Powder metallurgy crucible for aluminum nitride crystal growth

Abstract

A crucible for growing III-nitride (e.g., aluminum nitride) single crystals is provided. The crucible includes an elongated wall structure defining an interior crystal growth cavity. Embodiments include a plurality of grains and a wall thickness of at least about 1.5 times the average grain size. In particular embodiments, the crucible includes first and second layers of grains the first layer including grains forming an inside surface thereof and the second layer being superposed with the first layer. The crucible may be fabricated from tungsten-rhenium (W—Re) alloys; rhenium (Re); tantalum monocarbide (TaC); tantalum nitride (Ta 2 N); hafnium nitride (HfN); a mixture of tungsten and tantalum (W—Ta); tungsten (W); and combinations thereof.

1 .- 31 . (canceled) 
   
   
       32 . A crucible comprising at least one of hafnium or a carbide, and having an elongated wall structure extending in a longitudinal direction, the wall structure
 (i) comprising a plurality of grains and defining an interior crystal growth cavity; and   (ii) having a thickness dimension (a) extending in a direction substantially perpendicular to said longitudinal direction and (b) being at least about 1.5 times the average grain size.   
   
   
       33 . The crucible of  claim 32  wherein the plurality of grains
 (i) form at least first and second layers, the first layer including a portion of the plurality of grains forming an inside surface of the wall structure and the second layer being adjacent to the first layer; and   (ii) define a plurality of diffusion pathways within the wall structure, the plurality of grains swelling upon absorption of either nitrogen or a column III element, thereby substantially obstructing at least some of the diffusion pathways.   
   
   
       34 . The crucible of  claim 33  wherein the diffusion pathways defined by boundaries between adjacent grains are substantially obstructed by others of the plurality of grains when they swell upon absorption. 
   
   
       35 . The crucible of  claim 32  wherein the crystal growth cavity includes a substantially cylindrical portion and a tapered conical end portion. 
   
   
       36 . The crucible of  claim 32  comprising hafnium. 
   
   
       37 . The crucible of  claim 32  comprising a carbide. 
   
   
       38 . A method for fabricating a crucible, the method comprising fabricating a wall structure from a granular material comprising at least one of hafnium or a carbide, the wall structure defining an interior crystal growth cavity and comprising a plurality of grains forming at least first and second layers, the first layer including a portion of the plurality of grains forming an inside surface of the wall structure and the second layer being superimposed on the first layer. 
   
   
       39 . The method of  claim 38  wherein at least a portion of the wall structure is fabricated by steps comprising:
 (i) pressing the granular material into a desired shape;   (ii) sintering the granular material to form a sintered structure; and   (iii) heating the sintered structure at a temperature ranging from at least about 2000° C. to about 2500° C. under conditions suitable to effect grain swelling.   
   
   
       40 . The method of  claim 39 , wherein, in step (iii), the sintered structure is heated in an atmosphere selected from the group consisting of inert atmospheres and chemically active atmospheres. 
   
   
       41 . The method of  claim 38  wherein the granular material comprises hafnium. 
   
   
       42 . The method of  claim 38  wherein the granular material comprises a carbide. 
   
   
       43 . A method for fabricating an aluminum nitride crystal, the method comprising:
 (i) depositing aluminum nitride in a crystal growth cavity of a crucible comprising an elongated wall structure defining the crystal growth cavity, the elongated wall structure comprising a plurality of grains, the grains forming at least first and second layers, the first layer including grains forming an inside surface of the wall structure and the second layer being superimposed on the first layer;   (ii) sealing the crucible; and   (iii) heating at least a portion of the crucible to a temperature in excess of about 2000° C.,   wherein the crucible comprises at least one of hafnium or a carbide, and during step (iii), in at least the portion of the crucible, grains of at least the second layer swell to substantially obstruct diffusion of aluminum along diffusion pathways defined by boundaries between grains of at least the first layer.   
   
   
       44 . The method of  claim 43  wherein the crucible comprises hafnium. 
   
   
       45 . The method of  claim 43  wherein the crucible comprises a carbide. 
   
   
       46 . A crucible comprising:
 at least one of hafnium or a carbide, and   a wall structure defining an interior crystal growth cavity and comprising a plurality of grains defining a plurality of diffusion pathways within the wall structure, the plurality of grains swelling upon absorption of at least one of aluminum or nitrogen, thereby substantially obstructing at least some of the plurality of diffusion pathways.   
   
   
       47 . The crucible of  claim 46  wherein the diffusion pathways are defined by boundaries between adjacent grains, the grains forming at least first and second layers, the first layer including grains forming an inside surface of the crucible and the second layer being superimposed on the first layer. 
   
   
       48 . The crucible of  claim 47  wherein the diffusion pathways of the first layer are substantially obstructed by swollen grains of the second layer upon absorption of at least one of aluminum or nitrogen by the grains of the second layer. 
   
   
       49 . The crucible of  claim 46  comprising hafnium. 
   
   
       50 . The crucible of  claim 46  comprising a carbide.