Classifications

• • C—CHEMISTRY; METALLURGY
  • C30—CRYSTAL GROWTH
  • C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
  • C30B29/00—Single crystals or homogeneous polycrystalline material with defined structure characterised by the material or by their shape
  • C30B29/02—Elements
  • C30B29/08—Germanium
• • C—CHEMISTRY; METALLURGY
  • C30—CRYSTAL GROWTH
  • C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
  • C30B11/00—Single-crystal growth by normal freezing or freezing under temperature gradient, e.g. Bridgman-Stockbarger method
  • C30B11/003—Heating or cooling of the melt or the crystallised material
• • C—CHEMISTRY; METALLURGY
  • C30—CRYSTAL GROWTH
  • C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
  • C30B11/00—Single-crystal growth by normal freezing or freezing under temperature gradient, e.g. Bridgman-Stockbarger method
  • C30B11/02—Single-crystal growth by normal freezing or freezing under temperature gradient, e.g. Bridgman-Stockbarger method without using solvents
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T117/00—Single-crystal, oriented-crystal, and epitaxy growth processes; non-coating apparatus therefor
  • Y10T117/10—Apparatus
  • Y10T117/1024—Apparatus for crystallization from liquid or supercritical state
  • Y10T117/1032—Seed pulling
  • Y10T117/1064—Seed pulling including a fully-sealed or vacuum-maintained crystallization chamber [e.g., ampoule]
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T428/00—Stock material or miscellaneous articles
  • Y10T428/24—Structurally defined web or sheet [e.g., overall dimension, etc.]
  • Y10T428/24355—Continuous and nonuniform or irregular surface on layer or component [e.g., roofing, etc.]

Definitions

• Systems and methods herein relate generally to monocrystalline germanium ingots/wafers and in particular to growth of such ingots/wafers with reduced micro-pit density (MPD).
• MPD micro-pit density
• the crystallization of the melt forms an essentially cylindrical crystal (an ingot) along a vertical axis with the seed crystal below the crystalline raw material(s).
• the equipment necessary to form the semiconductor crystal includes a crystal growth furnace, an ampoule, a crucible, and sometimes a crucible support.
• the crucible may also have a lower, narrow portion, called a seed well.
• Systems and methods consistent with the invention are directed to growth of moncrystalline germanium.
• a method of inserting an ampoule with raw material into a furnace having a heating source growing a crystal using, e.g., a vertical growth process wherein movement of a crystallizing temperature gradient relative to the raw material/crucible is achieved to melt the raw material and reform it in monocrystalline form, and growing, at a predetermined crystal growth length, the crystal using a vertical growth process to melt the material and reform it as a monocrystalline compound, wherein monocrystalline ingots having reduced micro-pit densities are reproducibly provided.
• Figures 1 A and 1 B are cross sectional views of exemplary crystal growth apparatus and crucible, consistent with certain aspects related to the innovations herein;
• FIG. 2 illustrate an exemplary micropit, consistent with certain aspects related to the innovations herein;
• Figure 3A and 3B illustrate exemplary methods of crystal growth, consistent with certain aspects related to the innovations herein;
• Figure 4 illustrates an exemplary method for loading a crystal growth furnace with a crucible loaded with germanium, consistent with certain aspects related to the innovations herein;
• Figures 5A-5D illustrate another exemplary implementation of germanium crystal growth, consistent with certain aspects related to the innovations herein;
• Figure 6 is a flow diagram showing another exemplary process of crystal growth, consistent with certain aspects regarding the innovations herein. DETAILED DESCRIPTION OF EXEMPLARY IMPLEMENTATIONS
• the apparatus and method are particularly applicable to an apparatus and method for germanium (Ge) crystal growth and it is in this context that the apparatus and method are described. It will be appreciated, however, that the apparatus and method may have greater utility since the apparatus and method can be used to produce other mono- and/or poly-crystalline ingots having low micropit densities.
• FIG. 1 A is a cross sectional view of an example of a crystal growth apparatus 20.
• the exemplary apparatus may include a crucible support 22 in a furnace 24, such as a furnace that establishes a crystallizing temperature gradient which may be used in a suitable vertical growth process, e.g., a vertical gradient freeze (VGF) and/or vertical Bridgman (VB) crystal growing and/or, if the furnace is moveable, a vertical Bridgman- Stockbarger process.
• a suitable vertical growth process e.g., a vertical gradient freeze (VGF) and/or vertical Bridgman (VB) crystal growing and/or, if the furnace is moveable, a vertical Bridgman- Stockbarger process.
• VVF vertical gradient freeze
• VB vertical Bridgman
• the crucible support 22 provides physical support for and allows for thermal gradient control to an ampoule 26 (that in one implementation may be made of quartz) containing a crucible 27.
• the crucible support 22 when the furnace is in operation, the crucible support 22 may be moved during the crystal growth process. In alternative implementations, the crucible support may be fixed and the furnace, when in operation, can be moved during the crystal growth process.
• the crucible 27 may contain a seed crystal 28, a grown monocrystalline crystal/compound 30 formed on top of the seed crystal and raw melt material 32.
• the crucible 27 may be a pyrolitic boron nitride (pBN) material with a cylindrical crystal growth portion 34, a smaller diameter seed well cylinder 36 and a tapered transition portion 44.
• the crystal growth portion 34 has a diameter equal to the desired diameter of the crystal product.
• the current industry standard crystal diameters are 2 inch, 3 inch, 4 inch, 5 inch, 6 inch and 8 inch ingots that can be cut into wafers.
• the diameter of 2 inch, 3 inch, 4 inch, 5 inch, 6 inch and 8 inch corresponds to 50.80 mm, 76.20 mm, 100.00 mm, 125.00 mm, 150.00 mm and 200.00 mm, respectively.
• the seed well cylinder 36 may have a closed bottom and a diameter slightly larger than that of a high quality seed crystal 28. In one illustrative implementation, for example, the diameter could be in the range of about 6-25 mm, and may have a length on the order of about 30-50 mm.
• the cylindrical crystal growth portion 34 and the seed well cylinder 36 may have straight walls or may taper outwardly on the order of one to a few degrees to facilitate the removal of the crystal from the crucible 27.
• the tapered transition portion 38 between the growth portion 34 and the seed well cylinder 36 has an angled side wall pitched at, for example approximately 45-60 degrees, with a larger diameter equal to and connected to the growth zone wall and a narrower diameter equal to and connected to the seed well wall.
• the angled side wall may also be at other angles that are more steep or less steep than about 45-60 degrees. The angle above is defined as an angle between the angled side wall and the horizontal line.
• the crucible 27 Before insertion in the crystal growth furnace 24, the crucible 27 is loaded with raw materials and inserted into the ampoule 26.
• the ampoule 26 may be formed of quartz material.
• the ampoule 26 typically has a shape similar to that of the crucible 27.
• the crucible may be cylindrical in a crystal growth region 40, cylindrical with a narrower diameter in its seed well region 42, and have a tapered transition region 44 between the two regions. Further, the crucible 27 may fit inside the ampoule 26 with a narrow margin between them.
• the ampoule 26 is closed at the bottom of its seed well region 42 and, like the crucible, sealed on top after the crucible and raw materials are loaded.
• the bottom of the ampoule 26 may have the same funnel shape as the crucible 27.
• an apparatus for germanium crystal growth may comprise a crystal growth furnace including a heating source (e.g., heating elements 60) and a plurality of heating zones, an ampoule configured to be loaded into the furnace, wherein the ampoule includes a loading container and a crucible with a seed well, optionally an ampoule support, and a controller coupled to the crystal growth furnace and the ampoule support, the controller controlling the one or more heating zones of the heating source and the movable ampoule support to perform a vertical gradient freeze process on the crucible when it is in the furnace.
• a heating source e.g., heating elements 60
• an ampoule configured to be loaded into the furnace, wherein the ampoule includes a loading container and a crucible with a seed well, optionally an ampoule support, and a controller coupled to the crystal growth furnace and the ampoule support, the controller controlling the one or more heating zones of the heating source and the movable ampoule support to perform a vertical gradient freeze process on the crucible when it
• the crystallizing temperature gradient and/or the crucible are then moved relative to each other to melt the raw material and then reform the material as a monocrystalline germanium ingot, wherein, as a result of vertical growth processes performed in the apparatus, the apparatus reproducibly provides germanium ingots having micro-pit densities of reduced quanta.
• germanium ingots having micropit densities of the following ranges may be reproducibly provided: greater than about 0.025/cm 2 and less than about 0.51/cm 2 ; greater than about 0.025/cm 2 and less than about 0.26/cm 2 ; greater than about 0.025/cm 2 and less than about 0.13/cm 2 ; less than about 0.13/cm 2 ; and greater than about 0.025/cm 2 and less than about 0.26/cm 2 .
• micro-pit densities may be further controlled (decreased) by controlling the cooling rate and other conditions.
• the controller coupled to the crystal growth furnace and the ampoule support may cool the interface between the grown
• the controller may cool the interface between the grown monocrystalline crystal/compound 30 and the raw melt material 32 at a cooling rate of about 0.1 to about 10 C /hour and a temperature gradient from about 0.5 to about 10 C /cm, during the crystal growth including a vertical Bridgman (VB) process.
• VVF vertical gradient freeze
• the controller may cool the interface between the grown monocrystalline crystal/compound 30 and the raw melt material 32 at a cooling rate of about 0.1 to about 10 C /hour and a temperature gradient from about 0.5 to about 10 C /cm, during the crystal growth including a vertical Bridgman (VB) process.
• VB vertical Bridgman
• the controller may cool the interface between the grown monocrystalline crystal/compound 30 and the raw melt material 32 at a cooling rate of about 3 ° C /hour for about the first 5 hours and of about 30 ° C /hour to about 45 ° C /hour for a remaining period of the cooling process, during the crystal growth/cooling including a vertical gradient freeze (VGF) process and/or vertical
• the ampoule and crucible may have tapered (funnel shaped) regions.
• the crucible support 22 In implementations where ampoule-crucible combination has a funnel shape, the crucible support 22
• the ampoule-crucible combination may retain different shapes, and the basic structure of the crucible support 22 would be changed accordingly to fit the specific different shape.
• the stability and strength to the ampoule and its contents are provided through a solid, thin- walled cylinder 50 of the crucible support 22.
• the solid, thin-walled cylinder 50 accommodates the funnel end of the ampoule structure 26.
• the crucible support cylinder 50 is made of a heat conducting material, preferably quartz. In other implementations, silicon carbide and ceramic may also be utilized to form the crucible support cylinder 50.
• the cylinder 50 makes a circle of contact with ampoule 26, where the upper rim of the cylinder 50 meets the shoulder of the ampoule's tapered region 38.
• Such configuration leads to minimal solid-to-solid contact which ensures that little or no undesirable, relatively uncontrollable heat conduction occurs. As a result, heating is able to be generated by other, more controllable processes.
• a low density insulating material such as ceramic fiber, fills the majority of the inside of the support cylinder 50 with only a hollow axial core 52 in approximately the center of the insulating material left empty to receive the seed well 42 of the ampoule 26.
• the low-density insulating material may also comprise alumina fiber (1 ,800.degree. C), alumina-silica fiber (1 ,426.degree. C), and/or zirconia fiber (2,200.degree. C). The insulating material is carefully placed in the crucible support 22. The weight of the ampoule 26, as it sits on top of the cylinder 50, pushes the insulating material down and forms the slanted insulating material edge 54.
• convection is an uncontrollable heat transfer method that may work to the detriment of the VGF/VB and other crystal growth process herein.
• the hollow core 52 extends downward to a small distance below the bottom of the ampoule seed well 42.
• the hollow core 52 may extend through the crucible support from the bottom of the seed well to the bottom of the furnace apparatus 24.
• the hollow core 52 provides a cooling path from the center of the crystal. It contributes to cooling in the seed well and in the center of the growing crystal . With this construction, heat energy can escape down through the center of the solid crystal and seed, down through this hollow core 52 in the insulating material within the crystal support 22. Without the hollow core 52, the temperature of the center of the cooling ingot would naturally be higher than the crystal material nearer to the outer surface. In this case, the center of the ingot in any horizontal cross section would crystallize later after its perimeter had solidified. Crystals with uniform electrical properties cannot be made under these conditions.
• heat energy is conducted down through the bottom of the ampoule 26 and the hollow core 52 from where it radiates back out of radiation channels 56. It is important to reduce heat energy from the center of the growing crystal so that the isothermal layers are kept flat across the crystal diameter. Maintaining a flat crystal-melt interface allows the production of crystals with uniform electrical and physical properties.
• low-density insulating material within the cylinder 50 may obstruct the flow of heat radiation from a set of furnace heat elements 60 to the ampoule 26 in the seed well region 42, so this method requires the creation of a plurality of horizontal radiation channels/openings/tunnels 56 through the insulation material.
• the radiation channels 56 penetrate the insulating material to provide heat radiation outlets to controllably transfer heat from the furnace heating elements 60 to the ampoule seed well 42.
• the number, shape and diameter of the radiation channels 56 varies depending on specific conditions.
• the radiation channels may also be slanted, bent or wave-like.
• the radiation channels also do not necessary have to be continuous, as they may extend only partially through the insulating material. This helps minimize convection currents.
• the diameter of these channels is small, on the order of a pencil width, so that convection airflow is insignificant. Larger holes with cross-sectional area on the order of a square inch or more can also be used according to other implementations of the invention.
• the radiation channels 56 through the insulating material also work in conjunction with the hollow core 52 in the center of the insulating material to radiate heat energy drawn from the center of the crystal, and cool the crystal with planar isothermal temperature gradient layers.
• the radiation channels 56 enable temperature control and directly relate to crystal growth yield.
• the furnace 24 as shown in Figure 1 A is an example of a furnace that may be used for both Vertical Gradient Freeze (VGF) and Vertical Bridgman (VB) or Vertical Bridgman-Stockbarger (VBS) crystal growth processes. Other furnaces may also be used.
• VGF Vertical Gradient Freeze
• VB Vertical Bridgman
• VBS Vertical Bridgman-Stockbarger
• Figure 1 B is a cross sectional view of exemplary crucible 99 consistent with certain aspects related to the innovations herein. Referring to FIG.
• an exemplary crucible for some of the illustrative crystal growth furnaces herein may have a tapered crystal growth region of about 25mm to about 50mm in length. Further, in some exemplary implementations the crucible 99 and ingots may have a growth length after the taper ("predetermined growth length") of about 1 10mm to about 200mm in length.
• Figure 2 illustrates a region of a crystal ingot or wafer containing a micropit 200, consistent with aspects related to the innovations herein. As seen in FIG. 2, presence of such micropits 200 produces noticeable dark spots and associated problems in the grown germanium material. When the micropit count is too high, resulting ingots or wafers may be unusable and thus require recycling. Therefore, micropits or
• an exemplary method may comprise loading raw Ge material into the crucible 280, sealing the crucible and/or container or vessel holding the crucible 282, placing the crucible into the crystal growth furnace, melting the raw Ge material in the crucible to create a melt, and performing a vertical growth process to form the monocrystalline germanium ingot 284.
• the method may include one or more further steps including controlling a crystallizing temperature gradient of the melt while placing the melt in contact with the seed crystal, forming a monocrystalline germanium ingot via movement of the crystallizing temperature gradient and/or the crucible relative to each other, and cooling the monocrystalline germanium ingot. Further, as a result of the vertical growth processes herein, germanium ingots having micro-pit densities of reduced quanta are reproducibly provided.
• germanium ingots having micropit densities of the following ranges may be reproducibly provided: greater than about 0.025/cm 2 and less than about 0.51 /cm 2 ; greater than about 0.025/cm 2 and less than about 0.26/cm 2 ; greater than about 0.025/cm 2 and less than about 0.13/cm 2 ; less than about 0.13/cm 2 ; and greater than about 0.025/cm 2 and less than about 0.26/cm 2 .
• micro-pit densities may be controlled by controlling the cooling rate and other conditions.
• single crystal substrates produced according to the innovations herein may have, from starting growth portion to end of growth portion, a carrier concentration of about 9 x 10 17 to about 4 x 10 18 or about 5 x 10 18 /cm 3 , and a resistivity of about 7 x 10 "3 to 2 x 10 "3 or 3 x 10 "3 ⁇ . ⁇ , with a mobility of about 950 cm 2 /Vs to about 450 cm 2 /Vs.
• the dislocation density may less than about 500/cm 2 , or even less than about 200/cm 2 .
• Carrier concentration, mobility and dislocation density may also be controlled by controlling the cooling rate and other conditions.
• FIG. 3B illustrates another exemplary method 80 for crystal growth using Vertical Gradient Freeze (VGF) and Vertical Bridgman (VB) process steps that may reduce the micropit densities and result in higher yields, consistent with aspects related to the innovations herein.
• VGF Vertical Gradient Freeze
• VB Vertical Bridgman
• the furnace is prepared for crystal growth (82) as described above.
• the VGF process 84) is used.
• the VB process (86) or the VBS process may be used to complete the crystal growth.
• the melt/solid line is held at a level and then the process is continued with fixed conditions since the process changes typically required for VGF process as the volume decreases are not needed.
• the VB process may be used at
• an exemplary method may comprise loading raw Ge material into the crucible, sealing the crucible and the container, placing the crucible into the crystal growth furnace, melting the raw Ge material in the crucible to create a melt, controlling a crystallizing temperature gradient of the melt while placing the melt in contact with the seed crystal, forming a monocrystalline germanium ingot via movement of the crystallizing temperature gradient and/or the crucible relative to each other, and cooling the monocrystalline germanium ingot.
• germanium ingots having micro-pit densities of reduced quanta are reproducibly provided.
• germanium ingots having micropit densities of the following ranges may be reproducibly provided: greater than about 0.025/cm 2 and less than about 0.51 /cm 2 ; greater than about 0.025/cm 2 and less than about 0.26/cm 2 ; greater than about 0.025/cm 2 and less than about 0.13/cm 2 ; less than about 0.13/cm 2 ; and greater than about 0.025/cm 2 and less than about 0.26/cm 2 .
• such micro-pit densities may be controlled by controlling the cooling rate and other conditions.
• the method may further comprise adding arsenic (As), gallium (Ga) and/or antimony (Sb) as a dopant.
• the method may include growth via a vertical gradient freeze (VGF) process and include a cooling process performed at a cooling rate of about 0.1 to about 10 C /hour and at a temperature gradient of between about 0.5 to about 10 C/cm.
• VVF vertical gradient freeze
• the method may include crystal growth including a vertical Bridgman (VB) process, at a cooling rate of about 0.1 to about 10 C /hour and a temperature gradient from about 0.5 to about 10 C /cm.
• VB vertical Bridgman
• the method of crystal growth may include crystal growth/cooling including a vertical gradient freeze (VGF) process and/or vertical Bridgman (VB) process, at a cooling rate of about 3 ° C /hour for about the first 5 hours and of about 30 ° C /hour to about 45 ° C /hour for a remaining period of the cooling process.
• VVF vertical gradient freeze
• VB vertical Bridgman
• a loading crucible 90 may be located above the crucible 27 and allows the crucible 27 to be loaded with more raw material .
• the raw germanium material 92 is solid and therefore cannot be tightly packed into the crucible 27 to be melted.
• the loading crucible is used to hold extra raw material that can be melted and then drain down into the crucible which results in a larger germanium charge in the crucible 27 which in turn results in a larger length germanium crystal .
• about 35 to about 65% of the raw material may be initially loaded into the loading crucible 90 and about 65 to about 35% of the raw material is loaded directly into the crucible 27.
• a charge of approximately 10 kg may be loaded into the furnace to produce a 200 mm 4 inch ingot having the low micropit densities herein.
• the dimensions of the crucible were 100 mm diameter and 200 mm length crystal growth region 40.
• the diameter of the crucible in the seed well region 42 was 7 mm.
• a 10 kg of germanium precursor material may be loaded for ingot growth.
• the germanium seed crystal is inserted in the bottom portion of the pBN crucible 27
• about 10 kg of germanium material and about 36 g of a boron oxide as the liquid sealant may be added therein.
• the charge loaded pBN crucible was inserted in a quartz ampoule.
• the quartz ampoule was sealed under reduced pressure with a quartz cap.
• the quartz ampoule is then loaded in the furnace and placed on the crucible support. Once the ampoule is loaded into the furnace, the quartz ampoule may be heated at the rate of approximately 150-200 C /hour.
• the temperature reaches the melting point at the seed portion and about 3-18 ° C over the melting ranges of germanium (-940-955 C) at the crystal growth region, the
• temperature point may be held until all of the monocrystalline germanium material melts (e.g., in some implementations, approximately 2-4 hours). Once the monocrystalline germanium material melt, a VGF method was first used for crystal growth. The temperature may then be reduced in the lower heating zone slowly to let crystal growth starting at the seed part begin and continue through the transition region until the crystal growth region cools, in association with a VGF and/or VB process(es), at a cooling rate of about 3 ° C /hour for about the first 5 hours and of about 30 ° C /hour to about 45 ° C /hour for a remaining period of the cooling process after crystal growth process is completed.
• crystal growth cooling may occur at a cooling rate of about 0.1 to about 10 C /hour and at a temperature gradient of between about 0.5 to about 10 ° C/cm (e.g., associated with a VGF process). Further, in an exemplary VB process, a crystal growth cooling rate of 0.3-0.47 ° C /hour may be used, while maintaining the temperature gradient from 1 .2 to 1 .8 C/cm.
• the VB process when the crystal has grown about 1 to about 3 inches high in the crystal growth region, the VB process may be started.
• the crucible down speed is controlled to precise cooling/growing parameters, such as a cooling rate of about 0.2 to about 0.5 °C/hr and/or a temperature gradient of about 0.3 to about 2.5 °C/cm in the crystal growth zone.
• Resulting crystals of about 190 mm length and high quality i.e., low micro-pit density or "low MPD" may be achieved via such a process, from a 200 mm long ingot, which is a crystal yield of about 95%.
• germanium ingots having micropit densities of the following ranges may be reproducibly provided: greater than about 0.025/cm 2 and less than about 0.51 /cm 2 ; greater than about 0.025/cm 2 and less than about 0.26/cm 2 ; greater than about 0.025/cm 2 and less than about 0.13/cm 2 ; less than about 0.13/cm 2 ; and greater than about 0.025/cm 2 and less than about 0.26/cm 2 .
• single crystal substrates produced according to the innovations herein may have, from starting growth portion to end of growth portion, a carrier concentration of about 9 x 10 17 to about 4 x 10 18 or about 5 x 10 18 /cm 3 (range of about 9 x 10 17 to about 4.86 x 10 18 /cm 3 being measured), and a resistivity of about 7 x 10 "3 to 2 x 10 "3 or 3 x 10 "3 ⁇ -cm (range of about 7.29 x 10 "3 to about 2.78 x 10 "3 ⁇ . ⁇ being measured), with a mobility of about 950 cm 2 A/s to about 450 cm 2 A/s (values of 955 cm 2 /Vs and 467 cm 2 A/s being measured).
• the dislocation density may less than about 500/cm 2 , or even less than about 200/cm 2 .
• the method may include loading first raw Ge material into a crucible that includes a seed well holding a seed crystal, loading second raw Ge material into a container for supplementing the Ge melt material, sealing the crucible and the container in an ampoule, and placing the ampoule with the crucible into a crystal growth furnace having a movable ampoule support that supports said ampoule.
• exemplary implementations may include melting the first raw Ge material in the crucible to create a melt, melting the second raw Ge material in said container, and adding the melted second raw Ge material to said melt.
• exemplary implementations may include controlling the crystallizing temperature gradient of the melt so that the melt crystallizes when in contact with the seed crystal and forms a monocrystalline germanium ingot and, optionally, cooling the
• the step of forming the monocrystalline germanium ingot may include creating a temperature gradient of about 0.3 to about 2.5 °C/cm in the crystal growth zone. Additionally, the monocrystalline germanium ingot may be cooled at a rate of about 0.2 to about 0.5 °C/hr. Further, the crucible may be maintained stationary during movement of the crystallizing temperature gradient.
• the monocrystalline germanium ingot may have a diameter of between about 50 mm to about 200 mm (about 2 inch to about 8 inch). In one implementation, for example, the monocrystalline germanium ingot may have a diameter of 152.4 mm (6 inch). Moreover, monocrystalline
• germanium ingots and wafers having a diameter of between about 50 mm to about 200 mm (about 2 inch to about 8 inch) produced via the innovations herein may have micropit densities reproducibly provided within the following ranges: greater than about 0.025/cm 2 and less than about 0.51 /cm 2 ; greater than about 0.025/cm 2 and less than about 0.26/cm 2 ; greater than about 0.025/cm 2 and less than about 0.13/cm 2 ; less than about 0.13/cm 2 ; and greater than about 0.025/cm 2 and less than about 0.26/cm 2 .
• single crystal substrates having a diameter of between about 50 mm to about 200 mm (about 2 inch to about 8 inch) produced according to the innovations herein may have, from starting growth portion to end of growth portion, a carrier concentration of about 9 x 10 17 to about 4 x 10 18 or about 5 x 10 18 /cm 3 (range of about 9 x 10 17 to about 4.86 x 10 18 /cm 3 being measured), and a resistivity of about 7 x 10 "3 to 2 x 10 "3 or 3 x 10 "3 Q.cm (range of about 7.29 x 10 "3 to about 2.78 x 10 "3 Q.cm being measured), with a mobility of about 950 cm 2 /Vs to about 450 cm 2 /Vs (values of 955 cm 2 /Vs and 467 cm 2 /Vs being measured).
• the dislocation density may less than about 500/cm 2 , or even less than about 200/cm 2 .
• an exemplary apparatus for growing a large-diameter monocrystalline germanium crystal may comprise a crystal growth furnace including a heating source and a plurality of heating zones, an ampoule configured to be loaded into the furnace, wherein the ampoule includes a loading container and a crucible with a seed well, a movable ampoule support, and a controller coupled to the crystal growth furnace and the moveable ampoule support. Further, the controller may control one or more of the heating zones of the heating source and the movable ampoule support to perform a vertical gradient freeze process on the crucible when it is in the furnace.
• the crystal growth furnace may have a plurality of heating zones, such as between 4 to 8 heating zones, between 5 to 7 heating zones, or 6 heating zones. Consistent with the ingot/wafer diameter desired, exemplary crucibles may have an inner diameter of between about 50 mm to about 200 mm (about 2 to about 8 inches), or, in some implementations, of about 150 mm (about 6 inches).
• FIGs. 5A-5D illustrate another exemplary implementation of germanium crystal growth, consistent with certain aspects related to the innovations herein.
• FIGs. 5A-5D are diagrams of longitudinal cross-sections of the apparatus for growing a
• FIG. 5A illustrates a cross sectional view of an example of a crystal growth apparatus.
• the apparatus may include a furnace for use in vertical gradient freeze (VGF) growing processes and/or vertical Bridgman (VB) growing processes, and may include an ampoule support 1 1 in a furnace 1 , wherein the heater 2 is made up of multiple zones, each controlled
• An ampoule support 1 1 may be used to provide physical support and thermal gradient control for an ampoule 3 (that, in one implementation, is made of quartz) which contains a crucible 12, which in turn is capable of holding a seed in a seed well 18.
• the ampoule support 1 1 when the furnace is in operation, can be moved axially during the crystal growth process.
• the crucible 12 may contain a seed crystal 17 from which is grown a monocrystal formed on top of the seed crystal .
• the crucible 12 may be a pyrolytic boron nitride (pBN) structure with a cylindrical crystal growth portion 13, a smaller diameter seed well cylinder 18 and a tapered transition portion 7.
• the crystal growth portion 13 is open at the top of the crucible 12 and has a diameter equal to the desired diameter of the crystal product.
• the current industry standard crystal diameters are 50.8, 76.2, 100.0 and 150.0 mm (2, 3, 4 and 6 inch) diameter ingots that can be cut into wafers.
• the seed well cylinder 18 may have a closed bottom and a diameter slightly larger than that of a high quality seed crystal 17, e.g., about 6-25 mm, and a length on the order of 30-100 mm.
• the cylindrical crystal growth portion 13 and the seed well cylinder 18 may have straight walls or may taper outwardly on the order of one to a few degrees to facilitate the removal of the crystal from the crucible 12.
• the tapered transition portion 7 between the growth portion 13 and the seed well cylinder 18 has an angled side wall pitched at, for example approximately 45-60 degrees, with a larger diameter equal to and connected to the growth zone wall and a narrower diameter equal to and connected to the seed well wall.
• the angled side wall may also be at other angles that are steeper or less steep than 45-60 degrees.
• the ampoule 3 may be made of quartz.
• the ampoule 3 may have a shape similar to that of the crucible 12.
• the ampoule 3 is cylindrical in a seed growth region 19, cylindrical with a narrower diameter in its seed well region 19 and has a tapered transition region 8 between the two regions.
• the crucible 12 fits inside the ampoule 3 with a narrow margin between them.
• a second, upper container 4 as a raw material container, is seated on a quartz support 6.
• the quartz support 6 is sealed in the middle part of the ampoule 3.
• this second container 4 is made of pBN. It is this second container 4 into which most of the raw material 5 is filled.
• the raw material is melted and dropped down into the main crucible 12 from the bottom hole of the second container 4.
• the ampoule 3 is closed at the bottom of its seed well region 19 and sealed on top after the crucible and raw materials are loaded.
• Arsenic (As), gallium (Ga) and/or antimony (Sb) as a dopant may be added in the crucible 12 and/or in the second container 4.
• the cylinder 16 may be shaped to make a circle of contact with ampoule 3, where the upper rim of the cylinder 16 meets the shoulder of the ampoule's tapered region 8.
• Such configuration leads to minimal solid-to-solid contact, a contact which ensures that little or no undesirable, relatively uncontrollable heat conduction occurs. As a result, heating is able to be generated by other, more controllable processes.
• the furnace temperature may be decreased at a rate of about 0.2 to about 0.5°C/hour to allow the monocrystalline germanium ingot to grow.
• FIG. 5A illustrates an initial state of an exemplary process, where the solid germanium is present in both the upper container 4 and the crucible 12.
• FIG. 5B illustrates a state wherein the solid germanium has been melted to a liquid in the crucible 12.
• the heating elements of the heating zones of the furnace may be adjusted in association with the respective supply of power so that the upper container is provided with required heat energy.
• the upper container may be heated such that the germanium in the upper container 3 begins melting, and the molten germanium flows into the crucible 12 via a hole at the bottom of container 3.
• the region of the furnace where the upper container is present is heated to the range of about 940 to about 955 degrees Celsius, or of about 945 degrees to about 950 degrees Celsius. This process continues until all of the germanium in the upper container 3 is melted and flows into the crucible 12.
• the furnace 1 as shown in FIGs. 5A-5D is an example of a furnace that may be used for a Vertical Gradient Freeze (VGF) crystal growth process.
• VGF Vertical Gradient Freeze
• Other furnaces and configurations, such as Vertical Bridgman, may also be used.
• VGF crystal growth process the crystallizing temperature gradient within a fixed heat source is being moved electrically while the crystal is stationary.
• the furnace temperature fluctuation may be required to be within less than about ⁇ 0.1 °C.
• the raw germanium polycrystalline material is loaded into the ampoule 3 as described in more detail elsewhere herein.
• a pBN loading container 4 which has a hole in the tapered portion is seated on a support 6 which is made of quartz located above crucible 12 in the ampoule 3.
• the second container 4 may be placed over the crucible 12 and within the ampoule 3.
• the hole of the second container 4 may be placed at the center of the center of the bottom surface which has a tapered shape extending toward the ampoule 3.
• the crucible 3 may have opening receiving molten crystal which is dropped from the hole at the center of bottom surface of the second container 4.
• the loading container 4 allows the crucible 12 to be loaded with more raw materials.
• the raw germanium material 5 is typically solid chunks or pieces and therefore cannot be tightly packed into the crucible 12 to be melted.
• the loading container is used to hold extra raw material that can be melted and then drain down into the crucible 12 which results in a larger germanium charge in the crucible 12 which in turn results in a larger length and diameter germanium crystal.
• about 65% of the raw material may be initially loaded into the loading container 4 and 35 % of the raw material is loaded directly into the crucible 12.
• a 5.1 15 kg charge of raw material is loaded into the crucible 12 and a 9.885 kg charge is loaded into the loading container 4, resulting in a 15000 g (15 kg) charge that produces a 150mm (6 inch) diameter germanium ingot.
• the germanium may be doped with Arsenic (As).
• a 9° Off-orientation ⁇ 100> seed may be loaded into the crucible before the charge is loaded.
• the charge of raw material and an appropriate amount of dopant is loaded into the crucible and into the loading container which are placed into the quartz ampoule 3.
• the ampoule and contents are evacuated to a vacuum of about 2.00 x 10 "4 Pascal (about 1 .5 x 10 "6 Torr), after which the ampoule is sealed and loaded into the furnace, as shown in Figure 1 A.
• the furnace is started, and the ampoule and contents are heated so that the raw material in the crucible 12 melts.
• the furnace is at a temperature of approximately 1000 °C since the melting point of germanium is approximately 940 °C.
• the crystallization interface temperature gradient may be adjusted to be about 0.5 to about 10 °C/cm according to the different position of the ingot. Further, the overall temperature profile may be adjusted to give a
• Ge ingots resulting from such exemplary processes herein may have micropit densities reproducibly provided within the following ranges: greater than about 0.025/cm 2 and less than about 0.51 /cm 2 ; greater than about 0.025/cm 2 and less than about 0.26/cm 2 ; greater than about 0.025/cm 2 and less than about 0.13/cm 2 ; less than about 0.13/cm 2 ; and greater than about 0.025/cm 2 and less than about 0.26/cm 2 .
• the inventive apparatus is composed of a quartz ampoule into which both the pBN loading container and the crucible may be inserted, along with a support 6 to hold the pBN loading container.
• the crucible may have a diameter of about 150 mm in the growing crystal section, a length of about 160 mm in the growing crystal section, and a diameter of about 7 mm in the seed crystal section.
• a ⁇ 100> oriented Ge seed crystal was inserted in the seed well of the pBN crucible and 96 g of boron trioxide as the liquid sealant was put into the pBN crucible above the seed.
• the above-described quartz ampoule was heated at the rate of approximately 270 °C/ hr. When temperature was at about 30 °C over the melting point of the crystallizing material, the heating was maintained until all of the crystalline materials melted.
• an exemplary method for growing a monocrystalline germanium (Ge) crystals consistent with the innovations herein is disclosed.
• a method for loading a first raw Ge material into a crucible said crucible including a seed well holding a seed crystal, loading a second raw Ge material into a container for supplementing raw material, which is to be located within an ampoule, sealing the crucible and the container in said ampoule, placing said ampoule with said crucible and said container in it into a crystal growth furnace, controlling melt of the first raw Ge material in the crucible to create a melt, controlling melt of the second raw Ge material in said container.
• such methods may include one or more of controlling addition of the melted second raw Ge material to said melt, controlling the crystallizing temperature gradient of the melt so that the melt crystallizes when in contact with the seed crystal and forms a monocrystalline germanium ingot, and cooling the monocrystalline germanium ingot.
• controlling melt of the second raw Ge material in said container including controlling heating applied to the second raw Ge material and maintaining the melted second raw Ge material within a temperature range.
• controlling addition of the melted second raw Ge material to said melt may include maintaining said melt within a specified temperature range, and such range may be about 940 to about 955 degrees Celsius, or about 945 to about 950 degrees Celsius.
• controlling addition of the melted second raw Ge material to said melt may include maintaining said melt within a specified temperature range, such as the ranges listed above.
• heating power and/or one or more cooling rates may be controlled or reduced in a controlled manner to yield Ge ingots having crystal properties within reproducibly provided ranges.
• mono-crystalline germanium ingots having reduced micropit cavity densities e.g., within any of the other ranges set forth herein
• germanium crystals having micropit densities within the various ranges above may be reproducibly provided without use of external gas source supplied doping techniques.
• aspects of these advantages may relate to the use of sealed ampoules (e.g., sealed under vacuum, at a pressure or other conditions, etc.) and avoid associated complexities such as the need for expensive gas supply hardware and control system/electronics, etc.
• innovations herein may be advantageously associated with systems and methods that entail non-contact doping techniques.
• germanium crystals having dislocation densities within the various ranges above may be reproducibly provided without use of contact doping techniques and/or external gas source supplied doping techniques.
• VGF methods may be used to perform crystal growth.
• the heater power may be reduced first in the lowest heating zone to start crystal growth at the seed, and then the heater power may be reduced in the transition region, wherein the cooling rate was at about 0.3 to about 0.4 °C/hr. This cooling rate was maintained for approximately 70 hours.
• the heater power in the appropriate zone was reduced to give a cooling rate of about 0.4 to about 0.7 °C/ hr with a crystallization interface temperature gradient of about 1 .2 to about 3.0°C/cm, both of which were maintained for approximately 120 hours.
• the furnace was cooled at a rate of about 20 to about 40 °C /hour until it reached room temperature.
• An exemplary, resulting crystal ingot had a 125 mm body length, and is
• such crystals From the starting growth portion to the end of growth portion, for example, such crystals have low micropit densities, and may also have free carrier concentrations of about 9 x 10 17 to about 4 x 10 18 or about 5 x 10 18 /cm 3 (range of about 9 x 10 17 to about 4.86 x 10 18 /cm 3 being measured), and resistivity of about 7 x 10 "3 to 2 x 10 "3 or 3 x 10 "3 Q.cm (range of about 7.29 x 10 "3 to about 2.78 x 10 "3 Q.cm being measured), with a mobility of about 950 cm 2 A/s to about 450 cm 2 A/s (values of 955 cm 2 A/s and 467 cm 2 A/s being measured).
• the dislocation density may less than about 500/cm 2 , or even less than about 200/cm 2 .
• germanium crystal substrates e.g., ingots, wafers, etc.
• any products e.g., electronic or opto-electronic device, etc.

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