Research Inventy: International Journal Of Engineering And ScienceVol.2, Issue 11 (April 2013), Pp 26-35Issn(e): 2278-4721, Issn(p):2319-6483, Www.Researchinventy.Com26Investigation of Physical Properties in II-VI TernarySemiconductors of Sulphides, Selenides And Tellurides1,Alla Srivani , 2,Prof Vedam Rama Murthy , 3,G Veera raghavaiahAssistant professor in Vasireddy Venkatadri Institute Of Technology (VVIT) Engineering College, AndhraPradeshProfessor & Head Of The Department, T.J.P.S College, Guntur, Andhra Pradesh, Head Of The Department,PAS College, PedanandipaduAbstract: This work explains recent advances in II–VI Ternary Semiconductor Alloys. Current work hassignificant potential for low-cost, scalable solar cells. The close interplay among the properties of the materialsand their utility in solar cells is also briefly discussed. Almost group II–VI materials are direct band gapsemiconductors with high optical absorption and emission coefficients. Group II–VI materials are goodcandidates for use in solar cells. The Electrical and Optical Properties of II-VI Ternary Semiconductor Alloysfrom Binary Semiconductor Alloys are derived using Additivity rule with Quadratic expressions. The Electricaland Optical Properties studied in this group are confined to Refractive index, Optical Polarizability, Absorptioncoefficient and Energy gap. A comparison of these data is made with reported data available. The relative meritof Present method based on refractive indices without recourse to the experimental methods is stressed. Meritsof study of this group alloys is also outlined.Keywords: Semiconductors, II-VI Group, Sulphides, Selenides and Telluride Semiconductor alloysI. INTRODUCTIONCompound semiconductors formed from II–VI or III–V elements are key materials in plans to harvestenergy directly from sunlight in photovoltaic devices. In the search for low-cost alternatives to crystallinesilicon, thin film compound semiconductor materials are commonly used, it offer advantages over silicon. It ismore efficient to create an electric field at an interface among two different Semiconductor materials, known asa heterojunction. A typical polycrystalline thin film has a thin layer on top known as a „„window‟‟ material iflets almost of the light through the interface to the absorbing layer. The absorbing layer has to have a highabsorption to be weak in the generation of current and a suitable band gap to provide good voltage. This workshall focus on II–VI and III–VI materials, and emphasize their potential in solar cells and highlight challengesstill to be met. 7.1) CdSxSe1-xThe ternary compound CdSxSe1-x is a highly photosensitive material, and finds many practicalapplications such as in discrete and multielement photo resistors, in optical filters, signal memory devices, laserscreens, LSI circuits, Infrared imaging devices, Optoelectronic switches, linear image sensor for digitalfacsimile page scanners, Electro photography, Image intensifiers and exposure meters. CdSxSe1-x films weredeposited by thermal vacuum evaporation using the powders of CdS and CdSe synthesized in laboratory. Thefilms were characterized by x-ray diffraction, optical studies, photo conductivity studies and photoelectrochemical studies. By using the appropriate amount of pure selenium powder, sodium sulphide and triplydistilled water, sodium seleno sulphate is obtained after heating at 950C for nearly 20 hours.Before the preparation of the CdSxSe1-x thin films, CdSxSe1-x powder was prepared by sintering theappropriate ratio of CdS and CdSe powders in argon atmosphere at 5500C for 20 min. The substrates used wereglass and titanium, the substrate temperature was varied in the range of 300 to 473 K. The thickness of the filmswere found to be 2.5 m from weighing method. X-ray diffractograms of the CdSe, CdS and CdSxSe1-x filmsdeposited at different substrate temperatures in the range 30 -200°C.indicated reflections corresponding to singlephase hexagonal structure. As the substrate temperature is increased, the intensity of the peaks is found toincrease. Films prepared at a substrate temperature of 200°C indicated maximum intensity with better crystallinenature .
Investigation Of Physical Properties277.2) Zn1-xHgxTeThe Electro deposition and characterization of Zn1-xHgxTe (ZMT) thin films are reported. Many effortshave been focused on hetero structures based on popularly known ternary solid solution Zn1-xHgxTe (0<x<1)thin films as well as bulk materials. CdTe, HgCdTe and other compounds of II-VI group are sparinglypromising materials for use in optoelectronic and high-temperature electronic devices. Ternary alloys of II-VIcompounds are potential candidates for the detection of electromagnetic radiation. Zinc mercury telluride, asolid solution has a wide range of band gap tunable among 0 eV and 2.25 ev. Zn1-xHgxTe thin films Electrodeposition offers a low cost, scalable technique for the fabrication of thin films .7.3 CdSe1-xTexThe alloys of CdSe1-xTex compound have been prepared from their elements successfully with highpurity and stoichiometry ratio (x=0.0, 0.25, 0.5, 0.75 and 1.0) of Cadmium, Selenium and Telluride elements.Films of CdSe1-xTex alloys for different values of composition have been prepared by thermal evaporationmethod at cleaned glass substrates heated at 473K under sparingly low pressure of 4×10-5mbar at rate ofdeposition (3A˚/s), after that thin films have been heat treated under low pressure of 10-2mbar at 523K for twohours .7.4 Zn1-xHgxTeZn1-xHgxTe films were deposited on to SnO2 coated glass substrates from an aqueous solution bath ofZnSO4, HgCl2 and TeO2 at bath temperatures among 30°C and 80°C. Well adherent Zn1-xHgxTe thin films withcompositions various among x = 0 to x = 0.4 were obtained. The concern of growth parameters such asDeposition potential, concentration of electrolyte bath, pH and temperature on the properties of the film wasstudied. X-ray diffraction technique was used to determine composition, crystalline structure and grain size ofthe films. The films exhibited zinc blend structure with predominant (111) orientation. Optical and electricalstudies were also reported and the results are discussed .7.5 ZnxCd1-xSThe electronic and optical properties of ZnxCd1-xS thin films are fabricated using chemical spraymethod. ZnxCd1-xS thin films are deposited on glass substrates at 420°C substrate temperature. Optical data arerecorded in the wavelength range 200-700nm. In addition, the absorption coefficient is determined andcorrelated with the photon energy to estimate the direct transition energy band gap. The crystalline size anddegree of preferential orientation were found to decrease with the increase of Zn Concentration x. ZnxCd1-xSthin films have been prepared by a variety of techniques, including spray pyrolysis, ion beam deposition,molecular beam epitaxial growth and screen printing method .7.6 Pb1-xSnxTeThe optical properties of single-crystal Pb1-xSnxTe thin films in the fundamental absorption edge regionwere investigated in compositions of 0 < x < 0.24, where x is the mole fraction of SnTe. Two thin film sampleswith x = 0.70 and x = 0.85 were also studied in an try to confirm the inversion of the conduction and valencebands that had been previously predicted for this narrow-gap semiconductor. The index of refraction n and theabsorption coefficient a were determined from transmission and reflection measurements made on films 0.8 to5.0 microns thick, that were deposited on cleaved (100) faces of KCL rock salt substrates. The optical energygap was determined from the position of the absorption edge in the absorption spectrum. The index of refractionwas obtained using the interference fringe method. The absorption coefficient was calculated from an analysisof the theoretical reflectance R and transmittance T for a thin film on substrate .7.3 Method of studyThe refractive index, Optical polarizability, Absorption coefficient and Energy gap of II-VI Semiconductoralloys are evaluated by using Principle of additivity and quadratic expressions. The principle of additivity isused to study Physical properties even at very small compositions.The calculated Properties of refractive index, Optical polarizability, Absorption coefficient and Energy gapversus concentrations was fitted by equationsMethod 1A12=A1*x+A2*(1-x) + 1/1000*SQRT (A1*A2)*x*(1-x) (7.1)
Investigation Of Physical Properties28Method 2A12=A1*x+A2*(1-x) +1/1000* SQRT (A1*A2*x*(1-x)) (7.2)Method 3A12=A1*x+A2*(1-x) – 1/1000*SQRT (A1*A2)*x*(1-x) (7.3)Method 4A12=A1*x+A2*(1-x) – 1/1000*SQRT (A1*A2*x*(1-x)) (7.4)AdditivityA12=A1*x+A2*(1-x) (7.5)Where A12 denotes Refractive index (n12), Optical Polarizability (αm12), Absorption coefficient (α12) andEnergy gap (Eg12). A1 and A2 denotes Refractive index (n), Optical Polarizability (αm), Absorption coefficient(α), Energy gap (Eg) of two binary compounds forming ternary compound. The relations for OpticalPolarizability, Absorption coefficient and Energy gap from Wave length and Refractive index values are givenin previous III-Nitride MaterialsII. RESULTSThe refractive index values of Ternary semiconductor alloys are calculated by using differentexpressions of 7.1 to 7.5 for whole composition range (0<x<1) and are presented in tables from 7.1 to 7.8. Thesevalues are compared with literature reported data [11, 12]. It is found that calculated values are in goodagreement with reported values. Graphs are drawn for all these alloys by taking their composition values on xaxis and Refractive index values on y axis. These graphs are given from fig 7.1 to 7.2.The refractive indices at various wavelengths for the binary semiconductors are taken from hand book ofOptical constants of solids  are presented in table 7.1 to 7.8 along with and values. The graphsdrawn between and for these Semiconductors are shown in figures. From these graphs intercept αvalues and the slope β of the straight line are determined and γ values are calculated. All these values are givenfrom the table 7.1. The evaluated Optical Polarizabilities of Binary Semiconductors by using equation 7.8 arealso given from the table 7.6. The computed Optical polarizabilities by new dispersion relations are comparedwith reported values.The values of Molecular weight (M), density (ρ) and refractive index (n) of thesemiconductors which are required for evaluation of αm are taken from CRC Hand book .Table7.1: Optical polarizability, Absorption coefficient and Energy Gap of CdxHg1-xTeX=0.00Wavelengthλ)R.IvaluenOptical polarizabilityαmAbsorptioncoefficient(α)Energy Gape.v
Investigation Of Physical Properties2941334158423543154370442645434699490051205277548857655.8545.7845.5765.3715.2365.1054.8454.5294.1653.8153.5913.3203.0092.6642.6782.7272.7902.8442.9083.0563.1753.2393.2793.3133.3823.5860.6010.5960.5790.5590.5420.5240.4860.4590.4470.4390.4320.4190.387Calculated107.7108110111113115118121122123124128Reported82.03 2.422.214.171.124.142.12.011.831.591.351.211.051.01Calculated1.50Reported1.42Table 7.2- Optical polarizability, Absorption coefficient and Energy Gap of CdxHg1-xTeX=0.20WavelengthλR.IValuenOpticalpolarizabilityαmAbsorptioncoefficient(α)Energy Gape.v4133427544284592476949595166539156365904729382665.8545.4725.1004.7424.3974.0663.7473.4413.1482.8691.8801.4634.9434.7574.5474.3754.2354.1184.0223.9403.8713.8153.6353.4570.2540.2660.2820.2960.3090.3210.3310.3400.3480.3550.3790.407Calculated80.0Reported81.172.6571.9431.6451.3891.1700.9840.8220.6840.5660.4650.5910.2200.1930.112Calculated1.35Reported1.75Table7.3: Optical polarizability, Absorption coefficient and Energy Gap of CdxHg1-xTeX=0.29Wavelengthλ)R.IValuenOptical polarizabilityαmAbsorptioncoefficient(α)Energy Gape.v4133427544284592476949595166539156365904729382665.8545.4725.1004.7424.3974.0663.7473.4413.1482.8691.8801.4634.7814.5824.4044.2584.1354.0323.9453.8723.8153.7583.5093.4040.2640.2790.2940.3070.3190.3300.3390.3480.3550.3620.3980.416Calculated78.2Reported80.232.6042.5392.4782.4242.3782.3362.3002.2692.2442.2182.1592.334calculated1.42Reported1.85Table7.4: Optical polarizability, Absorption coefficient and Energy Gap of CdxHg1-xTe
Investigation Of Physical Properties30X=0.43Wavelengthλ)R.IValuenOptical polarizabilityαmAbsorptioncoefficient(α)Energy Gape.v4133427544284592476949595166539156365904729382665.8545.4725.1004.7424.3974.0663.7473.4413.1482.8691.8801.4634.6054.4304.2804.1594.0474.9573.8813.8203.7473.6863.4223.3410.2770.2910.3050.3170.3280.3380.3470.3550.3640.3720.4130.427Calculated79.44Reported79.402.2391.9111.6261.3791.6660.9820.8230.6870.6700.6540.0990.090Calculate1.30Reported1.05Table7.5: Optical polarizability, Absorption coefficient and Energy Gap of CdxHg1-xTeX=0.76Wavelengthλ)R.IValuenOptical polarizabilityαmAbsorptioncoefficient(α)Energy Gape.v4133427544284592476949595166539156365904729382665.8545.4725.1004.7424.3974.0663.7473.4413.1482.8691.8801.4634.4834.3284.1954.0813.9853.9033.8383.7613.6963.6653.3683.2830.2870.3000.3130.3240.3350.3440.3520.3620.3710.3750.4220.438Calculated81.49Reported78.83 2.0321.7381.4811.2581.0640.8980.7530.6260.1780.2740.1720.102Calculated1.25Reported1.65Table7.06: Optical polarizability, Absorption coefficient and Energy Gap of CdxHg1-xTeX=0.86Wavelengthλ)R.IValuenOptical polarizabilityαmAbsorptioncoefficient(α)Energy Gape.v4133427544284592476949595166539156365904729382665.8545.4725.1004.7424.3974.0663.7473.4413.1482.8691.8801.4634.3434.2084.0923.9923.9093.8373.7583.6903.6583.5463.3133.2870.2990.3120.3230.3340.3440.3520.3620.3720.3760.3930.4320.447Calculated79.20Reported78.041.8011.5431.3171.1200.9490.8010.6710.5820.4640.3770.1530.091Calculated2.30Reported2.05Table7.07: Optical polarizability, Absorption coefficient and Energy Gap of CdxHg1-xTe
Investigation Of Physical Properties31X=0.99Wavelengthλ)R.IValuenOptical polarizabilityαmAbsorptioncoefficient(α)Energy Gape.v4133427544284592476949595166539156365904729382665.8545.4725.1004.7424.3974.0663.7473.4413.1482.8691.8801.4634.1964.0843.9873.9063.8233.7463.6963.5953.5003.4253.2253.1530.3130.3240.3380.3440.3540.3640.3710.3880.4000.4120.4490.464Calculated77.96Reported77.165.8735.0424.2903.6773.1142.6252.2081.8171.4971.2220.5000.297Calculated2.50Reported2.36Table7.08: Optical polarizability, Absorption coefficient and Energy Gap of CdxHg1-xTeX=1.00Wavelengthλ)R.IValuenOpticalpolarizabilityαmAbsorptioncoefficient(α)Energy Gape.v41334275442845924769495951665391563659045.8545.4725.1004.7424.3974.0663.7473.4413.1482.8694.0503.9613.8723.7873.7833.6353.5193.4403.3783.3220.3280.3380.3480.3590.3650.3790.3970.4100.4200.431Calculated75.66Reported76.335.6784.8894.1813.5593.0322.5412.1061.7451.4400.180Calculated2.45Reported2.67Table 7.09 CdSxSe1-xCompositionx1-x R.IMethod1R.IMethod2R.IMethod3R.IMethod4R.IReported0.000.360.580.791.001.000.640.420.210.002.4572.4082.3772.3482.3192.4572.4082.3782.3482.3192.4572.4072.3762.3472.3192.4572.4062.3762.3472.3192.4572.4002.3682.3422.319
Investigation Of Physical Properties33Research on Physical properties of II-VI Ternary Semiconductor alloys is due to operating characteristics ofSemiconductor devices depending critically on the physical properties of the constituent materials. Thetheoretical study has been made on II-VI Ternary Semiconductor alloys as a function of composition x.The various applications of II-VI Semiconductor Alloys of CdSxSe1-X, CdSe1-xTex, Zn1-xHgxTe, CdxHg1-xTe as Electronic, Optical and Optoelectronic devices are determined by elementary material properties ofRefractive index, Optical Polarizability, Absorption coefficient, Energy gap and Mobility. Photonic crystals,wave guides and solar cells require knowledge of refractive index and Energy gap of all above Arsenide Groupalloys. The Energy gap of Semiconductor alloys determines Threshold for absorption of photons insemiconductors. Refractive index is measure of transparency of Semiconductor alloys to incident radiation.Refractive index and Energy gap of Ternary Semiconductor alloys has significant impact on Band structure.High absorption coeﬃcient Semiconductor alloys can be used for fabricating in thin ﬁlm hetero junctionphotovoltaic (PV) devices.Applications on these Ternary Semiconductor Alloy span from communications to biomedicalengineering. Narrow band gap semiconductor alloys allow Hetero junction Bipolar Transistors to presentterahertz (THz) operation capability. Sensors of this type exploit the unique piezoelectric, polarizationcharacteristics, as well as the high temperature stability of wide-band gap semiconductors in order to allowstable operation with high sensitivity. Using this material system one can also explore the possibility ofdeveloping fundamental sources operating in the Terahertz regime and employing Micro-Electro MechanicalSystems (MEMS) approaches.Recent progress and new concepts using narrow and wide-band gap Ternary semiconductor alloys ofCdSxSe1-X, CdSe1-xTex, Zn1-xHgxTe, CdxHg1-xTe and device concepts such quantum wells with very high mobilityand plasma waves will lead in Terahertz detectors and emitters. Semiconductors of this type may also be usedfor other novel applications such as spintronics and field emission. Terahertz signal sources based on superlattices have explored applications cover a wide range of devices, circuits and components for communications,sensors and biomedical engineering.Research on Physical properties of II-VI Ternary Semiconductor alloys is due to operatingcharacteristics of Semiconductor devices depend critically on the physical properties of the constituentmaterials.The Refractive index of Group II-VI Arsenide Semiconductor alloys of CdSxSe1-x reducessignificantly from 2.457 to 2.319 by adding a small amount of Sulphur to CdSe and also in Zn1-xCdxTeRefractive index decreases from 3.56 to 2.50 by adding small amount of Cadmium to ZnTe. But Refractiveindex of CdSe1-xTex increases from 2.46 to 2.50 by adding small amount of Tellurium to CdSe. This occurs dueto the large disparity in the electro negativity and the atomic sizeThe binding which was totally covalent for the elemental Semiconductors, has an ionic component inII-VI Arsenide Ternary semiconductor alloys. The percentage of the ionic binding energy varies for variousSemiconductor alloys. The percentage of ionic binding energy is closely related to electro negativity of theelements and varies for various compounds. The electro negativity describes affinity of electrons of the element.In a binding situation the more electro negative atoms will be more strongly bind the electrons than its partnerand therefore carry net negative charge. The difference in electro negativity of the atoms in a compoundsemiconductor gives first measure for Energy gap. A more electro negative element replacing a certain latticeatom will attract the electrons from the partner more strongly, become more negatively charged and thusincrease the ionic part of the binding. This has nothing to do with its ability to donate electrons to conductionband or accept electrons from the valence band.Mobility at high doping concentration is always decreased byscattering at the ionized dopants. Band gap increases with Electro negativity difference between the elements.Bond strength decreases with decrease of orbital overlapping. Electrons are more stabilized by more electronegativity atom..Semiconductor Materials with higher absorption coefficients more readily absorb photons, whichexcite electrons into the conduction band. Knowing absorption coefficients of various II-VI TernarySemiconductor alloys of CdSxSe1-x, CdSe1-xTeX, Zn1-xCdxTe, CdxHg1-xTe, ZnxCd1-xS aids engineers in determiningwhich material to use in their solar cell designs. The absorption coefficient determines how far into a materiallight of a particular wavelength can penetrate before it is absorbed. In a material with a low absorptioncoefficient, light is only poorly absorbed, and if the material is thin enough, it will appear transparent to thatwavelength. The absorption coefficient depends on the material and also on the wavelength of light which is
Investigation Of Physical Properties34being absorbed. II-VI Ternary Semiconductor Alloys have a sharp edge in their absorption coefficient, sincelight which has energy below the band gap does not have sufficient energy to excite an electron into theconduction band from the valence band. Consequently this light is not absorbed.The plot of hν versus (αhν)2of III-Arsenide Ternary Semiconductor alloys of CdxHg1-xTe at variousconcentrations of Cd forms a straight line, it can normally be inferred that there is a direct band gap, measurableby extrapolating the straight line to the α=0 axis. On the other hand, if a plot of hν versus αhν1/2forms a straightline, it can normally be inferred that there is an indirect band gap, measurable by extrapolating the straight lineto α=0 axis. Measuring the absorption coefficient for Ternary Semiconductor Alloys gives information about theband gaps of the material. Knowledge of these band gaps is extremely important for understanding the electricalproperties of a semiconductor. Measuring low values of Absorption coefficient (α) with high accuracy is photothermal deﬂection spectroscopy which measures the heating of the environment which occurs when aSemiconductor sample absorbs light.The energy levels adjust with alloy concentration, resulting in varying amount of absorption at differentwavelengths in II-VI Ternary Semiconductor alloys of CdSxSe1-X, CdSe1-xTex, Zn1-xHgxTe, and CdxHg1-xTe. Thisvariation in optical properties is described by the material optical constants, commonly known as Refractiveindex (n). The optical constants shape corresponds to the material‟s electronic transitions. Thus, the opticalconstants become a “fingerprint” for the semiconductor alloys.The Optical Polarizability of II-VI Ternary Semiconductor alloys CdSxSe1-x reduces significantly from83.855 to 70.439 by adding a small amount of Sulphur to CdSe, and in Zn1-xCdxTe Optical Polarizabilityincreases from 95.971 to 103.286 by adding small amount of Cadmium to ZnTe. This occurs due to the largedisparity in the electro negativityIn II-VI Ternary Semiconductor alloys replacing existing atom with high Atomic number results inDecreasing of Energy gap due to increase of charge carriers with increase of mobility and by replacing existingatoms of low atomic number result in Increase of Energy gap due to decrease of charge carriers transmittingfrom valence band to conduction band with decrease of mobility.
Investigation Of Physical Properties35ACKNOWLEDGEMENT:Foremost, I would like to express my sincere gratitude to my advisor Prof Vedam Ramamurthy for thecontinuous support of my Ph.D study, Management members of my working college of VVIT and Head of theScience and Humanities departmentReferences:-. Zimmer, J. P.; Kim, S. W.; Ohnishi, S.; Tanaka, E.; Frangioni, J. V.; Bawendi, M. G. J. Am. Chem. Soc. 2006, 128, 2526-2527. Reddy R.R., Rama gopal k., Narasimhulu k., Siva Sankara Reddy L., “Interrelationship between structural, optical, electronic andelastic properties of materials., Journal of Alloys and Compounds 473 (2009) 28–35. Mahalingam T., Kathalingam A., Velumani S., Soonil Lee., Hosun Moon., Yong Deak Kim., “Electrosynthesis And Studies onZn1-xHgxTe Thin Films, Journal of New Materials for Electrochemical Systems 10, 21-25 (2007). Bard, A. J.; Faulkner, L. R. in Electrochemical Methods: Fundamentals and Applications, 2ndEd. John Wiley & sons: New York,2001, p 290. Suparna Sadhu and Amitavapatra “Synthesis and spectroscopic study of high quality alloy CdxZn1-xS nanocrystals., J. Chem.Sci., Vol. 120, No. 6, November 2008, pp. 557–564.. Becerril M*, Silva-Lopez H, and Zelaya-Angel O., “Band gap energy in Zn-rich Zn1-xCdxTe thin ﬁlms grown by r.f. sputtering.REVISTA MEXICANA DE F ISICA 50 (6) 588–593 DECEMBER 2004.. Venu gopal Rayapati , Ping-I Lin, and Yit-Tsong Chen Photoluminescence and Raman Scattering from Catalytically GrownZnxCd1-xS Alloy., J. Phys. Chem. B 2006, 110, 11691-11696. http://www.cleanroom.byu.edu/EW_ternary.phtml-BRIGHAM YOUNG UNIVERSITY, Department of Electrical and ComputerEngineering, “Direct Energy Band Gap in Ternary Semiconductors”.. Sathyalatha K.C PhD Thesis”Optical and related properties of few II-VI and III-V Semiconductors” SKU University,Anantapuram (2012). 10)Murthy V.R, Jeevan kumar.R and Subbaiah, D.V., “New dispersion relation: Relation to ORD, MORD and MolecularPolarization‟ Proc viii Annual conference on IEEE/EMBS, Texas, XIV, P. 1636-1639 (1986).. Edward D. Palik, Handbook of Optical Constants of Solids, Volume 2, Academic press, 21 march 1991. William M. Haynes, David R. Lide, CRC Hand book of Physics and chemistry, Taylor & Francis Group, 91stEdition, 26-May-2010.. Ravindra N M, preethi Ganapathi, Jinsoo choi Energy gap-Refractive index relations in Semiconductors- An overviewDepartment of physics, New jersey institute of technology, New york, USA, Infrared physics and Technology (2006).