| Infrared detection material and method of production -> Monitor Keywords |
|
|
 
Infrared detection material and method of productionInfrared detection material and method of production description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20060102870, Infrared detection material and method of production. Brief Patent Description - Full Patent Description - Patent Application Claims
PRIORITY INFORMATION [0001] This application claims priority from U.S. provisional applications Ser. Nos. 60/620,612 filed on Oct. 20, 2004, and 60/629,622 filed on Nov. 19, 2004, both of which are incorporated by reference herein in their entireties. BACKGROUND OF THE INVENTION [0002] The invention relates to a quaternary compound semiconductor comprising arsenic (As), selenium (Se), tellurium (Te) and copper (Cu) atoms, whose covalent atomic arrangement is predominantly amorphous or polycrystalline, and whose electronic properties can be tuned by an adjustment of the molar concentration of tellurium and copper atoms in the said compound, and whose electronic bandgap can be tuned to detect infrared radiation energy. The invention also relates to the method of fabricating thin films of this quaternary compound semiconductor at low cost. [0003] There has been a major effort on the study of infrared semiconductor materials, such as In--Ga--As--P, Pd--Te and Hg--Cd--Te crystalline compounds, and on the monolithic integration of those materials on a variety of integrated circuit substrates for the fabrication of infrared detectors and infrared digital cameras. Unfortunately, the large lattice constant mismatches between the substrates and the epitaxial layers cause many defects to be created in crystalline semiconductor compound thin film, with detrimental effects on the material integrity, on the infrared detection performance and on the ability to fabricate infrared detectors or large infrared focal plane arrays at low cost. Some of the major problems facing heteroepitaxial growth of crystalline infrared compounds are the lattice constant mismatch, polarity mismatch and thermal expansion mismatch with the substrate, such that infrared device fabrication typically requires the use of expensive and exotic substrates, which involve severe constraints over the growth size and thickness of the heteroepitaxial layers, and which involve expensive fabrication processes such as molecular beam epitaxy. The development of crystalline infrared compounds for infrared detectors and cameras has been hampered time and again by the costs and constraints involving the heteroepitaxial growth of crystalline infrared compounds. [0004] Continuous progress in science and technology imposes new and increased requirements on semiconducting materials. Germanium, silicon and the III-V semiconducting compounds no longer satisfy all these varied and specific requirements, which involve advanced infrared detection, material stability, CMOS compatibility and low fabrication costs. The search is for new more effective semiconducting materials with properties that can be varied in a wide range. Chalcogenide compounds, having either an amorphous, glassy or polycrystalline atomic arrangement, are produced with analogs of oxygen, namely sulfur, selenium and tellurium, and are promising in many respects. Depending on the composition, the conductivity of amorphous chalcogenide compounds varies in the range .sigma.=10.sup.-2 to .sigma.=10.sup.-18 .OMEGA..sup.-1cm.sup.-1, and the bandgap energy is in the range Eg=0.1 eV to Eg=3 eV. The conductivity increases exponentially with temperature and they have pronounced photoconductivity. SUMMARY OF THE INVENTION [0005] It is an object of the invention to provide a new type of infrared detection material and a method of producing thin films of the same material on standard substrates at low processing costs. The invention relates to a quaternary compound semiconductor comprising arsenic (As), selenium (Se), tellurium (Te) and copper (Cu) atoms with adjustable molar concentrations during processing, whose atomic arrangement is predominantly amorphous or polycrystalline, and dominated by covalent chemical bonds between the said atoms. The amorphous nature of the atomic arrangement gives predominance to short range atomic order, eliminating the constraints of lattice constant mismatch and polarity mismatch with the substrate, which opens the way to wide chemical compositional adjustments and to lower-cost deposition processes such as thermal evaporation or sputtering. The flexibility of the chemical formula can be used to adjust the electronic properties of the semiconductor compound. [0006] In one embodiment, the molar concentration of tellurium and copper atoms in the said quaternary compound is adjusted to modify the density of localized and extended electronic states in the material, and to modify the energy difference between the valence and conduction bands. This compositional adjustment provides a way to modify significantly the properties of the semiconductor compound, such as increasing its electrical conduction by up to 11 orders of magnitude and decreasing its electronic bandgap by 1 order of magnitude, and to tune the material for the detection of infrared light waves having energies between 1.8 eV and 0.15 eV. In another embodiment, a thin film of semiconductor compound with As.sub.wSe.sub.xTe.sub.yCu.sub.z chemical formulation is obtained by a thermal co-evaporation of As.sub.2Se.sub.3 glass and CuTe mineral. [0007] The quaternary semiconductor compound comprising arsenic (As), selenium (Se), tellurium (Te) and copper (Cu) atoms can be produced in thin film form by a mixed physical vapor deposition process involving a vapor combination of at least two different vaporized sub-compounds of different enthalpies of evaporation. The co-evaporation process provides a way to adjust easily the molar composition of the semiconductor compound, and to deposit thin films uniformly over a large area, with a wide range of thin film thicknesses, and onto various surfaces. The design is amenable to the production of infrared detectors of tunable infrared detectivity and of various light collecting areas. [0008] The above and other features of the invention including various novel details of combinations of parts, and other advantages, will now be more particularly described with reference to the accompanying figures and pointed out in the claims. It will be understood that the particular method embodying the invention are shown by way of illustration and not as a limitation of the invention. The principles and features of this invention may be employed in various and numerous embodiments without departing from the scope of the invention. BRIEF DESCRIPTION OF THE DRAWINGS [0009] FIG. 1 is a table showing exemplary compositions of the semiconductor compound, showing large variations of electrical conductivity and bandgap energy upon addition of tellurium and copper; [0010] FIG. 2 is a phase diagram of the As.sub.wSe.sub.xTe.sub.yCu.sub.z system of the invention, with x.about.0%, showing the compositional region where glassy atomic arrangement is obtained; [0011] FIG. 3 is a diagram of the bandgap energy for varying molar concentration of copper in the compound of composition (As.sub.50Se.sub.1Te.sub.49).sub.100-xCu.sub.x and (As.sub.25Se.sub.1Te.sub.74).sub.100-xCu.sub.x, where x corresponds to the molar concentration of copper in percent; [0012] FIG. 4 is a diagram of the optical absorption spectra .alpha.(.lamda.) as function of copper molar concentration in the compound of composition (As.sub.40Se.sub.30Te.sub.30).sub.100-xCu.sub.x, where x is the molar concentration of copper in percent; and [0013] FIG. 5 is a diagram of the optical absorption spectra of thin films of As.sub.wSe.sub.xTe.sub.yCu.sub.z, with y.about.0%, produced by the method of thermal co-evaporation of As.sub.2Se.sub.3 and CuSe sub-compounds. DETAILED DESCRIPTION OF THE INVENTION [0014] The invention involves a quaternary compound semiconductor comprising arsenic (As), selenium (Se), tellurium (Te) and copper (Cu) atoms, whose atomic arrangement is predominantly amorphous or polycrystalline, and whose electronic properties can be tuned during processing by an adjustment of the molar concentration of tellurium and copper atoms in the said compound, and whose electronic bandgap can be tuned to detect infrared radiation energy from the near-infrared regime to the long-infrared regime. [0015] Continuous progress in science and technology imposes new and increased requirements on semiconducting materials. Germanium, silicon and the III-V semiconducting compounds no longer satisfy all these varied and specific requirements, which involve performance, material stability and fabrication costs. The search is for new more effective semiconducting materials with properties' that can be varied in a wide range. Chalcogenide compounds, having either an amorphous, glassy or polycrystalline atomic arrangement, are produced with analogs of oxygen, namely sulfur, selenium and tellurium, and are promising in many respects. Depending on the composition, the conductivity of amorphous chalcogenide compounds varies in the range .sigma.=10.sup.-2 to .sigma.=10.sup.-18 .OMEGA..sup.-1cm.sup.-1, and the bandgap energy is in the range Eg=0.1 eV to Eg=3 eV. The conductivity increases exponentially with temperature, and they have strongly pronounced thermoelectric powers, photo-emfs, and photoconductivity. There are a wide variety of different compositions having varying semiconductor properties within the family of chalcogenide compounds. [0016] Investigation of the electrical conductivity and other physicochemical properties of amorphous chalcogenide compounds shows that in three-component systems, just as in binary ones, a regular change takes place in the parameters of the electrical conductivity, microhardness, thermal stability, crystallizing ability, and other properties when each of the chemical components is replaced by its analogs in the periodic system. The increased delocalization of the chemical bonds in the sequences P--As--Sb--Bi and S--Se--Te causes the conductivity to increase and the corresponding bandgap energy to decrease. The greatest increase of conductivity is observed on going from phosphorous-containing to arsenic-containing amorphous compounds. The replacement of arsenic by antimony or bismuth is not accompanied by so appreciable a change in the electrical conductivity; however, it is accompanied by an appreciable reduction of the glass network stability and increased ability for crystallization. In the sixth group of the periodic table, the most appreciable increase of the conductivity is observed on going from selenides to tellurides amorphous chalcogenide compounds. This replacement is accompanied by an appreciable reduction of the glass network stability and increased ability for crystallization. [0017] The electrical conductivity of binary chalcogenide compounds, such as As--S and As--Se is relatively low. Because of their low electrical conductivity and large bandgap energy, these amorphous compounds can be more readily regarded as dielectrics than semiconductors. A substantial increase of the conductivity of binary compounds is obtained by introducing into them a third component in the metal group--thallium, copper, silver, etc. The electrical conductivity is then increased by 6-10 orders of magnitude. A concomitant decrease of the bandgap energy is also observed when these metals are introduced into arsenic chalcogenides. With increasing content of metals in the arsenic chalcogenides a transition is observed from compounds having dielectric properties to semiconductor properties. The largest contribution to the increase of the conductivity and to the decrease of the bandgap energy of arsenic chalcogenides is made by thallium and copper. [0018] The character of the change of the mechanical, thermal and other properties of the compound when metals are introduced in them depends on the composition and structure of the glassy network structural units produced in the material. Thus, when the large thallium atom is introduced into the glassy network, the mechanical and thermal stability of the arsenic chalcogenide compound decreases substantially. When the smaller copper atom is introduced, on the contrary, it is observed that the structure of the chalcogenide becomes stronger. [0019] The semiconducting character of the conductivity, just as the high chemical stability of the glassy network, is determined by the predominance of covalent bonds in the compound. An increase of the fraction of the ionic component in the chemical bonds lowers both the conductivity and the chemical stability of the glassy network. When the delocalization of the covalent chemical bonds is strengthened, the conductivity of the compound is increased together with their chemical stability. Elemental copper can be introduced in appreciable amounts in arsenic chalcogenides and alter substantially the structural-chemical makeup of the glassy network, causing an abrupt change of the electrical conductivity and bandgap energy, and also an appreciable increase of chemical stability. This can counteract the reduction of chemical-interaction energy, and therefore the concomitant glassy network instability, of selenides being replaced by tellurides in the arsenic chalcogenides. Continue reading about Infrared detection material and method of production... Full patent description for Infrared detection material and method of production Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Infrared detection material and method of production patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. Each week you receive an email with patent applications related to your keywords. Start now! - Receive info on patent apps like Infrared detection material and method of production or other areas of interest. ### Previous Patent Application: Reinforced ionic conducting material, use thereof in electrodes and electrolytes Next Patent Application: Novel composition Industry Class: Compositions ### FreshPatents.com Support Thank you for viewing the Infrared detection material and method of production patent info. IP-related news and info Results in 0.83796 seconds Other interesting Feshpatents.com categories: Daimler Chrysler , DirecTV , Exxonmobil Chemical Company , Goodyear , Intel , Kyocera Wireless , 174 |
 * Protect your Inventions * US Patent Office filing 
PATENT INFO |
|
