cascade lasers Steven Slivken; Manijeh Razeghi Proc. SPIE 9755, Quantum Sensing and Nano Electronics and Photonics-- February 13, 2016 ...[Visit Journal] Mid-infrared laser sources (3-14 μm wavelengths) which have wide spectral coverage and high output power are attractive for many applications. This spectral range contains unique absorption fingerprints of most molecules, including toxins, explosives, and nerve agents. Infrared spectroscopy can also be used to detect important biomarkers, which can be used for medical diagnostics by means of breath analysis. The challenge is to produce a broadband midinfrared source which is small, lightweight, robust, and inexpensive. We are currently investigating monolithic solutions using quantum cascade lasers. A wide gain bandwidth is not sufficient to make an ideal spectroscopy source. Single mode output with rapid tuning is desirable. For dynamic wavelength selection, our group is developing multi-section laser geometries with wide electrical tuning (hundreds of cm-1). These devices are roughly the same size as a traditional quantum cascade lasers, but tuning is accomplished without any external optical components. When combined with suitable amplifiers, these lasers are capable of multi-Watt single mode output powers. This manuscript will describe our current research efforts and the potential for high performance, broadband electrical tuning with the quantum cascade laser. [reprint (PDF)] |
| 14. | GaInAs/InP nanopillar arrays for long wavelength infrared detection A. Gin, Y. Wei, A. Hood, D. Hoffman, M. Razeghi and G.J. Brown SPIE Conference, Jose, CA, Vol. 5732, pp. 350-- January 22, 2005 ...[Visit Journal] Nanopillar devices have been fabricated from GaInAs/InP QWIP material grown by MOCVD. Using electron beam lithography and reactive ion etching techniques, large, regular arrays of nanopillars with controllable diameters ranging from 150 nm to less than 40 nm have been reproducibly formed. Photoluminescence experiments demonstrate a strong peak wavelength blue shift for nanopillar structures compared to the as-grown quantum well material. Top and bottom metal contacts have been realized using a polyimide planarization and etchback procedure. I-V and noise measurements have been performed. Optical measurements indicate photoconductive response in selected nanopillar arrays. Device peak wavelength response occurs at about 8 µm with peak device responsivity of 420 mA/W. Peak detectivity of 3×108 cm·Hz½/W has been achieved at -1V bias and 30 K. [reprint (PDF)] |
| 14. | Optical Investigations of GaAs-GaInP Quantum Wells Grown on the GaAs, InP, and Si Substrates H. Xiaoguang, M. Razeghi Applied Physics Letters 61 (14)-- October 5, 1992 ...[Visit Journal] We report the first photoluminescence investigation of GaAs‐Ga0.51In0.49P lattice matched multiquantum wells grown by the low pressure metalorganic chemical vapor deposition simultaneously in the same run on GaAs, Si, and InP substrates. The sharp photoluminescence peaks indicate the high quality of the samples on three different substrates. The temperature dependence of the photoluminescence indicates that the intrinsic excitonic transitions dominate at low temperature and free‐carrier recombinations at room temperature. The photoluminescence peaks of the samples grown on Si and InP substrates shift about 15 meV from the corresponding peaks of the sample grown on the GaAs substrate. Two possible interpretations are provided for the observed energy shift. One is the diffusion of In along the dislocation threads from GaInP to GaAs and another is the localized strain induced by defects and In segregations. [reprint (PDF)] |
| 14. | High operating temperature MWIR photon detectors based on Type II InAs/GaSb superlattice M. Razeghi, S. Abdollahi Pour, E.K. Huang, G. Chen, A. Haddadi and B.M. Nguyen SPIE Proceedings, Infrared Technology and Applications XXXVII, Orlando, FL, Vol. 8012, p. 80122Q-1-- April 26, 2011 ...[Visit Journal] Recent efforts have been paid to elevate the operating temperature of Type II superlattice Mid Infrared photon detectors. Using M-structure superlattice, novel device architectures have been developed, resulting in significant improvement of the device performances. In this paper, we will compare different photodetector architectures and discuss the optimization scheme which leads to almost one order of magnitude of improvement to the electrical performance. At 150K, single element detectors exhibit a quantum efficiency above 50%, and a specific detectivity of 1.05x10(12) cm.Hz(1/2)/W. BLIP operation with a 300K background and 2π FOV can be reached with an operating temperature up to 180K. High quality focal plane arrays were demonstrated with a noise equivalent temperature difference (NEDT) of 11mK up to 120K. Human body imaging is achieved at 150K with NEDT of 150mK. [reprint (PDF)] |
| 14. | GaInN/GaN Multi-Quantum Well Laser Diodes Grown by Low-Pressure Metalorganic Chemical Vapor Deposition P. Kung, A. Saxler, D. Walker, A. Rybaltowski, X. Zhang, J. Diaz, and M. Razeghi MRS Internet Journal of Nitride Semiconductor Research 3 (1)-- January 1, 1998 ...[Visit Journal] We report the growth, fabrication and characterization of GaInN/GaN multi-quantum well lasers grown on (00·1) sapphire substrates by low pressure metalorganic chemical vapor deposition. The threshold current density of a 1800 µm long cavity length laser was 1.4 kA/cm² with a threshold voltage of 25 V. These lasers exhibited series resistances of 13 and 14 Ω at 300 and 79 K, respectively. [reprint (PDF)] |
| 14. | Quantum Sensing Using Type-II InAs/GaSb Superlattice for Infrared Detection M. Razeghi, A. Gin, Y. Wei, J. Bae, and J. Nah Microelectronics Journal, 34 (5-8)-- May 1, 2003 ...[Visit Journal] Large, regular arrays of bulk GaSb and InAs/GaSb Type-II superlattice pillars have been fabricated by electron beam lithography and dry etching. A 2.5 keV electron beam lithography system and metal evaporation are used to form the Au mask on superlattice and bulk substrates. Dry etching of these materials has been developed with BCl3:Ar, CH4:H2:Ar and cyclic CH4:H2:Ar/O2 plasmas. Etch temperatures were varied from 20 to 150 °C. The diameter of the superlattice pillars was below 50 nm with regular 200 nm spacing. Bulk GaSb pillars were etched with diameters below 20 nm. Areas of dense nanopillars as large as 500 μm×500 μm were fabricated. The best height/diameter aspect ratio was approximately 10:1. To date, these are the smallest diameter III–V superlattice pillar structures reported, and the first nanopillars in the InAs/GaSb material system. The basic theory of these devices and surface passivation with SiO2 and Si3N4 thin films has also been discussed. [reprint (PDF)] |
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