Apparatus for retrograde solvothermal crystal growth, method of making, and method of use
According to the present disclosure, techniques related to processing of materials for growth of crystals are provided. More particularly, the present disclosure provides apparatus and methods for heating of seed crystals suitable for use in conjunction with a high-pressure vessel for crystal growth of a material having a retrograde solubility in a supercritical fluid, including crystal growth of a group III metal nitride crystal by an ammonobasic or ammonoacidic technique, but there can be others. In other embodiments, the present disclosure provides methods suitable for synthesis of crystalline nitride materials, but it would be recognized that other crystals and materials can also be processed. Such crystals and materials include, but are not limited to, GaN, AlN, InN, InGaN, AlGaN, and AlInGaN, and others for manufacture of bulk or patterned substrates. Such bulk or patterned substrates can be used for a variety of applications including optoelectronic devices, lasers, light emitting diodes, solar cells, photoelectrochemical water splitting and hydrogen generation, photodetectors, integrated circuits, and transistors, among other devices.
1 . An apparatus for solvothermal crystal growth, comprising:
an enclosure configured to contain a material at a pressure above about 5 megapascal and at a temperature above about 200° C., wherein the enclosure comprises an interior region and a central axis that extends in a first direction;
one or more heating elements disposed within the interior region of the enclosure; and
a plurality of seed mounts disposed within the interior region, wherein a surface of each of the seed mounts is configured to receive a seed crystal, wherein;
each of the plurality of seed mounts are disposed in an array that extends in the first direction,
at least a portion of a seed mount region is disposed between the surface of each of the seed mounts and at least one of the one or more heating elements disposed within the interior region of the enclosure, wherein the seed mount region comprises a heat transfer medium, and
the seed mount regions are in direct contact with at least one of the one or more heating elements disposed within the interior region of the enclosure or are disposed proximate to at least one of the one or more heating elements disposed within the interior region of the enclosure.
2 . The apparatus of claim 1 , wherein the heat transfer medium comprises at least one material having a thermal conductivity above about 50 W/m-K.
3 . The apparatus of claim 1 , further comprising a seed crystal gap formed between a back side of a seed crystal and the seed mount, wherein the seed crystal gap is between about 25 micrometers and about 5 millimeters (mm).
4 . The apparatus of claim 1 , further comprising a heater that at least partially surrounds an outer surface of the enclosure, wherein each of the plurality of seed mounts are positioned a distance from at least one of the one or more heating elements disposed within the interior region of the enclosure so that an average temperature formed across the surface of the seed mount is between zero and about 10° C. below the maximum value of a temperature of at least one of the one or more heating elements disposed within the interior region of the enclosure at the same height as the seed mount during a solvothermal crystal growth process.
5 . The apparatus of claim 4 , wherein an average temperature formed across the surface of the surface of each of the seed mounts within the array of seed mounts is less than about 5° C. below the maximum value of a temperature of at least one of the one or more heating elements disposed within the interior region of the enclosure at the same height as the seed mount during a solvothermal crystal growth process.
6 . The apparatus of claim 1 , wherein one or more heating elements of the plurality of heating elements are disposed within a sheath that is hermetically sealed with respect to the interior region.
7 . The apparatus of claim 6 , wherein one or more heating elements are disposed within at least one seed mount region of a seed mount, wherein the seed mount is disposed on a vane member of at least two vane members that are arranged symmetrically around a central axis of the enclosure.
8 . The apparatus of claim 6 , wherein the one or more heating elements are disposed within at least one seed mount region of a seed mount, wherein the seed mount is disposed on a vane member of a plurality of vane members.
9 . The apparatus of claim 6 , wherein the one or more heating elements are disposed within at least one seed mount region of a seed mount, wherein the at least one seed mount region comprises a wall defining and enclosing the seed mount region and is filled with a supercritical fluid having essentially the same composition as a supercritical fluid present within the interior region.
10 . The apparatus of claim 9 , wherein each of the seed mount regions further comprises at least one horizontal baffle, the horizontal baffles having a percent open area between 0.5% and 20% with respect to a cross-sectional area of the seed mount region in a direction perpendicular to the central axis.
11 . The apparatus of claim 10 , wherein each wall defining and enclosing a seed mount region comprises an opening that defines a seed mount region of the seed mount regions, wherein the opening comprises an open cross-sectional area, which expressed as a percentage of a cross-sectional area of the interior region, is less than about 1%.
12 . The apparatus of claim 1 , further comprising at least one basket member for nutrient that is positioned laterally with respect to at least one seed mount of the plurality of seed mounts.
13 . The apparatus of claim 12 , further comprising at least two zone separators, a first zone separator of the at least two zone separators separating a first region of nutrient from a second region of nutrient and a second zone separator of the at least two zone separators separating at least one first seed mount from at least one second seed mount, and the first and second zone separators, the first nutrient region and the at least one first seed mount forming a growth tier within the interior region.
14 . The apparatus of claim 1 , wherein the heat transfer medium comprises at least one material having a thermal conductivity above about 100 W/m-K.
15 . The apparatus of claim 1 , further comprising at least one seed bracket, the seed bracket being configured to hold at least one seed crystal at a separation of one millimeter or less with respect to a seed mount of the plurality of seed mounts.
16 . The apparatus of claim 1 , wherein at least one seed mount is configured to receive a seed crystal having a maximum dimension or diameter that is within at least 75% of an inner diameter of the interior region.
17 . The apparatus of claim 1 , wherein an angle θ between a plane that is parallel to a surface of at least one of the seed mounts that is configured to receive a seed crystal and the central axis has a value between 0 degrees and 90 degrees.
18 . The apparatus of claim 17 , wherein θ has a value between 20 degrees and 70 degrees.
19 . The apparatus of claim 17 , wherein θ has a value between 40 degrees and 60 degrees.
20 . The apparatus of claim 17 , further comprising at least one growth baffle positioned between at least one pair of axially-adjacent seed mounts, the at least one growth baffle being tilted from horizontal by an angle within 10 degrees of the value of θ.