Large aluminum nitride crystals with reduced defects and methods of making them

Abstract

Reducing the microvoid (MV) density in AlN ameliorates numerous problems related to cracking during crystal growth, etch pit generation during the polishing, reduction of the optical transparency in an AlN wafer, and, possibly, growth pit formation during epitaxial growth of AlN and/or AlGaN. This facilitates practical crystal production strategies and the formation of large, bulk AlN crystals with low defect densities—e.g., a dislocation density below 10 4 cm −2 and an inclusion density below 10 4 cm −3 and/or a MV density below 10 4 cm −3 .

What is claimed is: 
     
         1 .- 38 . (canceled) 
     
     
         39 . An AlN single crystal having at least one of (i) an optical absorption coefficient of less than 5 cm −1  at all wavelengths in a range spanning 500 nm to 3,000 nm or (ii) an optical absorption coefficient of less than 1 cm −1  at any wavelength in a range spanning 210 nm to 4,500 nm. 
     
     
         40 . The AlN single crystal of  claim 39 , wherein the AlN single crystal has an optical absorption coefficient of less than 5 cm −1  at all wavelengths in a range spanning 500 nm to 3,000 nm. 
     
     
         41 . The AlN single crystal of  claim 40 , wherein the AlN single crystal has an optical absorption coefficient of less than 1 cm −1  at any wavelength in a range spanning 210 nm to 4,500 nm. 
     
     
         42 . The AlN single crystal of  claim 39 , wherein the AlN single crystal has an optical absorption coefficient of less than 1 cm −1  at any wavelength in a range spanning 210 nm to 4,500 nm. 
     
     
         43 . The AlN single crystal of  claim 39 , wherein the AlN single crystal has a microvoid density less than approximately 10 4  cm −3 . 
     
     
         44 . The AlN single crystal of  claim 39 , wherein the AlN single crystal is substantially crack-free. 
     
     
         45 . The AlN single crystal of  claim 39 , wherein the AlN single crystal is in the form of a wafer with a surface having a crystalline orientation within 2° of the (0001) c-face and an Al polarity. 
     
     
         46 . The AlN single crystal of  claim 40 , wherein the AlN single crystal is in the form of a wafer with a surface having a crystalline orientation within 2° of the (0001) c-face and an Al polarity. 
     
     
         47 . The AlN single crystal of  claim 39 , wherein the AlN single crystal is in the form of a wafer with a surface having a crystalline orientation within 2° of the (0001) c-face and an N polarity. 
     
     
         48 . The AlN single crystal of  claim 40 , wherein the AlN single crystal is in the form of a wafer with a surface having a crystalline orientation within 2° of the (0001) c-face and an N polarity. 
     
     
         49 . The AlN single crystal of  claim 39 , wherein the AlN single crystal is in the form of a wafer with a surface having a crystalline orientation within 2° of the m-face. 
     
     
         50 . The AlN single crystal of  claim 40 , wherein the AlN single crystal is in the form of a wafer with a surface having a crystalline orientation within 2° of the m-face. 
     
     
         51 . The AlN single crystal of  claim 39 , wherein the AlN single crystal is in the form of a wafer with a surface having a crystalline orientation within 2° of the a-face. 
     
     
         52 . The AlN single crystal of  claim 40 , wherein the AlN single crystal is in the form of a wafer with a surface having a crystalline orientation within 2° of the a-face. 
     
     
         53 . The AlN single crystal of  claim 39 , wherein the AlN single crystal is in the form of a wafer having a diameter greater than approximately 2 cm. 
     
     
         54 . The AlN single crystal of  claim 40 , wherein the AlN single crystal is in the form of a wafer having a diameter greater than approximately 2 cm. 
     
     
         55 . A method of growing single-crystal AlN, the method comprising:
 providing in a crystal growth enclosure a vapor comprising Al and N 2 ;   depositing the vapor as single-crystalline AlN having a microvoid density less than approximately 10 4  cm −3 ; and   following deposition, annealing at least a portion of the single-crystalline AlN at a first temperature and a first pressure,   wherein the first temperature is greater than approximately 2000° C. and the first pressure is greater than approximately 35 bar.   
     
     
         56 . The method of  claim 55 , wherein the first temperature is less than approximately 2350° C. 
     
     
         57 . The method of  claim 55 , wherein depositing the vapor as single-crystalline AlN comprises pushing the crystal growth enclosure at a rate less than an intrinsic growth rate of the AlN. 
     
     
         58 . The method of  claim 55 , further comprising slicing an AlN wafer from the single-crystalline AlN.