US20120045887A1 - Compositions of doped, co-doped and tri-doped semiconductor materials - Google Patents

Compositions of doped, co-doped and tri-doped semiconductor materials Download PDF

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US20120045887A1
US20120045887A1 US13/286,829 US201113286829A US2012045887A1 US 20120045887 A1 US20120045887 A1 US 20120045887A1 US 201113286829 A US201113286829 A US 201113286829A US 2012045887 A1 US2012045887 A1 US 2012045887A1
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dopant
concentration
group
erbium
periodic table
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Kelvin Lynn
Kelly Jones
Guido Ciampi
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Washington State University WSU
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L31/18—Processes or apparatus specially adapted for the manufacture or treatment of these devices or of parts thereof
    • H01L31/1828—Processes or apparatus specially adapted for the manufacture or treatment of these devices or of parts thereof the active layers comprising only AIIBVI compounds, e.g. CdS, ZnS, CdTe
    • H01L31/1832—Processes or apparatus specially adapted for the manufacture or treatment of these devices or of parts thereof the active layers comprising only AIIBVI compounds, e.g. CdS, ZnS, CdTe comprising ternary compounds, e.g. Hg Cd Te
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L31/0248—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by their semiconductor bodies
    • H01L31/0256—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by their semiconductor bodies characterised by the material
    • H01L31/0264—Inorganic materials
    • H01L31/0296—Inorganic materials including, apart from doping material or other impurities, only AIIBVI compounds, e.g. CdS, ZnS, HgCdTe
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L31/0248—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by their semiconductor bodies
    • H01L31/0256—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by their semiconductor bodies characterised by the material
    • H01L31/0264—Inorganic materials
    • H01L31/0296—Inorganic materials including, apart from doping material or other impurities, only AIIBVI compounds, e.g. CdS, ZnS, HgCdTe
    • H01L31/02966—Inorganic materials including, apart from doping material or other impurities, only AIIBVI compounds, e.g. CdS, ZnS, HgCdTe including ternary compounds, e.g. HgCdTe

Definitions

  • the present disclosure is related to semiconductor materials for radiation detectors.
  • the selection of materials for radiation detector applications is governed by fundamental physical properties of the materials. It is desirable that the material should exhibit high electrical resistivity and an excellent ability to transport charge carriers generated by external radiation. Materials that allow an applied electric field to extend through the whole volume of the crystal (i.e., full depletion) are also preferred. None of these properties can be found in high-purity and intrinsic (i.e., undoped) cadmium-zinc-tellurium (Cd 1-x Zn x Te (0 ⁇ x ⁇ 1)) grown by known methods.
  • High-purity intrinsic CdZnTe compounds typically show low electrical resistivity due to intrinsic or native defects. It is believed that such defects can include cadmium (Cd) vacancies in tellurium (Te) rich growth conditions or cadmium interstitials in cadmium rich growth conditions. In addition, an intrinsic defect of Te antisite complexes forming, often in large concentrations, a deep electronic level at the middle of the band gap. This intrinsic defect can prevent full depletion of the device when the defect is present in significant concentrations.
  • Unknown impurities and/or other native defects can also render the intrinsic CdZnTe compounds to have strong carrier trapping tendencies, thereby deteriorating a radiation detector's performance
  • impurities, native defects, and their associations are incorporated in an uncontrolled manner, the properties of the CdZnTe compounds can vary from growth to growth and exhibit strong spatial variations within the ingots. Accordingly, there is a need for a compensation scheme that have result in CdZnTe compounds with improved carrier transport properties and depletion characteristics.
  • FIG. 1 is an electric field versus peak centroid diagram of a semiconductor material prepared in accordance with an embodiment of the disclosure.
  • FIG. 2 is a set of Gamma spectroscopy measurement diagram of semiconductor materials prepared in accordance with an embodiment of the disclosure.
  • FIG. 3 is a set of electron mobility diagram of semiconductor materials prepared in accordance with an embodiment of the disclosure.
  • FIG. 4 is a set of spatial resistivity diagram of a semiconductor material prepared in accordance with an embodiment of the disclosure.
  • FIG. 5 is a set of Gamma spectroscopy measurements of semiconductor materials prepared in accordance with another embodiment of the disclosure.
  • FIG. 6 is an electron mobility diagram of a semiconductor material prepared in accordance with another embodiment of the disclosure.
  • the present disclosure describes materials, compositions, and methods for preparing a bulk II-VI type semiconductor material containing CdTe, CdZnTe, CdZnSe or CdZnTeSe crystals (collectively referred to herein as CZT).
  • the CZT material may be used in manufacturing solid state, elementary or matrix detectors for detection of gamma or X-ray radiations. It will be appreciated that several of the details set forth below are provided to describe the following embodiments in a manner sufficient to enable a person skilled in the relevant art to make and use the disclosed embodiments. Several of the details and advantages described below, however, may not be necessary to practice certain embodiments of the invention. Additionally, the invention can include other embodiments that are within the scope of the claims but are not described in detail with respect to FIGS. 1-6 and attached Appendices A-B.
  • the CZT material includes a bulk II-VI type semiconductor material, a first dopant selected from Group III and/or Group VII of the periodic table, and a rare earth metal.
  • the bulk II-VI type semiconductor material can include elements of Group II (e.g., Cd, Zn) and Group VI (e.g., Te, Se) of the periodic table.
  • the bulk II-VI type semiconductor material can include Cd and Zn, with Zn having a concentration of between about 0 and about 20%. When Zn has a concentration of 20%, 1 out of every 5 Cd sites is occupied by a Zn atom.
  • the bulk II-VI type semiconductor material can also include Te and Se, with Se having a concentration of between about 0 and 2%. When Se has a concentration of 2%, 1 out of every 50 Te sites is occupied by a Se atom.
  • the bulk II-VI type semiconductor material can have a Group VI element to Group II element ratio between about 0.9 and about 1.1.
  • the first dopant can include a Group III element including boron (B), aluminum (Al), gallium (Ga), indium (In), and thallium (TI).
  • the Group III element can have a concentration of about 10 to 10,000 parts per billion (ppb).
  • the first dopant can also include a Group VII element including fluorine (F), chlorine (Cl), bromine (Br), and iodine (I).
  • the Group VII element can have a concentration of at least 10 ppb (e.g., about 10 to about 10,000 ppb).
  • the second dopant can include a rare earth metal including cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu).
  • the rare earth element can have a concentration of at least 10 ppb (e.g., about 10 to about 400,000 ppb).
  • the second dopant includes Er having a concentration of about 15,000 ppb to about 400,000 ppb.
  • the second dopant includes Er having a concentration of about 15,000 ppb to about 300,000 ppb.
  • the CZT material includes cadmium, zinc, and tellurium with aluminum as the first dopant and erbium as the second dopant.
  • the aluminum has a concentration of about 10 to about 10,000 ppb, and the erbium has a concentration of about 10 to about 400,000 ppb.
  • the present disclosure also describes co-doping (use of two doping elements) or triple doping (use of three doping elements in parallel) compensation schemes for at least partially remedy the intrinsic defects of a high-purity CZT material.
  • the first and second dopants can be selected and introduced to the bulk II-VI type semiconductor material in a controlled way and in quantities appropriate to a particular growth method to reliably produce useful extrinsic (i.e., doped) CZT materials with improved resistivity (semi-insulating) and depletion characteristics.
  • Embodiments of the compensation schemes can enable the use of individual dopants to achieve full compensation and excellent charge transport in the CZT materials.
  • the first dopant can be an impurity selected from elements in Group III and/or Group VII of the periodic table.
  • the selected first dopant can provide donors and makes A-centers.
  • the second dopant e.g., a rare earth element
  • a third element can be used as a deep level dopant that secures full electrical compensation to control the resistivity.
  • Embodiments of this arrangement at least reduces the adverse effects of the common single doping schemes on the carrier transport properties of the CZT materials through the use of large concentrations of compensating doping elements. It is believed that the high concentration of dopants in the single-dopant schemes mask the effects of the intrinsic deep level defects without passivating them, thereby causing incomplete depletion of the detectors and space charge build up during operation of the device and the collapse of the internal electric field in the radiation detector, commonly called as polarization.
  • a particular compensation scheme can include selecting a first dopant having an element from Group III and/or Group VI of the periodic table to improve resistivity of the CZT materials.
  • undoped CZT materials can vary in resistivity due to native defects, such as cadmium vacancies, dislocations, and intrinsic deep level defects incorporated to the material during crystal growth. Some of these crystal defects can be ionized at ambient temperature to provide a supply of free charge carriers (electrons or holes) resulting in low-resistivity.
  • a Group III and/or Group VII element can occupy the sites normally occupied by elements from Group II or Group VI in the CZT material, and so vacancies, antisites, and/or other defects can be reduced.
  • Group III elements e.g., Al, In
  • Group VII elements e.g., Cl, Br
  • A-centers impurity-vacancy pairs commonly known and referred to as A-centers.
  • the energy level of the cadmium vacancy defect can be shifted to the lower energy level of the A center. The lower energy level reduces the residency time of charge carriers (holes) at the defect and improves the carrier transport property of the CZT material.
  • the CZT materials doped with an element of Group III and/or Group VII typically cannot achieve full depletion in operation because other Group II related intrinsic defects can result in charge trapping.
  • formation of deep level defects from intrinsic or native defects in sufficient concentrations can produce crystals that cannot be fully depleted by an external bias voltage.
  • the charge transport properties of the CZT material is reduced.
  • selecting a second dopant to provide new carrier pathways through the CZT material and/or through structural perturbation of the Group II related defects can reduce such charge trapping.
  • the second dopant can be selected to include a rare earth metal element based on whether the formation energy (e.g., enthalpy and/or entropy of formation) of a Group II and/or Group VI element and the rare earth metal is above a threshold.
  • Er is selected as the second dopant because Er can react with Te to form Er—Te complexes.
  • the reaction can have a large heat of formation, and Er can irreversibly combine with Te while in a liquid phase, the product of which may form solid domains that can remain intact during subsequent cooling to be integrated into the bulk CZT material. It is believed that this interaction can decrease the frequency of intrinsic defects related to the Group VI element in the CZT material.
  • the second dopant e.g., Er
  • the second dopant can have a concentration of at least 10 atomic parts per billion.
  • the Er concentration can be about 10,000 to about 400,000 atomic parts per billion.
  • the Er can have a molar concentration that is generally similar to that of tellurium in the CZT material. Surprisingly, such high doping levels can limit the spatial variations within grown ingots.
  • doping practice common to the art typically utilizes doping levels of between 10-10,000 ppb to avoid degradation of the desired material properties.
  • One expected advantage of several embodiments of the compensation scheme is the improved accuracy in predicting whether incorporating a particular second dopant would yield a useful material.
  • Conventional techniques for selecting the second dopant generally involve a comparison of the electronic properties between the selected second dopant and the Group II and/or Group VI elements in the CZT material.
  • the second dopant is selected to pin the Fermi level at a midpoint between the energy levels of the valance band and the conduction band.
  • such a technique does not provide adequate information relating to the resulting solid state electronic properties and the interaction between the second dopant and the Group II and Group VI elements.
  • the selection criterion based on formation energy discussed above can at least provide a general guide for choosing a second dopant that might yield useful materials.
  • Compensating for Group VI element related defects and larger volume defects such as precipitates and inclusions utilizing the compensation schemes can limit the spatial variations within grown ingots. With fewer defects, a larger active area can be realized to enable applications that require larger detectors. Moreover, dopant combinations that minimize group II related defects and provide full depletion have particular utility in devices that have a large detector size and a high detection rate requirement. Specific examples include gamma and/or X-ray imaging methods (e.g., Computed Tomography).
  • a few degrees of freedom are allowed in the progression of runs and include the quantity and type of the dopant.
  • Small concentrations of chosen binary (or tertiary) dopants are added to the growth.
  • the melted charge in one embodiment, goes through a quick freeze and a re-melt step before the actual growth starts to stop element segregation and to increase solubility. The results of the prepared charges are reflected in the examples below.
  • the charge which contains Cd and/or Zn, Te and/or Se, and one or more dopants from group III and/or VI and/or a rare earth element, was loaded into a crucible in an argon filled glove bag.
  • the crucible and charge were then placed in an ampoule and sealed under vacuum at less than 10-7 Torr with a quartz end cap. Ingots were grown under vacuum or with a partial pressure of an inert gas.
  • the preparation of the charge was done in a glove bag or clean room conditions to reduce residual impurities. For low pressure growth methods, the crucible was then placed into a quartz ampoule and connected to a vacuum system.
  • the air was evacuated from the ampoule and a partial pressure of an inert gas or a mixture of gases was supplied to the ampoule and then sealed shut by a torch.
  • a partial pressure of an inert gas or a mixture of gases was supplied to the ampoule and then sealed shut by a torch.
  • up to 100 atmospheres was used to decrease charge loss, and the ampoule may be optional. In other embodiments, this procedure may be varied.
  • the setup of the ampoule can limit vapor transport that occurs during the growth.
  • the over pressure of molten CZT allows for vapor transport to condense at the coldest region within the ampoule, resulting in material lost from the ingot.
  • the majority of the charge loss was deposited at the tip and shoulder regions of the ampoule outside of the crucible.
  • Four crystal growth runs were done using different positions of the end cap to affect the open volume.
  • the crystal growth setup was listed in Table 1. In the 1 st growth run, the end cap was positioned approximately 4 inches from the end of the crucible. In the 2 nd run, a lid constructed from the same material as the crucible was placed on the crucible and the end cap was positioned at the same approximate distance of 4 inches away from the crucible.
  • a lid was placed and the end cap was positioned much closer, approximately 1 inch from the end of the crucible.
  • the ampoule was backfilled with a partial pressure of an inert gas, and a lid for the crucible and the end cap were positioned approximately 1 inch from the lid.
  • the 1 st run had a charge loss of 11.0%; the addition of the lid in the 2 nd run slightly decreased the charge loss to 9.0%.
  • the 3 rd run greatly improved reduction of the loss to 4.2%.
  • the ampoule had been backfilled with a partial pressure. This back filling step was done with the lid and end cap positioned approximately 1 inch from the crucible. This process further decreased the charge loss to 0.5%, as shown in Table 1.
  • each ingot was cut vertically through the center for characterization and sample preparation. Samples from each ingot were cut using a diamond wire saw. Then each sample was prepared by polishing with alumina powder and/or etching in a bromine methanol solution to remove saw damage. Finally they were sputtered with gold planar contacts. Many variations on the specific dimensions of the material cross section, the arrangement and composition of the contacts can be implemented here. One skilled in the art can tailor these particular aspects of the solid state detection element for use in a specific manifestation of radiation detection instruments. Table 2 gives the average values from samples made from each ingot. The conductivity type of each ingot has been confirmed by thermoelectric effect spectroscopy (TEES). The Bulk Resistivity of each sample was determined by applying voltages from ⁇ 1 to 1 volts. The ⁇ products for electrons were determined by 0.5 ⁇ ec shaping with a 241 Am source.
  • TEES thermoelectric effect spectroscopy
  • Samples were also placed in a Multi Channel Analyzer (MCA) to check response to incident radiation.
  • MCA Multi Channel Analyzer
  • No pulse processing or post processing was used to enhance the energy resolution.
  • the pulser resolution averaged 2.4% for the 57 Co spectra and was 1.2% for the 137 Cs spectra.
  • the first ingot to have a significant response to ionizing radiation was GLC 3.
  • the two ingots grown in PBN were high purity, but low resistivity, p-type, that shows no response to ionizing radiation.
  • the group III dopant does not seem as soluble in CZT when using the PBN crucible. All PBN growths had lower than intended doping levels. All samples that show any significant response to incident radiation have been from n-type growths with group III doping.
  • the 57 Co isotope was used to analyze the response of the detectors at room temperature.
  • the x-rays from this source display the mobility and lifetimes of both electron and hole carriers.
  • GLC 3 has good energy resolution at the 122 keV peak, however, the 14 keV peak was not observed, indicating that the sample was not completely active.
  • the peak position of the 122 keV energy was low in channel numbers, showing the ⁇ of both the holes and electrons were similar for this resolution at this channel number.
  • the ⁇ product for the electrons was not high enough to resolve the 14 keV peak, making the sample not fully active through the 1.9 mm detector thickness.
  • the GLC 3 spectrum for the 137 Cs source displays the 662 keV peak was not sharp in resolution, but high in counts because of the large hole ⁇ .
  • PYC 1 and 4 122 keV peak position were higher in channel number, but not equal ⁇ s.
  • the hole tailing in both spectra indicates that the hole ⁇ was lower than the electron's.
  • PYC 4 has high resolution and the best ⁇ for electrons. ⁇ products have been determined by the Hecht relation as follows:
  • CZT undoped has a low resistivity caused primarily by defects including the cadmium vacancy.
  • a group III dopant was intended to compensate this defect and likely would increase the resistivity of the material. This compensation technique creates an A-center. However this compensation alone does not produce intrinsic characteristics or fully active regions of the material.
  • the introduction of a second dopant, Erbium does compensate remaining defects creating a fully active material. ( FIGS. 3-6 and Table 7)
  • This combination of dopants results in high resistivity, and large charge carrier mobility and lifetimes.
  • the properties of large electron and hole mobility and lifetimes throughout the bulk of the material create fully active material, suitable for solid state radiation detectors. Elemental compositions as measured by glow discharge mass spectrometry are provided in Appendix B.
  • Tellurium inclusions and precipitates can be the most common and detrimental bulk defects in CdTe and CdZnTe materials. These kinds of inclusions can create charge trapping and degradation in detector performance. It was believed that higher temperature gradients across the melt during growth can limit the tellurium precipitates that usually occur along grains boundaries. Tellurium inclusions are opaque under infrared, whereas the bulk material is transparent. Thus infrared microscopy was used on the samples and wafers cut from ingots to map and monitor these inclusions in the material.
  • Electron mobility multiplied by the lifetime of the charge carrier was calculated from grown samples. The product was calculated by fitting applied bias voltage versus the 59.5 keV x-ray peak from the 241 Am source. FIG. 3 shows results from two ingots.
  • thermo-electrical effect spectroscopy Trapping levels associated with Cadmium vacancies, tellurium anti-sites and their complexes were identified using thermo-electrical effect spectroscopy in CdTe and CdZnTe crystals grown by the vertical and high pressure Bridgman techniques.
  • transition energies thermal ionization energies
  • Trapping levels were identified at E 2 and E 4 with the first and second ionized state of the isolated cadmium vacancy, E 1 and E 3 to the first and second ionized state to cadmium vacancy-isoelectronic oxygen complex.
  • Other levels assigned were E 5 with tellurium antisite-divacancy, E 6 with tellurium anti-site-single vacancy complex, E 7 with tellurium antisite-cadmium vacancy-donor in the cadmium site complex and E 8 with tellurium antisite-cadmium vacancy.
  • the latter complex acts as a donor.

Abstract

Semiconductor materials suitable for being used in radiation detectors are disclosed. A particular example of the semiconductor materials includes tellurium, cadmium, and zinc. Tellurium is in molar excess of cadmium and zinc. The example also includes aluminum having a concentration of about 10 to about 20,000 atomic parts per billion and erbium having a concentration of at least 10,000 atomic parts per billion.

Description

    CROSS-REFERENCE TO RELATED APPLICATION(S)
  • This application is a divisional application of U.S. application Ser. No. 11/910,504, which is a U.S. National Phase of PCT/US2007/063330, which claims priority to U.S. Provisional Application No. 60/779,089, filed on Mar. 3, 2006, the disclosures of all of the foregoing applications are incorporated herein by reference in their entirety.
    • STATEMENT REGARDING FEDERALLY-SPONSORED RESEARCH
  • This work was partially funded by the Department of Energy (DE-FG07-06IDI4724), and the United States government has, therefore, certain rights to the present invention.
    • TECHNICAL FIELD
  • The present disclosure is related to semiconductor materials for radiation detectors.
    • BACKGROUND
  • The selection of materials for radiation detector applications is governed by fundamental physical properties of the materials. It is desirable that the material should exhibit high electrical resistivity and an excellent ability to transport charge carriers generated by external radiation. Materials that allow an applied electric field to extend through the whole volume of the crystal (i.e., full depletion) are also preferred. None of these properties can be found in high-purity and intrinsic (i.e., undoped) cadmium-zinc-tellurium (Cd1-xZnxTe (0≦x≦1)) grown by known methods.
  • High-purity intrinsic CdZnTe compounds typically show low electrical resistivity due to intrinsic or native defects. It is believed that such defects can include cadmium (Cd) vacancies in tellurium (Te) rich growth conditions or cadmium interstitials in cadmium rich growth conditions. In addition, an intrinsic defect of Te antisite complexes forming, often in large concentrations, a deep electronic level at the middle of the band gap. This intrinsic defect can prevent full depletion of the device when the defect is present in significant concentrations.
  • Unknown impurities and/or other native defects can also render the intrinsic CdZnTe compounds to have strong carrier trapping tendencies, thereby deteriorating a radiation detector's performance When impurities, native defects, and their associations are incorporated in an uncontrolled manner, the properties of the CdZnTe compounds can vary from growth to growth and exhibit strong spatial variations within the ingots. Accordingly, there is a need for a compensation scheme that have result in CdZnTe compounds with improved carrier transport properties and depletion characteristics.
    • BRIEF DESCRIPTION OF THE DRAWINGS
  • FIG. 1 is an electric field versus peak centroid diagram of a semiconductor material prepared in accordance with an embodiment of the disclosure.
  • FIG. 2 is a set of Gamma spectroscopy measurement diagram of semiconductor materials prepared in accordance with an embodiment of the disclosure.
  • FIG. 3 is a set of electron mobility diagram of semiconductor materials prepared in accordance with an embodiment of the disclosure.
  • FIG. 4 is a set of spatial resistivity diagram of a semiconductor material prepared in accordance with an embodiment of the disclosure.
  • FIG. 5 is a set of Gamma spectroscopy measurements of semiconductor materials prepared in accordance with another embodiment of the disclosure.
  • FIG. 6 is an electron mobility diagram of a semiconductor material prepared in accordance with another embodiment of the disclosure.
    •  DETAILED DESCRIPTION A. Semiconductor Material
  • The present disclosure describes materials, compositions, and methods for preparing a bulk II-VI type semiconductor material containing CdTe, CdZnTe, CdZnSe or CdZnTeSe crystals (collectively referred to herein as CZT). The CZT material may be used in manufacturing solid state, elementary or matrix detectors for detection of gamma or X-ray radiations. It will be appreciated that several of the details set forth below are provided to describe the following embodiments in a manner sufficient to enable a person skilled in the relevant art to make and use the disclosed embodiments. Several of the details and advantages described below, however, may not be necessary to practice certain embodiments of the invention. Additionally, the invention can include other embodiments that are within the scope of the claims but are not described in detail with respect to FIGS. 1-6 and attached Appendices A-B.
  • In one embodiment, the CZT material includes a bulk II-VI type semiconductor material, a first dopant selected from Group III and/or Group VII of the periodic table, and a rare earth metal. The bulk II-VI type semiconductor material can include elements of Group II (e.g., Cd, Zn) and Group VI (e.g., Te, Se) of the periodic table. For example, the bulk II-VI type semiconductor material can include Cd and Zn, with Zn having a concentration of between about 0 and about 20%. When Zn has a concentration of 20%, 1 out of every 5 Cd sites is occupied by a Zn atom. The bulk II-VI type semiconductor material can also include Te and Se, with Se having a concentration of between about 0 and 2%. When Se has a concentration of 2%, 1 out of every 50 Te sites is occupied by a Se atom. The bulk II-VI type semiconductor material can have a Group VI element to Group II element ratio between about 0.9 and about 1.1.
  • The first dopant can include a Group III element including boron (B), aluminum (Al), gallium (Ga), indium (In), and thallium (TI). The Group III element can have a concentration of about 10 to 10,000 parts per billion (ppb). The first dopant can also include a Group VII element including fluorine (F), chlorine (Cl), bromine (Br), and iodine (I). The Group VII element can have a concentration of at least 10 ppb (e.g., about 10 to about 10,000 ppb).
  • The second dopant can include a rare earth metal including cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu). The rare earth element can have a concentration of at least 10 ppb (e.g., about 10 to about 400,000 ppb). In a particular embodiment, the second dopant includes Er having a concentration of about 15,000 ppb to about 400,000 ppb. In another particular embodiment, the second dopant includes Er having a concentration of about 15,000 ppb to about 300,000 ppb. In a further particular embodiment, the CZT material includes cadmium, zinc, and tellurium with aluminum as the first dopant and erbium as the second dopant. The aluminum has a concentration of about 10 to about 10,000 ppb, and the erbium has a concentration of about 10 to about 400,000 ppb.
    • B. Compensation Scheme
  • The present disclosure also describes co-doping (use of two doping elements) or triple doping (use of three doping elements in parallel) compensation schemes for at least partially remedy the intrinsic defects of a high-purity CZT material. The first and second dopants can be selected and introduced to the bulk II-VI type semiconductor material in a controlled way and in quantities appropriate to a particular growth method to reliably produce useful extrinsic (i.e., doped) CZT materials with improved resistivity (semi-insulating) and depletion characteristics.
  • Embodiments of the compensation schemes can enable the use of individual dopants to achieve full compensation and excellent charge transport in the CZT materials. The first dopant can be an impurity selected from elements in Group III and/or Group VII of the periodic table. The selected first dopant can provide donors and makes A-centers. The second dopant (e.g., a rare earth element) can passivate the intrinsic deep level defects to enable full depletion of the devices. Optionally, a third element can be used as a deep level dopant that secures full electrical compensation to control the resistivity.
  • Embodiments of this arrangement at least reduces the adverse effects of the common single doping schemes on the carrier transport properties of the CZT materials through the use of large concentrations of compensating doping elements. It is believed that the high concentration of dopants in the single-dopant schemes mask the effects of the intrinsic deep level defects without passivating them, thereby causing incomplete depletion of the detectors and space charge build up during operation of the device and the collapse of the internal electric field in the radiation detector, commonly called as polarization.
  • In one embodiment, a particular compensation scheme can include selecting a first dopant having an element from Group III and/or Group VI of the periodic table to improve resistivity of the CZT materials. Without being bound by theory, it is believed that undoped CZT materials can vary in resistivity due to native defects, such as cadmium vacancies, dislocations, and intrinsic deep level defects incorporated to the material during crystal growth. Some of these crystal defects can be ionized at ambient temperature to provide a supply of free charge carriers (electrons or holes) resulting in low-resistivity. It is believed that a Group III and/or Group VII element can occupy the sites normally occupied by elements from Group II or Group VI in the CZT material, and so vacancies, antisites, and/or other defects can be reduced. For example, Group III elements (e.g., Al, In) and/or Group VII elements (e.g., Cl, Br) can combine with the cadmium vacancies to form impurity-vacancy pairs commonly known and referred to as A-centers. In this process, the energy level of the cadmium vacancy defect can be shifted to the lower energy level of the A center. The lower energy level reduces the residency time of charge carriers (holes) at the defect and improves the carrier transport property of the CZT material.
  • However, the CZT materials doped with an element of Group III and/or Group VII typically cannot achieve full depletion in operation because other Group II related intrinsic defects can result in charge trapping. For example, formation of deep level defects from intrinsic or native defects in sufficient concentrations can produce crystals that cannot be fully depleted by an external bias voltage. As a result, the charge transport properties of the CZT material is reduced. Thus, selecting a second dopant to provide new carrier pathways through the CZT material and/or through structural perturbation of the Group II related defects can reduce such charge trapping.
  • The second dopant can be selected to include a rare earth metal element based on whether the formation energy (e.g., enthalpy and/or entropy of formation) of a Group II and/or Group VI element and the rare earth metal is above a threshold. In a particular example, Er is selected as the second dopant because Er can react with Te to form Er—Te complexes. The reaction can have a large heat of formation, and Er can irreversibly combine with Te while in a liquid phase, the product of which may form solid domains that can remain intact during subsequent cooling to be integrated into the bulk CZT material. It is believed that this interaction can decrease the frequency of intrinsic defects related to the Group VI element in the CZT material.
  • The second dopant (e.g., Er) can have a concentration of at least 10 atomic parts per billion. In some embodiments, the Er concentration can be about 10,000 to about 400,000 atomic parts per billion. In further embodiments, the Er can have a molar concentration that is generally similar to that of tellurium in the CZT material. Surprisingly, such high doping levels can limit the spatial variations within grown ingots.
  • Typically, conventional techniques do not use such a high doping concentration because a number of factors pose practical limitations on the useful range of dopant concentrations. Major factors include both solubility and utility provided by any given dopant element. It is believed that there are limits to the solubility of an element within a liquefied mixture of Group II and Group VI elements. The limited solubility in turn restricts the potential dopant range. Additionally, the maximum and minimum dopant levels that can provide useful materials can vary with the specific electronic properties of the dopant. In particular, for dopants that impart positive or beneficial properties to the material (e.g., to increase resistivity or charge carrier transport ability), there is typically a doping level over which the dopant begins to impart adverse effects on the utility of the material. Generally, once a doping level exceeds this critical value, the dopant will act as charge trap and diminish the charge carrier transport ability of the material. With these restrictions, doping practice common to the art typically utilizes doping levels of between 10-10,000 ppb to avoid degradation of the desired material properties.
  • One expected advantage of several embodiments of the compensation scheme is the improved accuracy in predicting whether incorporating a particular second dopant would yield a useful material. Conventional techniques for selecting the second dopant generally involve a comparison of the electronic properties between the selected second dopant and the Group II and/or Group VI elements in the CZT material. Typically, the second dopant is selected to pin the Fermi level at a midpoint between the energy levels of the valance band and the conduction band. However, such a technique does not provide adequate information relating to the resulting solid state electronic properties and the interaction between the second dopant and the Group II and Group VI elements. As a result, in many cases, there is little information available for accurate prediction of whether incorporating the second dopant would yield a useful material. Thus, the selection criterion based on formation energy discussed above can at least provide a general guide for choosing a second dopant that might yield useful materials.
  • Materials with full depletion have optimal charge transport properties. Specifically, fully depleted materials can transport both “holes” (positive charges) and “electrons” (negative charges). This property enables a more rapid equilibration of charges after the perturbation of charge associated with the detection of a photon. The net result is a material with a rapid refresh rate, which allows for said material to be applied as a detector in applications requiring a rapid, repetitive detection (e.g. medical imaging and time resolved imaging).
  • Compensating for Group VI element related defects and larger volume defects such as precipitates and inclusions utilizing the compensation schemes can limit the spatial variations within grown ingots. With fewer defects, a larger active area can be realized to enable applications that require larger detectors. Moreover, dopant combinations that minimize group II related defects and provide full depletion have particular utility in devices that have a large detector size and a high detection rate requirement. Specific examples include gamma and/or X-ray imaging methods (e.g., Computed Tomography).
  • During preparation of a charge, in accordance with some embodiments, a few degrees of freedom are allowed in the progression of runs and include the quantity and type of the dopant. Small concentrations of chosen binary (or tertiary) dopants are added to the growth. To ensure the dopants are uniformly spread throughout the ingot, the melted charge, in one embodiment, goes through a quick freeze and a re-melt step before the actual growth starts to stop element segregation and to increase solubility. The results of the prepared charges are reflected in the examples below.
    • EXAMPLES Example 1 Crystal Growth of Doped Materials
  • The charge, which contains Cd and/or Zn, Te and/or Se, and one or more dopants from group III and/or VI and/or a rare earth element, was loaded into a crucible in an argon filled glove bag. The crucible and charge were then placed in an ampoule and sealed under vacuum at less than 10-7 Torr with a quartz end cap. Ingots were grown under vacuum or with a partial pressure of an inert gas. The preparation of the charge was done in a glove bag or clean room conditions to reduce residual impurities. For low pressure growth methods, the crucible was then placed into a quartz ampoule and connected to a vacuum system. The air was evacuated from the ampoule and a partial pressure of an inert gas or a mixture of gases was supplied to the ampoule and then sealed shut by a torch. For high pressure growth techniques, up to 100 atmospheres was used to decrease charge loss, and the ampoule may be optional. In other embodiments, this procedure may be varied.
  • The setup of the ampoule can limit vapor transport that occurs during the growth. The over pressure of molten CZT allows for vapor transport to condense at the coldest region within the ampoule, resulting in material lost from the ingot. The majority of the charge loss was deposited at the tip and shoulder regions of the ampoule outside of the crucible. Four crystal growth runs were done using different positions of the end cap to affect the open volume. The crystal growth setup was listed in Table 1. In the 1st growth run, the end cap was positioned approximately 4 inches from the end of the crucible. In the 2nd run, a lid constructed from the same material as the crucible was placed on the crucible and the end cap was positioned at the same approximate distance of 4 inches away from the crucible. During the 3rd run, a lid was placed and the end cap was positioned much closer, approximately 1 inch from the end of the crucible. In the 4th run the ampoule was backfilled with a partial pressure of an inert gas, and a lid for the crucible and the end cap were positioned approximately 1 inch from the lid.
    • Example 2 Materials Characterization
  • The 1st run had a charge loss of 11.0%; the addition of the lid in the 2nd run slightly decreased the charge loss to 9.0%. The 3rd run greatly improved reduction of the loss to 4.2%. In the 4th run the ampoule had been backfilled with a partial pressure. This back filling step was done with the lid and end cap positioned approximately 1 inch from the crucible. This process further decreased the charge loss to 0.5%, as shown in Table 1.
  • TABLE 1
    Crystal growth setup
    All growths have the same ratio Te/(Cd + Zn) = 1.033
    Run 1st 2nd 3rd 4th
    Crucible GLC GLC GLC PYC
    Ampoule pressure 10−7 Torr 10−7 Torr 10−7 Torr <200 Torr Ar
    End cap position 4 inches 4 inches 1 inch 1 inch
    Lid No Yes Yes Yes
    Charge loss 11.0% 9.0% 4.2% 1.5%
  • Each ingot was cut vertically through the center for characterization and sample preparation. Samples from each ingot were cut using a diamond wire saw. Then each sample was prepared by polishing with alumina powder and/or etching in a bromine methanol solution to remove saw damage. Finally they were sputtered with gold planar contacts. Many variations on the specific dimensions of the material cross section, the arrangement and composition of the contacts can be implemented here. One skilled in the art can tailor these particular aspects of the solid state detection element for use in a specific manifestation of radiation detection instruments. Table 2 gives the average values from samples made from each ingot. The conductivity type of each ingot has been confirmed by thermoelectric effect spectroscopy (TEES). The Bulk Resistivity of each sample was determined by applying voltages from −1 to 1 volts. The μτ products for electrons were determined by 0.5 μec shaping with a 241Am source.
  • TABLE 2
    Properties of 5 ingots
    57Co
    Conduc- Bulk 122 keV μτ for
    Growth tivity Resistivity Ave. resolution electrons Ave.
    GLC 1 p-type 1.7 × 1010 Ohm*cm No No response
    response
    GLC 3 n-type 1.0 × 1010 Ohm*cm 15.8 keV 6.80 × 10−5 cm2/V
    12.9%
    PBN p-type 2.2 × 107 Ohm*cm No No response
    response
    PYC 1 n-type 1.0 × 1010 Ohm*cm 19.5 keV 2.59 × 10−4 cm2/V
    16.0%
    PYC 4 n-type 2.0 × 1010 Ohm*cm 11.6 keV 2.68 × 10−4 cm2/V
     9.5%
  • Samples were also placed in a Multi Channel Analyzer (MCA) to check response to incident radiation. No pulse processing or post processing was used to enhance the energy resolution. The pulser resolution averaged 2.4% for the 57Co spectra and was 1.2% for the 137Cs spectra. The first ingot to have a significant response to ionizing radiation was GLC 3. The two ingots grown in PBN were high purity, but low resistivity, p-type, that shows no response to ionizing radiation. According to the GDMS analysis the group III dopant does not seem as soluble in CZT when using the PBN crucible. All PBN growths had lower than intended doping levels. All samples that show any significant response to incident radiation have been from n-type growths with group III doping.
  • The 57Co isotope was used to analyze the response of the detectors at room temperature. The x-rays from this source display the mobility and lifetimes of both electron and hole carriers. GLC 3 has good energy resolution at the 122 keV peak, however, the 14 keV peak was not observed, indicating that the sample was not completely active. The peak position of the 122 keV energy was low in channel numbers, showing the λτ of both the holes and electrons were similar for this resolution at this channel number. The λτ product for the electrons was not high enough to resolve the 14 keV peak, making the sample not fully active through the 1.9 mm detector thickness. The GLC 3 spectrum for the 137Cs source, displays the 662 keV peak was not sharp in resolution, but high in counts because of the large hole λτ. PYC 1 and 4 122 keV peak position were higher in channel number, but not equal λτs. The hole tailing in both spectra indicates that the hole λτ was lower than the electron's. PYC 4 has high resolution and the best λτ for electrons. λτ products have been determined by the Hecht relation as follows:
  • Q = Q O * μ τ * E Th * ( 1 - exp ( - Th μτ * E ) )
  • Q was the charge collection (peak centroid), QO was the maximum collectible charge, λτ was the mobility*lifetime, E was the applied electric field; Th was the thickness of the sample.
    For electron characterization, a 241Am source was positioned facing the cathode end of the detector. Plotting the peak centroid position of the 59.5 keV line on the y-axis, and the applied electric field on the x, the Hecht relation was fitted to equation 1. The λτ product for electrons can be determined and shown, in FIG. 1 for growth PYC 4. A shaping constant of 0.5 μseconds was used for simplicity of keeping all measurements consistent. By simply increasing the shaping constant, λτ can be increased.
    • Physical Characterization of the Material, Where Er Was Co-Dopant
  • CZT undoped has a low resistivity caused primarily by defects including the cadmium vacancy. A group III dopant was intended to compensate this defect and likely would increase the resistivity of the material. This compensation technique creates an A-center. However this compensation alone does not produce intrinsic characteristics or fully active regions of the material. The introduction of a second dopant, Erbium, does compensate remaining defects creating a fully active material. (FIGS. 3-6 and Table 7) This combination of dopants results in high resistivity, and large charge carrier mobility and lifetimes. The properties of large electron and hole mobility and lifetimes throughout the bulk of the material create fully active material, suitable for solid state radiation detectors. Elemental compositions as measured by glow discharge mass spectrometry are provided in Appendix B.
  • TABLE 3
    7 crystal growths co-doping with erbium.
    μτ PRODUCT Resistivity
    Er (ppb) Al (ppb) Cl (ppb) (0.5 shaping) (Ω*cm)
    460 2200 — 2.60E−04 2.38E+10
    600 2400 — 1.80E−04 2.45E+10
    260 4200 100 1.50E−04 1.78E+10
    330 2400 — 4.95E−05 1.22E+10
    220,000 2500 — 2.91E−04 1.76E+10
    392,000 2400 — 1.34E−04 1.19E+10
    μτ was the product of μ = mobility and τ = lifetime. The product of these two properties was a common method to quantify the material. The larger the μτ number the better the charge carrier mobilityand lifetimes are. Fully active material has large μτ values (~1.0 × 10−3 cm2/V).
  • Tellurium inclusions and precipitates can be the most common and detrimental bulk defects in CdTe and CdZnTe materials. These kinds of inclusions can create charge trapping and degradation in detector performance. It was believed that higher temperature gradients across the melt during growth can limit the tellurium precipitates that usually occur along grains boundaries. Tellurium inclusions are opaque under infrared, whereas the bulk material is transparent. Thus infrared microscopy was used on the samples and wafers cut from ingots to map and monitor these inclusions in the material.
  • Gamma spectroscopy was performed on all samples cut from grown ingots. Numerous samples have a resolution and efficiency similar to the commercially available CdZnTe detectors. Four examples are shown in FIG. 2.
  • Electron mobility multiplied by the lifetime of the charge carrier was calculated from grown samples. The product was calculated by fitting applied bias voltage versus the 59.5 keV x-ray peak from the 241Am source. FIG. 3 shows results from two ingots.
  • Trapping levels associated with Cadmium vacancies, tellurium anti-sites and their complexes were identified using thermo-electrical effect spectroscopy in CdTe and CdZnTe crystals grown by the vertical and high pressure Bridgman techniques. The corresponding thermal ionization energies, which were extracted using initial rise and/or variable heating rate methods and first principles calculations are at E1=0.09±0.01, E2=0.12 ±0.01 eV, E3=0.18±0.01 eV, E4=0.23±0.01 eV, E5=0.36±0.01 eV, E6=0.79±0.08 eV, E7=0.39±0.01 eV, and E8=0.31±0.01 eV. Based on the first principles method calculation of transition energies (thermal ionization energies), purity data from glow discharge mass spectroscopy, and growth conditions of the crystals trapping levels have been determined.
  • Trapping levels were identified at E2 and E4 with the first and second ionized state of the isolated cadmium vacancy, E1 and E3 to the first and second ionized state to cadmium vacancy-isoelectronic oxygen complex. Other levels assigned were E5 with tellurium antisite-divacancy, E6 with tellurium anti-site-single vacancy complex, E7 with tellurium antisite-cadmium vacancy-donor in the cadmium site complex and E8 with tellurium antisite-cadmium vacancy. The latter complex acts as a donor.
  • From the foregoing, it will be appreciated that specific embodiments of the invention have been described herein for purposes of illustration, but that various modifications may be made without deviating from the scope of the invention. Aspects of the invention described in the context of particular embodiments may be combined or eliminated in other embodiments. While advantages associated with certain embodiments of the invention have been described in the context of those embodiments, other embodiments may also exhibit such advantages, and not all embodiments need necessarily exhibit such advantages to fall within the scope of the invention. The following examples reflect further embodiments of the invention.
  • APPENDIX A
    Summary of Crystal Growth (CG) Conditions and Material Compositions Associated With Selected CG's
    GROWTH CG1 CG2 CG3 CG4
    Charge Honeywell Honeywell Honeywell Honeywell
    Excess Te Te/ 1.0018 1.018 1.018 1.018
    (Cd + Zn)
    Dopants ppb
    Crucible Glassy Carbon #1 GlyC #2 GlyC #3 GlyC #4
    Lid none none none none
    Partial Pressure vacuum vacuum vacuum vacuum
    N or P Type
    Ave. Resistivity
    57Co response
    Ave. μτ electrons
    IMPURITIES ppb
    Li
    B
    C
    N
    O
    Na
    Mg
    Al
    Si
    P
    S
    Cl
    K
    Ca
    Ti
    V
    Cr
    Fe
    Ni
    Cu
    Ge
    As
    Se
    Nb
    Sn
    Er
    Pt
    Pb
    Total
    Total w/o Dopants
    Average:
    Zn %
    GROWTH CG1 CG2 CG3 CG4
    GROWTH CG5 CG6 CG7 CG8
    Charge 1191 grams 1199 grams 1199 grams 1071 grams
    Excess Te Te/ 1.018 1.033 1.033 1.033
    (Cd + Zn)
    Dopants ppb Al, Pb, V 1500, 1000, 500 Al, Pb, V 1500, 1000, 500 Al, Pb, V 1500, 1000, 500 Al, Pb, V 1500, 1000, 500
    Crucible GlyC #5 GlyC #6 GlyC #7 GlyC #7
    Lid none none None yes
    Partial Pressure vacuum vacuum vacuum vacuum ×10 − 7 torr
    N or P Type P-type P-type P-type
    Ave. Resistivity 1.7E10 Ohm*cm 1.2E9 Ohm*cm 1.8E9 Ohm*cm
    57Co response N/A poor N/A N/A
    Ave. μτ electrons N/A N/A N/A N/A
    IMPURITIES ppb Tip Mid Heel Tip Mid Heel Tip Mid Heel Tip Mid Heel
    Li 5 7 25 6 5 9 5 0 12 0 10 24
    B 1 24 6 34
    C 100 7500 380 100 210 42 300 230 22 1600 65 1200
    N 15 50 25 30 29 16 10 15 5 35 4 40
    O 370 690 130 120 1000 44 83 140 30 1300 55 140
    Na 55 13000 65 20 550 67 17 16 20 110 11 82
    Mg 990 660 120 40 78 70 36 44 300 660 54 150
    Al 140 11000 13000 2000 57000 5400 120 160 1500 20000 1400 4000
    Si 800 1100 29 93 740 39 170 129 0.7 1700 49 1300
    P 2 11 2 4 7 2 14 7 10
    S 97 450 660 350 540 300 130 0 510 520 400 450
    Cl 40 2 75 90 100 52 28 77 70 250 120 86
    K 8 180 10 63
    Ca 12 3400 33 74 170 120 220 0 200
    Ti 5 380 4 24 14 8 1 0.6 0.3 270 28 28
    V 140 130 2400 3700 8300 1800 120 120 85 1800 180 26
    Cr 18 5 18 6 16 10 20 8 24 29 30 78
    Fe 10 10 10 82 50 140 50 62 210 150 78 240
    Ni 320 380 640 0 0 4
    Cu 1 0.5 1 21 15
    Ge 12 64 18
    As 8 32 72
    Se 1 38 11
    Nb 0.3 10 1
    Sn 20 15 15
    Er
    Pt 4 5 7 160 0 2100
    Pb 340 1500 170 300 420 180 40 34 23 1000 160 1700
    Total 3514 40644 17927 7039 69347 8314 1130 1036 2816 29818 2651 11854
    Total w/o Dopants 2894 28014 2357 1039 3627 934 850 722 1208 7018 911 6128
    Average: 11088.26667 1866.666667 926.5333333 4685.666667
    Zn % 1.9 3.1 6.2 2.3 3.7 2.5 2.1 3.9 6.7 6.1 3.0 2.6
    GROWTH CG5 CG6 CG7 CG8
    GROWTH CG10 CG11 CG12 CG13
    Charge 1070 grams 1071 grams 665 grams
    Excess Te Te/ 1.033 1.033 1.033
    (Cd + Zn)
    Dopants ppb Al, Pb, Sn 500, 300, 100 Al, Pb, Ge 500, 400, 200 Al, Pb, Ge 500, 400, 300 Al, Pb, Fe 1000, 500, 500
    Crucible GlyC #7 GlyC #8 GlyC #9 PBN #1
    Lid yes yes yes yes + snap ring
    Partial Pressure vacuum 7.8 × 10 − 7 torr vacuum 3.8 × 10 − 8 torr vacuum 9.3 × 10 − 8 torr vacuum 3.8 × 10 − 8 torr
    N or P Type N-type + P-type N-type P-type
    Ave. Resistivity 1.0E10 Ohm*cm 1.0E10 Ohm*cm 3.9E5 Ohm*cm
    57Co response two peaks two peaks N/A
    Ave. μτ electrons 6.8E−5 cm2/V 4.7E−-5 cm2/V N/A
    IMPURITIES ppb Tip Mid Heel Tip Mid Heel Tip Mid Heel
    Li 5 5 3
    B 0 0 100
    C 140 110 30 890 120 680 490 720 580
    N 31 35 60 14 15 10 310 130 140
    O 110 100 80 440 80 330 420 380 410
    Na 5 0 3 4 13 8 0 15 15
    Mg 110 69 60 59 50 50 55 42 84
    Al 1200 1500 1600 290 680 1500 150 48 53
    Si 6 24 3 8 0 0 170 34 210
    P
    S 230 260 300 190 240 420 200 270 460
    Cl 22 35 37 13 9 27 19 27 50
    K
    Ca
    Ti 11 2 34
    V 2 0.4 0.3 5 5 4
    Cr 14 0 4 30 13 15
    Fe 52 53 120 63 83 450 150 220 490
    Ni
    Cu
    Ge <50 <35 <40
    As
    Se
    Nb
    Sn <20 <15 <18
    Er
    Pt
    Pb 6 8 4 3 5 0 14 7 88
    Total 1933 2199 2404 2009 1313 3494 1989 1895 2614
    Total w/o Dopants 727 691 800 1716 628 1994 1675 1620 1983
    Average: 739.5666667 1446 1759.333333
    Zn % 5.0 4.4 3.7 3.4 3.4 3.2 4.7 3.8 3.5
    GROWTH CG10 CG11 CG12 CG13
    GROWTH CG14 CG15 CG16 CG16a
    Charge 665 grams 887 grams 887 grams 887 grams
    Excess Te Te/ 1.033 1.033 1.033
    (Cd + Zn)
    Dopants ppb Al, Pb, Fe 2000, 500, 500 Al, Pb, Fe 1500, 300, 500 Al, Pb, Ge 1000, 1000, 500 Al, Pb, Ge 1000, 1000, 500
    Crucible PBN #1 PyC #1 PyC #1 PyC #1
    Lid yes #2 + 2 snap rings yes yes yes
    Partial Pressure vacuum 5.0 × 10 − 8 torr 90 mtorr Ar 90 mtorr Ar vacuum 1.4 × 10 − 7 torr
    N or P Type P-type N-type P-type
    Ave. Resistivity 2.2E7 Ohm*cm 1.03E10 Ohm*cm 1.0E8 Ohm*cm
    57Co response poor three peaks N/A
    Ave. μτ electrons N/A 2.6E−4 cm2/V N/A
    IMPURITIES ppb Tip Mid Heel Tip Mid Heel Tip Mid Heel
    Li
    B 66 29 0 5 0 0
    C 300 720 200 570 95 300 20 1000 360
    N 36 34 15 60 15 20 5 47 29
    O 530 500 110 370 60 170 32 1100 300
    Na 8 43 24 11 8 13 5 15 21
    Mg 130 40 89 45 40 46 90 80 81
    Al 210 170 630 4400 3100 2100 23 13 0
    Si 61 8 62 150 9 8 15 13 3
    P 0 3 3 13 8 0 9 18 7
    S 98 390 420 300 240 200 220 420 320
    Cl 460 240 73 34 380 110
    K
    Ca
    Ti 27 0.8 77 1 0 0
    V 0.7 0.6 0
    Cr 0 5 4 0 10 0 0 9 5
    Fe 390 400 630 1900 820 720 100 240 120
    Ni
    Cu
    Ge <25 35 <25
    As
    Se
    Nb 21 0.5 110
    Sn
    Er
    Pt
    Pb 64 11 170 0 24 7 24 48 20
    Total 1941 2354 2544 8286 4670 3657 577 3418 1376
    Total w/o Dopants 1277 1773 1114 1986 726 830 530 3322 1356
    Average: 1388.1 1180.433333 1736
    Zn % 6.0 3.5 3.4 2.8 2.6 3.1 3.0 3.2 3.1
    GROWTH CG14 CG15 CG16 CG16a
    GROWTH CG18 CG19 CG20 CG21
    Charge 887 grams 887 grams 887 grams 887 grams
    Excess Te Te 1.033 1.033 1.033 1.033
    (Cd + Zn)
    Dopants ppb Al, 0.1% Pb, Fe Al, Pb Al, Fe Al, Pb, Ge
    1000, 0.1%, 300 1000, 3000 1000, 300 1000, 15000, 300
    Crucible PyC #2 PyC #1 PyC #1 PyC #2
    Lid yes yes yes yes
    Partial Pressure 0.05 atm Ar/1% Hy 0.1 atm Ar/1% Hy 0.19 atm Ar/1% Hy 0.16 atm Ar/1% Hy
    N or P Type N-type N-type N-type P-type
    Ave. Resistivity 1.5E9 Ohm*cm 1.63E10 Ohm*cm 2E10 Ohm*cm 1E9 Ohm*cm
    57Co response N/A one peak discriminator grade N/A
    Ave. μτ electrons N/A 2.8E−4 cm2/V 2.7E−4 cm2/V N/A
    IMPURITIES ppb Tip Mid Heel Tip Mid Heel Tip Mid Heel Tip Mid Heel
    Li 17 0 6
    B 0 300 0 65 100 0
    C 17 43 100 130 21 49 738 220 160 460 170 150
    N 4 7 12 9 10 5 49 35 10 4 5 5
    O 50 120 110 120 160 79 550 200 140 380 170 100
    Na 12 11 11 15 14 17 20 16 9 6 5 7
    Mg 54 52 40 16 15 62 0 16 29 28 16 15
    Al 880 1400 2300 110 1200 1800 0 1500 7600 560 590 1200
    Si 57 37 0 28 11 50 8 0 15 20 5 3
    P 4 0 0 0 9 0
    S 75 150 70 0 35 70
    Cl 3 12 0 28 120 110 17 75 29
    K
    Ca 0 0 40
    Ti
    V
    Cr 3 4 5
    Fe 580 630 720 0 52 66 <5 250 560 49 38 62
    Ni 0 6 0
    Cu
    Ge 67 65 44
    As
    Se 61 0 0
    Nb
    Sn
    Er
    Pt
    Pb 120 m 73 m 220 m 58 75 150 980 790 510
    Total 596 2138 2463 1525 2456 8628 2554 1854 2096
    Total w/o Dopants 197 282 313 428 863 513 1525 956 1028 947 409 342
    Average: 264 601.3333333 1169.666667 566
    Zn % 6.0 5.0 6.0 4.7 5.8 3.0 0.8 3.2 2.4 5.1 3.9 4.8
    GROWTH CG18 CG19 CG20 CG21
    GROWTH CG22 CG23 CG24 CG25
    Charge 882 grams 882 grams 883 grams 883 grams
    Excess Te Te/ 1.023 1.023 1.025 1.025
    (Cd + Zn)
    Dopants ppb Al, Pb 1000, 3000 Al, Fe 1000, 300 Al, Er 2000, 15000 Al, Pb 1500, 15000
    Crucible PyC #2 PyC #1 PyC #1 PyC #2
    Lid yes yes yes yes
    Partial Pressure 0.256 atm Ar/1% Hy 0.263 atm Ar/1% Hy 0.105 atm Ar/1% Hy 0.1 atm Ar/1% Hy
    N or P Type P-type N-type N-type
    Ave. Resistivity 5E7 Ohm*cm 1.5E10 Ohm*cm 1.8E10 Ohm*cm 1.6E10 Ohm*cm
    57Co response N/A three peaks discriminator grade two peaks
    Ave. μτ electrons N/A 1.7E−4 cm2/V 2.8E−4 cm2/V
    IMPURITIES ppb Tip Mid Heel Tip Mid Heel Tip Mid Heel Tip Mid Heel
    Li 0 4 4 4 0 11 0 0 9
    B 120 0 0 0 0 130
    C 210 58 90 25 30 7 79 26 15 77 18 19
    N 24 11 8 35 20 4 20 20 10 50 18 15
    O 160 36 52 45 65 45 95 55 30 180 110 55
    Na 18 19 13 12 6 13 9 12 18 3 0 17
    Mg 15 18 23 13 21 22 14 21 26 32 24 33
    Al 2300 5000 4300 490 360 740 2100 5400 18000 830 2300 8100
    Si 27 0 5 20 21 19 160 13 10 10 4 6
    P 22 12 5 6 0 0 2 0 0
    S 130 80 41 70 40 0 68 110 150 44 44 57
    Cl 130 50 56 26 23 35 23 43 44 24 20 35
    K
    Ca
    Ti 6 0 0
    V
    Cr 0 6 0 6 0 0 14 6 7
    Fe 360 970 940 51 37 130 63 83 240
    Ni
    Cu 0 0 90
    Ge
    As 0 8 0
    Se
    Nb
    Sn
    Er 5400 7600 9800
    Pt
    Pb 80 85 72 390 400 940
    Total 3122 5379 4669 1226 1564 1836 8025 13337 28453 1719 3027 9533
    Total w/o Dopants 822 379 369 376 234 156 525 337 653 499 327 493
    Average: 523.3333333 255.3333333 505 439.6666667
    Zn % 3.0 2.9 3.1 3.5 6.2 4.0 3.3 3.0 2.4 4.6 4.2 3.3
    GROWTH CG22 CG23 CG24 CG25
    GROWTH CG26 CG27 CG28 CG29
    Charge 883 grams 883.5 grams 770 grams 880.47 grams
    Excess Te Te/ 1.025 1.025 1.018 1.018
    (Cd + Zn)
    Dopants ppb Al, Er 1500, 1500 Al, Er 1500, 1500 Al, Er 1500, 1500 Al, Er 1500, 1500
    Crucible PyC #1 PyC #2 PBN #1 PyC #2
    Lid yes yes yes #3 slit, 2 snap rinqs yes
    Partial Pressure 0.105 atm Ar/1% Hy 0.1 atm Ar/2% Hy 0.24 atm Ar/2% Hy 0.25 atm Ar/2% Hy
    N or P Type N-type
    Ave. Resistivity 1.6E10 Ohm*cm 1.0E10 Ohm*cm 2.0E6 Ohm*cm 3.0E10 Ohm*cm
    57Co response discriminator grade discriminator grade N/A discriminator grade
    Ave. μτ electrons 1.94E−4 cm2/v 2.0E−4 cm2/V N/A 2.75E−4 cm2/V
    IMPURITIES ppb Tip Mid Heel Tip Mid Heel Tip Mid Heel Tip Mid Heel
    Li 5 0 5 8 4
    B 980 9
    C 250 260 750 230 290 240 130 110 160 86 26 100
    N 49 30 30 70 37 63 80 30 26 37 19 21
    O 900 300 630 250 320 590 250 160 130 160 50 200
    Na 200 37 17 21 7 20 21 25 24 5
    Mg 20 18 23 19 38 33 14 26 44 61 34 31
    Al 2200 2400 4200 1000 2600 3700 160 270 250 2300 12000 7500
    Si 78 5 16 6 21 32 25 7 7 5 63 22
    P 7 3 0 7 5 2 7
    S 200 150 260 140 110 51 120 22 240 49 100 140
    Cl 60 30 100 53 71 50 61 20 94 7 12 79
    K
    Ca 130 62 45 72
    Ti
    V
    Cr 9 4 10 3 14 5 4
    Fe 120 61 150 250 87 160 260 96 96 240
    Ni
    Cu 47 56
    Ge
    As
    Se 20 0 10 48
    Nb
    Sn
    Er 460 600 260 420 630 680 5500 330 530 720 1700 630
    Pt
    Pb
    Total 4578 3898 6461 2216 4124 5887 7436 1168 1888 3582 14192 9019
    Total w/o Dopants 1918 898 2001 796 894 1507 1776 568 1108 562 492 889
    Average: 1605.666667 1065.666667 1150.666667 647.6666667
    Zn % 6.0 3.2 4.7 3.8 7.2 5.5 3.0 4.6 2.9 3.8 2.8 3.6
    GROWTH CG26 CG27 CG28 CG29
    GROWTH CG30 a & b CG31 CG32
    Charge 883.59 875.82 875.82
    Excess Te Te/ 1.025 1.009 1.009
    (Cd + Zn)
    Dopants ppb Al, Er 1500, 1500 Al, Er 2000, 4500 Al, Er 2000, 4500
    Crucible PyC #3 & #5 PyC #4 PyC #3
    Lid yes yes yes
    Partial Pressure 0.25 atm Ar/2% Hy 0.25 atm Ar/2% Hy 0.13 atm Ar/2% Hy p. trans
    N or P Type
    Ave. Resistivity 2.0E10 Ohm*cm 1.0E10 Ohm*cm
    57Co response two peaks discriminator grade
    Ave. μτ electrons 3.5E4−cm2/V 1.0E−3 cm2/V
    IMPURITIES ppb Tip Mid Heel Tip Mid Heel
    Li 7 62
    B
    C 290 120 120 470 62 21
    N 56 67 49 34 83 6
    O 440 230 340 390 75 33
    Na 9 12 44 50 160
    Mg 56 36 51 47 28 87
    Al 250 690 3500 1400 4400 50000
    Si 12 12 11 21
    P 4
    S 100 100
    Cl 36 320 1400 340 1700 5000
    K
    Ca
    100
    Ti
    V
    Cr
    Fe 110 110 150 100 56 130
    Ni
    Cu 86
    Ge
    As
    Se
    Nb
    Sn
    Er 310 450 440 1900 2400 3700
    Pt
    Pb
    Total 1560 2044 6162 4725 8876 59506
    Total w/o Dopants 1000 904 2222 1425 2076 5806
    Average: 1375.333333 3102.333333
    Zn % 7.8 5.4 6.0 4.9 3.7 2.8
    GROWTH CG30 a & b CG31 CG32
    GROWTH CG32a CG33a CG33b
    Charge 874.99 872.9 + 0.21 Te
    Excess Te Te/ 1.009 1.0074 1.0074
    (Cd + Zn)
    Dopants ppb Al, Er 2000, 4500 plus Al 2000 Al, Er 2000, 10000 Al, Er 2000, 10000
    Crucible PyC #5 PyC #2 PyC #6
    Lid yes yes yes
    Partial Pressure 0.17 atm Ar/2% Hy 0.14 atm Ar/2% Hy p. trans 0.18 atm Ar/2% Hy
    N or P Type
    Ave. Resistivity
    57Co response three peaks
    Ave. μτ electrons 3.0E−3 cm2/V
    IMPURITIES ppb Tip Mid Heel Tip Mid Heel
    Li 7 6 13
    B 21
    C 12 20 940
    N 4 4 20
    O 20 30 620
    Na 10 6 5400
    Mg 29 50 990
    Al 320 590 1200
    Si 39 490
    P 6
    S 50 24 43
    Cl 350 710 400
    K
    Ca 340
    Ti 540
    V
    Cr 11
    Fe 50 110 330
    Ni 19
    Cu 40
    Ge
    As
    Se
    Nb 730
    Sn
    Er
    4000 8700 2500
    Pt
    Pb 4100
    Total 4897 10250 18747
    Total w/o Dopants 577 960 15047
    Average: 0 5528
    Zn % 3.5 4.2 4.5
    GROWTH CG32a CG33a CG33b

Claims (30)

I/we claim:
1. A method for processing a semiconductor material, comprising:
placing at least one element from Group II of the periodic table and at least one element from Group VI of the periodic table in a container;
mixing the at least one element from Group II and the at least one element from Group VI of the periodic table with a first dopant and a second dopant to form a mixture, wherein the first dopant includes at least one element from Group III or VII of the periodic table, and wherein the second dopant includes erbium at a concentration of about 10 to about 400,000 atomic parts per billion or dysprosium at a concentration of about 10 to about 10,000 atomic parts per billion; and
converting the mixture into a solid material.
2. The method of claim 1 wherein the first dopant includes aluminum at a concentration of about 10 to about 20,000 atomic parts per billion, and wherein the second dopant includes erbium.
3. The method of claim 1 wherein the first dopant includes indium at a concentration of about 10 to about 20,000 atomic parts per billion, and wherein the second dopant includes erbium.
4. The method of claim 1 wherein the at least one element from Group II of the periodic table includes cadmium, and wherein the at least one element from Group VI of the periodic table includes tellurium.
5. The method of claim 4 wherein the mixture further includes zinc, and wherein the mixture has a molar excess of tellurium over cadmium and zinc, the molar excess being between about 0.5% to about 75%.
6. The method of claim 1 wherein the first dopant includes chlorine at a concentration of about 10 to about 20,000 atomic parts per billion, and wherein the second dopant includes erbium.
7. A method for preparing a co-doped semiconductor material having at least one element from Group II of the periodic table and at least one element from Group VI of the periodic table, wherein the method comprising:
selecting a dopant from the group consisting of aluminum, chlorine, and indium;
selecting a co-dopant based on a formation energy of a complex between the at least one element from Group VI of the periodic table and the co-dopant; and
doping the semiconductor material with the selected dopant and the co-dopant.
8. The method of claim 7 wherein selecting a co-dopant element includes determining whether the co-dopant irreversibly combines with the at least one element from Group VI of the periodic table in a liquid phase.
9. The method of claim 7 wherein the at least one element from Group VI includes Tellurium, and wherein the co-dopant includes erbium.
10. The method of claim 7 wherein doping the semiconductor material includes doping the semiconductor material with the selected co-dopant at a concentration of about 10 to about 400,000 atomic parts per billion.
11. The method of claim 7, further comprising decreasing intrinsic defects related to the at least one element from Group VI with the co-dopant.
12. A method for forming a co-doped semiconductor material containing a first element from Group II of the periodic table and a second element from Group VI of the periodic table, the method comprising:
selecting a first dopant from elements in Group III or Group VII of the periodic table based on a target resistivity of the semiconductor material;
determining a formation energy of a compound containing a rare earth metal and at least one of the first element and the second element; and
selecting the rare earth metal as a second dopant based on the determined formation energy and a target threshold of formation energy.
13. The method of claim 12 wherein determining the formation energy includes determining at least one of an enthalpy of formation and an entropy of formation of the compound containing the rare earth metal and at least one of the first element and the second element.
14. The method of claim 12 wherein if the formation energy is above the target threshold, selecting the rare earth metal as the second dopant.
15. The method of claim 12 wherein the determined formation energy corresponds to a heat of formation of the compound containing the rare earth metal and at least one of the first element and the second element, and wherein if the heat of formation is above the target threshold, selecting the rare earth metal as the second dopant.
16. The method of claim 12 wherein:
the second element contains tellurium (Te);
the rare earth metal contains erbium (Er); and
determining the formation energy includes determining a formation energy of Er—Te complexes.
17. The method of claim 12 wherein:
the second element contains tellurium (Te);
the rare earth metal contains erbium (Er);
determining the formation energy includes determining a formation energy of Er—Te complexes;
comparing the determined formation energy of Er-Te complexes to the target threshold; and
if the determined formation energy of Er-Te complexes is greater than the target threshold, selecting erbium (Er) as the second dopant.
18. The method of claim 12 wherein determining the formation energy includes determining if the rare earth metal combines with at least one of the first element and the second element irreversibly to form the compound in a liquid phase.
19. The method of claim 12 wherein determining the formation energy includes determining if a reaction product between the rare earth metal and at least one of the first element and the second element form stable solid domains in the bulk semiconductor material.
20. The method of claim 12, further comprising selecting a concentration of the second dopant based on a target depletion characteristic of the semiconductor material.
21. The method of claim 20 wherein the target depletion characteristic includes a target charge carrier mobility and lifetime, and wherein selecting the concentration of the second dopant includes selecting a concentration of the second dopant based on the target charge carrier mobility and lifetime.
22. The method of claim 20 wherein the target depletion characteristic includes full depletion under a bias voltage, and wherein selecting the concentration of the second dopant includes selecting a concentration of the second dopant to achieve the full depletion under the bias voltage.
23. The method of claim 20 wherein the selected second dopant contains erbium (Er), and wherein selecting the concentration of the second dopant includes selecting a concentration of the second dopant to be about 10 to about 400,000 atomic parts per billion.
24. A method for forming a co-doped semiconductor material, comprising:
forming a mixture with at least one element from Group II of the periodic table, at least one element from Group VI of the periodic table in a container, a first dopant, and a second dopant, wherein the first dopant includes at least one element from Group III or VII of the periodic table, and wherein the second dopant contains erbium (Er) or dysprosium (Dy);
adjusting a concentration of the second dopant in the mixture based on a target depletion characteristic of the semiconductor material; and
converting the mixture into a solid material.
25. The method of claim 24 wherein the target depletion characteristic includes a charge carrier mobility and lifetime, and wherein adjusting the concentration of the second dopant includes adjusting a molar concentration of the second dopant based on the target charge carrier mobility and lifetime.
26. The method of claim 24 wherein:
the target depletion characteristic includes a charge carrier mobility and lifetime;
the second dopant contains erbium (Er); and
adjusting the concentration of the second dopant includes increasing a molar concentration of erbium (Er) in the mixture to increase the charge carrier mobility and lifetime of the semiconductor material.
27. The method of claim 24 wherein:
the second dopant contains erbium (Er); and
adjusting the concentration of the second dopant includes adjusting a molar concentration of erbium (Er) in the mixture between about 10 to about 400,000 atomic parts per billion.
28. The method of claim 24 wherein:
the second dopant contains erbium (Er); and
adjusting the concentration of the second dopant includes adjusting a molar concentration of erbium (Er) in the mixture between about 10 to about 10,000 atomic parts per billion.
29. The method of claim 24 wherein:
the second dopant contains erbium (Er); and
adjusting the concentration of the second dopant includes adjusting a molar concentration of erbium (Er) in the mixture between about 10 to about 20,000 atomic parts per billion.
30. The method of claim 24 wherein:
the second dopant contains erbium (Er); and
adjusting the concentration of the second dopant includes adjusting a molar concentration of erbium (Er) in the mixture between about 10 to about 200,000 atomic parts per billion.
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