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Crystals for a semiconductor radiation detector and method for making the crystalsRelated Patent Categories: Single-crystal, Oriented-crystal, And Epitaxy Growth Processes; Non-coating Apparatus Therefor, Processes Of Growth From Liquid Or Supercritical StateCrystals for a semiconductor radiation detector and method for making the crystals description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20070181056, Crystals for a semiconductor radiation detector and method for making the crystals. Brief Patent Description - Full Patent Description - Patent Application Claims
RELATED APPLICATION [0001] This application is a divisional of application Ser. No. 11/082,846 filed Mar. 18, 2005, the entirety of which is incorporated by reference. BACKGROUND OF THE INVENTION [0002] The field of the invention is high grade, II-VI semiconductor crystal growth using high-pressure hydrothermal processes and, in particular, growth of large Cadmium Telluride (CdTe) and Cadmium Zinc Telluride (CZT) crystals. [0003] CdTe and CZT crystals have applicability for compact radiation detectors. CdTe and CZT detectors have been shown to exhibit good energy resolution, especially as compared to scintillator-based detectors. Since they are direct conversion devices, CdTe and CZT detectors eliminate the need for bulky photomultiplier tubes. Furthermore, CdTe and CZT detectors do not require cryogenic cooling as do high-purity germanium detectors. [0004] CdTe and CZT crystals are conventionally grown by melting CdTe and CZT and allowing the melt to crystallize. Traveling heater systems, horizontal Bridgman, vertical Bridgman and high pressure Bridgman methods have been used to grow CdTe and CZT crystals from the melt or from the vapor phase. CdTe and CZT crystals grown by such melt and vapor phase processes tend to suffer from high cost and small crystal size. In addition, the crystals produced by these melt and vapor phase processes tend to have poor electrical and physical characteristics that greatly limit their sensitivity and application to economical radiation detectors. There is a long felt need for a robust technique for growing high purity, low-cost single CdTe and CZT crystals of a size suitable for high sensitivity detection at high resolution. BRIEF DESCRIPTION OF THE INVENTION [0005] A method for making solid-state, spectrometer grade cadmium telluride (CdTe) and cadmium zinc telluride (CZT) crystals has been developed. CdTe and CZT crystals may be grown by a high-pressure hydrothermal process that produces large single crystals. The process delivers high crystal yields at a low cost and with good spectral resolution. [0006] The CdTe and CZT crystals may be applied in gamma ray and x-ray detectors to provide high resolution and improved detector sensitivity. Examples of other uses of the CdTe and CZT crystals include enhanced Hand-Held Radioisotope Identification Devices, Area Search Devices and image arrays for Radiography, digital x-ray detector arrays, and computed tomography systems. [0007] The invention may be embodied as a method for a growing solid-state, spectrometer grade II-VI crystals using a high-pressure hydrothermal process including the following steps: positioning seed crystals in a growth zone of a reactor chamber; positioning crystal nutrient material in the nutrient zone of the chamber; filling the reactor with a solvent fluid; heating and pressurizing the chamber until at least a portion of the nutrient material dissolves in the solvent and the solvent becomes supercritical; transporting nutrient material dissolved in the supercritical fluid from the nutrient zone to the growth zone, and growing the seed crystals as nutrient material dissolved in the supercritical fluid deposits onto the crystals. [0008] The invention may also be embodied as a method for growing Cadmium Telluride (CdTe) and Cadmium Zinc Telluride (CZT) crystals comprising: positioning CZT or CdTe seed crystals in a growth zone of a reactor chamber divided by a porous baffle into the growth zone and a nutrient zone; positioning CZT or CdTe nutrient material in the nutrient zone; filling the reactor chamber with a solvent fluid; heating and pressurizing the reactor such that the solvent fluid becomes supercritical; heating the reactor such that the nutrient zone at a different temperature than the growth zone; dissolving the nutrient material into the supercritical fluid; transporting the supercritical fluid with dissolved nutrient through the baffle and to the growth zone, and growing crystals from the seed crystals as the dissolved nutrients deposit on the crystals. [0009] Further, the invention may be embodied as a solid-state, spectrometer grade crystal, wherein the crystal is formed by: positioning seed crystals in a growth zone of a reactor chamber; positioning crystal nutrient material in the nutrient zone of the chamber; filling the reactor with a solvent fluid; heating and pressurizing the chamber until at least a portion of the nutrient material dissolves in the solvent and the solvent becomes supercritical; transporting supercritical fluid from the nutrient zone to the growth zone, and growing the seed crystals as nutrients from the supercritical fluid deposit onto the crystals. BRIEF DESCRIPTION OF THE DRAWINGS [0010] FIG. 1 is a cross-sectional view of a zero-stroke-type pressure apparatus with a chamber for growing crystals. [0011] FIG. 2 is a schematic diagram of the chamber for growing CdTe and CZT crystals by a high-pressure hydrothermal method. [0012] FIG. 3 is a flow chart of an exemplary method for growing these crystals. [0013] FIG. 4 is a scanning electron micrograph (SEM) image of spiral growth features on a CdTe (111) seed, indicating high quality crystal growth on screw dislocations. DETAILED DESCRIPTION OF THE INVENTION [0014] For direct conversion detection of x-rays or gamma rays, a high quality, wide-bandgap semiconductor comprising high-atomic-number elements is desired to provide a high cross section for absorption of radiation, a low electrical conductivity for a low background count rate, and a high carrier mobility and lifetime, for efficient detection of carriers. Pure CdTe may be suitable for these purposes, but incorporation of unintentional impurities and defects may increase the electrical conductivity to an undesirably high value. The conductivity may be reduced by addition of at least one compensatory dopant, but at the cost of a reduced carrier mobility. ZnTe may be added to the CdTe, forming CdZnTe (or CZT) order to increase the bandgap and decrease the conductivity. A similar effect may be achieved by incorporation of CdSe or ZnSe, forming Cd.sub.1-xZn.sub.xSe.sub.yTe.sub.1-y, where 0.ltoreq.x, y.ltoreq.1. [0015] Hydrothermal processes are conventionally used to grow .alpha.-quartz crystals commercially. The term hydrothermal also refers to solvothermal processes where the supercritical fluid is a substance other than water, such as ammonia or methanol. These processes provide a highly isothermal and uniform crystal growth environment due to the gas-like viscosity of the supercritical fluid solvent in the reactor chamber and the self-convection of the fluid produced by the reactor. Conventional hydrothermal autoclave systems operate at pressures and temperatures up to about 2 kbar and 400.degree. C., respectively or, with the use of nickel-based superalloys, up to about 5 kbar and 550.degree. C. When working with strongly corrosive solvents, Morey-type autoclaves with a maximum pressure of about 0.5-1 kbar are typically used. Hydrothermal pressure vessel reactors and pressure chambers with enhanced pressure and temperature capability, up to as high as 80 kbar and 1500.degree. C., are disclosed in US Patent Application Publications 2003/0141301, 2003/0140845, 2004/0134415, and 2006/0177362, all of which are commonly owned with this application and are incorporated by reference herein in their entirety. [0016] FIG. 1 illustrates a zero-stroke-type pressure apparatus 10. The performance of a high-pressure and high temperature (HP/HT) apparatus may be characterized by its pressure response, which is defined as the percent increase in chamber pressure divided by the percent increase in press force that produces the increased chamber pressure, relative to a reference operating condition. As known in the art, a zero stroke apparatus is one in which the pressure response is below 0.2, and, more preferably below, 0.05. [0017] A zero stroke apparatus is typically easier to control in supercritical-fluid-processing applications than other apparatuses, and is able to capture or contain the pressure generated within the capsule with little or no tendency to crush it. Although some stroking (e.g., an increase or decrease in the separation between the punches or anvils) may occur during operation, the extent of stroking is much smaller than in other designs. Alternatively, a conventional pressure device may be used to pressurize the chamber. A suitable pressure device having a chamber, pressure transmission medium, restraint seal and heater is described in published U.S. Patent Application Pub. No. 2003/0140845, published on Jul. 31, 2003, entitled "Improved Pressure Vessel," and incorporated herein by reference in its entirety. [0018] The zero-stroke apparatus 10 is a HP/HT apparatus comprising a chamber 12 for growing crystals (or processing material) in a liquid or solid pressure transmitting medium 13, with at least one electrical insulator in the apparatus for establishing at least two different electrical heating paths in a heating element and a power system, for independently controlling the temperatures of at least two locations in the cell, wherein the temperature gradient between the seed crystal and the source material is temporally varying so as to produce an increasing growth rate during at least a portion of the growing process. [0019] The zero-stroke-type pressure apparatus 10 may include opposite steel endcaps 14 that are each surrounded by an annular pyrophyllite bushing 16 which, along with gasket 50, electrically insulates opposite anvils 18 from the annular die 20. Electrically-conductive element 52 establishes an electrical path between anvils 18 and endcaps 14. An electrically conductive annulus 22 is interposed about midway between the top and bottom of annular heating element 24 to thermally divide the reaction chamber 12 into an upper section and a lower section. The heating element 24 may be in the form of a heating tube, or a heated foil, ribbon, bar, wire, ring, or combinations thereof. The conductive annulus 22 has an inner surface in contact with the heating element 24 and an outer surface in contact with the die 20. Continue reading about Crystals for a semiconductor radiation detector and method for making the crystals... Full patent description for Crystals for a semiconductor radiation detector and method for making the crystals Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Crystals for a semiconductor radiation detector and method for making the crystals 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 Crystals for a semiconductor radiation detector and method for making the crystals or other areas of interest. ### Previous Patent Application: Meter device Next Patent Application: Epitaxial deposition process and apparatus Industry Class: Single-crystal, oriented-crystal, and epitaxy growth processes; non-coating apparatus therefor ### FreshPatents.com Support Thank you for viewing the Crystals for a semiconductor radiation detector and method for making the crystals patent info. IP-related news and info Results in 0.461 seconds Other interesting Feshpatents.com categories: Canon USA , Celera Genomics , Cephalon, Inc. , Cingular Wireless , Clorox , Colgate-Palmolive , Corning , Cymer , 174 |
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